Influence of geographic origin on post-stocking survival and condition of European grayling (Thymallus thymallus) in a small river

The post-release survival and condition of 1+ year old European grayling Thymallus thymallus reared in a local (Husinec) and two 250-300 km distant, hatcheries (Pardubice and Hyncice) were evaluated by the recapture of tagged fish five months after release into the Blanice River, Czech Republic, the fish population of which was depleted by cormorant predation during several previous winters. The fish were marked using Visible Implant Elastomer tags and released into six sites along the river in May 2014: 100 locally sourced fish and 100 of a strain from a distant source per site. Significantly higher recapture of Husinec (33%) than Pardubice (20%) was found at one site but was offset by results in the remaining two sites into which they were stocked. Significantly higher site fidelity was shown by Husinec (12%) than Hyncice (7%) fish in the three sites. Lower initial weight and condition factor of the Husinec fish was equal to or higher than fish from the distant hatcheries at recapture. Some differences in final weight, length, and condition factor were found among groups regardless of release site. Lower recapture rate, growth, and condition were displayed in fish released into the three downstream sites (Husinec 1 and Hyncice). The results indicated the potential for successful use of non-autochthonous stock for grayling population recovery.