Growth and longevity in fishes of the family Scaridae

Abstract

Systematic check-marks in the sagittal otoliths from 6 species of scarids sampled from the Great Barrier Reef, Australia, were used to develop size-at-age plots. The species were Chlorurus gibbus, C. sordidus, Scarus frenatus, S. niger, S. psittacus and S. rivulatus. Comparative information for a seventh species, S. schelgeli, for which otolith increment data were available, was also included. Systematic check-marks in the form of alternating opaque and translucent bands were observed in the sectioned sagittae of all species. Regression of numbers of sagittal increments on sagittal weights revealed consistent linear relationships between these variables indicating continuous growth in sagittal thickness over the life span. For C. sordidus, S. frenatus, S. niger and S. rivulatus recapture of specimens injected with tetracycline confirmed an annual pattern in increment formation, with an opaque band being formed in early summer. Additional confirmation of the annual formation of opaque increments in S. rivulatus was obtained by marginal increment analysis. Size-at-age plots identified variable growth patterns and longevities among the 7 species. Growth in C. gibbus, S. psittacus, S. schelgeli and S. rivulatus was continuous with little evidence of an asymptotic size. Life spans ranged from 5 yr (S. psittacus) to 14 yr (C. gibbus). In C. sordidus, S. frenatus and S. niger there were clear asymptotic sizes achieved early in life and greater longevities (10 to 20 yr). All species were protogynous with evidence of sex- specific growth patterns. Transition to the terminal male identity was associated with enhanced growth resulting in larger and younger terminal males than females of equivalent size.