Nonlinear growth models of dusky grouper in nursery and grow-out across three rearing systems

The dusky grouper Epinephelus marginatus is a fish currently undergoing domestication. As with other aquaculture species, the growth rate, a trait of economic interest, varies among production systems. We estimated the growth curves for dusky groupers reared in three different culture systems using nonlinear models. The growth of 445 individuals was monitored over 730 days in a sea cage system (SCS), a recirculating aquaculture system (RAS), and an earthen pond system (EPS). Using data from the three respective systems, growth curves were fitted using the Brody, Gompertz, logistic, Richards, and von Bertalanffy models. The Brody and Richards models failed to converge and therefore were unsuitable for describing grouper growth. The Gompertz, logistic, and von Bertalanffy models achieved convergence and were used to fit the growth curves for the dusky grouper. Among these, the logistic model provided the best fit to the data. The growth patterns varied among the systems, reflecting culture and environmental conditions that influenced fish performance. Groupers reared in the RAS had lower asymptotic weights and higher growth rates (p < 0.05), indicating greater precocity. The average body weight at 730 days was 838 g in the sea cages, followed by that in the RAS (587 g) and earthen ponds (428 g). The maximum asymptotic growth rate was 1.8 g/day in the sea cages, 1.7 g/day in the RAS, and 0.9 g/day in the earthen ponds. The low salinity in the earthen ponds may have contributed to the reduced growth performance. Although the groupers reached the commercial harvest weight in all systems, the grow-out time was shorter in the sea cages and the RAS. The findings of this study will inform future work with replicated culture systems to refine the production methods for the dusky grouper.