The biological background for the production of stocking material of 11 European rheophilic cyprinids. A review
Kamler, Ewa; Wolnicki, Jacek
The conservation status of the 11 rheophilic cyprinid species was considered and compared in Austria, Czech Republic and Poland. Eight of these species are threatened. The critical importance of maternal effects on offspring performance (egg size, larval size at first feeding, resistance to starvation) was revealed at the inter-specific level. The descriptions of morphological changes in the yolk feeding stages, and during larval and juvenile periods are available for all species except Gobio albipinnatus. The response of embryogenesis to temperature was estimated by a combination of three characteristics (spawning temperature, viable temperature for embryogenesis and the temperature of biological zero) that were assessed independently, but are inter-related at an interspecific level. Relative growth rate (RGR, % d-1) was used as an index of the response to temperature of feeding larvae. The species considered maximized their growth at 25-28 °C, a temperature of 25 °C was recommended as the standard for rheophilic cyprinids. Within the range of 25-75 larvae dm-3 negative density-dependence of individual growth was described for six species, but a density of 75 larvae dm-3 was recommended as the most economically profitable. High survival rates (> 90 %) and maximum RGR values (up to 30 % d-1) were recorded in larvae fed on natural food. Sources of variability in growth rates were identified. When these factors were kept constant, intrinsic growth potential could be compared between species. At the start of external feeding the larvae of most cyprinids have limited ability to utilize formulated diets and their growth rates and survival rates are depressed. None of the presently existing formulated diets can be considered an equivalent substitute for a natural diet. Satisfactory growth and survival of juvenile cyprinids can be achieved on formulated diets, but they need to be supplied with care, because overfeeding with such diets adversely affects the quality of the fish stocking material.