35-150 billion fish are raised in captivity to be released into the wild every year


  • Fish stock­ing[1] is the prac­tice of rais­ing fish in hatcheries and re­leas­ing them into rivers, lakes, or the ocean.

  • 35-150 billion fin­fish are stocked ev­ery year.

  • Fish are stocked to:

    • in­crease the catch in com­mer­cial fish­eries (prob­a­bly tens of billions of stocked fish an­nu­ally),

    • in­crease the catch in recre­ational/​sport fish­eries (billions of stocked fish an­nu­ally),

    • re­store a pop­u­la­tion of threat­ened or en­dan­gered species (the num­ber of stocked fish seems to be lower)

  • Fish can be stocked when they are any­where be­tween the egg stage and mul­ti­ple years old. The mean time spent in hatcheries/​farms seems to be some­where be­tween 8 days and 4 months. Fish stocked to en­hance recre­ational fish­eries tend to be re­leased when they are older than those stocked to en­hance com­mer­cial fish­eries.

  • Usu­ally, fish are stocked to max­i­mize eco­nomic out­puts so we shouldn’t ex­pect fish welfare to be given suffi­cient con­sid­er­a­tion. It’s un­clear how much hatcheries are in­cen­tivized to breed healthy and un­stressed fish that would have higher sur­vivor­ship af­ter the re­lease. Big­ger fish may also starve and suffer af­ter their re­lease due to their lack of sur­vival skills.

  • I was un­able to find any an­i­mal ad­vo­cacy or­ga­ni­za­tion that is work­ing on re­duc­ing the suffer­ing caused by fish stock­ing. I found very few ar­ti­cles that talk about fish stock­ing from an an­i­mal welfare per­spec­tive.[2]

  • Pos­si­ble in­ter­ven­tions in­clude lob­by­ing to de­crease the num­ber of fish stocked for recre­ational fish­ers and re­quiring bet­ter con­di­tions in hatcheries. I am very un­cer­tain if such in­ter­ven­tions would be cost-effec­tive com­pared to ACE’s recom­mended char­i­ties.

  • Fish stock­ing has var­i­ous ecolog­i­cal effects (e.g., a de­crease in the ge­netic di­ver­sity of wild pop­u­la­tions) that would need to be well-un­der­stood be­fore se­ri­ously con­sid­er­ing try­ing to re­duce the num­ber of stocked fish.


This ar­ti­cle is a part of a se­ries of ar­ti­cles by Re­think Pri­ori­ties about an­i­mals farmed for var­i­ous pur­poses. We chose to write about this topic be­cause it seems fairly im­por­tant and it’s pos­si­ble that an­i­mal ad­vo­cates haven’t ad­dressed welfare prob­lems re­lated to fish stock­ing sim­ply be­cause they didn’t know about them.

Char­ity En­trepreneur­ship (CE) has re­cently re­leased a re­port that con­sid­ered the ad­van­tages and dis­ad­van­tages of found­ing a char­ity that tack­les prob­lems re­lated to fish stock­ing and bait­fish. The re­port used my pre­limi­nary re­search on fish stock­ing, but it was writ­ten be­fore I wrote most of this ar­ti­cle. CE’s re­port pro­vi­sion­ally con­cluded that in­ter­ven­tions in these ar­eas are only “some­what promis­ing” com­pared to other in­ter­ven­tions they con­sid­ered. I dis­agree with some as­pects[3] of their re­port, but I have no opinion on whether the con­clu­sion is cor­rect. In gen­eral, I think that more in-depth re­search would be needed to de­ter­mine whether this is a prob­lem that should even­tu­ally be tack­led by an­i­mal ac­tivists. I am un­cer­tain if such re­search should cur­rently be a pri­or­ity.

The num­ber of fish stocked an­nu­ally worldwide

I haven’t found any es­ti­mates of the num­ber of fish stocked wor­ld­wide, but I found es­ti­mates for var­i­ous coun­tries and re­gions:

  • China: A 2006 pro­gramme planned to re­lease 20 billion ju­ve­nile fish an­nu­ally and to in­crease it to 40 billion by 2020. China’s 2011-2015 Fish­eries Plan in­cludes re­leas­ing 150 billion ju­ve­nile fish (which is 30 billion per year)[4] and claims that 109 billion young fish were re­leased since a pre­vi­ous five-year plan was made in 2006.[5] It should be noted that these statis­tics are from China’s gov­ern­ment and some doubt whether China’s gov­ern­ment is a re­li­able source. For ex­am­ple, China has prob­a­bly over-re­ported the catch from wild fish­eries in the 1990s.

  • EU: Cooke and Cowx (2006) cites Cowx and God­kin’s (2000) es­ti­mate that “some 40 billion in­di­vi­d­u­als are stocked an­nu­ally in Euro­pean fresh wa­ters”. I could not ac­cess Cowx and God­kin (2000), but its sum­mary con­tains the fol­low­ing text:

In­for­ma­tion on quan­tities of fish stocked was difficult to ac­cess. Sal­mon prob­a­bly rep­re­sents the species that has re­ceived the great­est at­ten­tion, with an es­ti­mated 20 billion in­di­vi­d­u­als, of var­i­ous ju­ve­nile life stages, mainly eggs and fry, were stocked in 1998. High lev­els of stock­ing were also recorded for rain­bow trout, core­go­nids, whitefish, eel, com­mon carp and var­i­ous cyprinids to sup­port recre­ational and com­mer­cial in­land fish­eries.

Note that this data is from over 20 years ago, and I was un­able to find other au­thors that make similar claims. Fur­ther­more, it in­cludes stocked eggs. Ac­cord­ing to Figure 2 of Cowx (2002), out of the ~20 billion At­lantic salmon stocked in the EU in 1998, less than 4 billion were eggs, and the rest were hatched ju­ve­niles.

  • Ger­many: Ar­ling­haus, et al. (2015) claims that in Ger­many around 77 mil­lion fish were stocked in 2010 by an­glers in clubs. Note that more fish may have been stocked by other groups in Ger­many.

  • Rus­sia: NPAFC (2019) claims that Rus­sia re­leases around 1 billion salmon ev­ery year. Che­banov and Billard (2001) claim that at the time of writ­ing the ar­ti­cle, Rus­sia was pro­duc­ing 100 mil­lion stur­geon ju­ve­niles per year. Dick­in­son (2018) men­tions that cur­rently Rus­sia is “re­leas­ing 50 mil­lion or more stur­geon raised in hatcheries.” Vorot­nikov (2019) claims that a new hatch­ery “is de­signed to pro­duce five mil­lion ster­let finger­lings and one mil­lion trout (Salmo gaird­neri) finger­lings per year at full ca­pac­ity.” Rus­sia may be stock­ing other species as well.

  • U.S.: Ac­cord­ing to aqua­cul­ture cen­suses, the num­ber of fish stocked in the U.S. was over 2.9 billion in 2005, and over 3.6 billion in 2013.[6]

  • Canada: NPAFC (2019) claims that in 2017 Canada re­leased 368 mil­lion salmon. There also seems to be sig­nifi­cant stock­ing in in­land wa­ters for recre­ational fish­ers. For ex­am­ple, On­tario’s Com­mu­nity Hatch­ery Pro­gram claims that com­mu­nity hatcheries it sup­ported re­leased 6.7 mil­lion fish in 2017.

  • Ja­pan: NPAFC (2019) claims that Ja­pan is stock­ing ~1.8 billion salmon to ev­ery year. Also, ac­cord­ing to Koichi, et al. (2015), in 2011, Ja­pan re­leased around 15 mil­lion flounders, 12 mil­lion red seabreams, and lesser num­bers of other fin­fish.[7]

  • Thailand: Ju­ta­gate and Rat­tanachai (2010) claim that 2.5 billion fish and gi­ant wa­ter prawn were stocked into in­land wa­ters in 2009 and 1.95 billion fish were stocked in 2008. How­ever, num­bers in an ac­com­pa­ny­ing table are much lower which makes me un­cer­tain if these to­tals are cor­rect.

  • Myan­mar: Ac­cord­ing to the table 3 in Oo (2010), 740.6 mil­lion seed were pro­duced for stock en­hance­ment by fin­fish hatcheries in 2008-2009. It seems that the word seed here refers to hatched fish.

  • Iran: Brown and Day (2002) claims that in 1996, Iran re­leased over 250 mil­lion fish.

  • Caspian sea: Vorot­nikov (2018) claims that Azer­bai­jan and Kaza­khstan are re­leas­ing about 20 mil­lion stur­geon finger­lings per year into the Caspian sea and that this num­ber is ex­pected to in­crease.

  • The rest of the world: Le­ber (2012) claims that “marine fish­eries en­hance­ment is hap­pen­ing around the world and in some coun­tries on a mas­sive scale (e.g., China).” After claiming that “some 40 billion in­di­vi­d­u­als are stocked an­nu­ally in Euro­pean fresh wa­ters”, Cooke and Cowx (2006) state that “stock­ing to a similar scale is com­mon across the world.” I don’t think that there are other re­gions that stock at the same scale as China and pos­si­bly Europe, but it does seem that al­most all coun­tries do at least some stock­ing. FAO page Stock­ing tech­niques for in­creased pro­duc­tion claims that:

Stock­ing is wide­spread in Latin Amer­ica where the great­est de­vel­op­ment has been achieved in Cuba, Mex­ico and parts of Brazil. [...] As re­gards Asia, suc­cess­ful stock­ing pro­grammes are re­ported from In­dia and China. Vari­able re­sults are re­ported from South­east Asia where it has been pos­si­ble to raise catch lev­els from 20 to 100 kg/​ha in some wa­ters in Thailand, In­done­sia, the Philip­pines and Malaysia. Data for Africa are rather scarce al­though this con­ti­nent has fish­eries that are sup­ported by stock­ing.

The FAO ar­ti­cle also claims “[n]in­ety-four coun­tries have re­ported stock­ing to FAO as part of their fish­ery statis­tics”, but I haven’t found these statis­tics on the FAO’s web­site.

To es­ti­mate how many fish are stocked wor­ld­wide an­nu­ally, I cre­ated a Guessti­mate model in which I used sub­jec­tive 90% con­fi­dence in­ter­vals to re­flect the un­cer­tainty about the num­bers above and guessed how many fish are stocked in re­gions for which I didn’t find any statis­tics. I guessed that num­bers of fish stocked per cap­ita in coun­tries that I haven’t found the statis­tics for are lower that the ones above.[8] Ac­cord­ing to the model, 35-150 billion fish are stocked ev­ery year. The es­ti­mate ex­cludes:

  • Stocked eggs. The stock­ing of eggs doesn’t lead to the same welfare con­cerns as the stock­ing of ju­ve­niles. In some cases, it wasn’t clear whether the num­bers in figures cited above in­cluded stocked eggs. Con­se­quently, I low­ered the lower bounds of the 90% con­fi­dence in­ter­vals in my Guessti­mate model for some re­gions.

  • Shel­lfish. I fo­cused on fin­fish to avoid the un­cer­tainty about shel­lfish sen­tience. How­ever, shel­lfish are also stocked in big num­bers. Ac­cord­ing to Koichi et al. (2015), in 2011, Ja­pan stocked over 10 billion Manila clams, and 3 billion scal­lop spats, hun­dreds of mil­lions of ku­ruma prawns, and tens of mil­lions of crabs. Ac­cord­ing to the U.S. Aqua­cul­ture Cen­sus, in 2013 U.S. stocked 1.25 billion eggs or seed stock of clams, and 1.59 billion eggs or seed stock of oys­ters. I am un­cer­tain about whether all shel­lfish stock­ing is done in the form of eggs, and what is the scale of shel­lfish stock­ing in other coun­tries.

  • Ille­gal stock­ing. Ac­cord­ing to John­son (2011), ille­gal stock­ing is a global prob­lem. The ar­ti­cle seems to as­sume that in North Amer­ica fish are stocked ille­gally for the benefit of recre­ational fish­ers. Ac­cord­ing to the ar­ti­cle, the main prob­lem is that such stock­ing sub­jects “the en­tire fish­ery and ecosys­tem to a de­gree of un­nec­es­sary risk from dis­eases, par­a­sites, and in­va­sive species that could have been ac­ci­den­tally in­tro­duced with the stocked fishes.” Fur­ther­more, “some an­gler in­tro­duc­tions have turned into tremen­dously ex­pen­sive cleanup pro­jects.” I haven’t seen any es­ti­mates of the num­ber of ille­gally stocked fish. My in­tu­ition is that they are a small per­centage of all stocked fish.[9]

  • Fish deaths in hatcheries be­fore the stock­ing. FRS (2003) claim that for salmon and trout, “[s]molt rear­ing hatcheries can have a 90% sur­vival rate com­pared with less than 1% in the wild.” Similarly, Araki et al. (2008) cite Reisen­bich­ler et al. (2004) to claim that for salmon “sur­vival from egg to smolt is usu­ally 85–95% in hatcheries ver­sus 1–5% in the wild.”[10] I haven’t found sur­vival rates for other species. Also note that there are oc­ca­sional mass die-off events in hatcheries, which may not be in­cluded in such mor­tal­ity es­ti­mates.

  • Translo­cated fish. In­gram and Silva (2015) claims that:

Most stock­ing pro­grams have re­quired, and usu­ally pre­ceded by, the de­vel­op­ment of hatch­ery and nursery pro­duc­tion tech­niques for the tar­get species, though some stock­ings may in­volve the cap­ture of ju­ve­niles/​seed­stock in one area, where re­cruit­ment is healthy, and translo­ca­tion to an­other area where re­cruit­ment is in­ad­e­quate or lack­ing.

I was un­able to find any statis­tics on what per­centage of stocked fish are translo­cated rather than raised in hatcheries. Some sources for the num­bers of stocked fish (e.g. NPAFC (2019), the U.S. Aqua­cul­ture Cen­sus, Oo (2010)) ex­plic­itly say that the fish were pro­duced in hatcheries. In other cases it was un­clear whether given statis­tics in­clude translo­cated fish. I guessed that be­tween 0.1% and 20% of stocked fish that are in­cluded in num­bers cited above were translo­cated, and sub­tracted them from the to­tal in the Guessti­mate model. My guessed per­centage is low be­cause some of the ar­ti­cles I read as­sumed that all fish were in hatcheries. The few ar­ti­cles that did men­tion translo­cated fish also men­tioned that it is not the most com­mon prac­tice (like in the quote above).

The num­ber of stocked fish (35-150 billion) is com­pa­rable with an es­ti­mated 75 billion farmed land an­i­mals (FAO[11], 2017 data), and 48-160 billion farmed fish that are slaugh­tered for meat ev­ery year. How­ever, fish farmed for food gen­er­ally stay in farms longer than fish raised for stock­ing. Many stocked fish are re­leased when they are less than five days old. Fur­ther­more, it seems that many more fish ju­ve­niles are raised to be stocked in aqua­cul­ture sys­tems (see the ap­pendix).


In­gram and Silva (2015) claims that:

Stock­ing hatch­ery-pro­duced fish is seen as a means of meet­ing the de­mands for seafood prod­ucts and to meet the need for food se­cu­rity in an in­creas­ingly pop­u­lated world. Stock­ing as a means of pro­vid­ing a food re­source will be a pri­or­ity for fu­ture aqua­cul­ture.

Figure 6 in Shen and Heino (2013) re­port that the num­ber of fish used in marine stock en­hance­ment by China has in­creased from around 2 billion in 2001 to 13 billion in 2010. Note that this ex­cludes stock­ing for in­land wa­ters.

Figure 5 in NPAFC (2019) in­di­cates that the com­bined num­ber of salmon stocked by the U.S., Ja­pan, Rus­sia, and Canada has re­mained fairly sta­ble at 5 billion per year over the last 30 years.

Table 2 in Halver­son (2008) pro­vides some statis­tics about the to­tal num­ber and weight of fish stocked by the U.S. fed­eral gov­ern­ment and the 33 states for which data was available for all rep­re­sented years. The statis­tics are sum­marised in the graph be­low. The graph sug­gests that the num­ber of fish stocked was much higher in the 1930s, but has been rel­a­tively sta­ble be­tween 1958 and 2004. The to­tal weight of stocked fish seems to have been in­creas­ing be­tween 1936 and 2004.

Ac­cord­ing to the aqua­cul­ture cen­suses, the num­ber of fish stocked in the U.S. was 3.4 billion (147 mil­lion kilo­grams) in 1998, 2.9 billion (28.8 mil­lion kilo­grams) in 2005, and over 3.6 billion (42.6 mil­lion kilo­grams) in 2013. This sug­gests that the av­er­age weight of stocked fish (and the mean amount of time fish spend in hatcheries) can be very differ­ent in differ­ent years. We will have more in­for­ma­tion about the cur­rent situ­a­tion when the 2018 U.S. aqua­cul­ture cen­sus is re­leased. Figure 10 in Stopha (2018) sug­gests that Alaska’s salmon re­leases have re­mained rel­a­tively sta­ble at ~1.6 billion.

Note that the data from Halver­son (2008) only in­cludes data from 33 states and seems to ex­clude most of the stocked salmon. Con­se­quently, its figures can­not be com­pared to the U.S. cen­sus, which is why I did not in­clude the data from the cen­suses to the graph above.

Over­all, I think that the num­ber of fish stocked wor­ld­wide is more likely to be in­creas­ing than de­creas­ing, but I am un­cer­tain.

Pur­poses of stocking

In­gram and Silva (2015) claims that:

The pri­mary pur­poses of stock­ing in de­vel­oped coun­tries is for re­cov­ery of threat­ened species and to sup­port recre­ational fish­ing, whereas in de­vel­op­ing coun­tries it is more to in­crease food fish sup­plies for ru­ral com­mu­ni­ties and im­prove their liveli­hood through in­come from fish har­vested.

Similarly, FAO page Stock­ing tech­niques for in­creased pro­duc­tion claims that

Stocks of core­go­nids, perch and zan­der are main­tained in many alpine and north­ern Euro­pean lakes in sup­port of com­mer­cial as well as recre­ational fish­eries. [...] Stock­ing pro­grammes are also widely used through­out the USA and Canada where the em­pha­sis is on man­age­ment for bal­anced pop­u­la­tions for recre­ational fish­eries. [...] In gen­eral, stock­ing pro­grammes aim at sup­port­ing com­mer­cial fish­eries. In Brazil, stock­ing was a statu­tory re­quire­ment for miti­ga­tion of effects of dams.

Braith­waite and Sal­vanes (2010) claim that stock­ing is also some­times used “to counter the detri­men­tal effects of an­thro­pogenic dis­rup­tions, such as dam build­ing, river straight­en­ing or effluent pol­lu­tion that are be­lieved to have con­tributed to high lev­els of mor­tal­ity in nat­u­ral pop­u­la­tions.”

This graph from In­gram and Silva (2015) sug­gests that in 1999 in Asia and Ocea­nia most stock­ing pro­grams (~60) were im­ple­mented for the pur­pose of “food & in­come”, but there were also some pro­grams that stocked for recre­ation (~13), bio­ma­nipu­la­tion (~8), con­ser­va­tion (~6), miti­ga­tion (2), or restora­tion (1) pur­poses.

The pur­pose of a 2006 pro­gramme in China that (amongst other ac­tions) planned to re­lease 20-40 billion ju­ve­nile fish an­nu­ally was to “re­verse the trend of de­te­ri­o­ra­tion of the aquatic en­vi­ron­ment, de­cline of fish­eries re­sources and the in­creas­ing num­ber of en­dan­gered species, re­duce over­ca­pac­ity, and im­prove the effi­ciency of fish­ing op­er­a­tion and eco­nomic benefits.” Devel­op­ing recre­ational fish­eries is men­tioned amongst the rea­sons for the pro­gram, but it doesn’t seem to be the main goal.

Ac­cord­ing to Table 2 in Halver­son (2008), in 2004 out of 1.75 billion fish stocked in the U.S., 1.43 billion were sport fish (stocked for the benefit of recre­ational fish­ers), 292 mil­lion were salmon and steel­head (pur­pose not speci­fied), and 24 mil­lion were “rare and de­clin­ing” fish, prob­a­bly stocked for con­ser­va­tion/​restora­tion pur­poses. This sug­gests that stock­ing for con­ser­va­tion is small in scale, at least in the U.S. How­ever, the ar­ti­cle men­tions that some fish stock­ings could be put in sev­eral cat­e­gories.

Note that Halver­son (2008) doesn’t in­clude most of the ~1.9 billion salmon stocked by the U.S. ev­ery year, of which ~1.6 billion is stocked by Alaska. Ac­cord­ing to the figure 12 in Stopha (2018), in 2017, 73% of Alaska salmon hatch­ery pro­duc­tion was har­vested in the com­mon prop­erty com­mer­cial fish­eries, 19% was cost-re­cov­ery com­mer­cial har­vest (which funds hatch­ery op­er­a­tions), 8% was “[o]ther (brood­stock, etc.)”, and <1% was sport, per­sonal use, and sub­sis­tence har­vests. Morita et al. (2006) as­sumes that the ma­jor­ity of salmon stocked in Hokkaido Is­land (where ~1.2 billion salmon are re­leased an­nu­ally) is caught by com­mer­cial fish­er­man, but also men­tions sig­nifi­cant catches by recre­ational fish­ers. Over­all, it seems that most of the salmon is stocked for com­mer­cial fish­ers though there are also sig­nifi­cant num­bers stocked for recre­ational fish­ers.

In gen­eral, my im­pres­sion is that tens of billions of the fish are stocked to en­hance com­mer­cial fish­eries, billions of fish are stocked to en­hance recre­ational fish­eries, and the num­ber of fish stocked for other pur­poses is lower. How­ever, I am un­cer­tain. It could be that a big­ger pro­por­tion is stocked for recre­ational fish­ers or con­ser­va­tion.

Time spent in hatcheries

Wel­comme and Bartley (1998) claim that:

Mi­gra­tory and anadro­mous fish such as salmonids are usu­ally stocked at a small stage (fry) to ac­cli­mate to the na­tal river and to pre­pare for mi­gra­tion as their size in­creases. Cyprinids on the other hand are gen­er­ally stocked at a larger stage (finger­lings). Re­cre­ational fish­eries in­creas­ingly tend to rely on even larger fish of cacheable size and to rely less on grow-out in the nat­u­ral en­vi­ron­ment, al­though be­havi­our con­sid­er­a­tions may limit the up­per size at which fish can be stocked due to con­di­tion­ing in the hatch­ery en­vi­ron­ment.

Many other sources also use words like fry and finger­ling to de­scribe the age of stocked fish. How­ever, not all sources use these words con­sis­tently and the age of the fish it refers to de­pends on the species. In gen­eral, it seems that fry can be any­where be­tween 2 days to a cou­ple of months old,[12] while finger­lings are older than 3 weeks but younger than one year.[13]

Fry and fingerling

Wikipe­dia uses these images to illus­trate what fry and finger­ling look like.

Ac­cord­ing to the U.S. Aqua­cul­ture Cen­sus, in 2013 U.S. stocked:

  • 2.5 billion salmon (mean weight is 3.2 grams)

  • 719 mil­lion wall­eye (0.6 grams)

  • 177 mil­lion trout (89 grams)

  • 8.5 mil­lion cat­fish (250 grams)

  • 168 mil­lion other fish (3 grams)

The stats above sug­gest that the mean weight at re­lease can be very differ­ent for differ­ent species, which sug­gests that the mean age at re­lease can de­pend a lot on species as well. Note that these stats ex­clude eggs and that a more de­tailed (but older and less com­plete) break­down of fish stocked in the U.S. and their to­tal weights can be found in Halver­son (2008).

There is also a var­i­ance based on lo­ca­tion. For ex­am­ple, Mona­celli (2015) claims that in 2015 in New Jersey it was planned to stock nearly 600,000 trout of which the vast ma­jor­ity[14] would be 18 months old, 10.5 inches (27 cm) and about half a pound (227 grams). That is sig­nifi­cantly higher than the 89 grams av­er­age for trout in the U.S.[15] Table 1c in Munro and Wal­lace (2018) show that in Scot­land steel­head trout over 900 grams are pro­duced for stock­ing.

Such var­i­ance makes it very difficult to un­der­stand what is the mean age at stock­ing of all fish. Fur­ther­more, fish that are stocked for recre­ational fish­ers re­ceive more at­ten­tion, es­pe­cially if they are big­ger, which leads to un­rep­re­sen­ta­tive web search re­sults. Nev­er­the­less, I sum­marise my find­ings on the age and size of stocked fish be­low.

Ac­cord­ing to NPAFC (2019), about 90%[16] of the salmon stocked by Canada, Ja­pan, Korea, Rus­sia, and the U.S. are pink and chum salmon. Stopha (2018) claims that “pink and chum salmon are the most eco­nom­i­cal to raise be­cause fry can mi­grate to salt­wa­ter soon af­ter hatch­ing.” Ki­tada (2014) claims that chum salmon re­main in hatcheries (from eggs to re­lease) for about 6 months. Less com­monly stocked salmon and trout species seem to stay in hatcheries longer. Tatara et al. (2017) and Salmi­nen et al. (2007) dis­cuss re­leas­ing steel­head and At­lantic salmon when they are two years old ver­sus one-year-old. How­ever, not all stocked salmon are raised un­til this age. Ac­cord­ing to Figure 2 of Cowx (2002), in 1998 EU coun­tries stocked al­most ~4 billion salmon eggs, 14 billion salmon fry, and ~0.4 billion older salmon (parr or smolts). Similarly, Morita et al. (2006) cite Miyakoshi (2004) to claim that dur­ing 1993-2000 in Hokkaido Is­land, Ja­pan, 60-70% of re­leased masu salmon ju­ve­niles were fry and 10-20% were smolts (1-year-olds), but I was un­able to con­firm it in the cited ar­ti­cle. Also, masu salmon is only a small per­centage of the ~1.2 billion salmon stocked an­nu­ally by the is­land. Wel­comme and Bartley (1998) also men­tion that most salmon are stocked when they are fry. Sal­mon stocked for recre­ational fish­ers seem to be stocked when they are older, but they seem to be fewer in num­bers.

De Silva (2010) claims that in China, “strict guidelines are ad­hered to on the size of seed for stock­ing, of­ten around 15 cm in body length.” This sug­gests that China stocks rel­a­tively ma­ture fish. How­ever, it’s very un­clear to what pro­por­tion of fish stocked by China this ap­plies.

Ju­ta­gate and Kwangkhang (2015) claim that gi­ant fresh­wa­ter prawn “is nor­mally re­leased as 30 day old post lar­vae”, al­though in some coun­tries they are stocked when they are 45-90 days old.


As I un­der­stand it, all of the fol­low­ing sources in this sec­tion talk about fish stocked mostly for the benefit of recre­ational an­glers, al­though in some cases ecolog­i­cal rea­sons are also men­tioned.

Enger (2014) claims that 350 mil­lion small fish are stocked into Min­nesota’s lakes ev­ery year. It also states that “the vast ma­jor­ity of those are wall­eye fry, two- or three-day-old fish.” This video also shows that wall­eye are stocked soon af­ter hatch­ing.

Ac­cord­ing to figure 2 in Halver­son (2008), around 57% of fish stocked in the U.S. in 2004 (ex­clud­ing most of the salmon) were large (> 15.2 cm), ~36% were finger­lings (2.5 to 15.2 cm), and ~7% were fry (<2.5 cm).

Jano­nis (2014) claims that most of the fish stocked in Lithua­nia are one year old, or 3-4 months old. The ar­ti­cle also claims that 18-19 mil­lion fish were stocked in Lithua­nia in 2014, but at least 10 mil­lion of them were eggs.

Ar­ling­haus et al. (2015) claim that in Ger­many around 77 mil­lion fish were stocked in 2010 by an­glers in clubs and that in to­tal they weighed about 3,691 tons. That means that the av­er­age weight of a fish was around 48 grams which sug­gests that many of them spent con­sid­er­able time in hatcheries.

It seems that most of the trout are stocked when they are over one year old:

  • New York State’s 2017 and 2019 stock­ing plans show that over 80% of the 3 mil­lion trout and salmon stocked in Lake On­tario in both years were year­lings, and the rest are finger­lings. (Year­ling is gen­er­ally defined as “an an­i­mal that is one year old or has not com­pleted its sec­ond year.”)

  • Out of 1.2 mil­lion salmonid (mostly trout) re­port­edly re­leased in Vic­to­ria, Aus­tralia in 2017, 30% were “Fry up to 20gm”, 62.1% were “Year­lings − 20g to 150g”, 7.7% were “Ad­vanced Year­ling 150gm+”, and 0.2% were “Ex Brood Stock 1kg+”.

  • Us­ing the in­for­ma­tion in the ap­pendixes of Kerr (2006), I calcu­lated that out of 8.9 mil­lion fish stocked in On­tario in 2004, 0.8% were eyed eggs, 1.7% were fry, 16.8% were finger­lings, 79.5% were year­lings, 1.4% were subadults, and 0.1% were adults. Most of the stocked fish were trout.

  • Ki­tada (2014) claims that steel­head trout re­main in hatcheries for about a year.

Trout stocking Most trout seem to be stocked when they are over a year old

Welfare concerns

I don’t have the ex­per­tise re­quired to re­view fish welfare in depth. Su­perfi­cially, videos of U.S. sport fish hatcheries sug­gest that con­di­tions are not good.[17] In many cases, fish seem to be over­crowded, and no en­vi­ron­men­tal en­rich­ment can be seen. Fur­ther­more, many of the fish stocked in Cal­ifor­nia, Alaska, Bri­tish Columbia, and prob­a­bly many other places are triploid (with three com­plete sets of chro­mo­somes in­stead of the typ­i­cal two) to pro­tect the ge­netic in­tegrity of wild fish pop­u­la­tions. Ac­cord­ing to Greig (2019), all these fac­tors can be bad for fish welfare. We also see in videos that there are mul­ti­ple changes in the en­vi­ron­ment in hatcheries that may cause fish stress, es­pe­cially dur­ing the trans­porta­tion and stock­ing. Some fish are trans­ported in back­packs or thrown to lakes from air­planes and he­li­copters. Ur­ness (2017) men­tions that about 95% of trout finger­lings sur­vive the fall from a he­li­copter. It’s also pos­si­ble that many fish are in­jured by the fall. What is more, ac­cord­ing to Brown and Day (2002), “there is a large body of ev­i­dence show­ing that trans­porta­tion has a sig­nifi­cant effect on the stress lev­els of hatch­ery fish.” Fi­nally, there is suffer­ing in­volved in the col­lec­tion of eggs (e.g., see this video), al­though it has to be en­dured by rel­a­tively few in­di­vi­d­u­als.

Note that the con­cerns above may only ap­ply to fish grown in par­tic­u­lar coun­tries or for a par­tic­u­lar pur­pose. Con­di­tions in other hatcheries could be very differ­ent. How­ever, al­most all of these sys­tems are de­signed to max­i­mize eco­nomic out­puts. Judg­ing from the con­di­tions for an­i­mals farmed for food, we should ex­pect an­i­mal welfare to be com­pro­mised when­ever it is in con­flict with eco­nomic in­cen­tives.

It’s pos­si­ble that the welfare of stocked fish is al­igned with eco­nomic in­cen­tives more than the welfare of food an­i­mals. The healthier fish are at the time of stock­ing, the more likely they are to sur­vive in the wild and even­tu­ally get caught. Woot­ten (1998) claims:

The treat­ment of stocked fish once re­leased is ex­tremely difficult be­cause of the vol­ume of wa­ter in­volved. [...] It fol­lows then, that it will be es­pe­cially ad­van­ta­geous to en­sure that the health sta­tus of fish is as high as pos­si­ble be­fore they are stocked. [...] It is in any case im­por­tant to use fish of as high a qual­ity as pos­si­ble, prefer­ably from known, rep­utable sources. [...]. They must not be over­crowded or ex­posed to ex­ces­sively high tem­per­a­tures. Badly-trans­ported and thus highly stressed fish will be very vuln­er­a­ble to out­breaks of dis­ease.

On the other hand, in­cen­tives of hatcheries may not always be so straight­for­ward. Brown and Day (2002) claim:

Con­ser­va­tion biol­ogy has long em­pha­sized the im­por­tance of prac­tices such as en­vi­ron­men­tal en­rich­ment, pre-re­lease train­ing pro­grammes and soft re­lease to im­prove the post-re­lease sur­vivor­ship of cap­tive-bred an­i­mals. In con­trast, the pro­duc­tion of ecolog­i­cally vi­able in­di­vi­d­u­als is not part of the hatch­ery equa­tion be­cause the pro­duc­tion of large quan­tities of fish, rather than nat­u­ral his­tory, be­havi­our and ecol­ogy, largely guides hatch­ery prac­tices. Agers­borg (1934) states that rapid growth and high sur­vivor­ship within the hatch­ery have been the fun­da­men­tals of aqua­cul­ture for years. This po­si­tion still reigns supreme to­day. Many hatcheries are gov­ern­ment funded or at least heav­ily sub­si­dized. The level of suc­cess, and hence fund­ing is of­ten be­ing de­ter­mined by the num­ber of fish re­leased rather than by the sur­vival rates of those fish or the re­turn to an­glers and the in­dus­try.

If that is still true to­day, we should ex­pect there to be more prob­lems with fish health in hatcheries as well. Fur­ther­more, Brown and Day (2002) also de­scribe how be­hav­ioral defic­its re­sult in poor sur­vival rates (com­monly 1-5%[18]) and suffer­ing af­ter the re­lease:

Fol­low­ing re­lease many cap­tive-reared fish may not eat at all for sev­eral days, weeks or up to a month. When they do start to for­age, they typ­i­cally take up high risk and en­er­get­i­cally costly po­si­tions[...] As a re­sult hatch­ery-reared fish show sub­stan­tial weight loss com­pared to trans­planted wild fish and their mor­tal­ity rates can be up to 10 times greater than that of wild fish.
Fish reared in cap­tivity are com­pletely preda­tor naïve be­cause they are pro­vided with no op­por­tu­nity to in­ter­act with preda­tors prior to re­lease. Pre­da­tion is thought to be the prin­ci­pal cause of mor­tal­ity among re­leased hatch­ery fish

Com­par­i­son with fish farming

Lym­bery (2002) sug­gests that re­leas­ing fish to grow in their nat­u­ral en­vi­ron­ment and re­cap­tur­ing them when they are ma­ture (sea ranch­ing) could be bet­ter for fish welfare than grow­ing fish in farms for all their lives. The re­port calls it “free range farm­ing.” It states that it has a po­ten­tial for high welfare but “it brings with it nat­u­ral threats such as in­creased pre­da­tion and food short­age.” I think that the com­par­i­son be­tween the two sys­tems is more com­pli­cated. Since the mor­tal­ity of stocked fish af­ter the re­lease is much higher than in farms, more fish have to be raised in hatcheries for the same amount of meat. Bet­ter data on mor­tal­ity rates, age at re­lease, and size at slaugh­ter would be needed to calcu­late whether farmed fish re­quire less or more time spent in hatcheries/​farms than stocked fish for the same amount of meat. It should also be noted that stocked fish only live in hatcheries when they are young. I am not sure if there are rea­sons to think that young fish are less morally rele­vant than adults. How­ever, stocked fish may also suffer af­ter the re­lease, in­clud­ing pos­si­bly cruel deaths. Fi­nally, the two sys­tems have differ­ent ecolog­i­cal effects, which could be the most im­por­tant fac­tor.

Ecolog­i­cal effects

In­gram and Silva (2015) claim that fish stock­ing can also have nega­tive effects on wild pop­u­la­tions, in­clud­ing:

  • A pos­si­ble loss of ge­netic di­ver­sity.

  • Trans­mis­sion or in­tro­duc­tion of in­fec­tious dis­eases and pathogens.

  • Re­leas­ing chem­i­cals that are com­monly used in aqua­cul­ture fa­cil­ities.

  • Non-en­demic stocked fish may out-com­pete, dis­place or prey on na­tive en­demic species al­ter­ing food web and com­mu­nity struc­ture (e.g., see MacDon­ald (2018)).

Cooke and Cowx (2006) state that fish stock­ing is rec­og­nized as a global en­vi­ron­men­tal degra­da­tion prob­lem. Young et al. (2014) sum­marises a sci­en­tific con­sen­sus on salmon stock­ing. It claims that stock­ing may in­crease the num­ber of adults tem­porar­ily, but is likely to re­duce the longer-term pro­duc­tivity of a pop­u­la­tion, partly due to loss of ge­netic in­tegrity.

It should also be noted that many of the stocked fish are preda­tors. Not only does this mean that they prey on other fish, worms, and in­sects when re­leased, but also that in hatcheries they are fed diets that in­clude fish, poul­try and other an­i­mal prod­ucts, just like fish farmed for food.[19] Fish­count.org.uk es­ti­mated that roughly 440-1,200 billion wild fish were used as aqua­cul­ture feeds in the late 2000s and this num­ber has prob­a­bly in­creased since due to the fast growth of aqua­cul­ture. Even though aqua­cul­ture of stocked fish is prob­a­bly only re­spon­si­ble for a small frac­tion of this num­ber, it may still af­fect many in­di­vi­d­u­als.

There are prob­a­bly many other effects of fish stock­ing, some of which are nor­mally con­sid­ered to be pos­i­tive and hence are less dis­cussed within the liter­a­ture. Be­fore se­ri­ously con­sid­er­ing re­duc­ing the num­ber of stocked fish, it’s vi­tal to un­der­stand how fish stock­ing af­fects wild an­i­mal welfare as this could be the most im­por­tant fac­tor. How­ever, this is a com­plex topic that is be­yond the scope of this ar­ti­cle.

Who are the de­ci­sion mak­ers?

If we want to in­fluence fish stock­ing de­ci­sions, we will need to know the de­ci­sion mak­ers. In­gram and Silva (2015) sum­marises the situ­a­tion:

A wide range of stake­hold­ers are in­volved in stock­ing pro­grams, both di­rectly and in­di­rectly, and in­clude de­ci­sion-mak­ers at all lev­els from village lead­ers to coun­try agen­cies, fish­eries, aqua­cul­ture, wa­ter, en­vi­ron­men­tal and con­ser­va­tion man­agers, wa­ter agen­cies and end users (e.g. com­mer­cial and recre­ational fish­ers, fish­mon­gers and con­sumers). Water­ways and wa­ter bod­ies that are stocked may be man­aged by agen­cies for the state as com­mon pool (non-pri­vate own­er­ship), or be owned by in­di­vi­d­u­als, com­mu­ni­ties or cor­po­rate bod­ies. [...] Often, par­tic­u­larly in de­vel­oped coun­tries, stock­ing ac­tivi­ties are gov­erned by var­i­ous poli­cies, reg­u­la­tions and leg­is­la­tion, to en­sure that stock­ing is con­ducted in a re­spon­si­ble an ecolog­i­cally sus­tain­able man­ner. Stock­ing of pub­lic wa­ters tends to be more heav­ily reg­u­lated by au­thor­i­ties [...] In con­trast, stock­ing of pri­vate wa­ters (on pri­vate land) tends to be less reg­u­lated.

Halver­son (2008) claims that in the U.S. most of the stock­ing was done by state agen­cies and that some stock­ing was also done by the U.S. Fish and Wildlife Ser­vice. It also claims that man­agers have made sub­stan­tial changes in their ap­proach to fish stock­ing in re­sponse to crit­i­cism and de­bate about the ecolog­i­cal im­pact. It cites Jack­son et al. (2004) which con­cluded from a sur­vey of fish­eries man­agers that “pub­lic pres­sure to stock cul­tured fishes is an im­por­tant in­fluence on agency de­ci­sions to use cul­tured fishes.” This sug­gests that pub­lic pres­sure could maybe be used to miti­gate welfare con­cerns as well. It should also be noted that agen­cies some­times con­sult with the an­gling pub­lic to de­cide how to stock wa­ters.

Sim­cock (2017) claims that “in Alaska, large-scale salmon en­hance­ments are run by com­mu­nity-based Aqua­cul­ture As­so­ci­a­tions.” De­ci­sions about the num­ber of stocked fish seem to be at least par­tially made by the Alaska Board of Fish­eries which some­times calls the pub­lic for pro­pos­als. Smoker and Heard (2007) men­tions that some hatcheries in Alaska re­lease over 100 mil­lion ju­ve­nile salmon an­nu­ally. This shows that a large num­ber of in­di­vi­d­u­als could be helped by in­fluenc­ing a sin­gle hatch­ery.

Silva et al. (2015) claim that in Thailand stock­ing is im­ple­mented by many agen­cies such as Depart­ment of Fish­eries, Tam­bon (Lo­cal) Ad­minis­tra­tion Or­ga­ni­za­tion, provin­cial agen­cies, Elec­tric­ity Gen­er­at­ing Author­ity of Thailand and other pri­vate sec­tor and gov­ern­ment agen­cies. The ar­ti­cle also claims that in 2013, the Depart­ment of Fish­eries stocked 1.3 billion finger­lings which seems to be the ma­jor­ity of fish stocked in Thailand.

Pos­si­ble interventions

Re­cre­ational fishing

Re­duc­ing the num­ber of fish stocked for recre­ational fish­ing would de­crease the num­ber of:

  • fish that are be­ing raised hatcheries,

  • fish that starve and strug­gle to sur­vive af­ter stock­ing,

  • fish that have to en­dure be­ing caught by fish­ers (many of which are then re­leased in­jured, most of the oth­ers die with­out a hu­mane slaugh­ter),

  • worms, fish, and other an­i­mals used as a live bait

All of these effects seem to be pos­i­tive. How­ever, it would also have var­i­ous ecolog­i­cal effects, which would need to be well-un­der­stood be­fore tak­ing ac­tion be­cause they could be more im­por­tant than the effects listed above. Also, I think it would be im­por­tant to make it clear that we are not against stock­ing for con­ser­va­tion as such a po­si­tion would prob­a­bly be much more con­tro­ver­sial.

The num­ber of stocked sport fish could maybe be re­duced by lob­by­ing rele­vant agen­cies. Or per­haps the pro­hi­bi­tion of stock­ing for recre­ational fish­ers could be achieved by bal­lot ini­ti­a­tives.[20] Maybe the pro­hi­bi­tion could be added to some propo­si­tions that are pri­mar­ily about im­prov­ing con­di­tions for farmed food an­i­mals (per­haps to­gether with pro­hi­bi­tions of other cruel prac­tices like farm­ing fish to be used as live bait and sel­l­ing pet snakes). I imag­ine that many vot­ers wouldn’t like that the tax­payer money is spent to stock fish for recre­ational an­glers, es­pe­cially if many of them die in­stead of be­ing caught. Fur­ther­more, con­trary to welfare re­forms, such cam­paign­ing for pro­hi­bi­tions can be com­pat­i­ble with a more rights-based per­spec­tive of an­i­mals (see Fran­cione (2007)), which could al­low an­i­mal ac­tivists to cam­paign as more of a united front or at least to avoid in­fight­ing.[21]

Another op­tion is try­ing to re­duce the de­mand for sport fish stock­ing by de­creas­ing the pop­u­lar­ity of recre­ational fish­ing. It may be difficult to change peo­ple’s be­hav­ior di­rectly, but per­haps an­gling reg­u­la­tions could be made more re­stric­tive. Note that stock­ing is just one of many po­ten­tially nega­tive effects of recre­ational fish­ing, as billions[22] of fish are caught by an­glers wor­ld­wide, and countless an­i­mals are used as live bait. Fur­ther­more, ar­gu­ing against hu­mans get­ting plea­sure from di­rectly kil­ling or in­jur­ing an­i­mals could help to ex­pand so­ciety’s moral cir­cle. Fi­nally, re­stric­tions on an­gling could be eas­ier to in­fluence than re­stric­tions on food pro­duc­ers who have pow­er­ful lob­bies.

It could be that it’s eas­ier to pre­vent the emer­gence of new recre­ational fish­eries rather than re­duc­ing the scale of ex­ist­ing ones. Ac­cord­ing to Funge-Smith et al. (2018), fish­ing li­cense sales have been de­clin­ing in coun­tries like the U.S. and France, but “[t]here is ev­i­dence that recre­ational fish­eries are grow­ing strongly in emerg­ing economies.” If this is true, pre­vent­ing the de­vel­op­ment of sport fish­eries and sport fish stock­ing in emerg­ing economies could be more promis­ing than tar­get­ing de­vel­oped coun­tries.

Com­mer­cial fishing

Loren­zen (2014) claims that “[m]any en­hance­ments fail to meet their ob­jec­tives and some do con­sid­er­able ecolog­i­cal or ge­netic harm, yet such en­hance­ments of­ten per­sist.” This sug­gests that the num­ber of fish stocked could maybe be re­duced by ar­gu­ing to stop in­effec­tive and ecolog­i­cally harm­ful pro­grams. How­ever, I’m un­cer­tain whether stock­ing fishes to en­hance com­mer­cial fish­eries is bad from the an­i­mal welfare per­spec­tive. If fish were not stocked, that would still likely re­sult in less ‘wild’ fish be­ing caught. It’s pos­si­ble that there would be an in­crease in fish farm­ing to com­pen­sate for the loss, as this is how de­creas­ing catches are already in­creas­ingly com­pen­sated. It’s un­clear which of these sys­tems in­volves more suffer­ing.

Brown and Day (2002) sug­gests re­quiring higher sur­vival rates of stocked fish and sug­gests ways to do it. It would also likely in­crease the cost per fish and lead to fewer in­di­vi­d­u­als be­ing needed to achieve similar effects for fish­eries. This could be good be­cause fewer fish would need to en­dure be­ing raised in hatcheries, and there could be less suffer­ing af­ter the re­lease due to lack of sur­vival skills. How­ever, Brown and Day (2002) also claim that this could make fish stock­ing more effi­cient. It’s un­clear whether that would be bet­ter for an­i­mals in the long run be­cause it could make stock­ing more pop­u­lar.

Also note that when con­sid­er­ing in­ter­ven­tions in this space, it’s also im­por­tant to take into ac­count the effect on peo­ple who de­pend on fish­ing and fish stock­ing as the source of liveli­hood or food.

Im­prov­ing con­di­tions in hatcheries

The Open Philan­thropy Pro­ject has re­cently recom­mended sev­eral grants to im­prove con­di­tions of farmed fish. Per­haps im­prov­ing the con­di­tions of fish raised for stock­ing is also an op­tion. How­ever, it would be differ­ent cam­paigns be­cause de­ci­sion mak­ers are differ­ent. Fur­ther­more, it could be harder for the gen­eral pub­lic to un­der­stand the ask. Re­quiring bet­ter con­di­tions in hatcheries may also de­crease the num­ber of fish stocked, and we may still have to make sure that it would be good for an­i­mals.

Over­all, I am very un­cer­tain whether this or other in­ter­ven­tions I sug­gested could be cost-effec­tive.

Ques­tions for fur­ther research

I am un­cer­tain if more re­search on this topic should cur­rently be a pri­or­ity. How­ever, if such re­search was done, these are the top­ics that I think are the most im­por­tant:

  • What are the most promis­ing in­ter­ven­tions? In which coun­tries could they be im­ple­mented? How cost-effec­tive could they be com­pared to other an­i­mal welfare in­ter­ven­tions? If they could be effec­tive, what should be the next steps? I think that re­search­ing these prac­ti­cal ques­tions is of the high­est pri­or­ity.

  • How does fish stock­ing im­pact wild an­i­mal welfare? It’s clear that fish stock­ing has sig­nifi­cant ecolog­i­cal im­pacts. There seems to be quite a lot of liter­a­ture about its effects on the health of ecosys­tems and how it may be caus­ing en­vi­ron­men­tal degra­da­tion, but I haven’t seen any dis­cus­sion about the effects on wild an­i­mal welfare.

  • Would re­duc­ing the num­ber of stocked fish re­duce the over­all amount of an­i­mal suffer­ing? Note that the an­swer may be differ­ent for differ­ent species, coun­tries, and pur­poses of fish stock­ing.

  • What are the biggest sources of suffer­ing for stocked fish? Are there cheap ways to re­duce suffer­ing? It should be taken into ac­count that suffer­ing can hap­pen both in hatcheries, and af­ter the re­lease.

  • How much time do fish spend in hatcheries? I was sur­prised by how lit­tle in­for­ma­tion I was able to find about it. Since peo­ple who work in fish stock­ing may know the an­swers, maybe some in­for­ma­tion could be gained by sim­ply ask­ing them.

  • Are ju­ve­nile fish less sen­tient and morally rele­vant than adult fish? When do fish be­come sen­tient? For ex­am­ple, Birch (2018) ar­gues that ze­brafish may already be sen­tient at five days post fer­til­iza­tion be­cause they seem to re­spond to nox­ious stim­uli the same way adults do. More ev­i­dence like this could help to see how im­por­tant are con­di­tions in hatcheries dur­ing the early stages of fish de­vel­op­ment.

Note that I (and Re­think Pri­ori­ties in gen­eral) cur­rently have no plans to re­search any of these ques­tions.

Ap­pendix: huge num­bers of ju­ve­niles raised for an un­known reason

Dur­ing my re­search for this ar­ti­cle, I en­coun­tered some sur­pris­ingly high num­bers of ju­ve­niles that are raised in hatcheries, seem­ingly to be farmed for food. Hishamunda and Subas­inghe (2003) provide the fol­low­ing statis­tics about China’s aqua­cul­ture:

In 2000, it took about 2.56 mil­lion tonnes of finger­lings to stock fresh­wa­ter aqua­cul­ture sys­tems. Th­ese were pro­duced from 602.2 billion fish fry. Of these, 542 billion fry, or about 92 per­cent, were pro­duced ar­tifi­cially. For marine aqua­cul­ture seed pro­duc­tion was as fol­lows: 3 882 mil­lion of fish fry; 58.3 billion shrimp post-larvae

Ac­cord­ing to an es­ti­mate from Fish­count, China pro­duced much fewer (28-92 billion) farmed fish in 2015. I don’t think that the quote is a mis­take be­cause the table 7 in Li (2003) con­tains the same num­ber. Fur­ther­more, Le­ung et al. (2007) claim that “in 2004, 711.6 billion fresh­wa­ter fish fry and 2.41 billion marine/​brack­ish fish fry were pro­duced in China.” Honglang (2007) claims that, ac­cord­ing to an in­ves­ti­ga­tion re­port in 2001, there are 16 435 fish seed pro­duc­tion units in China, and the “to­tal pro­duc­tion of all the hatch­ery is 13 385 billion in­di­vi­d­u­als which meet the need for grow-out pro­duc­tion.” The num­ber is big­ger at least partly be­cause it in­cludes shel­lfish, crabs and rep­tiles. Grow-out refers to a stage when in­di­vi­d­u­als be­come big­ger which sug­gests that these ju­ve­niles are farmed un­til slaugh­ter. How­ever, Daqing et al. (2010) cites the ex­act same num­ber of fish seed pro­duc­tion units but seems to as­sert that they are pro­duc­ing very high num­bers of lar­vae that are stocked into nat­u­ral wa­ters:

The hy­brids, trans­genic and im­pure species should not be stocked in the nat­u­ral wa­ter. [...] Cur­rently, China has 16 435 lar­vae bases [...] More than 90 species are used in en­hance­ment ac­tivi­ties. The num­ber of lar­vae of shrimp, fresh­wa­ter fish and shel­lfish for re­leas­ing was 392.8 billion, 687.3 billion and 1262.2 billion respectively

Hishamunda and Subas­inghe (2003) also claim that China has “a rel­a­tively well-es­tab­lished fresh­wa­ter seed pro­duc­tion tech­nol­ogy” which sug­gests that seed pro­duc­tion of a similar scale is hap­pen­ing in other coun­tries as well. Ku­mar et al. (2018) that in In­dia “Quan­tity of carp seed pro­duc­tion has gone up to 49.5 billion fry in 2015-16.” Ac­cord­ing to an es­ti­mate from Fish­count, In­dia pro­duced sig­nifi­cantly fewer (3-15.5 billion) farmed fish in 2015.

On the other hand, the num­ber of ju­ve­niles pro­duced by Brazil seems to be similar to the num­ber of slaugh­tered fish. Su­plicy (2007) claims that in Brazil “the sum of the seed pro­duc­tion of all fresh­wa­ter fish species was 617 mil­lion seed in 2005.” It seems that most of these fish are used for fish farm­ing and less than 75 mil­lion were used for fish stock­ing into nat­u­ral wa­ters. The num­ber of seeds used for aqua­cul­ture is in the range of the es­ti­mated 460-1,545 mil­lion farmed fish pro­duced by Brazil’s aqua­cul­ture in 2015.

I am con­fused about what some of these big num­bers are. I think they are the num­bers of ju­ve­niles pro­duced for aqua­cul­ture. But if they are, it’s un­clear why these num­bers of ju­ve­niles pro­duced by In­dia and es­pe­cially by China are so much higher than es­ti­mates of slaugh­tered farmed fish. I’m not sure if pre-slaugh­ter mor­tal­ity rates can ex­plain it. Ac­cord­ing to Greig (2019), “pre-slaugh­ter mor­tal­ity rates for some of the most com­monly farmed fishes range from ap­prox­i­mately 15%–80% over the en­tire pro­duc­tion cy­cle” and “the mor­tal­ity rates may be quite high in very young fishes and much lower as fishes ap­proach slaugh­ter.” Since hatch­ery-pro­duced ju­ve­niles are already past the first stage of their lives in which pre-slaugh­ter mor­tal­ity is the high­est, mor­tal­ity dur­ing the grow-out pe­riod shouldn’t be that high. It could also be that the num­ber of farmed fish that are slaugh­tered is higher than is es­ti­mated, but I would be sur­prised if it was that much higher. I think this ques­tion should be in­ves­ti­gated fur­ther.


Tip: to nav­i­gate be­tween the main text and end­notes more effi­ciently, you can use Ctrl + F to search for strings like “[1]”. This can help you to both, find the end­note, and get back to the part of the text where the foot­note was placed.

[1] There are many syn­onyms for fish stock­ing, in­clud­ing stock en­hance­ment, fish­eries en­hance­ment, fish stock prop­a­ga­tion, ocean ranch­ing, sea ranch­ing, ocean ranch­ing, marine ranch­ing, aqua­cul­ture-based en­hance­ment, aqua­cul­ture-based fish­eries en­hance­ment, restora­tion aqua­cul­ture, cul­ture-based fish­eries, and re­stock­ing. Many of these terms have slightly differ­ent mean­ings. For ex­am­ple, see defi­ni­tions here.

[2] Ar­ti­cles that talk about fish stock­ing from an­i­mal welfare per­spec­tive in­clude Brown and Day (2002), Braith­waite and Sal­vanes (2010), and Braith­waite and Sal­vanes (2011). I was un­able to ac­cess Braith­waite and Sal­vanes (2011).

[3] I have the fol­low­ing dis­agree­ments with Char­ity En­trepreneur­ship’s re­port on fish stock­ing and bait­fish:

  • Ac­cord­ing to the re­port, fish stock­ing in­ter­ven­tions may be less promis­ing be­cause the in­dus­try is on the de­cline. The main cited ev­i­dence for the de­cline is the claim in Halver­son (2008) that in the U.S., “based on the data from the fed­eral gov­ern­ment and the 33 states for which data was available in all years, it ap­pears that the to­tal num­ber of fish stocked in the 1930s was about 7 times higher than in 2004.” I think that figures of the 1930s are not very rele­vant for de­ter­min­ing the cur­rent trends. The graph in the trends sec­tion of this ar­ti­cle sug­gests that the num­bers stopped de­clin­ing in the 1950s. Fur­ther­more, Halver­son (2008) also claims that the to­tal weight of the stocked fish in the U.S. has in­creased dra­mat­i­cally since the 1930s. Fi­nally, this ev­i­dence is only from one coun­try and ig­nores much of the stocked salmon. Over­all, my re­search in this ar­ti­cle weakly sug­gests that the num­ber of stocked fish is more likely to be in­creas­ing than de­creas­ing. Fi­nally, fish stock­ing seems likely to re­main very big in scale even if it is de­clin­ing.

  • I think that their cited lengths of the time that fish re­main in hatcheries are not rep­re­sen­ta­tive. The ev­i­dence in this ar­ti­cle sug­gests that most stocked fish spend much less than a year in hatcheries. Note that CE’s claims on this is­sue were based on my own pre­limi­nary re­search which in­cor­rectly sug­gested that most fish re­main in hatcheries for longer.

  • The re­port claims that “it is also hard to in­crease the welfare of fish once they have been stocked.” While tech­ni­cally I agree with this point, I’d like to point out that Brown and Day (2002) ar­gue that con­di­tions in hatcheries that pre­pare fish for life in the wild can greatly in­crease the welfare af­ter stock­ing.

  • The re­port cites crit­i­cisms of fish stock­ing from ecolog­i­cal and effec­tive­ness per­spec­tives to claim that fish stock­ing is likely to be reg­u­lated in the fu­ture with­out any ad­di­tional in­ter­ven­tion (i.e., that it has a high “coun­ter­fac­tual re­place­abil­ity”). While I agree that this is true, I would also like to point out that fish stock­ing has been prac­ticed for over a hun­dred years and it doesn’t seem to be on the de­cline. Over­all, the fact that it is crit­i­cized in other ways makes me more (not less) op­ti­mistic about the area be­cause it makes it eas­ier to achieve change. It means that we would have al­lies and that it would be more difficult for op­po­nents to ar­gue that fish stock­ing should con­tinue.

Note that CE did not look into the is­sues deeply and limited the time spent on the re­port to 25 hours be­cause they found it un­likely that they will de­cide to found a char­ity tack­ling these prob­lems.

[4] The word­ing in the trans­la­tion of China’s Fish­eries Plan is un­usual, but Mal­lory (2016) also as­sumes that the plan in­cludes stock­ing 150 billion ju­ve­nile fish. The sen­tence in ques­tion is “计放流各类水产苗种1500亿尾”. I asked a Chi­nese per­son, and they told me that it seems only to in­clude hatched fish, but it is vaguely defined in Chi­nese dic­tio­nar­ies.

[5] Also, Cao et al. (2017) claim that “[b]y 2008, stock en­hance­ment was prac­ticed for over 100 species of fin­fish, crus­taceans, and shel­lfish, and al­most 20 billion ju­ve­niles were re­leased an­nu­ally”.

[6] Halver­son (2008) es­ti­mated that 1.75 billion fish were stocked by 50 state agen­cies and the U.S. Fish and Wildlife Ser­vice in the United States in 2004. The differ­ence be­tween the es­ti­mates is mostly due to Halver­son (2008) not in­clud­ing most of the 1.9 billion salmon that the U.S. stocks ev­ery year.

[7] Daniels and Watan­abe (2011) claims that be­tween 1977 and 2005 Ja­pan re­leased 50 billion red seabream, 43 billion flounders, and 14 billion black seabream. How­ever, I’m not sure if these num­bers are cor­rect. Figure 8 in Koichi, et al. (2015), Table 1 in this Asian Aqua­cul­ture ar­ti­cle, and Table 1.1 in this FAO ar­ti­cle all claim that much lower num­bers of these fish were re­leased.

[8] This is be­cause I think that the big­ger the stock­ing pro­ject, the more likely I was to find a num­ber of fish stocked by it. Both, be­cause the num­ber was more likely to be re­ported, and more likely to be men­tioned in the ar­ti­cles I read. Also, I didn’t in­clude some smaller num­bers I found from the list (they were mostly num­bers of a spe­cific fish stocked in a spe­cific re­gion). Fi­nally, of­ten I searched with a key­word “billions” be­cause that tended to give more gen­eral and in­ter­est­ing re­sults. How­ever, it may have also bi­ased my search to­wards big­ger num­bers.

[9] As I un­der­stand it, rais­ing big num­bers of fish re­quires spe­cial­ized build­ings, ponds (un­less fish are re­leased when they are very small), and non-triv­ial re­lease op­er­a­tions. I think it would be difficult to do all this ac­tivity on a large scale with­out be­ing de­tected. Fur­ther­more, from ar­ti­cles like Lamp (2018), it seems that ille­gal stock­ing is done by an­glers who want to im­prove their own an­gling ex­pe­rience. I find un­likely that they would make sub­stan­tial in­vest­ments into the ac­tivity. How­ever, I am not con­fi­dent that my un­der­stand­ing of the topic is cor­rect.

[10] Ac­cord­ing to Stopha (2018), from 1995 to 2016 in Alaska’s salmon hatcheries, an­nual egg col­lec­tions have ranged from about 1.6 to 2 billion eggs, and an­nual salmon re­leases have ranged from about 1.4 to 1.7 billion ju­ve­niles. This also sug­gests that mor­tal­ity in salmon hatcheries is less than 15%. If some eggs re­main un­fer­til­ized, it could be less.

[11] This ar­ti­cle ex­plains how to find slaugh­ter to­tals within the FAO web­site.

[12] Fry is defined as “a re­cently hatched fish that has reached the stage where its yolk-sac has al­most dis­ap­peared and its swim blad­der is op­er­a­tional to the point where the fish can ac­tively feed for it­self.” Be­fore yolk-sac dis­ap­pears, salmon and trout are called alevin. How long the alevin stage lasts de­pends on wa­ter tem­per­a­ture (Ojan­guren et al. (1999)) and species:

  • Park et al. (2017) claim that the com­mon carp (and most other cyprinids) ab­sorb their yolk sac in 4-5 days.

  • This hatch­ery brochure claims that its trout are alev­ins for 4-6 weeks. FAO claims that steel­head trout’s yolk sac lasts for 2-4 weeks.

  • In na­ture, salmon re­main alevin for a few weeks or a few months. In hatcheries, con­di­tions are op­ti­mized for fast growth, so yolk sac is prob­a­bly ab­sorbed in less than a month.

FAO (2003) refers to 7-day-old stocked fish as fry. Penn­syl­va­nia Fish & Boat Com­mis­sion claims that fry are “[t]yp­i­cally be­tween 3 and 5 days old. Th­ese fish are dis­tributed to pub­lic fish­ing wa­ters at a time soon af­ter hatch­ing while the yolk sac is be­ing ab­sorbed.” It calls 21-day-old fish ad­vanced fry. Nei­ther of these sources men­tions species. An FAO page claims that alev­ins can also be referred to as yolk-sac fry which sug­gests that the word fry can be used for ju­ve­niles re­gard­less of whether their yolk-sac is ab­sorbed. Over­all, I’m un­cer­tain how old are stocked fish which are referred to as fry.

[13] Finger­ling is defined as “a young fish, es­pe­cially one less than a year old and about the size of a hu­man finger.” Ac­cord­ing to the Penn­syl­va­nia Fish & Boat Com­mis­sion, “de­pend­ing upon the species, these fish are 3 or more months in age.” How­ever, Horváth et al. (1985) claim that “the in­ten­sive pro­duc­tion of ad­vanced carp fry about 3 cm long, in well pre­pared earthen ponds, takes 21-30 days. They are then trans­ported to finger­ling ponds for fur­ther rear­ing” which sug­gests that carp can be called finger­ling when they are 21 days old or older.

[14] In ad­di­tion, Mona­celli (2015) claims that some fish stocked in New Jersey in 2015 would be “young,” and oth­ers would be be­tween 2.5 and 3.5 years old. Th­ese older large fish were used to ob­tain and fer­til­ize eggs for the breed­ing pro­gram in a hatch­ery. Spence (2013) men­tions see­ing 13 kilo­gram trout in hatcheries. I guess that such big fish were also used to ob­tain fer­til­ized eggs.

[15] Another ex­am­ple of var­i­ance can be seen in Alaska’s database of sport fish stock­ings. Stocked fish vary from less than 0.1 oz. (3 grams) to 3 lbs., 7.1 oz. (1.6 kg). There is even a lot of var­i­ance in the size of in­di­vi­d­u­als of the same species stocked in the same lake.

[16] See figure 6 in NPAFC Statis­tics: Pa­cific Sal­monid Catch and Hatch­ery Re­lease Data.

[17] Many of these hatcheries are open to vis­i­tors, per­haps some more in­for­ma­tion can be gained this way if needed. The main value would prob­a­bly come from ask­ing ques­tions.

[18] I’m not sure if these sur­vival rates are typ­i­cal, or if Brown and Day (2002) cited the low­est sur­vival rates to illus­trate the point. Kennedy et al. (2012) claim similarly low sur­vival rates of hatch­ery-bred salmon. Lym­bery (2002) cites much higher sur­vival rates for salmon (be­tween 6% and 40%) and say that they are com­pa­rable with 10% of wild salmon re­turn­ing to their home river af­ter ma­tur­ing at sea. Over­all, sur­vival af­ter the re­lease un­doubt­edly de­pends on many fac­tors that are be­yond the scope of this ar­ti­cle.

[19] Braith­waite and Sal­vanes (2010) claims that

Many of the fish pro­teins and oils are now be­ing re­placed with plant-based prod­ucts, but from a welfare per­spec­tive, the use of plant pro­tein and oils in a car­nivorous fish diet is not nat­u­ral. The effects of new feeds must be care­fully as­sessed, not just in terms of growth rate of the farmed fish, but also in terms of the effect they have on ap­petite and hunger. Cur­rent re­search is fo­cus­ing on ways to man­u­fac­ture more veg­etable-based feeds or feeds based on other sources of pro­tein, such as poul­try.

Also, note that very young fish seem to be of­ten fed live in­ver­te­brates (such as brine shrimp and ro­tifers).

[20] It’s pos­si­ble that pro­hibit­ing fish stock­ing for the benefit of recre­ational fish­ers could in­crease the scale of ille­gal stock­ing. The num­ber of fish stocked ille­gally would prob­a­bly still be much lower than the num­ber of fish stocked to­day. How­ever, if ille­gal stock­ing would be done with less aware­ness of the im­pact on the ecosys­tem, it could still cause sig­nifi­cant en­vi­ron­men­tal dam­age.

[21] Some an­i­mal rights ac­tivists are against many of the changes that the an­i­mal welfare move­ment is cam­paign­ing for. They ar­gue that these changes can be coun­ter­pro­duc­tive in the long term be­cause they send the mes­sage that treat­ing an­i­mals as prop­erty can be ac­cept­able. This some­times leads to in­fight­ing which can re­duce the le­gi­t­i­macy of an­i­mal ad­vo­cacy as the whole. For ex­am­ple, PETA op­posed Cal­ifor­nia’s Prop 12 which de­manded bet­ter con­di­tions for farmed an­i­mals. Fur­ther­more, the op­po­si­tion to Prop 12 was en­tirely funded by a nom­i­nally farm-an­i­mal pro­tec­tion or­ga­ni­za­tion (HFA) which claimed that Prop 12 is bad for an­i­mals. HSUS ac­cused HFA of mis­in­for­ma­tion. Prevent­ing such in­fight­ing is one of the rea­sons why it’s prefer­able to fo­cus on in­ter­ven­tions that are good from both, An­i­mal Rights and An­i­mal Welfare per­spec­tives.

[22] Cooke and Cowx (2004) ex­trap­o­lated from Canada’s statis­tics from the year 2000 that the to­tal an­nual recre­ational catch wor­ld­wide may be on the or­der of 47 billion fish. It should be noted that the num­ber of fish caught in Canada de­creased from 233 mil­lion in 2000, to 194 mil­lion in 2015, of which 135 mil­lion were re­leased. Fur­ther­more, it’s un­clear whether Canada is rep­re­sen­ta­tive of the World as a whole in this re­gard. Funge-Smith et al. (2018) es­ti­mated that of the coun­tries where some data are available (com­bined pop­u­la­tion 2.6 billion), some 6.7% (174.5 mil­lion) of the pop­u­la­tion en­gages in recre­ational fish­ing in in­land wa­ters at some time in a year. The per­centage for Canada is only slightly big­ger than av­er­age (7.5%). How­ever, I ex­pect the per­centage of recre­ational fish­ers in coun­tries for which data is not available to be lower.


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This es­say is a pro­ject of Re­think Pri­ori­ties. It was writ­ten by Saulius Šimčikas. Thanks to David Moss, Derek Foster, Karolina Sarek, Mar­cus A. Davis, and Peter Hur­ford for re­view­ing drafts of this post and mak­ing valuable com­ments. I want to es­pe­cially thank Kieran Greig who made very many valuable sug­ges­tions.

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