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Previous studies have shown that the antipredator responsiveness of fish degenerates through generations in captive breeding. However, detailed knowledge of the underlying mechanism is still largely lacking. We tested the hypothesis that hatchery fish supposedly selected for faster growth in the hatchery environment are bolder towards predators than their slower-growing conspecifics. This was examined by comparing the antipredator behavior of predator- naïve fast- and slow-growing individuals of a captive-bred Arctic char (Salvelinus alpinus) population to chemical cues from natural predators burbot (Lota lota) and pikeperch (Sander lucioperca). As behavioral responses depended on char body size, we compared boldness towards predators of size-matched fast- and slow-growing char. We found no differences in four behavioral antipredator traits between size-matched groups of fast- and slow-growing char. According to these results, boldness to predator cues is not related to individual growth rate in captive-bred Arctic char.

Predator conditioning can be used to improve post‐release antipredator recognition of hatchery‐reared salmonids. However, possible negative stress‐related effects of prolonged predator conditioning on juvenile fish physiology are poorly understood. We studied the effects of prolonged (91 days) predator odour exposure on whole‐body cortisol level and spleen size in six full‐sib families of juvenile hatchery‐bred Arctic charr (Salvelinus alpinus). Chemical cues from water containing charr‐fed pikeperch (Sander lucioperca) were used as the predator exposure stimuli and lakewater was used as a chemical control. Our study revealed that juvenile body cortisol levels post‐predator conditioning were affected by treatment, fish size and their interaction. Importantly, among the smaller (i.e. slowest growing) charr, the predator‐exposed fish had higher cortisol levels than control fish, while the opposite pattern was true for the larger fish. These results suggest that chemical cues from charr‐fed predators induce a prolonged stress response in juvenile charr. As prolonged predation exposure seems to elevate stress levels in a size‐dependent manner, the larger, faster growing fish could possibly have intrinsically lower stress responses to predation threats than smaller, slower growing fish. Possible coupling between stress sensitivity and growth requires further attention due to the likely implications for the management of unintended domestication among captive‐reared salmonids.

Stocking hatchery-reared brown trout in different densities into a wild population -a comparison of growth and movementIn spring 2001 and 2002 a small stream was stocked with tagged hatchery-reared yearling brown trout (Salmo trutta), in order to study their influence on the resident brown trout population. The stream was separated into six sections: two sections without stocking, two sections where stocking doubled the trout population and two sections where the fish population was quadrupled. The working hypothesis was that due to food limitation (competition) growth of the wild fish will be negatively influenced by stocking, and wild fish will be displaced by the (possibly more aggressive) hatchery fish. Surprisingly, growth rate of wild and stocked fish of the same age was similar and independent of stocking density. Two main reasons may be responsible for this finding: only a low percentage of the stocked fish remained in the stream, and food was not limited during summer. Only 12-19% of the stocked fish were recaptured after six months, in contrats to 40-70% of one-year old and up to 100% of older wild trout. The wild fish were not displaced by hatchery-reared fish: During summer the wild fish remained more or less stationary, whereas most of the stocked trout had left their release site. The results indicate that in a natural stream stocking of hatchery reared brown trout does not influence negatively growth and movement of the wild fish independent of stocking density. Baer, J. (Fisheries Research Station of Baden-Wu¨rttemberg, Untere Seestraße 81, 88085 Langenargen, Germany). Swimming activity of seabass: comparing patterns obtained in natural environment and in re-circulating tanks under high density Genetic quality of domesticated African tilapia populations Anecdotal and empirical evidence exists for substantial (up to 40%) declines in growth among Oreochromis populations domesticated in both large and small-scale fish farms in Africa. These declines are at least partly attributable to poor genetic management, including inadvertent selection, inbreeding, bottle-necks and founder effects. Due to restricted cash flow and investment capital, genetic management and selective breeding for the improvement of domesticate populations are difficult for small-scale farmers, but feasible on larger-scale farms. In managing domesticated gene pools, feral populations can serve as a broodstock reservoir, making the use of indigenous species advantageous. A development model of large-scale hatcheries producing selected lines of sex-reversed, indigenous tilapia for sale to smaller-scale farmers is proposed as a solution to the problems of poor genetic management in African aquaculture. Brummett, R. E. & Ponzoni, R. (WorldFish Centre, BP 2008, Yaounde´, Cameroon). Polyculture production of juvenile fishes for survival in natureProduction of seed for stock enhancement projects requires consideration of the behavioural quality of the animals to be released in the wild. Our approach to improving behavioural quality of hat...