Aquaculture Research

In this study, a panel of 14 microsatellite markers was screened to determine the parentage of 144 progenies in 12 Chinese hooksnout carp (Opsariichthys bidens) full-sib families. The combined exclusion probabilities for 14 loci were 97.6% and 99.9%, respectively, when there was no available parent information or only one parent information was provided. Simulation analysis demonstrated that the power of five loci to exclude false parents exceeded 99.0%, while that of eight loci reached 99.9% based on allele frequency data obtained from full-sib families (168 individuals). Moreover, the cumulative assignment success rate reached 100% with known parental and filial information when utilizing 13 or more loci, even in cases where no parent information was available. The results showed that this set of microsatellite markers proved to be a reliable and efficient tool for parentage determination of O. bidens.

The goal of this study was to research the effects of Lactobacillus buchneri L3-9 and its extracellular products on growth, immunity, intestinal microorganisms, and disease resistance to Aeromonas hydrophila in grass carp. A total of 120 fish (80–90 g) were distributed into 12 aquariums (10 fish/aquarium) in three replicates and fed 1% of their body weight for 21 days. The grass carp were fed four different diets: a control (group C), a diet supplemented with 1 × 10⁶ cell g⁻¹ of L. buchneri L3-9 (group B), a diet supplemented with extracellular products of L. buchneri L3-9 (group E), and a diet supplemented with L. buchneri L3-9 and the extracellular products (group BE). Compared with the control diet, the B, E, and BE diets increased the weight gain rate by 4.49%, 2.59%, and 4.38%, respectively (), and significantly decreased the feed conversion ratio by 0.72, 0.57, and 0.76, respectively (). Groups B, BE, and E showed significant decreases in mortality, with values of 26.67%, 16.67%, and 23.33%, respectively (). Group B showed a significant increase in superoxide dismutase (SOD) activity and total antioxidant capacity (T-AOC) and decrease in malondialdehyde (MDA) content compared to the control group (). The highest catalase (CAT) activity was found in group E (). In group B, the expression of the gut proinflammatory gene TNF-α was downregulated (), and the expression of anti-inflammatory genes, including TGF-β1, IL-10, and Tlr-8, was upregulated compared to that in the control group (). Groups BE and E showed an increased abundance of Lactobacillaceae. Additionally, a drastic decrease in the abundance of pathogenic bacteria such as Aeromonadaceae and Enterobacteriaceae was in these groups compared to the control group. In conclusion, L. buchneri L3-9 and its extracellular products could improve the growth performance, immune responses, and resistance to A. hydrophila in grass carp. This study provides insights for the development and application of microecological preparations.

Numerous studies have reported the disadvantages of using plant protein in aquafeeds owing to the presence of antinutritional factors. Particularly, phytate can be overcome by dietary supplementation with exogenous phytase. On the other hand, the use of microalgae has been proven to be a valuable strategy for enhancing the digestive functionality in fish fed diets with high plant protein content. It was hypothesized that the simultaneous inclusion of phytase with microalgae can be useful to improve growth performance and digestive functionality in fish fed diets with high content of plant protein. In this study, the effects of feeds supplemented with different levels of exogenous phytase (FTU) and 2.5% of a blend of Arthrospira platensis and Nannochloropsis gaditana were evaluated on growth performance, metabolism, and gut functionality in European seabass (Dicentrarchus labrax) juveniles. Fish were fed ad libitum for 83 days with five diets containing different enzyme ratios (FTU), in triplicate: (i) control (0 FTU); (ii) 500 FTU; (iii) 1,000 FTU; (iv) 2,000 FTU; and (v) 10,000 FTU. At the end of the feeding period, zootechnical indexes were estimated, and biological samples were withdrawn for physiological determinations. The results obtained showed an overall improvement in the productive efficiency, general metabolism, and intestinal functionality in fish fed the highest phytase inclusion (2,000 and 10,000 FTU). Final weight (75.51 ± 1.01 g vs. 66.76 ± 1.26 g, ), SGR (1.15 ± 0.02 vs. 1.00 ± 0.02, ). and feed efficiency (0.80 ± 0.02% day⁻¹ vs. 0.67 ± 0.01% day⁻¹, ) were higher in fish fed 10,000 FTU. The chemical composition of muscle and plasma metabolites did not vary among dietary treatments, except for the high glucose and low glycogen content in the liver with 2,000 FTU group. Focusing on gut functionality, enzyme activities tended to be higher in fish fed diets supplemented with phytase and microalgae, and significant differences were found for trypsin, chymotrypsin, and alkaline phosphatase with 1,000, 2,000, and 10,000 FTU, and leucine aminopeptidase with 2,000 and 10,000 FTU (). Analysis of intestinal morphology revealed that 2,000 and 10,000 FTU combined with microalgae increased villi height and decreased villi diameter and enterocyte height. The presence of microalgae at low phytase supplementation level seems to lack of influence on the different parameters evaluated whereas only increased dietary phytase levels impacted on growth, nutrient utilization, and intestinal functionality. In addition, faecal samples were obtained by stripping the final portion of the intestines, from which the phosphorus and nitrogen were quantified. Apparent digestibility coefficient of phosphorus with 2,000 FTU and 10,000 FTU were higher, 74.3% and 77.8%, respectively, compared to control (52.4%). The results revealed a decrease in the amount of P shed with the excreta from the animals supplemented with phytase, a fact that evidenced an increased intestinal absorption of this element. Overall, the results obtained pointed out that phytase can be used at 10,000, and even 2,000, FTU in combination with microalgae as an approach to reducing feed costs and boost fish growth and digestive functionality of fish, while minimizing the environmental impacts of juvenile European seabass farms.

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.