Abstract:Acoustic deterrence has been identified as a potentially effective behavioral control method to reduce the feeding on macroalgae by Siganid fish. The hearing ability of the target fish species is a key prerequisite for selecting the appropriate sound frequency used in acoustic deterrence. The auditory capabilities of juvenile Siganus guttatus were examined through the analysis of auditory evoked potentials (AEPs) to determine their auditory frequency sensitivity and corresponding threshold. In this paper, the AEPs of 14 juvenile fish with different body lengths were studied using a TDT Auditory Physiological Workstation. It was observed that all juvenile fish exhibited discernible AEP waveforms when exposed to acoustic stimulation within the frequency range of 100–800 Hz. Additionally, the amplitudes of the AEP waveforms were found to increase in conjunction with the intensity of the acoustic stimulation. As the frequency of the sound increased, the hearing threshold of the juvenile fish did so simultaneously. In terms of low-frequency sounds, those within the range of 100–300 Hz evoked greater sensitivity, with the most sensitive frequency of hearing being 200 Hz and the average auditory threshold being 104 dB. The auditory sensitivities of individuals with different body lengths were significantly different at 200–300 Hz, at which point the auditory threshold of larger individuals (4.5−5.0 cm) was significantly lower than that of smaller individuals (4.1−4.4 cm). This suggests that larger fish have a lower auditory threshold, which is related to the development of their auditory organs. Due to the heightened sensitivity of juvenile S. guttatus to sound, their low hearing threshold, and the similarity of ambient noise, it is possible to employ acoustic deterrence in the wild to decrease the incidence of macroalgal consumption by S. guttatus, thereby mitigating the economic losses associated with important macroalgae.

Abstract:Leptobarbus hoevenii is an economically significant fish found in Malossia and worldwide that has been introduced to China owing to its high economic value and good aquaculture prospects. However, the existing culture population has been unselected and degraded in germplasm, generating a need for genetic breeding- related studies on L. hoevenii. Since karyotyping and phylogenetic analysis play an important role in the conservation and utilization of fish germplasm resources, the karyotype of L. hoevenii was prepared by the chromosome cold-drop method. In order to study the evolutionary and interspecific genetic relationship among 14 species of the Barbinae subfamily, the mitochondrial 16S rRNA gene sequences were compared and used to construct phylogenetic trees. The karyotype results of L. hoevenii showed a diploid chromosome number of 2n=50, containing 8 metacentric (m) chromosomes, 14 submetacentric (sm) chromosomes, 2 subtelocentric (st) chromosomes, and 1 telocentric (t) chromosome. Furthermore, the number of chromosome arms (NF) was 94, revealing the karyotype formula to be 2n=16m+28sm+4st+2t, NF=94. Regarding the comparison of mitochondrial 16S rRNA genes of the 14 Barbidae species, the genetic distances ranged from 0.016 to 0.134, with an average of 0.074. Notably, the interspecific genetic distances between L. hoevenii and Onychostoma barbata was the largest at 0.134, while that between L. hoevenii and Sikukia stejnegeri was the smallest at 0.090. Finally, the resulting phylogenetic tree showed that these 14 species were clustered into two respective branches, indicating a closer relationship between L. hoevenii and Barbodes hexagonlepis. L. hoevenii was basal in the phylogenetic tree. These results provide a foundation for the evaluation, breeding, and phyletic evolution of fish germplasm resources.

Abstract:Ovoviviparity is a reproductive strategy evolved by fish to adapt to specific environment. Gambusia affinis is a typical ovoviviparity fish. Clarifying whether its ovoviviparity characteristics have adaptive evolution in the process of invasion into the Yunnan-Guizhou Plateau will help us to understand the mechanism of its rapid population spread. Therefore, we conducted the research on the characteristics of embryonic development, changes in dry and wet weight, and the relationship with maternal nutrition in G. affinis Dianchi Lake population using conventional anatomical observation and weighing methods. The results showed that the embryonic development process of Dianchi Lake population depended on the supply of yolk nutrition. Before production, the yolk was basically consumed, and the body developed well, basically maintaining the inherent ovoviviparity characteristics of the species. The wet weight of embryos increased significantly during embryonic development, but at the same time, the dry weight loss was also very obvious (30.4%), and the nutrition index (matrotrophy index, MI) was 0.70, which suggested that the mother had no specific nutrition supply for embryos after fertilization, supporting the view that the G. affinis was a strictly lecithin trophic (ovoviviparity) fish. The embryo (fry) shows a trend of miniaturization, and key ecological adaptive traits such as wet weight, dry weight, and initial body length of the embryo are significantly lower than other lowland populations that have been studied, demonstrating an adaptive response to plateau environments. Whether this response contributes to its diffusion in higher altitude plateau environments deserves further in-depth research.

Abstract:The Pacific oyster (Crassostrea gigas) has become the economically valued shellfish with the widest range of cultivation and highest yield in the world because of its high nutritional value, strong reproductive ability, and extensive environmental adaptability. Its unique shell color not only influences the choice of consumers, but also affects the commodity value. In previous breeding practices, we found a purple shell color mutant in “Haida No. 4” of C. gigas, and combined the techniques of family selection and mass selection to construct the first generation of a C. gigas breeding population with purple shells. However, the genetic stability of shell color, growth, and survival performance of purple-shelled C. gigas remain unclear. To develop a new strain with excellent shell color and growth characteristics, a nested mating design was used to construct 36 full-sib families based on the first generation breeding population of purple-shelled C. gigas. Simultaneously, unselected individuals were used as parents to produce three control groups by mating in single pairs to compare and analyze the differences in growth and survival traits of these families at various developmental stages. The genetic parameters of shell height and shell length of purple-shelled C. gigas were evaluated using a multi-trait animal model. Compared to the control groups, all purple-shelled families had higher average shell height and survival rates at various developmental stages, which increased by 1.49%–10.18% and 3.75%–15.94% during the larval stage and 4.05%–16.94% and 15.95%–18.25% during the juvenile stage, respectively. There were also significant differences in the growth and survival traits among the different families. No family was found to excel in both survival and growth traits, which will need to be further improved for the following selective program. The heritability of shell height and shell length of C. gigas during the larval stage were 0.43–0.84 and 0.49–0.80, while those during the juvenile stage were 0.15–0.33 and 0.18–0.37, respectively, all indicating middle to high heritability. The genetic and phenotypic correlations of shell height and shell length at different developmental stages were positive, with correlation coefficients of 0.67–0.97 and 0.17–0.51 at the larval stage and 0.77–0.99 and 0.14–0.65 at the juvenile stage, respectively. This study demonstrated that the purple-shelled families of C. gigas have certain growth and survival advantages over other families and that the selection for shell height and shell length traits shows promising potential. This study provides a reference for the development of a purple-shelled strain of C. gigas.

Abstract:In order to determine the influence of key morphological traits on the body weight (BW) of three-line hybridizations (SCDF₃, SDCF₃) and the F3 generations of their parent populations (Dianshan Lake, DSF₃; Dongting Lake, DTF₃; Yangtze River, CJF₃) of Macrobrachium nipponense, the correlations between morphometric attributes and BW were explored using correlational, path, and regression analyses. Thirty individuals from each of the five populations were randomly sampled to measure their BW and 12 morphometric attributes, including the body length (BL), overall length (OL), rostrum length (RL), second pereiopod length (P₂L), carapace length (CL), carapace width (CW), sixth abdominal segment length (A₆L), sixth abdominal segment height (A₆H), abdomen length (AL), telson length (TL), number of upper frontal eminence spin (NUS), and number of lower frontal eminence spin (NLS). Correlation coefficients among all variables were calculated. Path coefficients were calculated by setting the BW as a dependent variable and other attributes as independent variables via stepwise elimination. The results showed that, except for those of the NUS and NLS, the correlations of the 10 other morphological traits were very significantly positively correlated with BW (P＜0.01). The multiple correlation coefficients between morphological traits and body mass of five populations were as follows: 0.935 for DSF₃, 0.906 for DTF₃, 0.902 for CJF₃, 0.958 for SCDF₃, and 0.988 for SDCF₃. The path coefficients showed that: (1) The CW, OL, P₂L, and TL of the Dianshan Lake population were significantly correlated with BW, and the multiple regression equation for the estimation of BW was Y_DSF3=−9.661+CW×0.365+OL×0.078+P₂L×0.32+TL× 0.28; (2) The CW, AL, and A6H of the Dongting Lake population were significantly correlated with BW, and the multiple regression equation for the estimation of BW was Y_DTF3=−7.009+CW×0.448+AL×0.129+A₆H×0.633; (3) The BL and RL of the Yangtze River population were significantly correlated with BW, and the multiple regression equation for the estimation of BW was Y_CJF3=−11.795+BL×0.258+RL×0.104; (4) The BL, A₆H, and P₂L of the SCDF₃ population were significantly correlated with BW, and the multiple regression equation for the estimation of BW was Y_SCDF3=–4.402+BL×0.093+A₆H×0.531+P₂L×0.013; (5) The P₂L, BL, and CL of the SDCF₃ population were significantly correlated with BW, and the multiple regression equation for the estimation of BW was Y_SDCF3=–2.861+P₂L×0.029+BL×0.062+CL×0.078. The clustering results showed that the progenies of the two hybrid populations were most similar in morphology. The results of this study can provide reference for the breeding of M. nipponense and the conservation and utilization of its germplasm resources.

Abstract:Bile acids (BAs) are important amphipathic biomolecules that play a key role in the emulsification of lipids and consumption of other fat-soluble nutrients. While fat is an essential energy source for fish growth, excessive dietary fat induces degradation of growth performance, metabolic disorders, and fat accumulation. There is evidence that BAs can promote growth, accelerate lipid breakdown, and maintain bile acid homeostasis in fish fed high-fat diets (HFDs). However, the regulatory mechanisms remain unclear. This study aimed to explore the effects of dietary BA supplementation on BA homeostasis and lipid metabolism in juvenile largemouth bass (Micropterus salmoides) fed HFDs. Five isonitrogenous diets were prepared: a control diet (10.6% lipid, C), high-fat diet (17.53% lipid, HF), and HF diets supplemented with 300, 600, and 900 mg/kg BA (HFB1, HFB2, and HFB3). A 7-week feeding trial was performed, and all the fish were fed to satiety twice daily. Samples were taken at the end of the trial to detect growth and plasma biochemical parameters as well as lipid and BA metabolism-related gene expression levels. The results showed that HF diet significantly decreased final body weight (FBW), specific growth rate (SGR), and weight gain (WG) (P＜0.05). In contrast, the addition of BAs to the HF diets improved growth performance, with the growth of largemouth bass significantly increased when supplement with 600 mg/kg BAs (P＜0.05). Moreover, the lipid content in muscle was increased by the HF diet (P＜0.05) and was decreased by supplementation with BAs (P＜0.05). The HF diet increased the triglyceride (TG) contents in the plasma and liver (P＜0.05), while BA supplementation decreased both (P＜0.05). Furthermore, the addition of BAs significantly decreased the expressions of sterol-regulatory element binding protein 1 (srebp1), fatty acid synthase (fas), and acetyl-CoA carboxylase 2 (acc2) and increased the expressions of lipoprotein lipase (lpl), hormone sensitive lipase (hsl), and hepatic lipase (hl) (P＜0.05). Additionally, BA supplementation increased the expressions of carnitine palmitoyltransferase 1 (cpt1) and acyl-CoA oxidase 1 (acox1) (P＜0.05), yet had no effect on expression of peroxisome proliferator-activated receptor α (pparα) (P＞0.05). These results indicate that BAs increase lipolysis and fatty acid β-oxidation, while decreasing lipogenesis. Moreover, fish fed a BA supplemented-diet showed increased total bile acid (TBA) levels in the liver and plasma (P＜0.05). When 600 mg/kg BA was added, the expression of farnesoid X receptor (fxr) was also increased (P＜0.05). Therefore, BA supplementation increased the expressions of cholesterol 7 alpha-hydroxylase (cyp7a1), bile salt export protein (bsep), and apical sodium dependent transporter (asbt) via activating fxr (P＜0.05). In conclusion, dietary BA supplementation improved growth performance, lipid digestion and absorption, and bile acid metabolism by activating the bile acid nuclear receptor FXR. The effects and possible mechanisms of BAs on lipid and bile acid metabolism were also preliminarily revealed. This study contributes to our understanding of the role of BAs in lipid metabolism in teleosts and enriches our knowledge of bile acid homeostasis under different conditions.

Abstract:This study aimed to investigate the tolerance and physiological differences between male and female turbot (Scophthalmus maximus) in response to hypoxic stress. Female (169.95±13.55) g and male (170.08± 19.02) g turbot of similar sizes were used to determine the concentration of dissolved oxygen at their critical oxygen tension (P_crit). Furthermore, changes in blood physiological and biochemical indexes, hepatic antioxidant activity, gas exchange rate, respiratory rate, and gill histomorphology were analyzed under hypoxic stress and again after reoxygenation. The results showed that the dissolved oxygen concentrations of male and female turbot under P_crit were (3.34±0.23) mg/L and (3.22±0.17) mg/L, respectively, with no significant difference observed (P＞0.05). Turbot plasma cortisol (COR) glucose (GLU) content, white blood cell (WBC) number, hepatic superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) activity, and malondialdehyde (MDA) content were all significantly increased (P＜0.05) after 6 h of hypoxic stress treatment. Meanwhile, significant differences in CAT activity, GSH-Px activity, and MDA content were observed between males and females after treatment with hypoxia for 6 h. The gas exchange rate, respiratory rate, secondary lamellar length (SLL), interlamellar distance (ID), and perimeter of gill lamella of both male and female turbot were significantly increased, whereas the secondary lamellar width (SLW) of gill lamella were significantly decreased (P＜0.05). The clubbing and matrix hyperplasia at the end of gill lamella of female and male turbot manifested similar results to those of the SLL (P＜0.05), with no significant difference observed between the sexes. All aforementioned parameters were recovered to normal levels after reoxygenation for 12 h. These results demonstrate that there were physiological differences observed between male and female turbot under hypoxic stress conditions, especially in CAT activity, GSH-Px activity, and MDA content. These changes aimed to meet the metabolic demand of the organism while enhancing the activity of liver antioxidant enzymes to alleviate the oxidative stress damage caused by hypoxic stress. Notably, males exhibited greater tolerance to low oxygen levels than females.

Abstract:To explore the nutritional structure and subsequently construct a brief food network of fish communities in the Wanshan Islands, this study analyzed the main nutritional characteristics of the key fishery organisms using stable isotope technology in autumn (September) of 2021, while simultaneously calculating various quantitative indicators. As a result, the δ¹³C value of fish from the Wanshan Islands ranged from –21.23‰ (Mugil cephalus) to –14.00‰ (Eubleekeria splendens), with a mean value of (–16.96±0.41)‰. Additionally, the δ¹⁵N value ranged from 9.93‰ (Trachinotus ovatus) to 14.83‰ (Pennahia anea), with a mean value of (12.52±0.34)‰. The trophic levels of these fish varied from 2.54 to 3.98, with an average trophic level of 3.30. Furthermore, the δ¹³C range (CR), δ¹⁵N range (NR), total area (TA), standard ellipse area (SEAc), mean distance to centroid (CD), mean nearest neighbor distance (MNND), and standard deviation of nearest neighbor distance (SDNND) of the fish were 7.23, 4.90, 23.64, 3.73, 1.30, and 0.24, respectively. Based on the stable isotope values of carbon and nitrogen, the fishes in the Wanshan Islands could be divided into three main groups: 4 species (3.57%) of planktivorous fishes, 7 species (6.25%) of benthic fishes, and 101 species (90.18%) of low-grade carnivorous fishes. According to the Bayesian mixed model, the main food source of fish in the Wanshan Islands is zooplankton with contribution rate of 62.54%, followed by algae with a contribution rate of 25.28%. This study constructed a novel continuous trophic spectrum of the fishes in the Wanshan Islands that was of great significance in examining the characteristics of food web and trophic structure and could provide strong data support for the protection and management of the Wanshan Islands ecosystem.

Abstract:The Pearl River, the largest river in Southern China, contains rich fish biodiversity and harbors a great number of cyprinid species. Ctenopharyngodon idellus, Megalobrama terminalis, Hypophthalmichthys molitrix, Squaliobarbus curriculus, Culter alburnus, Cirrhinus molitorella, and Cyprinus carpio are the most prevalent cyprinid species found in the lower reaches of the Pearl River where they play a key role in maintaining the stability of the food web. Due to the apparent differences in their feeding preferences, the morphological characteristics and degree of differentiation of their feeding organs may also vary. As a result, they are excellent candidates to investigate the morphological characteristics of feeding organs of cyprinid fish. The morphological variations of the feeding organs of these seven species were examined using a multi-faceted approach including traditional morphological anatomy, one-way analysis of variance (ANOVA), principal component analysis (PCA), and hierarchical clustering. The ANOVA results showed that the head length, snout length, mouth width, and mouth height of C. recurviceps were significantly greater than those of M. terminalis, S. curriculus, and C. idellus (P＜0.05), and the length of the pharyngeal forelimb of C. idellus was significantly shorter than those of M. terminalis and C. recurviceps (P＜0.05). Notably, the length of the gill rake of H. molitrix was remarkably longer than that of the remaining species (P＜0.05). The PCA results revealed that the morphological differences in the external feeding organs of the seven cyprinid species were primarily focused on mouth breadth and height, both of which are related to food capture. In contrast, the morphological differences in the interior feeding organs were primarily focused on the lengths of the pharyngeal bone and hindlimb, both of which are related to food chewing. Furthermore, we detected that the degree of differentiation in the interior feeding organs was higher than that in the external feeding organs. The cluster results of the morphological indexes of the external feeding organs of seven species highlighted that C. molitorella and C. carpio were clustered into one clade and C. idellus, M. terminalis, C. recurviceps, S. curriculus, and H. molitrix were clustered into another. Based on the morphological indexes of their internal feeding organs, the cluster results revealed that M. terminalis, C. recurviceps and C. carpio were clustered into one clade and S. curriculus, C. molitorella, H. molitrix, and C. idellus were clustered into another. A phylogenetic tree based on the mitochondrial Cyt b gene displayed that C. carpio and C. molitorella were clustered into one clade, while C. recurviceps, M. terminalis, S. curriculus, C. idellus, and H. molitrix were clustered into another. According to the correlational and significance tests between the Euclidean distance of external and internal feeding organs and pairwise phylogenetic genetic distance, the external feeding organs of the seven species were significantly correlated with phylogeny (P＜0.05), whereas the internal feeding organs were not (P＞0.05), indicating that the morphology of external feeding organs was easily influenced by phylogeny. This study demonstrated that diet was a key factor that influenced interior and external feeding organ morphology and examined significant relationships between phylogenetic relationships and morphological features of external feeding organs. External feeding characteristics show important reference potential for fish classification. Above all, our study revealed the differences in feeding organ morphological features of sympatric cyprinid fish and probed the relationships between the morphological characteristics of feeding organs, and feeding habits and phylogenetic status, which is of great significance to our understanding of their ecological adaptation mechanisms and protecting of fish resources in the Pearl River.

Abstract:Myxosporeans are a group of microscopic parasites that primarily parasitize fish with more than 2600 species currently discovered worldwide. The rich diversity of this group has led to extensive research on population divergence in myxosporeans. To investigate the impacts of infection site differentiation on the population divergence of myxosporeans, Thelohanellus kitauei Egusa & Nakajima, 1981 was isolated from the skin (S-type) and intestine (I-type) of different common carps Cyprinus carpio L. We compared the morphological differences in the T. kitauei found at the two infection sites by measuring the morphological characteristics of both plasmodia and spores. Tissue samples from the infected skin and intestine were examined by histopathology. The small subunit (SSU) ribosomal DNA (rDNA) and internal transcribed spacer (ITS)-5.8S rDNA sequences of two isolates were also amplified, aligned, and phylogenetically analyzed with other T. kitauei sequences from GenBank. The results showed that the S-type formed a single plasmodium with a diameter of 2.1 cm, while the I-type formed sixteen plasmodia of different sizes (diameters of 0.21–0.82 cm). The membrane sheath widths of the S- and I-types were approximately identical (P＞0.05). However, the spore lengths, polar capsule, and membrane sheath of the S-type were significantly greater than those of the I-type (P＜0.001), while other morphological characteristics were significantly smaller than those of the I-type (spore thickness: P＜0.01; the width of spore and polar capsule: P＜0.001). Histologically, most of the S-type spores were distributed in the stratum spongiosum of the dermis, with some spores penetrating the stratum compactum, causing curvature and deformation of the dense connective tissue. The I-type spores were primarily scattered over the intestinal submucosa, and the intestinal villi squeezed by the spores showed atrophy to varying degrees. Both types infected the connective tissue, causing inflammatory reactions such as lymphocyte infiltration and tissue hyperplasia. Molecular sequence comparison showed that the SSU rDNA sequence similarity between the S-type and I-type was 99.7%, with 4 variation sites. However, the ITS-5.8S rDNA sequence similarity was only 97.3%, with a total of 20 variation sites. The phylogenetic tree was constructed based on SSU and ITS-5.8S rDNA sequences, respectivly, demonstrating that the sequences of T. kitauei were divided into two lineages, ‘intestine’ and ‘skin’ subclades. In conclusion, the populations of T. kitauei infecting the skin and intestine of common carp showed varying degrees of difference in morphology, parasitic characteristics, and genetic information, providing obvious evidence of population divergence. It was demonstrated that the infection site differentiation is an important factor driving population divergence in myxosporeans.