Key metabolic enzymes and muscle structure in triplefin fishes (Tripterygiidae): a phylogenetic comparison

Metabolic potential and muscle development were investigated relative to habitat and phylogeny in seven species of New Zealand triplefin fishes. Activity was measured in three principal glycolytic enzymes (lactate dehydrogenase, pyruvate kinase and phosphofructokinase) and two oxidative enzymes (citrate synthase and L3-hydroxyacyl CoA:NAD(+) oxidoreductase). The non-bicarbonate buffering capacity of caudal muscle was also estimated. Phylogenetic independent contrast analyses were used to reduce the effects of phylogenetic history in analyses. A positive relationship between metabolic potential and the effective water velocity at respective habitat depths was found only after the exclusion from analyses of the semi-pelagic species Obliquichthys maryannae. O. maryannae showed high glycolytic enzyme activities, and displayed double the activity of both oxidative enzymes relative to the six benthic species. Histochemically stained sections taken immediately posterior to the vent showed that adult O. maryannae and larval Forsterygion lapillum had significantly more red muscle, and smaller cross-sectional areas of white and red muscle fibres, than adults of benthic species. The distribution of red muscle in adult O. maryannae resembled that of larval F. lapillum, and differed from the typical teleost pattern seen in adults of the six benthic species. Both adult O. maryannae and larval F. lapillum have an expansive lateralis superficialis muscle, typical of larval fish, which encompasses much of the caudal trunk. Results suggest that anaerobic potential in New Zealand triplefins: (a) increases with the locomotory requirements of different habitats, and (b) displays a negative relationship with depth-dependent water velocities in benthic species. O. maryannae appears to have increased aerobic potential for sustained swimming by paedomorphic retention of larval muscle architecture.