Thanks, MHR. Quick reply to say: Good question, but I don’t know the answer offhand, as I didn’t come up with that number myself. Many different people helped with the literature reviews. I’ll get in touch with the relevant person and get back to you.
Sorry for the delay, MHR! It took a bit to get to the bottom of this. In any case, the short version is that the 8-13M neuron count for both salmon and carp should be read as the lowest reasonable estimate, not our best guess. We got the number from the zebrafish literature—specifically, a study by Hinsch & Zupanc (2007) (cited in the table) who reported that the total number of brain cells for adult zebrafish varied between 8 and 13 million. In the notes associated with the Welfare Range Table, we had a caveat that neuron counts are very hard to come by in fish and, in any case, only represent a snapshot in time, because the teleost brain is constantly growing. Moreover, no one has done total neuron count estimates for salmon or carp, whereas zebrafish are often used as a model species and are well-studied; so, we simply used those values as a placeholder. Granted, then, the 8-13M number may well be an underestimate due to the size differences between zebrafish and salmon, and we do see the appeal of using Invincible Wellbeing’s curve fits to come up with a higher number. However, we tried to stick as close to the empirical literature as possible. And truth be told, because neuron counts are just one of several models we include, using a higher number wouldn’t make a major difference to our welfare range estimates for salmon or carp.
The upshot is that is one of many cases where our methodology is more conservative than many EAs have been when doing related projects (e.g., we were more inclined to default to “unknown,” we used lower-bound placeholder values in some cases, etc.). Advantages and disadvantages!
Just to see the magnitude of the change, I tried rerunning the model with a neuron count estimate of 100 million for salmon. That led to salmon’s 50th-percentile estimate increasing by 0.001 and 95th-percentile estimate increasing by 0.002. So you’re right that it’s not really a noticeable impact.
Thanks, MHR. Quick reply to say: Good question, but I don’t know the answer offhand, as I didn’t come up with that number myself. Many different people helped with the literature reviews. I’ll get in touch with the relevant person and get back to you.
Sorry for the delay, MHR! It took a bit to get to the bottom of this. In any case, the short version is that the 8-13M neuron count for both salmon and carp should be read as the lowest reasonable estimate, not our best guess. We got the number from the zebrafish literature—specifically, a study by Hinsch & Zupanc (2007) (cited in the table) who reported that the total number of brain cells for adult zebrafish varied between 8 and 13 million. In the notes associated with the Welfare Range Table, we had a caveat that neuron counts are very hard to come by in fish and, in any case, only represent a snapshot in time, because the teleost brain is constantly growing. Moreover, no one has done total neuron count estimates for salmon or carp, whereas zebrafish are often used as a model species and are well-studied; so, we simply used those values as a placeholder. Granted, then, the 8-13M number may well be an underestimate due to the size differences between zebrafish and salmon, and we do see the appeal of using Invincible Wellbeing’s curve fits to come up with a higher number. However, we tried to stick as close to the empirical literature as possible. And truth be told, because neuron counts are just one of several models we include, using a higher number wouldn’t make a major difference to our welfare range estimates for salmon or carp.
The upshot is that is one of many cases where our methodology is more conservative than many EAs have been when doing related projects (e.g., we were more inclined to default to “unknown,” we used lower-bound placeholder values in some cases, etc.). Advantages and disadvantages!
Thanks Bob, that makes sense!
Just to see the magnitude of the change, I tried rerunning the model with a neuron count estimate of 100 million for salmon. That led to salmon’s 50th-percentile estimate increasing by 0.001 and 95th-percentile estimate increasing by 0.002. So you’re right that it’s not really a noticeable impact.