There are studies on north vs. south (whatever that is) on LMB and BG comparing various factors including how far north and or south and its latitudinal effect. There are also a lot of feeding (bioenergetics) studies on various species. At some point (temp} fish growth stops (or is negligible - some near 32F some as high as 60F) and the energy is used for base body functions and not growth. The temp depends on both species and adaptation within a species. There are a couple species of warm blooded sharks (in that they don't slow metabolism in cold water - Great Whites and Salmon Sharks IIRC). There are plenty of northern forage species and southern ones also but there may be some one place and different ones another place. For example TShad in the south but not up north (to cold) but in place (same biologic niche) alewife a close cousin or blueback herring.