Effects of different feeding regimes on growth, cataract development, welfare, and histopathology of lumpfish (Cyclopterus lumpus L.)

To develop specific recommendations on the feeding strategies for farmed lumpfish, four duplicate groups (n = 70; N = 280) of lumpfish with a mean +/- SD start weight of 30.4 +/- 5.3 g were distributed among eight sea cages (5 x 5 x 5 m) each stocked with 220 one year old Atlantic salmon with a mean (+/- SD) weight of 1485.9 +/- 213.2 g. The fish were fed either pelleted feed at 3% BW-1 or with feed blocks at 1.5%, 2% and 3% BW-1 respectively for 66 days. There were clear differences in growth performance between the four treatment groups with lumpfish fed with pelleted feed attaining the highest weight gain. There were only minor histopathological changes observed between the dietary treatments with mainly mild focal and multifocal inflammation observed in sampled tissues. There were no significant differences in liver vacuolisation between the dietary groups and baseline samples with most of the livers evaluated appeared to be vacuolized within what is regarded as normal range for all four treatment groups. Only minor differences in welfare score between the four treatment groups were found. The incidence of cataracts varied between the treatment groups and was correlated to differences observed in growth between the four groups. Lumpfish fed once daily from automatic feeders with pelleted feed had the highest incidence and severity of cataracts. This study suggests that feeding lumpfish with moderate amounts of feed blocks (<= 2% BW-1) may be advantageous for maintaining slow growth and good welfare in salmon cages, and this should be further tested in large scale studies in commercial salmon farms.