Recapture and condition of pond-reared, and hatchery-reared 1 +  European grayling stocked in addition to wild conspecifics in a small river

Abstract

Key-words:Thymallus thymallus, river management, stocking, recapture, graylingThe relative performance of European grayling Thymallus thymallus reared in a hatchery on commercial dry feed or in a pond with natural food and their wild conspecifics, was assessed through recapture of tagged fish 5 months after their release into the Blanice River, Czech Republic. Oneyear old pond and hatchery reared fish from a resident broodstock were marked using Visible Implant Elastomer tags and released into 3 sections of river in May 2006. Wild one-year-old grayling were also tagged in these sections on the same days. The ratio of hatchery reared, pond reared, and wild fish was 1:1:1 in all sections. The recapture rate (hatchery 14.9%, pond 22.1%, and wild 51.3%) and site fidelity (hatchery 7.8%, pond 13.0%, and wild 35.1%) were significantly different among groups. Wild fish had a higher probability of recapture upstream of their original section than did hatchery or pond reared fish. Pond rearing was superior to conventional hatchery rearing for subsequent stocking of 1+ grayling in running water. Initially different mean condition factors were similar in all groups at recapture, suggesting adaptation of the artificially reared fish that remained in the river sections surveyed. RÉSUMÉRecapture et condition d'ombres communs 1+ élevés en étang ou en pisciculture déversés en complément de congénères sauvages dans une petite rivière Mots-clés :Thymallus thymallus, gestion de rivière, alevinage, recapture, ombre La performance relative des ombres communs Thymallus thymallus élevés dans une écloserie avec des aliments secs commerciaux ou dans un étang avec des aliments naturels et de leurs congénères sauvages a été évaluée par la recapture de poissons marqués 5 mois après leur déversement dans la rivière Blanice, Ré-publique tchèque. Des poissons d'un an issus de géniteurs sauvages, élevés en étang ou en écloserie, ont été marqués au moyen d'implants visibles élastomère et déversés en 3 sections de la rivière en mai 2006. Des ombres sauvages d'un an ont également été marqués dans ces sections ces mêmes jours. Le ratio de poissons d'élevage de pisciculture, d'étangs, et sauvages était dans toutes les sections 1:1:1. Le taux de recapture (écloserie de 14,9 %, 22,1 % étang, et sauvage 51,3 %) et la fidélité au site (écloserie de 7,8 %, d'étang de 13,0 %, et sauvage de 35,1 %) étaient significativement différents entre les groupes. Les poissons sauvages avaient une plus forte probabilité de recapture en amont de leur section d'origine que les poissons d'écloserie ou d'étang. L'élevage en étang a été plus performant que l'élevage en écloserie classique pour le déversement d'ombres 1+ en rivière. Les différents facteurs de condition étaient les mêmes dans tous les groupes à la recapture, ce qui suggère une bonne adaptation des poissons élevés artificiellement qui restaient dans les sections des rivières étudiées.

Environmental enrichment for fish in captive environments: effects of physical structures and substrates

“…The size of the fish, however, was smaller than in the hatchery (Ahlbeck and Holliland 2012). Pond rearing, as compared to tank rearing, had positive effects on recapture rates of European grayling Thymallus thymallus (Salmonidae) and brown trout stocked into natural rivers (N€ aslund 1992;Turek et al 2012). However, other studies on the same species have shown negligible or contrasting effects (Johnsen and Hesthagen 1990;Turek et al 2010).…”

“…Wild‐reared fish often perform better in the wild than pond‐reared fish (Miller ; Turek et al . ), suggesting that even if pond rearing increases the natural fitness of fish compared with tank‐rearing, it is still not alleviating all maladaptive effects of artificial rearing. There are also some other potential problems associated with pond rearing, like high temperatures, harvest inefficiency and distasteful flavour of the fish (Lawler et al .…”

Radio‐telemetry shows differences in the behaviour of wild and hatchery‐reared European grayling Thymallus thymallus in response to environmental variables

“…Stocking is routinely performed to limit the decline and to increase the population levels of fishes, despite the fact that it represents a significant risk for the conservation of indigenous, wild populations (Persat, 1996;Bohlin et al, 2002). Artificial rearing has been shown to substantially influence the behavioural traits of fishes, which may lead to reduced growth, survival rates and reproductive success of hatchery-reared fishes (Olla et al, 1998;Bohlin et al, 2002;Weir et al, 2004;Turek et al, 2012). For example, hatchery-reared fishes often display different foraging (Olla et al, 1998;Vehanen et al, 2009) or antipredator behaviours (Berejikian et al, 1999).…”

Stock enhancement by hatchery-released turbot, <em>Psetta maxima</em>, in the southeastern Black Sea: capture, migration, growth and diet analyses

“…Between 8 and 9 months could be considered the most suitable age and length for turbot release, because they have an increased ability of swimming and finding shelter, whereas higher losses in hatchery-reared fish may be associated with predation (Turek et al 2012). The efficiency of turbot restocking programmes is often difficult to evaluate as information on natural stock abundance is rarely or only partially available.…”