Résumé
The collector sea urchin (Tripneustes gratilla) is an echinoderm whose gonads (roe) have high commercial value on Asian markets. Due to its fast growth rate, early maturation and high gonadal production, it has been proposed as a viable candidate for aquaculture/echinoculture. Tripneustes also develops well in co-culture with seaweed and can be grown in similar productions systems as abalone, which is the primary aquaculture crop in South Africa, making it a good candidate for IMTA.To facilitate development of Tripneustes aquaculture it is important to develop feeds and feeding regimes that promote rapid somatic and gonadal growth, with the resulting gonads meeting the quality criteria of the Asian markets in terms of weight, colour, texture and firmness. Therefore, the aim of this study was to identify feeds that would promote rapid somatic and gonad growth, particularly during early stages of production. Juvenile sea urchins (ca. 2mm test diameter) were obtained from a commercial hatchery (Buffeljags Abalone) and stocked into 4 baskets per treatment (n=20 individuals/basket). Three feeds were tested: fresh Ulva lacinulata, fresh kelp (Ecklonia maxima), and a formulated feed (20U) containing 20% dried Ulva (w/w). Each feed was provided ad libitum over the 17-week growth period. To measure somatic development, urchin weight and diameter was measured once every week. Towards the end of the somatic period (week 13), gonad development was evaluated by assessing 10 gonads per treatment group. Gonads were weighed and texture and firmness were rated visually, whereas colour was rated both visually and with a hand-held reflected-light fibre-optic spectrophotometer. There was a significant impact of feed on test diameter and gonad development/quality. Somatic development was better in sea urchins fed with Ulva and kelp by the end of the trial. The formulated feed produced larger gonads compared with the seaweed treatments, but these gonads did not meet the marketing criteria in terms of texture, firmness and colour. In contrast, the gonads obtained from the Ulva and kelp treatments were marketable and of high quality. These trials provided valuable information on the impacts of feed on early development of Tripneustes gratilla for commercial production.