Fisheries Science最新文献

Endogenous opioids are found in the central nervous system and multiple peripheral organs and affect the hypothalamus–pituitary–gonad axis at several levels in vertebrates. However, the influence of these opioid peptides on fish spermatogenesis is poorly studied. This investigation examined the impact of the opioid peptide dynorphin-A (DYN) on the pituitary–testicular axis in the tilapia Oreochromis mossambicus. Intraperitoneal injections of 5 µg DYN/day/fish for 21 days did not affect the early developmental stages of germ cells, but caused a significant decrease in the numbers of secondary spermatocytes and early and late spermatids compared with the controls. Although the mean area of the lobule was significantly decreased, there was a significant increase in the areas of the lumen and the interstitium in the DYN-treated group relative to controls. These results were concomitant with significantly lower serum levels of 11-ketotestosterone (11-KT) and luteinizing hormone (LH) in DYN-treated fish than in controls. However, the serum level of cortisol was significantly higher in the DYN-treated fish group. Overall, these results, for the first time, indicate that DYN interferes with spermatogenesis at the late stage of meiosis, leading to impairment in spermiogenesis, possibly mediated through the suppression of 11-KT secretion in the testis and LH release from the pituitary. This study also suggests that DYN may bring about this inhibitory effect via activation of the stress axis in teleosts.

The β′-component, a major allergen found in fish roe, is synthesized in the liver of female fish as part of the precursor of the egg yolk protein vitellogenin (Vg). Vg is distributed through the bloodstream and contributes to ovary development. In the present study, β′-component, present in Vg fragments, was detected in the muscles and internal organs of mature female salmon, with concentrations exceeding the recommended labeling level under Japan's food allergy labeling system. Additionally, total protein extracted from tissues of female salmon reacted with immunoglobulin E antibody against the salmon roe β′-component. No β′-component was detected in the tissues of mature male fish in the absence of sex hormone stimulation from females nor in immature salmon without sexual differentiation, but excess stimulation of the female sex hormone induced Vg synthesis containing the β′-component in the male fish. These findings suggest that taking into account fish sex, maturity, and sexual isolation of mature male fish could improve the safety of salmon meat for individuals with salmon roe allergy.

Seafood is one of the most traded food commodities in the world. Traditionally, frozen seafood is evaluated using destructive chemical methods, which are complicated and time-consuming. Therefore, this study proposed a noninvasive method for evaluation of frozen seafood, focusing on fluorescence fingerprints (FFs). FFs, also known as an excitation–emission matrix (EEM), refer to an arranged fluorescence spectrum of emission stimulated by different excitation wavelengths. As FFs is a set of fluorescence spectra acquired at consecutive excitation wavelengths, it produces a three-dimensional diagram that is composite fluorescence of every fluorophore, similar to a fingerprint. Compared with conventional fluorescence spectroscopy, the FFs technique can measure complex samples that contain many fluorophores, because it includes emission spectra excited at many different excitation wavelengths. In this review, the applications of FFs technology for nondestructive prediction of seafood quality are summarized. Postmortem metabolism and seafood freshness indices are discussed comprehensively. We have also introduced multidimensional fluorescence imaging, a combination of FFs and imaging techniques for visualizing seafood product quality. Finally, the advantages of the FFs technique for nondestructive evaluation of seafood quality, even at the frozen state, over traditional methods and previous fluorescent spectroscopic techniques are enumerated.

An unmanned surface vehicle (USV) with a fish attraction lamp was developed to assist in the nighttime operations of a Japanese purse seine fishery. The USV weighs about 15 kg, is equipped with a 200 W underwater light-emitting diode (LED), and can be radio-controlled to move on the sea surface. The purse seiner shoots a net to surround the lighting boat to catch fish gathered by fish attraction lamps. The USV was deployed on the sea surface from the purse seiner during the net-hauling operation and replaced the lighting boat to continue fish attraction after shooting the net. The time required for each operation using the USV and conventional lighting boat operations was compared, and it was found that the time required for the lighting boat for fish attraction after shooting the net was reduced by about 10 min per haul when the USV was used. On the other hand, the time required by the purse seiner to shoot and haul the net and the catch amount did not change. The USV can contribute to time savings in operation and safety improvements in the purse seine fishery.

Abstract

The accuracy of the back-calculation method to estimate past individual growth based on the relationship between otoliths and body length is important. However, limited studies have examined the variation in accuracy by measurement site used for estimation, and little has been done to evaluate its effectiveness. Currently, effective utilization of juvenile fish in the blackthroat seaperch fishery in the Sea of Japan does not always take place, so it is necessary to investigate the complex relationship between population density and growth rate. This study estimates body length and weight from otolith length, weight, and area of blackthroat seaperch, analyzes variations in estimation accuracy at each measurement site, and provides a general quantitative protocol for evaluating the performance of each measurement site. The conversion models for body length and body weight indicate that models using otolith weight and area are more accurate than those using otolith length. There were no significant differences in the estimation accuracy of these models, and the estimation errors were all less than 0.7% of the original body length and weight means. Searching for the best model, verifying the estimation accuracy quantitatively, and selecting the model to use is important when performing back-calculations.

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.