Comparison of the Results from Induced Breeding of European Catfish (Silurus glanis L.) Broodstock Reared in an Intensive System or in Pond Conditions

摘要

European catfish, Silurus glanis, is an important species for aquaculture in temperate climates. At present, its production relies mainly on pond culture. However, European catfish could be a promising candidate for intensive aquaculture since it has a high growth rate on commercial diet, is resistant to handling and has relatively low requirement for water quality. In this study we compared the results from induced breeding of European catfish broodstock reared in an intensive system or in a pond environment.Induced breeding experiments were conducted in two consecutive spawning seasons using European catfish broodstocks with different origins. One broodstock was cultured in an intensive system, while the other was reared in artificial pond conditions. One day before the experiments, fish were transferred to the hatchery and placed in 4.0 m3 polypropylene tanks with running water. One experimental group contained fish cultured in an intensive system, while the other consisted of fish reared in pond conditions. Fish in both groups received an injection of dry carp pituitary administered in 0.7% NaCl at a dose of 4.0 mg kg-1 body weight. Assessment of ovulation was carried out by determining the ovulation ratio (number of ovulated females / number injected) and by the pseudo-gonadosomatic index (PGSI) calculated as follows: (weight of stripped egg mass / body weight of the female before stripping) ? 100. When ovulation was detected, the eggs were stripped and weighed. Fertilization rate of the eggs was used as a parameter for egg quality.In both spawning seasons, five out of six females reared in pond conditions ovulated after the treatment, while pituitary injection induced ovulation in all females cultured in an intensive system. Mean fertilization rates for the two groups were high and statistically similar in both seasons (P>0.05). The mean PGSI values, however, were significantly higher (P<0.05) for the females cultured in the intensive system in both seasons. In conclusion, this study shows that European catfish females reared in intensive conditions from larval stage to maturity at constant temperature of 21.0 ± 1.0°C can be induced to ovulate by pituitary injection. The reason for the high relative fecundity of these females was probably the constant temperature that secured continuous ovarian development all year round. Results from the propagation of fish reared in pond conditions were similar to those from hatchery breeding of European catfish that has been carried out routinely for years.