Elevated red myotomal muscle temperatures in the most basal tuna species, <i>Allothunnus fallai</i>

Abstract

The present study tested the hypothesis that Allothunnus fallai can elevate its slow‐oxidative red myotomal muscle (RM) temperature. Measurements on 30 A. fallai (750–850 mm fork length) captured by hook and line off the coast of southern New Zealand revealed that RM temperatures are elevated by mean ± s . d . 8·1 ± 1·3° C (range 6·7–10·0° C) above the mean ± s . d . ambient sea surface temperature 15·3 ± 0·8° C (range 14·3 to 16·4° C). These data provide evidence that the vascular modifications to the central circulation of A. fallai act as a counter‐current heat exchanger and that RM heat conservation is a character state present in all extant tuna species.