Fisheries Science最新文献

Abstract

White spot syndrome virus (WSSV) is causing significant economic losses in shrimp farming. Envelope proteins, which interact with host cells during viral attachment, are potential targets for drug development. In this study, the antiviral activity of Sargassum wightii was assessed using in-vitro and in-silico analyses. Crabs were injected with S. wightii extract and WSSV and were observed for 30 days post-infection. The antiviral activity was confirmed by bio-assay, histopathology, and in-silico analysis. GC–MS analysis identified 15 compounds in S. wightii, and in-silico docking revealed a strong interaction between VP28 and VP26 envelope proteins and stigmasta-4,22-dien-3-one. Molecular simulations validated the stability of the protein–ligand binding. These findings confirm the potential of S. wightii as a treatment for WSSV.

Abstract

Agouti-related protein (Agrp) is an orexigenic peptide hormone found in fish and other vertebrates. Understanding appetite regulation is important for improving production performance in aquaculture systems. However, information on appetite-related hormones in yellowtail is still fragmentary. In this study, two distinct agrpgenes (i.e., agrp1 and agrp2) were cloned from the yellowtail brain. Brain distribution and response of the agrp genes to fasting, along with other candidate orexigenic peptide hormone-related genes including neuropeptide Y (npy) and melanin-concentrating hormones (mch1 and mch2), were studied. The highest expression level of those genes was observed in the hypothalamus, except for npy. After fasting, agrp1 and npy increased significantly in the hypothalamus, whereas agrp2 in the olfactory bulb and cerebellum decreased significantly. After feeding with a fishmeal (FM)-based diet and addition of a fishmeal soluble fraction (FMS), hypothalamic agrp1, agrp2, mch1, and mch2 increased, whereas hypothalamic npy decreased significantly. From the fasting experiment, agrp1 and npy may function as orexigenic hormones in yellowtail; however, the function of other hormones warrants further research. Expression of all the analyzed appetite-related hormonal genes might respond to the smell/taste of fishmeal through sensory organs. Furthermore, npy and agrp1 may enhance appetite through different mechanisms in yellowtail.

Abstract

Genome editing by manipulating the embryos of Pacific bluefin tuna (PBT) was recently proposed for improving the breeding and aquaculture production of PBT. However, the yield of genome-edited eggs is limited due to the narrow timing of genome editing of embryos and the labor-intensive process. Therefore, the development of a small-scale larviculture method is necessary for efficient evaluation of the phenotype and traits of genome-edited PBT larvae. The plankton-kreisel tank can form a vertical rotating flow that may prevent the sinking syndrome of PBT larvae. In this study, we applied a plankton-kreisel tank (8-L) for PBT larviculture up to 10 days post-hatch (dph). We compared the survival rate and growth of PBT larvae reared in the 8-L plankton-kreisel tank and an 8-L cylindrical tank (CT). The survival rate in the plankton-kreisel tank at 10 dph (58.9 ± 4.8%) was significantly higher than that in the CT (4.8 ± 3.6%). Larval growth was not significantly different between these tanks. We observed that the larvae that sank to the tank bottom drifted with the strong vertical rotating flow along the tank wall during the night. This flow in the plankton-kreisel tank prevents the sinking syndrome. Thus, this apparatus is proposed for small-scale larviculture experiments in PBT.

Infections caused by snakehead vesiculovirus (SHVV) have seen frequent outbreaks in recent years, inflicting significant losses on the snakehead aquaculture industry. Early detection is therefore essential for effective prevention and control of pathogenic infections and reduction of economic losses caused by infections. There is an urgent need for a simple, rapid, specific, sensitive, and intuitive method to monitor snakehead infected with SHVV. The aim of the present study was to develop and evaluate a loop-mediated isothermal amplification (LAMP) assay for the rapid visual detection of SHVV in snakehead. Three pairs of primers were designed according to the conserved region of phosphoprotein (P) gene sequences of SHVV and were applied for the detection of SHVV from fish samples. Time and temperature conditions for the amplification of SHVV were optimized at 65 °C and 55 min. The LAMP assay demonstrated high specificity, with no cross-reactivity with seven other viruses. Amplification results were visualized by a color change after the addition of hydroxynaphthol blue (HNB) dye. Sensitivity test results showed that the minimum detection volume with this method was 1.76 × 10² copies/μL, which was 100 times more sensitive than RT-PCR assay. We used the established LAMP system to test 50 clinical samples and detected 32 positive responses, whereas 22 positive samples out of 50 samples were detected by RT-PCR. The establishment of a visual LAMP assay further shortens the virus detection process and allows visual reading of positive responses through color changes; it is suitable for use in quarantine and field detection. Therefore, this proposed method provides a sensitive, specific, and user-friendly method for the rapid diagnosis of SHVV in snakehead farming.

The present study was conducted to evaluate the availability of citrus byproduct (CBP) as a vitamin C additive compared with the L-ascorbyl-polyphosphate (LAPP) for juvenile Korean rockfish Sebastes schlegelii. Four experimental diets, based on the basal diet (Con; semi-purified, crude protein 48%), were prepared by supplementing LAPP or CBP to achieve a dietary vitamin C concentration of 90 or 360 mg/kg (designated as LAPP90, LAPP360, CBP90, and CBP360, respectively). Three replicate groups of S. schlegelii (mean body weight ± standard deviation = 4.5 ± 0.0 g) were fed the experimental diets for 13 weeks. After the feeding trial, growth performance, feed utilization efficiency, and survival were significantly lower in the Con group. Liver vitamin C concentration was significantly increased (36.7–117 mg/kg) with increasing dietary LAPP levels; however, there was no significant difference in the CBP groups (14.2–14.3 mg/kg) compared with the Con group. Bone collagen concentration was significantly affected by LAPP and CBP supplementation. The LAPP and CBP groups showed significantly higher lysozyme activity and total immunoglobulin levels than the Con group. Disease resistance against Streptococcus iniaewas significantly improved in the LAPP and CBP groups (60–92% survival) than in the Con group (39% survival). These results indicate that dietary vitamin C is essential for S. schlegelii and CBP could be a LAPP substitute as a vitamin C additive.

The present study investigates the effects of dietary alfalfa, Medicago sativa leaves, on growth performance, carcass composition, enzymatic activity, biochemical indices, intestinal histomorphometry, and disease resistance in fingerlings of common carp, Cyprinus carpio L. A feeding trial of 60 days was carried out in which common carp fingerlings were fed on experimental diets supplemented with alfalfa extract at rates of 0.0% (T₀) control, 0.25% (T₁), 0.50% (T₂), 0.75% (T₃), and 1.0% (T₄). At the end of the feeding trial, specific growth rate, protein efficiency ratio, and feed conversion ratio improved significantly (P < 0.05) in groups fed on diet supplemented with alfalfa in a dose-dependent manner. The blood biochemical parameters and the activity of the digestive enzymes were significantly (P < 0.05) elevated in the alfalfa supplemented groups in a dose-dependent manner. Additionally, T₄ had significantly (P < 0.05) more protein in fish carcasses than the control group. Intestinal histomorphometry and the relative percent survival following the challenge trial with Aeromonas hydrophila were also significantly (P < 0.05) enhanced by dietary alfalfa. The study concludes that alfalfa extract possesses antioxidant and immune-enhancing potential, which by improving growth and increasing the capacity to combat bacterial infections in fish proves beneficial for sustainable aquaculture.

We hypothesized that lactic acid bacteria (LAB) present in sediments at aquaculture sites can be employed as an indicator for the early prediction of deterioration, as the concentration of organic acids controls hydrogen sulfide production via sulfate-reducing bacteria. We selected two aquaculture sites with different acid volatile sulfide (AVS-S) values, St. OJ (average AVS-S = 0.24 mg S/g dry mud) and St. UM (average AVS-S = 1.16 mg S/g dry mud), which were less and critically deteriorated, respectively, and examined our hypothesis by performing a 3-year-long survey in Tanabe Bay, Wakayama Prefecture, Japan. In St. UM, the bacterial community showed positive correlations with AVS-S values and water contents. With AVS-S accumulation at the site, the abundances of LAB decreased below the detection limit, suggesting that LAB viable counts may be unsuitable for predicting early deterioration at sites with severe AVS-S accumulation. In St. OJ, the LAB viable counts, organic acid content, and AVS-S values increased after the beginning of sea bream aquaculture, and the bacterial community showed high correlations with the LAB counts, succinic and total organic acid concentrations, and the abundance of the class Bacilli. These on-site experiments indicated that LAB counts can be a reasonable indicator for evaluating deterioration in aquaculture sites.

In the tuna purse seine fishery, seiners spend a considerable amount of time detecting objects such as seabirds, for which radar is a very efficient method. In this study, we present a radar image seabird identification method that can calculate the number of clusters, the area of seabird clusters, and the activity level of seabird clusters. We used a fishing vessel’s radar to collect information on seabird groups within 29,632 km of the vessel and calculated a spatial clustering of the seabird-echoes. Generalized additive mixed models (GAMM) were used to investigate the relationship between drifting fish aggregating devices (FADs) and seabird dynamics in the Republic of Kiribati. The findings indicate that FAD variables affected seabird behavior. The random effects on cluster number, cluster area, and cluster ability were 3.27, 17.41, and −0.17, respectively. Then, we compared the radar image information that was calculated. The bird cluster around drifting FADs was found to be more concentrated and denser than in areas without FADs, with a lower level of activity observed. The longitude of 165°E had the highest number of bird clusters and the greatest area inhabited by birds, but these decreased to the east. However, model 3 showed that the minimum value of seabird cluster activity level occurred around 165°E and increased to the east.

Globally, the giant freshwater prawn Macrobrachium rosenbergii is considered as a commercially important aquaculture species. Genetically, this species is differentiated into western, central and eastern populations. Molecular studies have reported population differences in M. rosenbergii inhabiting Indian waters and have suggested possibilities for the existence of a separate genetic stock in Vembanad Lake (Kerala, S. India). This study was carried out to address this question regarding the lineages of M. rosenbergii inhabiting this lake. Since the lake is divided into ‘downstream’ and ‘upstream’ parts, M. rosenbergii samples were collected from both these regions, and COI sequences were developed. Sequence alignment revealed base substitutions for certain samples, indicating possible population differences. Analysis of molecular variance (AMOVA) also provided a significant Fst value (0.874; p value = 0.00000 ± 0.00000), confirming the population difference in individuals inhabiting the lake. Genetic lineages of these populations towards the global M. rosenbergii populations were investigated using developed and acquired COI sequences for this species. A phylogenetic tree based on neighbor-joining (NJ) analysis and population network revealed the presence of western and central populations in Vembanad Lake. This study recommends identification of natural stocks of M. rosenbergii inhabiting different geographical realms through genetic approaches.