| Summary: | Atlantic salmon is commercially a key species in the global aquaculture industry, and serves as a model species for teleost breeding, particularly regarding physiology and nutrition. Salmon is, however, sensitive to handling and solitary tank environment, and will respond to such stressors with reduced feed intake for extended periods. Therefore, we have validated an experimental protocol that incorporates a tank‐based system for analysis of individual feed intake in Atlantic salmon (N=16). It includes the use of sedation AQUI‐S prior to anaestesia (MS 222), allowing handling and experimental treatments like intraperitoneal (IP) injections. The protocol ensures low stress response and in the experiments described below, the salmon resumed voluntary feeding within 1–2 h of IP injections. The effects of leptin (Lep)on voluntary feed intake and appetite in post smolt Atlantic salmon was studied. Three experiments were conducted alltogether where individual salmon were placed in tanks and feed intake monitored until it stabilized at a high level, after which each individual was IP injected with recombinant salmon leptinA1 (rsLepA1) emulsified in vegetable oil. The fish were restocked into the tanks and feed intake (hand‐feeding 4 times daily) was monitored for up to 4 more days. For all experiments, fish were sampled 4 h after the last meal and samples collected from brain, liver and stomach for qPCR analysis of appetite‐ and growth‐related genes ( lepa1, 2; lepr1, 2; pomca1, a2, 2s, b; agrp1, 2; cart; npy; pyy; cckl) . Plasma was collected and analysed for levels of the energy‐related metabolites triglycerides, glucose, free fatty acids, lactate and D‐3‐hydroxybutyrate. Lep caused a significant reduction in feed intake for up to 3 days as well as a reduction in specific growth rate, compared to pre‐injection and sham controls. Brain expression of pomca1 and pomca2 was significantly (p<0.05) upregulated in the Lep‐treated fish. This supports earlier studies where pomc expression is linked to reduced appetite and ...
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