Although they cannot be seen in the picture due to the glare, the fish in this picture are considered ectothermic animals. Actually, all organisms except birds and mammals are considered ectothermic. Ectothermic animals are considered cold blooded creatures. They cannot generate their own heat, and therefore depend on their surroundings for it. Their body temperatures changes as the environment does. Any large fluctuation in temperature could put the lives of ectothermic animals in jeopardy. Ectotherms lose heat quickly, but can also acquire it quickly because they are poorly insulated.