Aquaculture Research

Potassium diformate (KDF) and calcium diformate (CaDF) are organic acids that modulate growth performance, stress, and biochemical status. So, the present study aimed to investigate the effects of different levels of potassium diformate and calcium diformate on growth performance, stress markers, oxidant/antioxidant status, microbial flora, and some serum biochemical analytes in juvenile Beluga (mean weight: 34 ± 4.5 g). Juvenile Beluga fed control food or diet supplemented with different levels of KDF (1, 1.5, and 2 g/kg) and CaDF (1, 1.5, and 2 g/kg) for 60 days. The results showed that fish fed the 0.15% (1.5 g/kg) KDF showed the favorable growth value at 30 days and relatively less, 0.15% CaDF improved significantly () fish growth performance following 60 days of application (). The results showed that dietary administration of KDF and CaDF significantly () increased digestive enzymes. Moreover, elevated biochemical parameters were observed in H. huso fed KDF and CaDF supplemented the diet. Serum oxidant/antioxidant status was significantly () improved in the KDF and CaDF treatments than the control group. Moreover, dietary administration of KDF and CaDF significantly () decreased stress markers of H. huso after 60 days. The liver enzymes activities considerably altered in the KDF and CaDF groups compared with the control group after 60 days. Furthermore, dietary administration of KDF and CaDF significantly () increased intestinal lactic acid bacteria (LAB) of H. huso after 60 days. Based on the results of this study, it appears that incorporating KDF and CaDF into the diet of H. huso can have positive effects on their growth performance and physiological response. The study found that a short-term use of 0.15% (1.5) g/kg of KDF for 30 days was the most effective in promoting growth. However, the potential use of 0.2% (2 g/kg) of KDF and 0.15% (1.5 g/kg) of CaDF for a longer period of 60 days may also be beneficial.

This experiment investigated the influences of different dietary fat levels on histology, oxidative status, and immune response in gill and kidney of yellow catfish (Pelteobagrus fulvidraco). Three diets with different fat levels of 63.1 g/kg (low-fat, LF), 93.3 g/kg (medium-fat, MF), and 153.2 g/kg (high-fat, HF) were prepared to feed yellow catfish. The experiment continued for 56 days, and at the end of the experiment, gill and kidney tissues were sampled. As a result, both gill and kidney showed different degrees of tissue damage in HF group in terms of histology observation. HF increased the malondialdehyde content in gill but showed no effect on kidney, indicating that gill is more susceptible to injury than kidney under high-energy intake conditions. Additionally, HF diet significantly increased the activities of total-superoxide dismutase and catalase to eliminate excess peroxides both in gill and kidney. Moreover, HF diet significantly upregulated the expressions of pro-inflammatory cytokines (il6 and tnfα) and downregulated the expression of anti-inflammatory cytokines (il10), indicating that HF-diet-induced inflammatory response both in gill and kidney. These findings reveal the potential regulatory approach for fish gill and kidney health by dietary fat level, which will help to understand the adverse impacts of dietary lipid imbalance on the health of fish.

The New Zealand Greenshell™ mussel (Perna canaliculus) is endemic to New Zealand and contributes to the success of the country’s aquaculture industry. However, summer mortality and potential disease outbreak events are having an increasing effect on the growth of this industry. The cause of these mortalities remains unknown, and histopathological studies of the pathogen and parasites in mussels are still incomplete. In the present study, a histological approach was used to identify pathogens and parasites, as well as immunological tissue responses in unhealthy- and healthy-looking P. canaliculus during a summer mortality event in 2018. A highly significant association between health conditions and the presence of Perkinsus olseni in mussels was observed. A higher prevalence of P. olseni, Apicomplexan-X (APX), and bacterial (rods and cocci) infections were noted in the unhealthy-looking mussels than in the healthy-looking mussels. In an assessment of stains, hematoxylin and eosin (H&E) staining appeared to be the best method for general pathological and anatomical characterization, while Giemsa provided the clearest visual definition of bacteria. In this aspect, it was comparable to Ziehl–Neelsen (ZN) in apparent sensitivity. Although Gram and ZN staining revealed bacterial cells marginally better than with H&E, their differential staining could not be assessed as no Gram-positive or acid-fast bacteria were seen, and no mussel-positive controls were available for comparison. This study also provides an illustrated guide to some significant mussel health indicators.

The spectrum is a key environmental factor, and light-emitting diodes (LEDs) can influence the growth and development of crustaceans by altering the composition of the spectrum. This study conducted a 30-day experiment to investigate the effects of five LED spectra (red, yellow, blue, green, and white light) on the growth, antioxidant and immune enzyme activities, stress hormone levels, and the expression of α-amylase (α-AMY), ecdysone receptor (EcR) and retinoid X receptor (RXR) genes in juvenile redclaw crayfish (Cherax quadricarinatus). The results show that the survival rate of juveniles is markedly higher in the yellow and red-light groups than in the other three groups (). The green light group exhibits the lowest survival rate, yet it demonstrates the highest weight gain rate and specific growth rate. Regarding enzyme activity and hormone levels, the yellow light group shows the lowest malondialdehyde content, with higher superoxide dismutase and acid phosphatase activity than the other groups; no significant differences are observed in lysozyme activity among the groups (). The melatonin content in the green and blue light groups is significantly higher than that in the other three groups (). In terms of growth gene expression, the expression of α-AMY, EcR, and RXR in juvenile C. quadricarinatus is regulated by the spectrum. In conclusion, when raised under the yellow light spectrum, juvenile C. quadricarinatus displays elevated survival rates, rapid growth, and robust antioxidant and immune defenses. This study provides important technical parameters for optimizing and enhancing the industrial cultivation of juvenile C. quadricarinatus.

Fingerlings of the rainbow trout, Oncorhynchus mykiss (n = 300, 10.63 ± 0.6 g), were fed tarragon (Artemisia dracunculus) essential oil (TGO) for 2 months to examine its effects on growth properties, immunity, and resistance to Yersinia ruckeri infection. The treatments were control or TG1, TG2 (fed 0.5% TGO), TG3 (1% TGO), and TG4 (2% TGO). According to the results, an improvement was observed in growth parameters in all TGO-treated groups compared to the control (). The digestive enzyme activities (protease and lipase) were significantly elevated in response to dietary TGO (). The immune system of the fish was enhanced by TGO, as it stimulated the immune parameters in serum (lysozyme, myeloperoxidase (MPO), alternative complement (ACH₅₀), Ig) and mucus (lysozyme, protease, ACH₅₀, Ig) (). The treatments, TG3 and TG4, showed more immune performance in response to TGO (). The fish in TG2 treatment had a higher levels of serum total protein than other groups (). The concentration of triglycerides (TRIG) and cholesterol (CHOL) in serum significantly decreased () in response to TGO, as the lowest levels were observed in the treatment, TG3. The antioxidant enzymes (superoxide dismutase (SOD) and catalase (CAT)) of serum elevated in TGO-treated fish, with the maximum values for the TG4 group (). TGO reduced () alanine aminotransferase (ALT) and alkaline phosphatase (ALP) levels in serum. After bacterial challenge, the TGO-treated fish showed lower mortality compared to the control, where the lowest mortality was observed in TG4 (). In conclusion, TGO improved growth, immunity, and survival after bacterial challenge in the rainbow trout, with more performance in fish fed 1%–2% TGO.

The culture of African catfish, Clarias gariepinus, is constrained by the high mortality of fry, occasioning a shortage of high-quality seeds for stocking by farmers. Asia, a continent with many success stories for aquaculture, leads in farmed production of some catfishes, a diverse group of 37 different families. Globally, the culture of catfishes ranks fifth in global farmed finfish production. Globally, Vietnam leads in the production and export of farmed striped catfish, Pangasianodon hypophthalmus, with 1,400,000 tonnes produced annually from about 7,000 hectares. Similarly, China farmed the non-native Channel catfish, Ictalurus punctatus, into the major crop, with a current annual production of 250,000 tonnes. On the contrary, C. gariepinus, the main farmed catfish species in Africa, records low annual yields, with 240,000 tonnes for the whole continent. This paper explores the factors behind the high production of P. hypophthalmus and I. punctatus in Vietnam and China, respectively, and draws lessons for C. gariepinus farmers in Africa. Specifically, the use of differentiated hatchery and nursery husbandry practices was critical in boosting seed production, quantity, availability, and distribution for expanding the culture of P. hypophthalmus in Vietnam. Improvement of fish species through well-designed genetic improvement programs helped China substantially increase production of I. punctatus. For both species, intensive fish production, as well as the adoption and implementation of suitable policies, increased seed production from hatcheries in both countries. These are discussed as some of the factors that spurred catfish production in the two Asian countries. We argue that if these are adopted by farmers in Africa, they could help improve the production of farmed C. gariepinus on the continent for food and nutrition security as well as generation of livelihood for local communities.