Feeding preferences of lumpfish (Cyclopterus lumpus L.) maintained in open net-pens with Atlantic salmon (Salmo salar L.)

Feeding preferences of juvenile lumpfish reared together with Atlantic salmon in sea pens were assessed. Juvenile lumpfish, initial mean (± SE) weight of 54.0 ± 0.9 g, were reared in small sea cages (125 m3, 5 × 5 × 5 m) together with Atlantic salmon with an initial mean (± SE) weight of 619 ± 2.5 g. Lumpfish were stocked at 10 and 15% density (12 and 18 lumpfish vs. 120 salmon, respectively) in replicate sea pens. To determine the feeding preferences of lumpfish in the cages gastric lavage was performed every two weeks and the feeding items were identified and categorized as: a) consumed sea lice, b) formulated feed fragments, c) crustacean species, d) hydrozoan species, e) Mytilus edulis, f) unidentified material or no contents found. The most common food item identified in the stomachs of lumpfish throughout the study period was fragments of salmon pellets. Results indicate that lumpfish in sea pens can be classified as strongly opportunistic and the fish do not restrict themselves or rely on a single food source if others are present. Lumpfish seemed to switch their preference towards which ever food item that was most readily available to them within their environment. The present data shows temporal changes in feed choice throughout the period, seemingly linked to food availability.