Gonad development in farmed male and female South African abalone, Haliotis midae, fed artificial and natural diets under a range of husbandry conditions

Background Growth rate is considered one of the most important factors in the farming of Haliotis midae and somatic growth rates decline after abalone reach sexual maturity. Artificial diets are suspected to accelerate maturation, in particular when soya meal is used as a protein source, because of this plant’s high concentration of phytoestrogens. Results We fed two artificial diets and a natural diet, kelp. The first artificial diet had fishmeal as its main source of protein while the other, Abfeed® S34, replaced some of the fish proteins with soya meal. The effect of diet on the gonad development of 27-month-old farmed Haliotis midae, raised at two stocking densities, was analysed. For each gonad sample the development phase was determined based on both histological criteria and the gonad bulk index (GBIn). The hypothesized link between dietary protein source and gonad development could not be established by either morphological criteria or GBIn. Similarly, stocking density did not have a significant effect on GBIn-values. GBIn values were significantly correlated to the results from the histological analyses in males and females. Conclusions The results from this study suggest that artificial diets including those using soya meal are a valid alternative in the feeding of abalone. Moreover, it provides a data base for future research on factors influencing gonad development in this species.