ECHINOCULTURE DEVELOPMENT IN SOUTH AFRICA: AN OVERVIEW

Tripneustes gratilla has been proposed as a viable candidate for aquaculture in South Africa due to its fast growth rate, early maturation and high gonadal production. A number of key areas have been identified that require research in order to successfully culture Tripneustes on a commercial scale worldwide, these include: (1) production of cost-effective diets; (2) development of protocols for uniform conditioning of adults prior to harvest;  (3) improving larval survival, settlement and post-settlement survival.

Over the past few years our research group has managed to address ea ch of the three critical areas mentioned above, and this presentation will provide an overview of some of this work . One of our main research focuses thus far has been  the  development of  an artificial diet  supplemented with macroalgae  and  the optimization of a feeding regime to produce high quality gonads. We have demonstrated that a formulated  feed supplemented with 20%  dried Ulva  (20U diet) produced high quality gonads in  terms of both size and  colour.  Moreover, dietary Ulva supplementation  significantly increased protein digestibility , the chemosensory properties of the formulated feed and feed consumption rates. G rowth studies on hatchery reared urchins to optimize feeding regimes indicated that somatic growth was similar for urchins fed fresh Ulva (FU) or the formulated feed (20U). However,  gonad growth of urchins fed  with FU was significantly less compared with urchins fed 20U . Feeding urchins that were previously fed FU  for 20 weeks  with the 20U diet for  an additional 6 weeks successfully produced gonads of  a similar size compared to urchins continually fed 20U. Currently, our research group is investigating  the effects of stocking density on a number of growth indicators and water quality parameters for commercial production. One of the most critic al factors affecting  stocking density is  basket depth. U rchins  show  a preference for occupying the side walls of baskets. However, when fed the urchins migrate to the bottom of the baskets and  collide with one another causing spine loss . Spine regeneration adversely affects resource allocation , resulting in stunted somatic and reproductive growth,  thereby adversely affecting the economic potential of a commercial sea urchin operation.  The combined effects of basket depth and feed type are also being investigated. Our research has also examined the effects of a range of inductive substrates and chemicals (including Ulva extracts) on larval settlement and metamorphosis as well as post-settlement survival and growth of the sea urchin Tripneustes gratilla , all of which have helped to reduce rearing times and improve larval survival and growth rates. These results will have important implications for the development of a cost-effective and successful echinoculture industry in South Africa.