The importance and volume of aquaculture is increasing worldwide. Along with food production, aquaculture also has an important role in maintaining endangered fish populations. One major threat to aquaculture and agriculture in general is the vulnerability of intensive farming units to parasitic infections. In aquaculture, infections can lead to economic losses through impaired fish growth and increased morbidity and mortality. Thus, economically and ecologically sustainable methods to control parasite infections are in high demand.
Rearing methods and conditions play a key role in determining well-being of farmed fishes. Tanks typically used in large-scale fish production provide simplified, low-stimulus environments compared to natural conditions, which may influence several aspects of fish physiology and life expectancy, including survival after re-stocking into wild. In the method of enriched rearing, tanks are supplied with shelters for fish as well as changing water dynamics (velocity, depth, direction) to mimic variation found in natural conditions.
Anssi Karvonen, Mariella Aalto-Araneda, Anna-Maija Virtala, Raine Kortet, Perttu Koski and Pekka Hyvärinen investigated for the first time the effects of enriched rearing on the occurrence of parasitic diseases in production-scale experiments comparing the mortality, parasite abundance and disease resistance of salmonid fishes under enriched vs. standard rearing conditions during parasite epidemics. The results showed that fish in enriched rearing conditions had significantly lower mortality rate and parasite abundance during most epidemics compared to fish in standard rearing. Fish from enriched rearing were also more resistant to infections. However, the results also showed that the effects of enriched rearing were not similar in all diseases, which, according to the results of this study, may be due to ecology of each pathogen as well as depend on the species and age of the fish.
Overall, the results suggest that fairly simple enrichment of the rearing environment can significantly decrease the harmfulness of some of the key pathogens found in aquaculture worldwide. These results may have important implications for ecologically and economically sustainable parasite prevention strategies in aquaculture.
This research was done in collaboration between the University of Jyväskylä, the University of Helsinki, the University of Eastern Finland, the Finnish Food Safety Authority Evira, and the Natural Resources Institute Finland (Luke). The method of enriched rearing was designed at the Kainuu Fisheries Research Station of the Natural Resources Institute Finland (Luke), where the research was also carried out. This study was supported by the Academy of Finland, the University of Eastern Finland, the University of Helsinki, Finnish Food Safety Authority Evira, and Natural Resources Institute Finland (Luke).