Paracentrotus lividus roe enhancement by a short-time rearing in offshore cages using two agar-based experimental feed

In this study, we tested the effect of two agar-based biocomposites (differing for the fish meal source), on the Paracentrotus lividus gonad cycle progression and biochemical composition, in an offshore pilot scale trial. The purpose of this study was to identify a feeding regime for P. lividus that would allow adequate gonadal growth without accelerating the gamete maturation, in order to extend the market period. The purpose was pursued through the use of agar as a binding agent in the manufacturing of biocomposites to be used as feed for P. lividus and the realization of special offshore cages. The gonad index, histology, biochemical composition of fatty acids (FA) and free amino acids (FAA) and volatile molecule fingerprint were evaluated. Both the gonad index and the histological analysis showed a slower gametogenesis progression in the gonads of caged sea urchins with respect to the field collected ones, consistent with our previous results obtained testing a similar feed composition in a recirculating system. The amount and the relative proportions of FA and FAA in the gonads of wild and cultured gonads were similar, while the analysis of the volatile substances of the gonads of the sea urchin conducted using the electronic nose, shows that they vary as a result of the different feeding treatments. These results show that P. lividus sea urchins can be housed, under this feeding regime during the recovery phase of the gonads, without acceleration of the maturation of the gametes and thus in conditions to allow the extension of the market period. Moreover, the here tested agar-based biocomposites make it possible to reduce the management costs of the rearing system as they need to be replaced only once a week, and its environmental impact as they guarantee a limited nutrient dispersion in the water.