The impact of diet on the growth and proximate composition of juvenile whelks, Dicathais orbita (Gastropoda: Mollusca)

Dicathais orbita is a predatory marine whelk of interest as a new source of protein for potential production in aquaculture. Establishment of a successful aquaculture industry based on this species will require optimisation of their diet for fast growth and survival, whilst maintaining a good proximate composition in the flesh. Here we compare the effects of four diets fed to juvenile D. orbita over a 12 week period, to evaluate consumption, feed conversion, growth rates, mortalities and proximate composition. It was found that diet impacts significantly on the growth and survival rates of this whelk, with bivalve feeds resulting in significantly higher consumption (P < 0.0001) and growth rates (P < 0.0001) compared to artificial pellets, despite similar feed conversion ratios (P = 0.359). The artificial pellets were found to have significantly less moisture, but higher protein, glycogen and lipid content than the bivalve feeds (P < 0.05) and resulted in whelk flesh with significantly higher energy and ash content (P < 0.05). D. orbita showed a preference for scavenging frozen bivalves over predation on live molluscs in captivity, which could reflect an optimal foraging strategy to minimise the energy required to subdue prey. Overall, juvenile D. orbita display similar growth (up to 0.8 g/month) and high survival (> 90%) compared to other gastropods in culture. Their flesh has a high calorific value (∼ 19 kJ/g), with significantly higher protein (> 26 mg/g) and glycogen (> 35 mg/g) content than their bivalve prey (P < 0.05). Consequently, this species has a promising future as a new species for molluscan aquaculture in Australia.