Title Studies on early mass mortality during hatchery rearing of three grouper species, Malabar grouper Epinephelus malabaricus, red spotted grouper Epinephelus akaara, and leopard coral grouper Plectropomus leopardus
Authers Kenzo YOSEDA
Keywords Hatchery-reared grouper, Epinephelus malabaricus, Epinephelus akaara, Plectropomus leopardus, mass mortality
Citation Bull. Fish. Res. Agen. supplement No. 23, 91-144, 2008
Some grouper species belonging to the genera of Epinephelus and Plectropomus, studies for aquaculture and stock enhancement in various countries have been undertaken because these species have a high economic importance for fisheries. However, mass-scale rearing of grouper species has not been successful compared to other target aquaculture species such a red sea bream Pagrus major and Japanese flounder Paralichthys olivaceus owing to an unknown cause of early mass mortality. For this reason, the cause and mechanism of the early mortality during endogenous nutrition and initiation of exogenous nutrition is urgently required to elucidate making improve on early survival under mass-scale rearing.
   In the present study, three species of hatchery-reared grouper, Malabar grouper Epinephelus malabaricus, red spotted grouper Epinephelus akaara, and leopard coral grouper Plectropomus leopardus were studied to elucidate the cause of early mass mortality under rearing conditions. The duration of absorption time in endogenous nutrition ranged from 0 to 28 hours after the onset of feeding, but that of the other five target species is longer than grouper and ranged from 43.5 to 90.5 hours. It means that larvae of grouper are characterized by the earliest exhaustion of the endogenous nutrition and for that reason the shortest time leeway to the onset of feeding. Moreover, the negative growth point exactly coincides with the time at which the larvae completely consumed the oil globule in the present study, and they also possess very short periods for resistance of food deprivation from the onset of feeding on 6 hours in the present study. These results indicate that early mass mortality of grouper species occurs due to food deprivation depending on unsuitable rearing environmental conditions related with first-feeding during the period that endogenous reserves still remain and/or immediately after they are exhausted. Based on these results, I conclude here that the most important matter to improve the mass-scale early survival in grouper species is to keep and maintain optimum environmental conditions such a water temperature, photoperiod, aeration, light intensity, and circulation methods in tanks related with the first feeding stage during the “critical point”. Such an experimental design and approach demonstrated in the present study is available to clarify the early stage of mortality not only new aquaculture target species but also natural larvae when and why the early mortality occurs.
URI http://www.fra.affrc.go.jp/bulletin/bull/bull23/yoseda.pdf