Marine fishes are largely thought of as being ectothermic and unable to regulate their body temperature, although some exceptions such as tuna exist. But a recent study study has shown that the Steephead parrotfish (Chlorurus microrhinos) is capable of very limited endothermy.
In the study, published in a recent issue of the online journal PLoS ONE, Justin Welsh and David Bellwood measured the temperature of the peritoneal cavities of parrotfish that were maintained in tanks, as well as those left in the wild over a 24-hour period.
Comparing this data with the ambient water temperatures, they found that while the body temperature was not significantly different for fish kept in tanks, the fish on the reef were consistently and significantly warmer than the environment at night.
Daytime body temperatures were more variable and followed the ambient water temperatures more closely in both tank-kept and wild fish.
The authors postulate that the heat is generated by the increase in metabolic activities of the liver when digesting a meal, and that some unknown physiological mechanism is working to retain the heat within the peritoneal cavity.
The function and potential benefits of this limited endothermy remain unknown.
For more information, see the paper: Welsh, JQ and DR Bellwood (2012) Regional endothermy in a coral reef fish? PLoS ONE 7, e33187.
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