The effect of fresh seaweed and a formulated diet supplemented with seaweed on the growth and gonad quality of the collector sea urchin, Tripneustes gratilla, under farm conditions

This gonad enhancement study investigates the effect of different fresh and formulated feeds and feeding regimes on the growth and gonad quality of wild-collected adult sea urchin, Tripneustes gratilla, under farm conditions for over 18 weeks. In the first 12 weeks (phase 1), urchins were fed fresh Ulva rigida (U); a 50:50 mixture of fresh U. rigida and Gracilaria gracilis (UG); fresh G. gracilis (G) and a formulated diet 20U (containing 20% U. rigida), and in the final 6 weeks (phase 2) of the study, diet was changed to a formulated feed (20U diet). By the end of phase 1, urchins fed the 20U diet produced gonads (50.72 ± 5.4 g) that were significantly heavier (p < .001) than the gonads of urchins fed the fresh seaweed diets (U, UG & G). By the end of phase 2, gonad weight of urchins in treatment groups UG-20U and G-20U were similar to those fed the 20U-20U diet. Gonad colour of urchins in the G-20U treatment became significantly lighter (ANOVA, p = .029) and poorer quality, compared with urchins in the U-20U group. This gonad enhancement study, conducted on wild collected adult T. gratilla, has shown that a formulated feed (20U diet) can enhance gonad growth and produce commercially acceptable gonads. This farm-based study supports previous findings from aquarium-based studies by our group and indicates that short-term sea urchin gonad enhancement can be carried out under farm conditions in South Africa