This study was conducted to investigate the effects of krill oil supplementation on growth performance, proximate composition and organo-somatic indices of Cyprinus carpio, reared in a recirculating aquaculture system, at different stocking densities. Four experimental diets were formulated: LD - low density (15 fish/rearing unit- 3.5 kg/m3), where fish were fed with commercial feed, HD - high density (35 fish/rearing unit-8 kg/m3 fed with commercial feed), LD-KO - low density, where fish were fed with commercial feed supplemented with 5 g/kg feed krill oil, and HD-KO- high density, were fish were fed with commercial feed supplemented with 5 g/kg feed krill oil. After 60-days of rearing, final fish weight and individual weight gain was significantly higher (P˂0.05) in fish stocked in lower density, with better values in LD-KO groups. Also, the best values of FCR, SGR and PER were obtained in LD-KO groups. Regarding the proximate composition of meat, no significant differences (P˃0.05) were registered between the experimental variants. The organo-somatic indices revealed no significant differences (P˃0.05) in the cardiosomatic index, while hepatosomatic, splenosomatic, and visceral index differed significantly (P˂0.05) between the experimental variants. Accordingly, we can conclude that supplementation of carp diet with 5 g/kg feed krill oil can improve growth performance, without any modification at proximate composition of meat.

The objectives of the present study were to evaluate the potential of the Korill (KO), a product based on krill oil, supplemented in fish feed (5 g/kg feed) to alleviate density-induced stress in carp fingerlings, and its protective capacity in case of anthelmintic drug administration (ABZ—albendazole). Thus, the fish were divided into four groups: LD (low density with normal feed), LD-KO (low density with KO supplementation feed), HD (high density with normal feed), and HD-KO (high density with KO supplementation feed). During the first trial, the fish held under different densities were fed normal feed and KO feed for two months, following a 2 × 2 factorial experimental design. In the second trial, seven fish per tank were subjected, for one week, to albendazole treatment (administered daily by an oral dose of 5 mg/kg body weight). For both trials, blood and plasma samples were used to quantify hematological and biochemical parameters. The results showed that the KO diet alleviated the negative impact of ABZ treatment on liver function and the metabolic profile of carp fingerlings reared in high densities. In addition, KO feeding improved lysozyme activity (LZM) and therefore the immune status of the fish, and reduced oxidative damage in the liver, demonstrated by a decrease of malondialdehyde (MDA) content and an increase of total antioxidant capacity (TAC).