Abstract
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.
Highlights
In this study we evaluate a suite of potential morphometric condition indices to see which correlate with an injurybased operational welfare indicators (OWIs) for a novel aquaculture species [lumpfish, Cyclopterus lumpus (Linnaeus, 1758)]
The application of the OWI of fin damage to size and condition data was important in identifying the impact fin damage had on C. lumpus. These results indicated significant variation in fin damage with size and life stage of the C. lumpus, which is to be expected of a species being held under a variety of husbandry conditions in environments that differ from its natural habitat
4.3 | Management implications of the selected index. This selection of the index based on size relative to peers highlights the importance of early grading in hatchery facilities where tanks are used to house hatchery C. lumpus
Summary
It is essential in many contexts to be able to monitor the health, welfare and reproductive status of fish. To find a condition index that predicts fin damage, we defined different indexes that can be calculated from the size measurements of the fish We divided these into two classes: (1) the first class refers to the weight of the fish relative to species-specific length–weight relationship; (2) the second class refers to the weight of the fish relative to its peers in the same tank or sea cage. This methodology was validated with a data set for fin damage of S. salar at a commercial farm These indices are intended to allow the detection of ill-health and poor welfare, to aid application of treatments and improve husbandry procedures like grading, both in tanks and sea cages. All indices have a multiplier of 100 to yield numbers of similar magnitude and for consistency with the usual calculation of Fulton's K
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