Fish Metabolism
Tech Talk 16

We refer to fish as being "cold blooded" (some people fit that description, too). That doesn't mean they don't give off heat. It works as follows:

• 100 pounds of fish fed @ 5 percent of weight per day.
• 5 pounds of feed x 700 kcal/lb feed = 3,500 kcal/day.
• 3,500 kcal/day = heat that would raise a 400-gallon culture tank's temperature (perfectly insulated) 2–3°C.

This explains how fish metabolism, together with pumps, lights, etc., is responsible for raising the temperature.