Cryopreservation of late embryos and early larvae of oyster and hard clam.
Cryopreservation of shellfish larvae and embryos may facilitate aquaculture management and stock enhancement programs. Late embryos and early larvae of oyster (Crassostrea gigas) and hard clam (Meretrix lusoria) were selected to establish the cryopreservation protocols. A survival rate of 73 9% was obtained in oyster using a stepwise freezing protocol. Late embryos or early larvae of oyster (4 h at 28C after artificial fertilization) were equilibrated in 2M DMSO + 0.06M Trehalose plus seawater for 10 min at 25C and then cooled at -1C min-1 from 0C to -12C. Straws containing embryos were held at -12C for 5 to 15 min allowing equilibration after seeding.
Larvae/embryos were then slowly cooled at -2C min-1 to -35C and allowed 10 to 20 min for equilibration before quenching in LN2. After rapid warming in a water bath at 28C, they were placed in seawater to remove DMSO. Besides the increase in survival rate, survived ones exhibited rotary motion immediately following thawing. For hard clam embryos/larvae with the protectants of 2M DMSO + 0.06M Glucose, survival rate of 72 10% was achieved using a similar freezing protocol. In a simplified procedure without seeding, 5 h-old embryos/larvae (at 34C incubation) were brought rapidly from room temperature to 0 C and then 0C to -7C. After holding at -7C for 3 min, a slow freezing rate of -0.3C min-1 was chosen until -35C was reached. Five minutes later, they were quenched in LN2. Satisfactory survival rates ranging from few to 76.3 13% and 25.8 9.0 to 79.2 5.9% were obtained, respectively, in oyster and hard clam.
(Dept of Aquaculture, Taiwan Fisheries Research Institute, Keelung, Taiwan, ROC)
Review on the dietary effects of selected phospholipids in fish and crustacean larviculture.
The role of phospholipids (PL) in fish and crustacean larviculture nutrition has already attracted much research interest. However, most of the studies published so far have used PL of unspecified composition or soybean lecithin, which is a mixture of various PL and other polar lipids. The inconsistency of the PL quality used has made the comparison between different diets and experimentors difficult. The aim of the present study was to investigate the effect of selected dietary PL on the growth, survival, stress resistance, incidence of deformities, gut histology and lipid composition of various species of fish and shrimp. The sources of PL used to study the functionality of PL in larval diets were provided by specialized laboratories (Lucas Meyer GmbH, Germany; Vandemoortele R&D Center, Belgium) and included deoiled soybean lecithin (DSL), DSL enriched in a specific phospholipid (PA, PE, PI, PC), highly purified phosphatidylcholine (from egg or soybean, hydrogenated), and lysolecithin. The study covered a range of species and stages, including start feeding of the common carp Cyprinus carpio L., weaning and first ongrowing of the European seabass Dicentrarchus labrax L. and turbot Scophthalmus maximus L., early postlarval culture of Penaeus japonicus Bate and Penaeus vannamei Boone. The results so far obtained confirm the requirement for dietary PL in the diet for all species. However, the response to the different PL sources were 'case dependent', e.g. different effects were observed for startfeeding of carp and weaning of marine fish, which could be related to differences in the functional role of PL depending on the stage (startfeeding versus weaning) and/or species.
(Laboratory of Aquaculture & Artemia Reference Center, Ghent University, Rozier 44, B-9000 Gent, Belgium)
Seasonal and age variability in the reproductive performance of Penaeus semisulcatus broodstock.
Consideration of the inherent reproductive patterns observed in wild shrimp populations is relevant to hatchery broodstock performance. In response to problems of variable hatchery performance of broodstock at some times of year, the inherent seasonal variability and the effects of broodstock age on reproductive performance of Penaeus semisulcatus were examined.
Reproductive performance of broodstock was assessed at each stage of the maturation and spawning process. Measures of maturation rate, spawning rate, fecundity, biochemical egg quality, hatching rate, larval survival rate, larval biochemical composition and hence larval production rate were obtained. During the 2 year study, assessments were made for broodstock collected from the wild over all seasons (at 2-monthly intervals) and from the two age-cohorts present in the same season. The stage of the maturation and spawning process where the effects of season and age have most impact can be ascertained from the staged-process approach used in this study.
Inherent seasonal patterns in some measures of reproductive performance were found. Spawning rates, egg production rates, naupliar production rates and protozoeal production rates were lowest in autumn, increased through to a spring peak, and then declined by early summer. Broodstock survival rates, egg hatching rates and metamorphosis of nauplii to protozoeae were unaffected by season. Trials with two-age cohorts present in the same season enabled separation of the effects of age and season. Twelve-month-old broodstock outperformed 6-month-old broodstock, regardless of season. An optimal season and age for best reproductive performance was established which can be used for the selection of broodstock for best hatchery production. Similar results with another species, P. esculentus, indicate that this pattern is likely the general case for tropical penaeids.
(CSIRO Division of Fisheries, CSIRO Marine Laboratories, P.O. Box 120, Cleveland, Queensland 4163, Australia)
