Development of techniques for enhancing seed production of Epinephelus coioides in Taiwan

Abstract

The Fisheries Research institute has conducted researches for enhancing grouper seed production since 1995. Our projects have focused on the measures to prevent viral infection during fry and fingerling production. This paper reviews the techniques developed for Epinephelus coioides including commercial egg production, egg incubation, rearing water treatment and management, feed regime, and live food preparations. The daily production of fertilized eggs by E. coioides during one month from four broodstock farmers averaged from 1.82 to 6.13 kg, with a peak production of 11.7 kg in one farm. To prevent viral contamination, eggs are disinfected with ozone and incubated in a flow-through system using treated seawater. The hatched larvae nursed in treated seawater (without feeding) had high survival rates. A vortex flow nursery system was designed and used to prevent surface tension related death among hatched larvae. Afterwards, the survival rate of the first feeding stage larvae could be improved using a recirculating system. Fertilized oyster eggs, small (S)- and super small (SS)-rotifers were tested either solely or in combination to find their suitability as feed for the early larval stage of E. coioides. Results show that growth and survival were better, and percentage of curved vertebra lower, among larvae fed with a combination of SS-rotifers and oyster eggs as live food. Larvae also grew better when Isochrysis is added in the rearing water compared with Nannochloropsis. Artemia should not be provided before D18, and should be given in combination with rotifers at D18 until D25. Afterwards, Artemia alone is given for fast growth of larvae. The pond-cultured copepods had high nutritional value and low cost, but present high risk of disease transfer, which is the main cause of low and erratic survival in grouper larviculture in Taiwan. From D8 onwards, debris, feces and dead fish are siphoned out from the tank bottom every four to one days, together with a 30-50% water change. When enriched Artemia is introduced, the water exchange rate is gradually increased to 320% to maintain optimal water quality. The fingerlings harvested from larval tanks are transferred and weaned in a recirculating system.