Growth performance in clonal crucian carp Carassius langsdorfii: effects of feeding history and genetic difference.
Growth depensation (divergence in size over time among individuals in the same age class) has been studied in a variety of marine and freshwater fishes. Genetic variance often makes it difficult to interpret this phenomenon conclusively. The use of clonal fish is a powerful tool to elucidate the mechanism of growth depensation because of the absence of genetic differences among fish. Crucian carp Carassius langsdorfii is an unisexual triploid species and reproduces gynogenetically in nature. Multilocus DNA fingerprinting techniques clearly demonstrated the presence of clonal lines in the wild population and clonal nature among sib-progeny of each female. We produced clonal lines by activating the eggs with heterospecific spermatozoa of carp Cyprinus carpio and then used them in following experiments. Otolith-tagging with fluorescent dye was used for stock identification.
When feeding was restricted at the 5th day, the 9th day or both 5th and 9th day after hatching within the clone, the growth of the larvae was relatively lower than that of the well-fed larvae. The reduction of growth due to restricted feeding at the 5th day was more evident than that of the 9th day after hatching. The results indicated that disproportional food acquisition in the early larval period gave rise to serious effects on the subsequent growth. When two genetically-different clones were reared in a communal condition, the growth difference was significant between the clonal lines in the larval period (0-30 days after hatching), but not in the juvenile period (90-150 days). The results suggest more involvement of genetic factors in the growth of the larvae than of the juveniles.
(Faculty of Applied Biological Science, Hiroshima University, Higashi-Hiroshima, Kagamiyama, 739, Japan)
Techniques for the hatchery conditioning of bivalve broodstocks and the subsequent effect on egg quality and larval viability.
Studies on the hatchery conditioning of bivalve broodstocks are reviewed. The emphasis is on scallops, oysters and clams, species that are of commercial importance. The technological requirements for broodstock conditioning, including holding systems and seawater treatment, are briefly described. This is followed by a more detailed analysis of the environmental and biological requirements including the effects of temperature, photoperiod and food supplements. Of particular importance is the optimisation of the quantity and quality of microalgae diets that are provided during the period of hatchery conditioning.
The effects of hatchery conditioning regimes on the fecundity of broodstock, egg quality and larval viability are shown. The number of eggs produced and the polyunsaturated fatty acid (PUFA) composition of the eggs are influenced by the quantity and quality of lipids in micoalgae diet supplements. Under optimal hatchery rearing conditions, differences in initial egg lipid reserves may not necessarily affect subsequent larval growth and survival. The role of lipid and PUFA reserves, in particular 20:5n-3, during the development of embryos and larvae can, however, be clearly demonstrated under more stressful rearing conditions. The importance of good hatchery practice is highlighted.
(Ministry of Agriculture, Fisheries and Food, Fisheries Laboratory, Benarth Road, Conwy, Gwynedd LL32 8UB, UK)
