Whole-body endothermy in a mesopelagic fish, the opah, Lampris guttatus

Abstract

Endothermy (the metabolic production and retention of heat to warm body temperature above ambient) enhances physiological function, and whole-body endothermy generally sets mammals and birds apart from other animals. Here, we describe a whole-body form of endothermy in a fish, the opah (Lampris guttatus), that produces heat through the constant "flapping" of wing-like pectoral fins and minimizes heat loss through a series of counter-current heat exchangers within its gills. Unlike other fish, opah distribute warmed blood throughout the body, including to the heart, enhancing physiological performance and buffering internal organ function while foraging in the cold, nutrient-rich waters below the ocean thermocline.

Ecological Influences and Morphological Correlates of Resting and Maximal Metabolic Rates across Teleost Fish Species

“…These cases of endothermy in highly active pelagic predators including the recently described endothermic fish Lampis guttatus (Wegner et al 2015), in conjunction with our results showing that MMR and RMR are highly correlated, provide strong support for the aerobic capacity model in some fish lineages. According to the aerobic capacity model (Bennett and Ruben 1979), a physiological linkage between RMR and MMR reflects a factorial limitation in oxygen-processing ability across vertebrate lineages that should also translate into a low FAS varying within a relatively narrow range.…”

“…Teleost fishes may provide a highly relevant model to study the aerobic capacity model for the evolution of endothermy (Bennett and Ruben 1979), given mounting evidence that multiple lineages exhibit some degree of endothermy (Block and Stevens 2001;Wegner et al 2015;Welsh and Bellwood 2012) and that elevated body temperatures translate into detectable ecological effects (Watanabe et al 2015). More generally, our results highlight that, because of their enormous range of phenotypic variation, teleosts constitute an excellent group to investigate how varying lifestyles and evolutionary pressures can ultimately give rise to an astonishing diversity in form and function.…”

“…Teleosts present a unique opportunity to examine these questions because they constitute the most diverse taxonomic group of vertebrates, represent an enormous range of body sizes, and occupy a wide array of ecological niches with varying modes and levels of activity, with some highly active species even displaying varying degrees of endothermy (Block and Stevens 2001;Wegner et al 2015). Our first major goal was to employ phylogenetically-informed interspecific analyses to investigate whether RMR, MMR, and aerobic scope are correlated across species.…”

Behavioral fever in ectothermic vertebrates

“…It may also increase the rate of digestion and absorption of food, as well as may improve vision and brain functions (Block and Carey, 1985;Carey and Teal, 1966;Goldman, 1997;Stevens and Fry, 1971). Very recently, a whole-body form of endothermy has been described in a large, mesopelagic fish, the oprah (Lampris guttatus) (Wegner et al, 2015). Oprah produces heat by the dark red aerobic pectoral musculature, which is used during swimming.…”

“…Oprah produces heat by the dark red aerobic pectoral musculature, which is used during swimming. Unlike other fish, oprah has retia mirabilia inside thick, fat-insulated gill arches and distributed heat through the whole body (including heart) by the circulatory system (Wegner et al, 2015).…”