Including wild fish (including those caught for fishmeal) can be misleading and hard to get right:

1. The price elasticity of supply of wild-caught fish can be negative when there's overfishing, because reducing fishing pressure (the percentage of the population caught per period) allows the population to recover enough to allow more fish to be caught in the long run. So the number of fishing deaths could actually increase from eating less fish, or animal products from animals fed fishmeal.
2. In well-managed fisheries with quotas, the elasticity should be basically 0 when the quotas are binding, so catch wouldn't change. It can be positive if there's underfishing and either there's no quota or catch is below the quota, so catch would decrease with a negative demand shift.
3. Wild-caught fish populations might increase in fisheries from reducing demand (if there's no quota that's binding). It's not clear those lives are worth having more of on average. Also, of course if the population increases, so will deaths, just not necessarily due to fishing (although fishing deaths may increase, too, if overfishing). On the other hand, the populations of their prey may decrease in response. Even anchovies eat crustaceans. Is this a good trade?