Body composition of Mugil cephalus,Liza dumerili,Liza richardsoni and Liza tricuspidens (Teleostei: Mugilidae) caught in the Swartkops Estuary

Body composition (protein, fat, ash and moisture) and energy content of four mullet species Mugil cephalus, Liza dumerili, Liza richardsoni and Liza tricuspidens were determined monthly for 13 months in specimens taken from the Swartkops Estuary. Six size classes (<2.5, 2.6–6.0, 6.1–10.0, 10.1–15.0, 15.1–23.0 and > 23 cm SL) were analysed separately. Statistical analyses of results could only be performed on three size classes of M. cephalus, L. dumerili and L. richardsoni due to inavailability of fish during certain months. Regression equations were calculated for those body components that were significantly correlated, viz.: energy and moisture, fat and moisture, protein and moisture and energy and fat. The influence of species, size as well as seasonal effects and reproductive cycle on body composition were investigated. It was found that in general Liza dumerili had the lowest mean body energy and fat values and Liza tricuspidens the highest. Smaller size fish were lower in energy and fat and larger size fish lower in moisture. Overall mean values showed that body energy reserves were the highest during the winter. Sexually mature specimens of Liza dumerili showed a build-up of energy before the commencement of the spawning season.