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.

In the present study, oxygen consumption of two sturgeon species, beluga (Huso huso), sterlet (Acipenser ruthenus), and their hybrid reared in a recirculating aquaculture system were compared over body intervals from 54–107 g to determine the interspecific variation of metabolic rate. Metabolic rates were measured using the intermittent-flow respirometry technique. Standard oxygen consumption rates (SMR, mg O2 h−1) of sterlet were 30% higher compared with beluga and 22% higher compared with bester hybrid. The routine metabolic rate (RMR, mg O2 h−1) averaged 1.58 ± 0.13 times the SMR for A. ruthenus, 1.59 ± 0.3 for H. huso, and 1.42 ± 0.15 for the hybrid bester. However, the study revealed no significant differences (p > 0.05) between mean values of SMR and RMR for beluga and bester hybrid. The scaling coefficient reflected a closed isometry for the hybrid (b = 0.97), while for the purebred species the coefficient of 0.8 suggests a reduction in oxygen consumption with increasing body mass. These findings may contribute to understanding the differences in growth performances and oxygen requirements of the studied species reared in intensive aquaculture system.

This study aimed to investigate the effects of the probiotic Betaplus® and prebiotic Technomos®as feed additives for Nile tilapia in terms of growth performance, health profiles, and resistance to infection with Aeromonas hydrophila and Pseudomonas fluorescens. A total of 960 healthy juvenile Nile tilapia (1.5 ± 0.01 g) were randomly divided into four experimental variants with three replicates for each variant. Fish were fed a commercial diet (control group, V0), supplemented with BetaPlus® probiotics–1%×BW (V1), TechnoMos® prebiotics–1% × BW (V2), and with BetaPlus® probiotics and TechnoMos® prebiotics in a ratio of 1:1%×BW (V3). Results on growth performance showed the best values in the probiotic variant, correlated with the health profile and the relative survival percentage after the challenge test with A. hydrophila and P. fluorescens. Similarly, the effects of dietary supplementation with probiotics and prebiotics on physiological conditions also recorded beneficial results in the synbiotic variant, where a high survival percentage was obtained after infection with the two pathogenic bacteria. In conclusion, the results of this study indicate that dietary supplementation with feed additives consisting of mentioned probiotics, prebiotic, and their combination as synbiotics has the potential to promote growth performance, improving tilapia immunity and increasing survival after the challenge test.

At ish, the evaluation of hematological pro ile is an important step in monitoring the welfare status. The aim of this research was to determine the in luence of dietary supplementation with some phytobiotics on hematological pro ile, some biochemical indices of blood and on the immune response at Oreochromis niloticus reared in a recirculating aquaculture system. The experimental variants were organized as follows: V1-control, V2-1% thyme, V3-1% fenugreek and V4-1% neem. Blood analysis, glucose and total protein were carried out by methods commonly used in ish hematology. Lysozyme activity was measured by a turbiometric assay and cortisol was determined by an immunoenzymatic assay. At the end of the experiment was observed that the phytobiotics administration has led to signi icant changes (p˂0.05) in case of erythrocytes number (p=0.002) and relative number of monocytes (%) (p=0.045). Comparing inal results with the value obtained at the beginning of the experiment were noted signi icant differences (p˂0.05) in case of erythrocytes number (p=0.037), PVC (p=0.001), MCHC (p=0.000), glucose (p=0.035), monocytes (%) (p=0.042). The best values were registered in V2 and V3 variant. The concentration of cortisol was lower in variants in which the dietary was supplemented with phytobiotics compared to the control variant. The neem (V4) administration led to intensifying the lysozyme activity than other experimental variants. In conclusion, we demonstrated that the dietary supplementation especially with thyme and fenugreek, but also with neem has improved the physiological status at Oreochromis niloticus species.

The present paper contributes to the modeling aquaculture. The