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.

Berberine (BBR) and silymarin (SM) are natural compounds extracted from plants known for their antioxidant and chemoprotective effects on the liver. The present study aimed to investigate the beneficial properties of BBR and SM and the association of BBR with SM on liver function using fish as “in vivo” models. Moreover, the study investigated their hepatoprotective role after acetaminophen (APAP) exposure. For this purpose, the fish (N = 360; 118.4 ± 11.09 g) were fed with control or experimental diets for 9 weeks. In the experimental diets, the feed was supplemented with either SM (1 g/kg feed), BBR (100 and 200 mg/kg feed), or a combination of BBR with SM (SM 1 g/kg feed + BBR 100 mg/kg feed and, respectively, SM 1 g/kg feed + BBR 200 mg/kg feed). After the feeding trial, seven fish from each tank were randomly selected and exposed to a single APAP dose. The selected serum biochemical markers, oxidative stress markers, and lysozyme activity were used to evaluate the efficiency of the supplements on carp’s health profile, particularly regarding the hepatopancreas function. Our results showed that the inclusion of SM and BBR (either as a single or in combination) reduced the serum contents of total cholesterol, triglyceride, and alanine transaminase. An increase in the high-density cholesterol was observed after the administration of BBR or BBR in association with SM. Both supplements showed hepatoprotective activity against APAP-induced hepatotoxicity, especially BBR. The ameliorative effects of SM (1 g) in association with BBR (100 mg) were highlighted by the modulation of the nonspecific immune system and oxidative stress alleviation after APAP exposure.

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 widespread use of antibiotics in aquaculture has raised concerns regarding adverse physiological effects on fish, creating a need for dietary strategies that enhance fish resilience during antibiotic administration and support animal welfare under therapeutic treatment conditions. This study evaluated, for the first time, a phytochemically characterized supercritical fluid extract of Ulva lactuca (Ul-SFE), rich in flavan-3-ols (epigallocatechin, epicatechin gallate) and other phenolics, as a dietary supplement in common carp (Cyprinus carpio). Juvenile carp (n = 360; 20.20 ± 0.13 g) received a control or Ul-SFE-supplemented diet (50 mg kg⁻¹) for 10 weeks, followed by 10 days of florfenicol or oxytetracycline exposure at therapeutic doses. Growth, plasma biochemistry, oxidative stress, and innate immunity were assessed. Ul-SFE significantly improved FCR, SGR, and PER during growth. Under antibiotic challenge, both florfenicol and oxytetracycline affected growth performance and biochemical status, though with different predominant patterns: florfenicol exposure was mainly characterized by reduced growth performance, while oxytetracycline exposure was mainly characterized by biochemical disturbance—reduced total protein and globulin, elevated glucose, ALT, and lipid peroxidation, and impaired antioxidant/immune status. Ul-SFE consistently attenuated these effects, reducing malondialdehyde by 24–30% and increasing antioxidant capacity by 5–7%; its protective effect on lysozyme was strongly diet-dependent (Diet × Antibiotic, p < 0.001), ranging from a 20% increase without antibiotics to negligible under oxytetracycline. These findings show Ul-SFE improves feed utilization and confers partial, treatment-dependent resilience against antibiotic-induced stress, supporting its potential as a functional feed additive in aquaculture.