Biology of Surgeonfish Acanthurus-nigrofuscus with emphasis on changeover in diet and annual gonadal cycles

A 3 yr study was conducted on the feeding biology and reproductive strategies of Acanthurus nigrofuscus (Acanthuridae, Teleostei) found along the coral reefs of the Gulf of Aqaba and forming there the major biomass of algivorous fish. The diet of this surgeonfish is based on algae selected from turf communities growing on subtidal rocky surfaces. At some sites A. nigrofuscus form schools that migrate daily from nocturnal refuges in coral reefs to foraging sites on the intertidal, covering distances of 500 to 600 m. During summer the main food items are brown and red algae; in winter, lush green algae. This changeover appears to provide the food-base for accumulation of fat and recrudescence of gonadal activity initiating in March-Apnl. Reproduction occurs in large schools of 2000 to 2500 fish and on selected sites, continuing from May to September. Spawning occurs daily from 1800 to 1830 h, after which the fish depart for their night refuges. Peak of gonadal activity is in July-August, after whch an increase of pre- and postovulatory atretic bodes is prominent. In female post-spawned gonads, cysts of spermatogonia appear and remain until renewed normal activity in February-March. Histological evidence and possible explanation of this phenomenon are provided