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अमूर्त

The Effect of the Feed Oil and Protein Source on the Deposition and Depletion of Oxolinic Acid in Farmed Atlantic Salmon (Salmo salar L.)

Bjørn Tore Lunestad, Merat Behzadzadeh, Ole Samuelsen, Marit Espe and Marc H.G. Berntssen

Fish feed has traditionally been based on the marine ingredients fish oil and fish meal. Pressure on feral fish stocks and rapidly growing aquaculture has lead to the need for development of novel aquafeeds that rely less on fish meal and fish oil, with plant ingredients or alternative marine feed components as feed ingredient replacements. The present study investigates the muscle and liver deposition and elimination of the antibacterial agent oxolinic acid (OA) administered per os to post smolt Atlantic salmon (Salmo salar L.) in conventional and a novel substitution fish feed based on vegetable ingredients and krill meal. Atlantic salmon post smolt (start weight ~350 g) was reared for 2.5 months on either a conventional or a maximum substitution diet. Subsequently, the fish were fed on OA supplemented conventional or substitution diets supplemented with 5 OA g/kg, with a target dose rate of OA of 15 mg/kg fish/day for 5 days, followed by a 28 day depuration period on OA free conventional or substitution feed. Fish in either group were held in three individual tanks, and at each sampling point three fish form each tank were sampled and analysed, giving a total number of nine parallels. The concentration of OA in muscle and liver were examined by an LC-MS (API-ES) method with a lower limit of detection (LOD) of 5.0ng/g and a lower limit of quantification (LOQ) of 10.0ng/g. To assess the relative muscle and liver deposition of OA among fish fed the two diets, the area under the curve (AUC) ratios in muscle and liver for replacement feed (r) and conventional feed (c) was calculated as AUCs / AUCc x 100 %. This ratio in muscle was 73.4 ± 2.2 %, whereas for liver samples it was 85.1 ± 4.0 %, indicating a lower OA deposition for substitution feed compared to conventional feed. The lower deposition is explained by a lower feeding rate for the fish fed on substitution diets compared to the conservative diets (0.024±0.0029 and 0.034±0.0027 mg OA g fish-1day-1 respectively), due to a lower voluntary feed intake. A minor though significant difference in elimination was observed between the two diets with halflives (t½ β h) of 189.6 ±4.3 and 211.2±8.4 hours for conventional and substitution feed, respectively.