The common carp (Cyprinus carpio) is farmed globally; as a subspecies, the Yellow River carp (C. c. haematopterus) is widely farmed in northern China. Since the Yellow River carp grows slowly in winter, it would benefit breeders to implement a breeding program targeting growth in winter. In May 2017, we established a Yellow River carp family and measured the body length, height, thickness, and weight of individuals before (October 2017) and after winter (February 2018). Based on the genetic linkage map established in our laboratory, the quantitative trait locus (QTL) mapping of these four traits led to the detection of 29 growth-related QTLs, of which 9, 7, 3, and 10 QTLs were associated with body length, height, thickness, and body weight, respectively. One consensus QTL contained seven QTLs associated with four traits. Through the two major-effect QTLs (qBL-p-1 and qBL-p-2), we screened three candidate genes (fnd3b, ghsr, and pld1), which were associated with biological activities, such as fat formation, growth, and membrane transport. These results are helpful in exploring the growth regulation mechanism and providing a reference for genetic breeding with regard to the overwintering growth of Yellow River carp. Full article

2,4-Dichlorophenoxyacetic acid (2,4-D) is commonly used to control invasive aquatic macrophytes, including Eurasian watermilfoil (Myriophyllum spicatum) (EWM). Potential influences of 2,4-D on non-target organisms are poorly understood; however, research has suggested the possibility of lethal effects on certain fish species. Lake Ellwood, Wisconsin was treated with 2,4-D to control EWM annually during 2003–2012. Fish surveys following treatment revealed natural recruitment failures of several regionally thriving species, including largemouth bass (Micropterus salmoides) and bluegill (Lepomis macrochirus). We hypothesized that these species had been negatively influenced by the chemical treatments. We monitored the post-chemical treatment fish community and aquatic ecosystem for responses during 2013–2019. Similar data were collected from Cosgrove (EWM absent) and Seidel lakes (EWM present, no chemical treatment) as reference systems. Limnological and submersed aquatic vegetation conditions did not change on Lake Ellwood post-chemical treatment. Total zooplankton density increased immediately post-chemical treatment on Lake Ellwood and then stabilized, whereas total zooplankton density did not change on the reference lakes over time. Analyses indicated immediate increases in recruitment post-chemical treatment for largemouth bass, smallmouth bass (Micropterus dolomieu), bluegill, and yellow perch (Perca flavescens). Back calculation of year class strength confirmed failures occurred during treatment for northern pike (Esox lucius), largemouth bass, bluegill, and black crappie (Pomoxis nigromaculatus). Our results provide evidence to suggest long-term 2,4-D treatments may negatively influence fish through lethal and sublethal mechanisms. Thus, there remains a critical need for directed research on whole-lake herbicide treatment side-effects. Full article

Individual aquaculture farmers in developing countries play an important role in ensuring food security. This study uses survey data from aquaculture households in Rongcheng and Xiangshan cities in China to explore the impact of cooperative participation on the benefits to the aquaculture households. The empirical results show that the participation of aquaculture farmers in cooperatives has effectively increased their net profit and output per unit area. On average, participating in cooperatives increased the net profit and output per unit area of farmers by approximately 15.55% and 11.47%, respectively. The test results of the mechanism show that the information services, technical training, and product sales guidance provided by the cooperatives have increased the net profit of the farmers. At the same time, the information services and product sales guidance provided by cooperatives are important reasons for the increase in the output per unit area. Full article

The Shantou-Taiwan shoal fishing ground in southeastern China supports a significant population of pelagic fish, which play a key role in the marine ecosystem. An acoustic survey was carried out using a digital scientific echosounder in June 2019. In this paper, the spatial distribution of pelagic fish is analyzed based on acoustic data using geostatistical analysis tools. Meanwhile, the relationship between fish density from acoustic data and sea surface environment factors were evaluated by using generalized additive models (GAMs) based on the satellite-based oceanographic data of sea surface temperature, sea surface chlorophyll-a concentration, sea surface height and sea surface wind. The results showed the following: (1) Fish density and acoustic biomass have strong spatial correlation; the optimal model for acoustic biomass is exponential and the optimal model for fish density is gaussian; based on optimal model, spatial interpolation analysis of fish density and acoustic biomass was performed using the ordinary kriging method, and the higher values of density and acoustic biomass were located in the central and eastern parts of the study area. The total fish density and acoustic biomass is 2.56 × 10¹⁰ ind. and 1908.99 m²/m, respectively. (2) In vertical distribution, fish gradually move to the middle and lower layers of water during daytime, and gather in the middle and upper layers of water at night. (3) The variance explanation rate of GAM was 88.2% which indicates that the model has an excellent fitting degree, and the results of GAM showed that longitude, sea surface temperature (SST), sea surface wind (SSW), and sea surface height (SSH) had significant effects on fish density. Results of this study were meaningful for understanding the distribution of fishery resources, and as a guide for fish management in the Shantou offshore water. Full article

A total of 756 yellowfin tuna (Thunnus albacares) caught by a Chinese drifting longliner in the tropical western and central Pacific Ocean (WCPO) from May 2018 to March 2019 were investigated to describe the reproductive biology of the species. Generalized linear model and polytomous logistic regression for the ordinal response model were employed to assess the effects of biometric and spatiotemporal factors (such as individual fork length (FL), fishing depth, dissolved oxygen, and month) on the reproductive traits of yellowfin tuna. The results showed that FLs ranged from 87 to 163 cm, averaging 115.8 cm (SD = ±14.2) for females and 121.8 cm (SD = ±16.8) for males. The proportion of males in the sampled fish was 0.61 (SD = ±0.29), and larger males (>130 cm) were proportionally predominant. Analyses based on the monthly variation of the gonadosomatic index and monthly proportion of sexual maturity stages of the gonads showed that the main spawning period of yellowfin tuna lasts from September to December. In addition, the 50% first maturity FLs of males and females were 111.96 cm (SD = ±1.04) and 119.64 cm (SD = ±1.30), respectively. This study provides new information on the reproductive development of T. albacares in the tropical WCPO region. These reproductive parameters reduce uncertainty in current stock assessment models, which will ultimately assist the fishery in becoming sustainable for future generations. Full article

Cysteine proteinase inhibitors (CPIs) protect tissues and organs against cysteine proteinases in animal blood and have attracted much attention for use in food processing and medical sciences for humans and animals. Several CPI proteins, which include stefins, cystatins, kininogens, histidine-rich glycoproteins (HRG) and fetuins, have been identified and characterized in mammals. Fish blood also contains high CPI activity, but the identity of the major protein responsible for this activity has not been clarified. This study was conducted to screen CPI activity by examining papain inhibitory activity from various different tissues in Nile tilapia Oreochromis niloticus and to identify major proteins for the activity in the blood. CPI activity was highest in the serum among the tissues screened in this study (at least fourfold higher than in other tissues)(P < 0.05). Major proteins for CPI activity in serum were purified using a CNBr-activated sepharose 4B column, gel filtration and an ion exchange FPLC column. From these purifications, two proteins with strong CPI activity were isolated and partially sequenced. Based on their molecular weights and partial amino sequences, the two major proteins with CPI activity from the blood in this species were found to be fetuin B (60 kDa) and kininogen (54 kDa). Full article

Despite mass mortality, hard clams remain among the main cultured shellfish in Taiwan. Using cross-sectional data, this study applies threshold regression modeling with stocking density and feed costs as the threshold variables to explore the nonlinear relationship between input and output factors. The findings show that the production output levels may be increased by different combinations of factor inputs and variations in input factors. More specifically, the higher output levels may be achieved by increasing labor input while reducing capital input factors in farming households with a higher stocking density (HSD > 1,087,870 inds/ha) or higher feed cost (HFC > 13,889 NTD/ha). Farming households with a lower stocking density (LSD ≤ 1,087,870 inds/ha) may enhance production output levels by increasing feed input while reducing capital inputs. Moreover, the maximum output level of HSD and HFC farming households was estimated to reach 9255 kg/ha and 9807 kg/ha, respectively. Results of the production output simulation suggest that the feeding cost per hectare in LSD households should not exceed 25,119 NTD to avoid overfeeding, which may cause culture deterioration and lower survival rates. As such, farmers are advised to adjust their feed costs according to the stocking density to maximize production output. Full article

Domestication can be defined as the artificial selection in animals to achieve morphological, physiological, and developmental conformity to human needs, with the aim of improving various limitations in species under a human feeding environment. The future sustainability of aquaculture may rely partly on the availability of numerous domesticated fish species. However, the underlying adaptive mechanisms that result in the domestication of fish are still unclear. Because they are poikilothermic, temperature is a key environmental element that affects the entire life of fish, so studying the association between physiological and behavioral changes in low-temperature domesticated fish can provide a model for understanding the response mechanisms of fish under cold stress. Through 5 generations and 10 years of artificial selection at low temperatures, we used cold-tolerant fugu as a biological model to compare transcriptome changes in brain and liver tissues to study the effects of cold stress on fish. It was found that the expression of genes such as apoptosis, p53, oxidative phosphorylation, and mitochondrial β-oxidation in the brain of cold-tolerant fugu was significantly lower than the wild type due to cold stress, while excessive energy metabolism would lead to the production of reactive oxygen species (ROS) and exacerbate the brain damage, thus causing rollover and coma. Meanwhile, under cold stress, the signaling pathways involved in glycogenolysis and lipid metabolism, such as insulin signaling, adipocytokines, and mTOR signaling pathways, were significantly up-regulated in the liver of cold-tolerant fugu. Although the mitochondrial β-oxidation pathway was increased in cold-tolerant fugu liver tissues, the transcriptome was not enriched in apoptotic. These phenomena predict that in response to low-temperature conditions, cold-tolerant fugu employs a dynamic inter-organ metabolic regulation strategy to cope with cold stress and reduce damage to brain tissues. Full article

Quality evaluation of koi (Cyprinus rubrofuscus) is essential to the koi industry. However, the community has a lack of knowledge about the quality evaluation of koi and about features of koi which are valuable. During the “All Japan Nishikigoi Show” competition, a quality evaluation of koi was conducted by authoritative experts. In the present study, photos of participants of this competition were used for analysis to discover features affecting the quality of the Kohaku variety of koi. The HSVA color model was used to define and extract from image red and pale red coverage rates in Kohaku body coloration. Body aspect ratio, body proportions, red coverage rate, and pale red coverage rate were extracted using tools written in Python programming language. Analyses of the extracted data revealed the significant impact body aspect ratio (p < 0.001) and pale red coverage rate (p < 0.001) on Kohaku quality. A low body aspect ratio has a positive impact on Kohaku quality, while a high pale red coverage rate has a very strong negative impact on Kohaku quality. This study and its results can be an important foundation for further research about koi quality. Full article

To describe the growth pattern of the bonnethead shark (Sphyrna tiburo) in the Gulf of Mexico, a von Bertalanffy (VB) model has been automatically fit, which indicated a single−phase continuous growth without oscillations, though this would generate biases if this hypothesis is not confirmed. The objective of this research was to describe the growth pattern of S. tiburo under a multimodel approach based on information theory and contrasting single−phase models (VB, Gompertz, logistic models, and variants) and biphasic models (Soriano model and variants). The VB model was not supported. The Soriano model, with the variant in growth rate (k) and including length at birth (L₀), was selected with 100% supporting evidence. The hypothesis of the two−phase growth of S. tiburo with an increase in k, more than L_∞, fitted to L₀, is confirmed, and a correspondence was identified between growth−phase change sizes and the sizes reported in the literature for change in the juvenile–adult stages in females and for onset of reproductive maturity in males and both sexes. Full article

In tropical regions, temperature is the fundamental environmental factor controlling the reproduction-related physiological activities of fish. Tropical fish are particularly sensitive to climate change since they develop in a relatively stable thermal environment. A review was done to assess the potential effect of temperature rise on reproduction and population structure in the commercially important hermaphrodite grouper and wrasse species, and in gonochoric snapper species in the southern Gulf of Mexico. Temperature increase can disturb the aromatase synthesis and/or activity, which can affect the reproductive cycle and sexual differentiation in all studied species and the sexual inversion process in sequential hermaphrodites. Moreover, a mistiming or discontinuity in spawning seasonality could occur, with an alteration in the sex ratio in favor of males and a consequent reduction in populations’ fecundity. Furthermore, if the level of fishing exploitation enhances species’ sensitivity to environmental changes, then the stock of red grouper Epinephelus morio would be more affected by temperature increases than other species because it is the only fish population in the Campeche Bank currently assessed as overexploited. Full article

The marine silverside (Odontesthes argentinensis) is an euryhaline species, distributed along the southwest coast of the Atlantic Ocean, present in estuaries, brackish coastal lagoons and shallow marine waters. It is a significant economic resource for local fisheries in southern Brazil, Uruguay and Argentina. The aim of this work was to contribute to knowledge on the stock spatial structure of the silverside, using otolith shape analysis, based on samples from nine locations in the Argentinian Sea, covering a large distribution range of the species. A combination of elliptic Fourier descriptors, Wavelet coefficients and otolith Shape indices were explored by multivariate statistical methods. The application of wavelet and combined wavelet, Fourier and Shape Indices were the most effective variables to discriminate between sampling sites (7.42 total error). PERMANOVA analysis of otolith shape revealed multivariate significant differences between north versus south locations (p < 0.0001). The results obtained show that the spatial structure of O. argentinensis presents a North–South gradient with marked differences between the extreme localities of the north (Mar del Plata, Quequén) with more elliptical shapes than those in the south (San Blas, San Antonio Este) and an isolated group conformed by Puerto Lobos. Full article

A 90-day study was performed under three different stocking densities, including high density (10,000 fishes/cage), medium density (8000 fishes/cage), and low density (6000 fishes/cage), in a deep-sea net cage for yellowtail kingfish (Seriola lalandi). The physiological characteristics and growth performance were tested, and structural characteristics of the gastrointestinal microbiota were systematically analyzed. The results show that fishes with high density had a lower weight gain rate and a specific growth rate, as well as higher serum cortisol content. The diversity, types and numbers of dominant microbiota with significant differences, and the numbers of shared genera among the different groups all changed. Core genera in the gastrointestinal tract were obtained according to the principles of dominance, commonality, and difference. The changes in the relative abundance of the core genera might be related to the growth and physiological characteristics of the host. The ratio of Firmicutes to Bacteroidetes in the stomach and pyloric caecum, which favors the accumulation of energy by the host from the diet, was higher in the medium-density group than in the other groups. This indicates that the higher density could cause physiological stress and affect growth performance. In order to reduce the resulting growth differences, gastrointestinal microbiota might assist the host in accumulating energy, participating in the energy distribution by adjusting its structure. Based on the growth, physiology, and production practices, the medium density was the appropriate density in this study. This study provides a reference for the improvement of deep-sea culture technology and the promotion of healthy growth through the gastrointestinal microecological regulation of yellowtail kingfish. Full article

The relationships between environmental factors and fish density are closely related, and species distribution models (SDMs) have been widely used in exploring these relationships and predicting the spatial distribution of fishery resources. When exploring the prediction of the spatial distribution of species in different seasons, the method of choosing the appropriate approach to the season will help to improve the predictive performance of the model. Based on data collected from 2015 to 2020 during a survey off southern Zhejiang, the Tweedie-GAM was used to establish the relationship between the density of Decapterus maruadsi and environmental factors at different modeling approaches. The results showed that water temperature, salinity and depth were the main factors influencing D. maruadsi, and they operated through different mechanisms and even resulted in opposite trends of density in different seasons. Spatially, the two modeling approaches also differed in predicting the spatial distribution of D. maruadsi, with the seasonal model showing a higher density trend in inshore waters than in offshore waters in spring but showing the opposite trend in summer and autumn, which was more consistent with the actual spatial distribution of the resource. By analyzing the effects of two different approaches on the prediction of fishery resources, this study aims to provide research ideas and references for improving the predictive performance of SDMs. Full article

The quality of sea urchin gonad is important to consumers with high standards for nutrition and taste. However, few studies have been conductedon the molecular mechanisms that determine the quality of male and female sea urchins. In this study, our goal was to understand the differences and characteristics of gonad quality between sea urchin (Strongylocentrotus intermedius) males and females. The transcriptomes of males and females were obtained, with totals of 43,797,146 and 56,222,782 raw reads, respectively, comprising 128,979 transcripts and 85,745 unigenes. After comparative transcriptome analysis, a total of 6736 differentially expressed genes (DEGs) between the males and females were identified, of which 2950 genes were up-regulated and 3786 genes were down-regulated in males. We compared the expression of twelve DEGs with significant differences their expression levels and functional annotations to confirm the reliability of the RNA-Seq data. Five DEGs related to gonadal quality were found through enrichment analysis of KEGG pathways: 17β-HSD8, PGDH, FAXDC2, C4MO, and PNPLA7. Our study analyzes genes related to the taste and flavor of sea urchin gonads among the sexes and provides reference sequences and fundamental information concerning the nutrition and taste of S. intermedius gonads. Full article