The Effect of the Live Diet Given to Hatchery-Reared Fry of the European Grayling (Thymallus thymallus) on Their Survival and Growth in the Wild

摘要

The survival rate and growth parameters of grayling fry were determined after stocking them in the wild. Before their release (7th July 2011) into the wild, the fry were reared for 7 weeks in the hatchery, in two groups: (i) fry fed on live daphnids and live chironomids larvae (LFG), (ii) fry fed on a pellet diet (PFG). On the 2nd October 2011, the fish survival rate was checked; the fish were caught in the wild. The survival rate and specific growth rates were higher in the LFG than in the PFG. The most effective food for hatchery-reared fish to be used as stock was natural live food: zooplankton and chironomids larvae. In the wild the mean number of chironomids larvae and gammarids found in the stomachs of fish was significantly higher in the LFG than in the PFG. The prevalence of almost all taxa of macroinvertebrates in the stomachs of the LFG was higher than those from the PFG. The live diet supplied in the rearing period has a positively impact on fish foraging skills and their survival in the wild.