We found little evidence that genetic effects influenced behaviour and survival in this study, but this was probably due to little genetic differences between wild and hatchery offspring. The environmental effects were clearly stronger, showing that salmon express high environmental plasticity. This study contributed to demonstrate how crucial the rearing environment is for phenotypical development of salmonids and should not be disregarded in stocking programs.
The enriched rearing methods used in the study are readily applicable to large rearing systems and have the potential to enhance post-release survival and fish welfare. The methods are simple, so that it would be easy for fish farmers everywhere to apply similar methods with low costs. Since this project started the rearing methods have already been taken into practice. A manual with instructions for enriched rearing is under preparation by the FGFRI and they are also organizing courses for private fish farmers and power company fish farmers on how to integrate the rearing methods into their rearing systems. The government buys Atlantic salmon for stocking from private fish farmers (sopimuskasvatus = contract rearing) and the FGFRI is responsible for transport and for stocking of the contract-reared fish. FGFRI is making the rules for the quality of fish (e.g. size, condition factor) and adopting enriched rearing methods for contract-reared fish has been discussed among the researchers of the FGFRI. However, enriched rearing has not always proven to promote survival in the wild (e.g. Berejikian et al. 1999 Brockmark et al. 2007; Fast et al. 2008). Moore et al. (2012) found great differences in
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post-release survival between smolts that had been reared in two different hatcheries.
This is showing how variable results can be when rearing fish under different conditions in different hatcheries. At the moment the FGFRI has an ongoing contract with four different aquaculture facilities. These are rearing Atlantic salmon with similar rearing methods as applied during the current study. Eggs from the same brood fish are under rearing at two different stations and will be released into the same river to examine if the hatchery effect can mask for the effect of enriched rearing. Whether or not these methods will be integrated into fish rearing depends partly on the practical experience from the other fish farms than the Paltamo facilities and also on more evidence of the cost-efficiency of this method.
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