The study aimed to compare the growth performance and physiological responses of bester (B) and backcrossed bester ♀ × beluga ♂ (BB) in response to crowding stress under different stocking densities, as well as to establish a threshold stocking density for rearing BB in a recirculating aquaculture system (RAS) without welfare impairment. For this purpose, in the first trial (T1), B (181.15 ± 21.21 g) and BB fingerlings (181.98 ± 28.65 g) were reared in two stocking densities of 2 kg/m2 and 4 kg/m2 in fiberglass tanks (1 m3) for 6 weeks. In a parallel trial (T2), the BB hybrids (335.24 ± 39.30 g) were kept in four initial stocking densities, ranging from 5 kg/m2 to 12 kg/m2. The results of T1 revealed better growth indices (i.e., final mean weight, weight gain, specific growth rate) at lower stocking densities for both hybrids; however, in terms of growth performance, the BB hybrid showed better results when compared with the B hybrid. BB hybrids registered significantly (p < 0.05) lower serum cortisol and MDA and higher lysozyme than B hybrids, showing higher tolerance to crowding stress. Nevertheless, at higher densities, selected serum parameters (i.e., hematological indices, cortisol, glucose, protein, malondialdehyde, lysozyme) and growth performance indices used to evaluate the hybrids indicate that high stocking density could affect the growth and welfare of BB hybrids, and that the selected serum parameters could be used as good indicators for chronic stress caused by overcrowding conditions.

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).

The aim of this paper was to analyze some morphometric characteristics and the correlation between them for Russian sturgeon juveniles (Acipenser gueldenstaedtii) reared in a recirculating aquaculture system fed at different fed with different ratio: 1% body weight (BW), 1.5% BW, 2% BW and ad libitum feeding (which was around 2.8% BW).Fish, with an average body mass around 248.194 ± 1.59 g. Following biometric measurements were made for each fish, including weight (W), total length (TL), standard length (SL), fork length (FL), maximum body depth (last depth of caudal peduncle, H); preanal distance (AD), predorsal distance (PD), length of head (C), preorbital distance (PO), length of pectoral fin (LPF), interorbital distance (ID), maximum width of head (MH), width of mouth (WM), width of the head at the level of the mouth (WHM). The obtained results showed significant differences between all morphometric measurements (p<0.05) for all the experimental variants, emphasizing that in the ad libitum feeding all morphometric measurements were significantly higher than in the other experimental variants. In order to highlight more eloquent these differences, were developed some linear regressions between the morphometric measurements and significant positive correlation (p<0.05) between dependent and independent variables were found.

The study was carried out with one summer-old Silurus glanis juveniles, having the mean size 23.04±2.05 cm and weight 73.84±19.12 g, reared in recirculating water condition, in order to assess the impact of feeding level on growth performances and body size variation of fish. Two feeding levels were tested (R1=1.5% BW/day and R2=2.5% BW/day), in duplicate, during 6 weeks, and the biomass gain (BG), feed conversion ratio (FCR), specific growth rate (SGR), protein efficiency ratio (PER), morphometric relationship between length-weight (LWR) and coefficient of variation (CV) were assessed. Data revealed that the overall mean weight of the biomass was doubled during the trial, from 14.92 kg to 31.17 kg, and the body growth significantly increases with the increment of the feeding rate (13.48 kg in R1 and 17.70 kg in R2), underlying the good potential of the species, at this life stage, for fast-growing under intense conditions. The calculated SGR in R1 was 1.43%/day and in R2, significantly higher, as 2.05 %/day, for the almost similar values of FCR (0.74 g/g) and PER (2.50 g/g) recorded between the treatments.