This study investigated growth and gonad production of Tripneustes gratilla fed four protein‐rich artificial diets supplemented with varying amounts (0%, 5%, 15% and 20% weight/weight (w/w); designated 0, 5, 15 and 20U, respectively) of the macroalga Ulva over a 12‐week period. Gonad size, texture, colour and a number of production performance parameters were quantified and compared with urchins fed fresh Ulva (FU) and a combination of FU and artificial feed (FB). All artificial diets significantly (P ≤ 0.05) increased gonad somatic indices (GSI) compared with the FU treatment. The 20U treatment increased GSI by 205% by week 9, compared with a 57% increase in the GSI of urchins fed FU. Gonad colour was calculated using three colour parameters, namely L* (lightness), a* (redness) and b* (yellowness). Whereas L* and a* values did not differ significantly between treatments, b* values for all treatments, with the exception of the 20U and FB treatments, were significantly (P ≤ 0.05) lower or less yellow than the FU treatment by week 12. These results show that we have successfully formulated a feed (20U) which can produce commercially acceptable gonads in terms of both size and colour, indicating the potential for this artificial feed to support commercial echinoculture.

The present study was performed to determine whether the palatability, consumption and digestibility of an artificial sea urchin diet could be improved by the addition of a highly preferred seaweed. Four species of macroalgae (Ulva rigida, Ecklonia maxima, Porphyra capensis and Gigartina polycarpa) were assessed by pairwise preference tests. Each macroalgal species was consumed at least once by Tripneustes gratilla and significant preferences always involved Ulva as the most preferred species. Four proteinrich artificial diets supplemented with varying amounts of Ulva [0, 50, 150 and 200 g kg À1 designated 0, 5, 15 and 20U, respectively] were then developed and fed to urchins over a 20-day period. Inclusion of 200 g kg À1 dried Ulva significantly improved the palatability of the artificial diet and mean dry feed consumption rates were higher in urchins fed the 20U and 15U diets compared with urchins fed diets with a lower Ulva content. Daily digestible protein (DP) intake also differed significantly, with urchins fed the 20U diet having a significantly higher DP intake compared with the 15U, 5U and 0U treatments. These results indicate that inclusion of the palatable seaweed Ulva acted as a feeding stimulant, increasing the acceptability of the diets and boosting protein intake.

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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.