Lumpfish are of interest to the aquaculture industry because of their usefulness as biological controls for sea lice infestations in salmonid ocean farms. Even though millions of lumpfish are produced annually, there is still little information on the ideal growing conditions. During the Summer of 2020, two experiments were conducted at the Coastal Marine Laboratory to determine the ideal nutritional parameters and stocking density for juvenile lumpfish. Diets with varying protein/lipid compositions were tested, including six experimental diets (50/15, 55/10, 50/20, 55/20, 55/15, 50/10), one commercially available lumpfish diet (Skretting Europa, 55/15), and one trout (salmonid) diet (BioTrout, 47/24), a food source that lumpfish would have access to in a trout ocean farm. Fish (initial mean size = 9 g) were stocked into 10 L flow through tanks at 13 g/L, and survival, growth, and aggressive behaviors were monitored for 10 weeks. In a separate study, the effects of different stocking densities (40, 60, 70, and 90 g/L) on growth, survival, and aggression of lumpfish (initial mean size = 13 g) were evaluated over 8 weeks. Mortality and fish aggression were not limiting factors in either experiment. Fish fed experimental diets with 55% protein compositions had the greatest growth, even surpassing growth of fish fed the commercially available lumpfish feed (p < 0.0001). Not surprisingly, lumpfish reared under lower densities had faster growth than fish reared in higher densities (p < 0.0001), however, given that juvenile lumpfish are cannibalistic, the lack of increased aggressive behaviors at higher densities was unexpected. These findings indicate that juvenile lumpfish growth is highest when provided high (55%) protein feeds and low (40g/L) rearing densities. However, lumpfish outgrow their usefulness as cleanerfish in the net pens, so being able to increase or suppress fish growth may prove to be a useful tool for grow out facilities.
