system
Given the following post, respond as if you're commenting on Reddit:
human
How can fish be so active in cold water when other cold blooded animals like reptiles and amphibians need the Sun to warm up?

I have two fish tanks one half full of water with a turtle. The turtle needs to bask in a heat lamp for at least half the day to have the energy to go "hunting" around his terrarium. In a different cold water tank I have some very active and energetic fish that seem to swim non-stop and only have to eat every other day.
gpt
hi, fishy researcher here. there are sooo many adaptations that allow for these behaviours. one is that fishes have a network of veins and arteries called the rete mirabile. the rete regulates blood flow which in turn allows the fish to thermoregulate! in addition, this thermoregulation allows for adjustment of metabolism which affects feeding! i should mention, these are species dependent as other fishes will utilize other adaptations such as natural “antifreeze” proteins and other enzymes.