Small-scale sea urchin (Tripneustes gratilla) aquaculture: evaluating locally sourced diets for gonad development and quality

Abstract

Sea urchin gonads (called uni) are highly valued in seafood markets, creating demand for sustainable production. In Seychelles, small-scale farming of Tripneustes gratilla is promising, but costly pelleted feeds for gonad enhancement limit feasibility. This study evaluated alternative fresh feeds, Sargassum spp., carrots (Daucus carota), moringa (Moringa oleifera), and a mixed diet, over 10 weeks using 200 T. gratilla (average wet weight: 492.6 ± 79.37 g). Gonad quality was assessed at weeks 6, 8, and 10, alongside disease and mortality monitoring. The overall mean gonadosomatic index (GSI) was 3.34 %, peaking at 10.38 % in week 8. Significant differences were found among feed types and durations (p < 0.05). Moringa had a strong negative effect on GSI (-3.54, p = 0.001), while other diets showed no significant difference. GSI rose from week 6 to 8 before declining at week 10 (estimate = -2.18, p = 0.035). However, 46.67 % of gonads were of unacceptable quality. Feed type and duration had no significant impact on gonad colour (p > 0.113), texture (p > 0.071), or firmness (p > 0.064). Mortality and disease rates were also unaffected (p > 0.415 and p > 0.963).  Although no tested diet improved gonad quality, the potential for artisanal T. gratilla farming may remain, but likely depends on improved enhancement diets and/or locally feasible formulated feeds, which require further evaluation.