Larval development and growth of the European Wels (Silurus glanis) under experimental conditions fed natural and pelleted diets

The development and growth rate were studied in two groups of the European Wels (Silurus glanis) larvae fed different diets. The first group was fed s ize-sorted live zooplankton, and the second group was fed the artificial un iversal pelleted so-called starter fee, prepared in the INRA in France. The rearing was performed under experimental conditions of aquaria in the Rese arch Institute of Fisheries and Hydrobiology of the South Bohemian Universi ty, Vodnany. The larval developmental period was divided ino 6 steps (L1-L6 ). In the first group of free embryos, exogeneous food was first taken on d ay 4 of age with a 10.2 mm TL, in the second group on day 5 of age with 11. 3 mm TL. Mixed, endogeneous and exogeneous nutrition occurred coincidentall y in both larval groups during the first two steps of development (L1-L2) D uring the third step of development (L3) at 8-9 days of age with 14.6-15.5 mm TL, a marked intensification of feeding appeared. The first signs of can ibalism were observed during the fifth step (L5) at 15-16 days of age with 21.0-21.7 mm TL. The termination of the larval developmental period occurre d in the first experimental group of larvae at 26-31 days of age with 30-35 mm TL, and in the second group of larvae at 33-39 days of age with 28-30 m m TL. Up to 16 days of age (21.9 mm TL), no differences in the development and growth rate were observed between the groups compared. The specific len gth and weight growth ratio (SLGR and SWGR) and also parameters of weight c ondition (FWC, coefficients of length-weight relationship) were very simila r. During the next rearing period up to the end of experiment, however, the intensity of growth rate dropped successively in the larvae fed artificial diet. At the end of experiment, the mean length of the larvae fed artifici al diet was lower by 46.6%, and their mean weight was lower by 137% (t = 2. 3575, p = 0.01) than those in the larvae fed live diet. On the contrary, th e mean FWC value was higher by 37.6% in the larvae fed artificial diet. In the present study, developmental deviations and predatory injuries are desc ribed. It is stated concluding that the artificial universal starter feed i s appropriate to initial feeding and rearing of larvae up to 16 days of age , i.e., to the mean total length (TL) of 22 mm and weight (w) of 0.1 g.