Elevated red myotomal muscle temperatures in the most basal tuna species, Allothunnus fallai

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.