The effect of artificial diets on gonad colour and biomass in the edible sea urchin Psammechinus miliaris

During two 12 week trials, groups of edible sea urchins, Psammechinus miliaris, were fed artificial diets containing carotenoid pigments. The aim was to improve both the biomass and the colour of the sea urchin gonad in terms of its acceptability as a human food-stuff in the European market place. The pigmented artificial diets, based on the formula used by Robinson et al. (2002), increased gonad index (GI), pigment deposition and improved gonad colour from that of the initial samples. In Trial I gonad β-carotene levels increased > 2 fold, echinenone and total carotenoid > 7 fold. Trial II showed greater increases. Diets containing high levels of β-carotene (500 mg per kg dry weight of diet) gave rise to the highest percentages of marketable gonad colours (61–73%), and GI of 17.87–19.81%, (Trial I and II respectively). There was some variation in the results for this particular diet treatment across the two trials presumably reflecting individual urchins varying capacity to ingest, deposit or express the carotenoids in their diet. Providing additional lipids in the diets gave no improvement to gonad colour (56% acceptable) or GI (15.95%) suggesting the lipid content of the basic formulation is adequate. Utilizing an esterified form of lutein and zeaxanthin as a pigment source gave no significant improvement in gonad colour (30–63% acceptable) suggesting that this form of xanthophyll cannot be assimilated by P. miliaris. Female urchins had acceptable gonad colouration more often than males. The dominant carotenoid in the successful diets was β-carotene and this was successfully metabolized into echinenone, the dominant carotenoid in all gonad samples. Total levels of echinenone positively correlated with acceptable gonad colour scores. This study demonstrates that 12 weeks is sufficient to effect the desired change in gonad biomass and colour in cultivated P. miliaris.