Regional endothermy in a coral reef fish?

David R. Bellwood,Justin Q. Welsh

doi:10.1371/journal.pone.0033187

Abstract

Although a few pelagic species exhibit regional endothermy, most fish are regarded as ectotherms. However, we document significant regional endothermy in a benthic reef fish. Individual steephead parrotfish, Chlorurus microrhinos (Labridae, formerly Scaridae) were tagged and their internal temperatures were monitored for a 24 h period using active acoustic telemetry. At night, on the reef, C. microrhinos were found to maintain a consistent average peritoneal cavity temperature 0.16±0.005°C (SE) warmer than ambient. Diurnal internal temperatures were highly variable for individuals monitored on the reef, while in tank-based trials, peritoneal cavity temperatures tracked environmental temperatures. The mechanisms responsible for a departure of the peritoneal cavity temperature from environmental temperature occurred in C. microrhinos are not yet understood. However, the diet and behavior of the species suggests that heat in the peritoneal cavity may result primarily from endogenous thermogenesis coupled with physiological heat retention mechanisms. The presence of limited endothermy in C. microrhinos indicates that a degree of uncertainty may exist in the manner that reef fish respond to their thermal environment. At the very least, they do not always appear to respond to environmental temperatures as neutral thermal vessels and do display limited, but significant, visceral warming.

Highlights

Marine fishes are largely regarded as ectotherms, incapable of metabolic thermoregulation, and have body temperatures similar to the ambient water temperature [1,2]
The optimal body temperatures of organisms, often occur within a narrow thermal range depending on the geographic location where they live [3,4,5]
The internal temperature of C. microrhinos held in tanks remained near ambient temperatures (Tdiff diurnal = 0.0460.02uC; mean 6 SE; temperature difference (Tdiff) nocturnal = 0.0860.03uC; Figure 1b, d) and consistently tracked environmental conditions with low variability (CV diurnal = 0.63; coefficient of variance (CV) nocturnal = 0.64)

Summary

Introduction

Marine fishes are largely regarded as ectotherms, incapable of metabolic thermoregulation, and have body temperatures similar to the ambient water temperature [1,2]. Tropical marine species are usually regarded as being stenothermal, i.e., adapted to a relatively narrow thermal range These tropical stenotherms may have little capacity to deal with large-scale climactic shifts when compared to temperate species [5,6,7]. Lizards and other ectotherms have been observed to behaviorally regulate internal temperatures and maintain their bodies within a narrow thermal range [8,9]. Like their terrestrial counterparts, several temperate ectothermic fish species are known to exhibit behavioral thermoregulation. In aquarium-based trials, the reef fish species Zebrasoma flavescens [11], Balistes fuscus, B. vidua, Canthigaster jactator, Cromileptes altivelis, Forcipiger longirostris and Naso lituratus [12] have all displayed the ability to behaviorally thermoregulate, actively seeking out relatively stable ambient temperatures

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