Improving Larval and Juvenile Lumpfish, Cyclopterus lumpus, Aquaculture: Nutrition and Growing Conditions

Salmonids play a major role in aquaculture globally and their production is expected to increase as the human population rises and wild fish stocks decline. Sea lice infestation is the largest economic burdens to salmonid net pen aquaculture with hundreds-of-millions of dollars lost due to the treatment, labor, and loss of biomass associated with these parasitic copepods. Chemotherapeutics were originally used to treat these infestations, but their effects on nontarget species resulted in them being banned in many countries. Many salmonid farmers now utilize cleanerfish technology to resolve this financial stressor. Lumpfish (Cyclopterus lumpus) are efficient delousers in salmonid aquaculture and are produced and used by the tens-of-millions in European countries and Atlantic Canadian provinces. However, standard protocols for raising these fish do not exist. Several knowledge gaps remain on the proper conditions for rearing Lumpfish. The goal of this thesis was to address some of these gaps by evaluating nutritional and rearing conditions for juvenile Lumpfish and providing guidelines for facilities to utilize. Few experiments have focused on the nutritional requirements of juvenile Lumpfish. Many Lumpfish facilities use feeds that are specifically marketed to Lumpfish, but there is a general lack of understanding of the nutritional requirements of juvenile Lumpfish. To address this, two diet trials were performed to determine the effects of varying protein and lipid concentrations, as well as plant versus fish meal-based protein sources, on the growth, survival, and aggression of juvenile Lumpfish. Six experimental diets and two commercial diets were tested that varied in their protein/lipid concentrations and protein source. Fish were fed five times per day at 3 % body weight. In general, protein and lipid concentrations did not influence growth, survival, or fish aggression of juvenile Lumpfish. However, fish fed an experimental diet had significantly faster and greater growth than those fed a commercial diet even though both diets had the same protein/lipid concentrations (55/15). This was likely due to ingredient differences between the two diets. The use of plant-based protein, however, did influence the growth of juvenile Lumpfish. Fish fed diets with plant-based protein showed significantly suppressed growth. Lumpfish have a ventral suction disk that they use to adhere to surfaces, including the sides and bottoms of the tanks they are grown in. This makes cleaning quite laborious and may increase stress in these fish as they encounter cleaning implements. To improve tank design for culturing juvenile Lumpfish, two trials were performed in which tank color and tank bottom type were evaluated. In the “Tank Color Trial,” six tank colors were tested (red, green, grey, black, white, and blue) to determine if color impacted the growth, survival, and aggression of juvenile Lumpfish. In the “Tank Bottom Trial,” six bottom treatments were tested (rough-dark, rough-light, smooth-dark, smooth-light, false bottom, and control) that varied in their texture, color, and bottom type to determine if these surfaces affected Lumpfish adhesion, and therefore cleaning efficiency, as well as fish growth, survival, or aggression. Neither color nor tank bottom influenced the growth, survival, or aggression of juvenile Lumpfish. However, tank bottom did influence the occurrence of Lumpfish adhesion and cleaning efficiency. “Rough bottomed” treatments deterred Lumpfish adhesion significantly more than “smooth bottomed” treatments. Light colored, smooth bottomed treatments resulted in less Lumpfish adhesion than dark, smooth bottomed treatments. The false-bottom treatment resulted in the least amount of Lumpfish adhesion and fastest cleaning times. Juvenile Lumpfish are territorial and bite at the fins of other individuals. Density dependent interactions are not well understood with this species, therefore the effects of stocking density for different size classes of fish needs to be evaluated. Facilities generally use the amount of surface area allotted to the Lumpfish as a proxy for how dense to grow their fish, but if densities are too high, cannibalism may ensue. To determine the effects of stocking density on juvenile Lumpfish and to determine if fish aggression occurred at specific ontogenetic period, two stocking density trials were performed, one using 2 g fish and one using 13 g fish. Fish were stocked at four different rearing densities (40, 60, 70, and 90 g/L) with growth, survival, and fish aggression measured. Stocking density was negatively correlated with growth but did not influence survival or fish aggression. As stocking density increased, growth decreased. Also, there was no difference in aggression rates between the two size classes of fish, supporting the null hypothesis that there is no ontogenetic shift in fish aggression. Lumpfish are a hardy species but outgrow their usefulness as cleanerfish on salmonid farms. Facilities can use the results from these trials to increase or suppress the growth of their fish to better meet the financial and temporal needs of their operations. Lumpfish facilities can feed their fish diets utilizing plant-based protein and increase rearing densities to suppress their growth. To increase growth, more fish meal-based protein should be used in the Lumpfish feeds as well as using lower stocking densities. However, this may result in higher expenses with more expensive feed ingredients being used and less individuals being produced under these lower densities. Lumpfish operations can manipulate these nutritional and rearing densities without impacting survival or fish aggression. If facilities are producing juveniles in large quantities, it will be vital to increase cleaning efficiency and decrease cleaning implement-fish interactions in the Lumpfish rearing tanks. When budgets and resources are limited, facilities can use light colored or possibly textured bottoms to limit the adhesion of juvenile Lumpfish. But to maximize cleaning efficiency and minimize cleaning interaction, false-bottomed tanks may be more efficient. With the demand for Lumpfish increasing, rearing protocols need to be refined so that the culture of these fish can be as efficient as possible. These foundational results can help improve the economic gain and animal welfare of juvenile Lumpfish.

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