Whether it’s warm outside or cold, people generally eat about the same amount. But a fish’s appetite can vary enormously with the temperature. As coldblooded animals, their metabolism is governed by external conditions: It’s slow going for a cold fish, but high temperatures kick them into high gear.

To better understand how temperature affects our finned friends, researchers at UC Santa Barbara studied opaleye fish under a variety of temperatures and diets. They found that both diet and temperature influenced fish physiology and metabolism, but the effects were specific to each trait. The results, published in the Journal of Experimental Biology(link is external), further chip away at the assumption that an animal’s biological processes all respond the same way to different temperatures.

Opaleye were an ideal model to study this interaction. The omnivorous fish are a common sight in kelp forests and reefs from Point Conception to southern Baja California. In 2006, UCSB researchers found that wild opaleye eat more algae in the warmer, southern part of their range than in the colder north. And other omnivorous fish show a similar trend.

“We hypothesized they were doing this because it benefitted them,” said lead author Emily Hardison(link is external), a doctoral student in the Department of Ecology, Evolution, and Marine Biology.