Using model selection to choose a size-based condition index that is consistent with operational welfare indicators.

Quantitative and qualitative measures of fish health and welfare are essential for management of both wild capture and aquaculture species. These measures include morphometric body condition indices, energetic condition and aquaculture operational welfare indicators (OWIs). Measures vary in ease of measurement (and may require destructive sampling), and it is critical to know how well they correlate with fish health and welfare so appropriate management decisions can be based on them. Lumpfish (Cyclopterus lumpus) is a new farming species that needs nondestructive OWIs to be developed and validated. In this study, we developed a C. lumpus fin damage score. Four different body condition indexes based on individual weight relative to either length-weight relationships or relative to other fish in its local environment were tested (using model selection) as predictors of individual fin damage. Results showed severity of fin damage was predicted by small size relative to the other individuals in the tank or cage. Body condition based on length-weight relationship was not found to predict fin damage, indicating that using established indices from fisheries or from other species would not predict welfare risks from fin damage. Implications are that especially in hatchery conditions grading will improve the condition index, and is expected to mitigate fin damage, but that low weight at length was not of use in predicting fin damage. Model selection to choose between a suite of possible indices proved powerful and should be considered in other applications where an easily measured index is needed to correlate with other health measures.

The effect of shelter on welfare of juvenile Atlantic salmon Salmo salar reared under a feed restriction regimen.

This study investigated whether shelter (presence or absence) affected the frequency of fin damage in Atlantic salmon Salmo salar exposed to feed restrictions (0·73 or 0·33% of body mass day(-1) ). The presence of shelter had a positive effect on the pectoral fins at both feed ration levels and on the dorsal fin at the higher ration level but it had a negative effect on survival. The reduced feed rations resulted in fish of the same size and nutritional status as wild fish. The provision of shelter has potential to mitigate the negative effects of feed restrictions on fin quality, but the optimal shelter design requires some additional investigation.

Fin Erosion of Salmo salar (Linnaeus 1758) Infested with the Parasite Caligus rogercresseyi (Boxshall & Bravo 2000).

Fin condition is a simple indicator of fish welfare, which anticipates detrimental effects on fish in aquaculture systems. This study evaluated the fin condition of Salmo salar at different abundances of the parasite Caligus rogercresseyi. Fish were exposed to infestation with copepodids and the cohort was allowed to develop to the adult stage. The relative fin index was measured. Significant differences between infested and control fish for both pectoral and anal fins were observed. Moreover, there were significant negative relationships between fin condition and parasite abundances for pectoral, anal, and pelvic fins, suggesting that infestations with C. rogercresseyi could be a possible cause for fin damage in Atlantic salmon. Moreover, this damage was associated with increased stress levels, suggesting that damage can be related to physiological changes on infested fish. According to these results, pectoral fin assessments have the potential to provide information on the welfare of fish with C. rogercresseyi infestation. Determining the causes of poor fin development may improve fish welfare, even when infested by parasites.