Abstract:本研究旨在克隆梭鲈(Sander lucioperca)生长激素(growth hormone, GH)基因, 探究其序列特征及其表达量与梭鲈生长的相关性, 以期为梭鲈生长的分子机理研究鉴定基础。研究采用 RACE 技术从梭鲈垂体中克隆了 GH 基因, 其 cDNA 全长为 926 bp, 包含 74 bp 的 5′非翻译区、237 bp 的 3′非翻译区和编码 204 个氨基酸的开放阅读框。 氨基酸多重比对发现, 梭鲈 GH 与黄金鲈(Perca flavescens)、河鲈(Perca fluviatilis)的氨基酸序列相似性分别为 97.04%和 94.05%, GH 基因在鱼类和哺乳动物中都存在四个保守的半胱氨酸残基位点。应用实时荧光定量 PCR 技术分析了 GH 基因在梭鲈各组织和体重极端差异个体间的表达特征, 结果显示, GH 基因在梭鲈各组织中均有表达, 垂体中相对表达量最高, 脑次之, 与其他组织相比差异极显著(P＜0.01)。GH 基因表达量与梭鲈体重呈正相关, 4 个组织中 GH 基因表达量均为体重极大组高于极小组, 其中垂体和脑中差异极显著(P＜0.01), 肌肉中差异显著 (P＜0.05)。因此, GH 基因可以作为梭鲈生长候选基因用于分子选择。本研究结果可为进一步解析 GH 基因调控梭鲈生长发育的分子机制研究提供参考。

Abstract:Schizothorax prenanti is a rare fish in the upper reaches of the Yangtze River and used to be an important economic fish in its production area. However, in recent years, due to diseases and environmental changes, the number of Schizothorax prenanti in the wild has decreased sharply. Thus, there is an urgent need to protect this fish species. The establishment of Schizothorax cell lines is a cost-effective method to protect its germplasm resources. Since the establishment of the fish cell line RTG-2 in 1962, research on the establishment of fish cell lines has developed rapidly. A total of 783 cell lines have been established from various fish tissues, including embryos. However, thus far, reports on the establishment of cell lines from Schizothorax prenanti are lacking. The establishment of the Schizothorax prenanti cell line not only enables the protection of its germplasm resources but also facilitates research on its living environment toxicology, nutrition, immunology, and disease control without harming the existing population of this rare fish. Schizothorax prenanti can be infected with Streptococcus agalactiae in the natural environment, resulting in exophthalmos, surface hemorrhage, and neurological symptoms, as well as marked degeneration, necrosis, and inflammatory cell infiltration in various internal organs. Mucosal immunity is an important part of the immune system of this fish, wherein the gills, skin, and intestinal mucosa constitute the first line of defense against pathogenic microorganisms. Thus, the establishment of a stable growth of the gill filament cell line of Schizothorax prenanti will enable the study of immune mechanism and disease control of Schizothorax prenanti. The most commonly used media for fish cell culture are MEM and L-15, where L-15 is an amino acid-rich medium that does not require CO₂ to maintain the pH of the medium. Among the 280 newly established fish cell lines in the world from 2010 to 2020, 180 use L-15 medium, accounting for 64% of the total. In this study, L-15 was used as the basis to prepare the Schizothorax prenanti culture medium. The primary cell medium was based on L-15 medium supplemented with 5 ng/mL bFGF, 5 ng/mL EGF, 27.5 μmol/L beta-mercaptoethanol, 100 U/mL penicillin, 100 μg/mL streptomycin, 0.25 μg/mL amphotericin B, and 20% fetal bovine serum (FBS). The cell subculture medium was based on L-15 supplemented with 5 ng/mL bFGF, 5 ng/mL EGF, 27.5 μmol/L beta-mercaptoethanol, and 15% fetal bovine serum. The cell cryopreservation solution was made of 50% L-15 medium supplemented with 40% FBS and 10% DMSO. Schizothorax prenanti with a body length of about 11 cm was taken and placed in purified water containing 500 U/mL penicillin, 500 μg/mL streptomycin, and 1.25/mL amphotericin B overnight. On the second day, anesthesia was used, and the fish was wiped with 75% alcohol and moved to an ultra-clean bench. Ophthalmic scissors were used to cut the gill arches and gill filaments, which were transferred to a Petri dish containing PBS. The gill filaments were cut along the gill arch with a scalpel before rinsing five times in PBS containing 500 U/mL penicillin, 500 μg/mL streptomycin, and 1.25 μg/mL amphotericin B, changing the PBS wash solution each time. After washing, the gill filaments were placed in a petri dish containing PBS. Then, a scalpel was used to cut the gill filaments into 1-2 mm³ sections. A disposable Pasteur pipette was used to transfer the gill filament sections into a 15-mL centrifuge tube, to which PBS washing solution was added three times to remove surface debris and mucus. Then, the tissue sections were inoculated into T25 culture flasks, and as little medium as possible to cover the tissue blocks was added, without causing the tissue blocks to float or move. The cells were placed in a 24 ℃ incubator for static culture, to which 1 mL of fresh primary medium was replaced after 48 h. Cell migration was observed daily. When the cells migrated from the tissue section, 3 mL of medium was added to continue the culture, which was changed every three days to remove non-adherent cells and impurities. In this study, a cell line derived from Schizothorax prenanti (SPG strain) was established for the first time. The cells were isolated from the gill filament tissue of Schizothorax prenanti with a uniform epithelium. These were then cultured with L-15 containing 15% serum and successfully passed to 55 passages in 15 months. Mitochondrial COI gene identification proved that this cell was derived from Schizothorax prenanti, wherein the number of chromosomes in the karyotype was 2n = 96. Cells stored in liquid nitrogen for 12 months can maintain over 75% viability after resuscitation. EGFP-N3 plasmid was transfected into SPG cells, and marked green fluorescent protein expression was observed. The viral analog poly(I:C) and Escherichia coli lipopolysaccharide LPS increased the expression of immune-related genes, such as IL-1β, IL-8, TNFa, and TLR22, indicating that the SPG strain can be used for immunological and toxicological studies. In addition, this cell line also plays an important role in germplasm preservation, exogenous protein expression, and in vitro biological studies of Schizothorax prenanti. Although over 783 fish cell lines have been established in the world today, many of these have not been fully explored. Furthermore, a major problem in the field of fish cell line development is that many of the developed cell lines are not deposited in user-friendly cell banks. To facilitate the acquisition of this cell by researchers, the cell line established in this study has been stored in the National Marine Aquatic Germplasm Bank (YSFRI-C-2020-SPG).

Abstract:Specific antibody secreting cells (ASC) play an important role in the immune response. In this study, to detect changes in specific ASCs in the Nile tilapia (Oreochromis niloticus) in response to exogenous stimuli, the number of ASCs in the head kidney, peripheral blood, and spleen of this fish after immunization with human IgG was detected by enzyme-linked immunospot assay (ELISPOT). The results showed that ASCs could be detected in the head kidney on day 1 after the first immunization, while ASC could be detected in the peripheral blood and spleen on day 3. The number of ASCs in the head kidney, peripheral blood, and spleen all reached their peak on day 12. While the number of ASCs in the kidney and peripheral blood was significantly reduced, that in the spleen was not significantly reduced. Subsequently, ASCs could be detected in the head kidney, peripheral blood, and spleen on day 1 after the second immunization, with the number of ASCs reaching their peak on day 9, earlier than the first immunization. In both the first and second immunizations, the number of ASCs in the head kidney tissue was the highest among the three tissues. Using enzyme linked immunosorbent assay (ELISA) to detect the antibody levels in serum after the first and second immunizations, the change trend was found to be the same as that of the ASCs. These results indicate that the Nile tilapia developed immune memory after the first immunization and produced more ASCs and antibodies during the second immunization. Furthermore, the head kidney was identified as the main source of ASCs. These findings provide an important scientific basis for the study of immune memory in fish.

Abstract:The large yellow croaker Larimichthys crocea is an important marine fish species. The output of this fish is the highest among the sea cage-cultured fishes in recent years in China, however, this species is susceptible to Cryptocaryon irritans, which causes a high death rate. Although CuSO₄ is currently the best treatment for C. irritans, it can lead to Cu pollution in aquaculture water bodies. At the same time, low temperatures have resulted in mass mortality during overwintering. To evaluate the effects of Cu acclimation on oxidative damage and gene expression in the liver of large yellow croaker under cold stress, fish (74.6 ± 4.2 g) were pre-exposed to 0 and 10 μg Cu/L for 14 d and subsequently subjected to cold stress (8 ℃) for 24 h. The results indicated that cold stress enhanced reactive oxygen species (ROS) and lipid peroxidation (LPO), indicating that cold stress had a negative effect on fish. Although Cu acclimation had no effect on ROS and LPO, Cu acclimation with cold stress increased ROS and LPO compared with cold stress alone, suggesting that Cu acclimation exacerbated cold stress-induced oxidative damage. A total of 2288, 1425, and 1382 differentially expressed genes (DEGs) were obtained from the Cu acclimation group vs. control, cold stress group vs. control, and Cu acclimation with cold stress group vs. cold stress group, respectively. The results of GO functional enrichment and KEGG pathway enrichment showed that DEGs were significantly enriched in the PPAR signaling pathway, fatty acid elongation, unsaturated fatty acid biosynthesis, glycolysis/gluconeogenesis, oxidative phosphorylation, glutathione metabolism, endoplasmic reticulum protein processing, FoxO signaling pathway, regulation of autophagy, MAPK signaling pathway, and apoptosis, highlighting the adaptive mechanism of fish in response to Cu and cold stresses involved in fatty acid metabolism, energy metabolism, antioxidant, endoplasmic reticulum stress, autophagy, and apoptosis. Cluster analysis showed that cold stress upregulated the majority of gene expression related to unsaturated fatty acid synthesis, endoplasmic reticulum stress, autophagy, and apoptosis. However, Cu acclimation had an antagonistic effect on the regulation of these genes under cold stress, indicating that Cu acclimation reduced the cold stress tolerance of the large yellow croaker by inhibiting unsaturated fatty acid synthesis, endoplasmic reticulum stress, autophagy, and apoptosis. These results provide a scientific basis for the study of the effects of Cu contamination on cold stress tolerance in the large yellow croaker and the underlying molecular mechanism.

Abstract:Growth is one of the most important economic traits in aquaculture and is directly related to the financial benefits of farming. It is influenced by a number of factors, including genetic and environmental factors. When faced with different environments, fish growth is not only regulated by their own physiological conditions but also by symbionts, such as gastrointestinal microbiota. To investigate the differences in the growth of yellowtail kingfish juveniles under two culture modes, namely indoor tank and deep sea cage culture, and their relationship with gastrointestinal flora, as well as with feed microbiota and culture water microbiota, six-month-old fish of the same size at (17.23±0.99) cm and body mass at (77.44±11.58) g were selected for a 30-day culture experiment under these two culture modes. The differences in the rate of yellowtail kingfish juvenile growth under these two culture modes were recorded. The structure and abundance of gastrointestinal microbiota (stomach, pyloric blind sac, and intestine), as well as feed and culture water microbiota, were analyzed by 16S rRNA high-throughput sequencing and bioinformatic analysis. The results showed that the growth of cage cultured juvenile yellowtail kingfish was significantly faster than that of indoor tank cultured fish. As for the gastrointestinal microbiota of juveniles cultured in cage, the abundance of Bacteroidetes and Firmicutes at the phylum level, as well as the abundance of Alloprevotella and Bacteroides at the genus level, were higher than in indoor tank cultured fish, wherein the abundance of Bacteroides was significantly higher. The composition of the gastrointestinal microbiota of the indoor tank cultured fish was different from that of the feed microbiota and significantly different from that of culture water microbiota, whereas the composition of the gastrointestinal microbiota of fish from cage culture was more similar with that of the feed microbiota but also significantly different from that of the culture water microbiota. Beta diversity analysis showed that the gastrointestinal microbiota of juvenile yellowtail kingfish was more influenced by feed microbiota and less by the culture water bacterial community. KEGG annotation analysis showed that the main functional pathways involved in the gastrointestinal microbiota of juvenile yellowtail kingfish in the cage culture were the phosphotransferase system (PTS) and NOD-like receptor signaling pathway, whereas carbohydrate metabolism and the carotenoid biosynthesis pathway were found in the indoor tank cultured fish. These results indicate that the gastrointestinal microbiota regulate the growth of yellowtail kingfish juveniles under indoor tank and cage culture conditions by changing their structure and abundance, as well as via functional pathways. Moreover, feed microbiota had a greater influence on gastrointestinal microbiota than culture water microbiota. According to these results, the faster growth of cage cultured fish may be due to the production of more short-chain fatty acid (SCFA) by gastrointestinal microbiota (e.g., Alloprevotella and Bacteroides) to induce the production of insulin-like growth factor 1 (IGF-1). These findings provide micro-ecological support for high-efficient commercial feed and healthy culture technology for yellowtail kingfish.

Abstract:Immunoglobulin is one of the major effector factors in the adaptive immunity of fish. Thus, the study of immunoglobulin is crucial for the prevention and control of disease in fish. In this study, the complete cDNA sequence of secretory immunoglobulin Z heavy chain gene (GenBank accession no. MZ274344.1) of Carassius auratus indigentiaus was cloned by PCR and RACE. The complete cDNA sequence of C. auratus indigentiaus sIgZ heavy chain gene was 2083 bp, and its open reading frame (ORF) was 1668 bp, which encoded a peptide chain composed of 556 amino acids, with a relative molecular weight of 61.59 kD and theoretical isoelectric point of 7.03. The sIgZ heavy chain gene structure of C. auratus indigentiaus is composed of one variable region (V), four constant regions (CH1-CH4), and one secretory tail (Sec tail). According to the homologous sequence retrieval in GenBank, the similarity of sIgZ amino acid sequence between C. auratus indigentiaus and other fish was as follows: Megalobrama amblycephala (63.17%), Ctenopharyngodon idellus (60.82%), Cyprinus carpio (52.98%), Oncorhynchus mykiss (37.06%), and Sparus aurata (60.82%). Constructing a phylogenetic tree using the neighbor-joining method in MEGA 5.1, sIgZ of C. auratus indigentiaus was found to cluster into one branch with the IgZ of Cypriniformes, wherein the genetic evolution relationship between C. auratus indigentiaus and M. amblycephala was the closest. qPCR analysis revealed that C. auratus indigentiaus sIgZ gene expression was highest in the head kidney, followed by mesonephron, intestine, spleen, and gonad. After artificial infection with Aeromonas hydrophila, the C. auratus indigentiaus sIgZ mRNA levels first increased and then decreased in different tissues within 28 d. The relative expression levels of sIgZ in mucosal immune tissues (intestine and skin) peaked earlier than that in systemic immune tissue (head kidney and spleen), wherein the relative expression of sIgZ in the intestine and skin at peak was significantly higher than that in the head kidney. These results showed that sIgZ of C. auratus indigentiaus may play an important immune function in mucosal immune tissue (e.g., intestine and skin).

Abstract:The Kizil River belongs to the Kashgar River system in the southern Xinjiang Uygur Autonomous Region. Inhabited by a variety of indigenous fishes, the food habits and trophic levels of the fish in the Kizil River have yet to be investigated. In this study, the food composition and trophic levels of five indigenous fish species from the Kizil River were determined. To this end, 46 samples of Schizothorax biddulphi, Schizothorax eurystomus, Schizothorax irregularis, Ttriplophysa yarkandensis and Triplophysa tenuis from the Kizil River were evaluated. The fish samples were analyzed for the morphological traits of the five feeding organs using traditional morphological methods. Furthermore, their intestinal food composition was analyzed using high-throughput sequencing techniques, and carbon and nitrogen stable isotopes were measured to analyze their trophic levels. δ¹⁵N and δ¹³C of Schizothorax and Triplophysa were used to construct the trophic structure and calculate the values of ecological indicators and parameters of the biotope. The results showed that the morphological differences of the feeding organs of the five indigenous fish species were comprised mainly of the intestinal length ratio and lip thickness. The two highland loaches had the same feeding organ morphology, a short intestinal length ratio, a small mouth cleft, and a slender body. A total of 4442842 valid sequence fragments were obtained from 46 samples using Illumina high-throughput sequencing. The lowest number of sequences in the samples was 60269, while the highest was 134,129, and the average number of sequences was 96583±16515. A total of 554 OTUs were obtained from 46 samples after clustering. The main bait organisms found in the stomach of the 46 specimens belonged to Chordata, Streptophyta, and Nematoda, among which the gut length ratio of S. irregularis was about 2.95. The main food source was primary producers, including Tamarix hispida, Glycine soja, and Nitraria tangutorum. During foraging in the riverbed substrate, the small individual benthic nematodes of S. irregularis were accidentally ingested by S. irregularis, resulting in a higher abundance of nematodes in its intestine. S. eurystomus had a shorter intestinal length ratio of approximately 2.56, with the main food source being primary producers, such as Brachypodium distachyon, which also prey on some small fish. S. eurystomus scrapes attached plant debris by means of sharp cuticles and wider mouth fissures. Benthic nematodes passively enter the gut of the wide-mouthed schizothorax when feeding. S. biddulphi has a relatively short gut length, with a ratio of approximately 2.38, and feeds mainly on Schizothorax fish, followed by Citrus latifolia, S. eurystomus and S. biddulphi were dissected, and a large number of small Schizothorax fish were found in their intestines. The intestinal length ratio in T. yarkandensis and T. tenuis were both less than one, and the proportion of Schizothorax fish in the intestine was over 95% of the food contents. Large plants and sand particles were also found in the highland loach, most likely ingested while chasing prey, due to water disturbance, via accidental ingestion. The intestinal contents of the two types of highland loach and S. biddulphi were similar while those of S. irregularis and S. eurystomus were similar. S. biddulphi, S. eurystomus, S. irregularis, T. yarkandensis, and T. tenuis δ¹⁵N ranged from 4.32‰ to 10.13‰, 1.94‰ to 9.78‰, 3.67‰ to 7.58‰, 2.22‰ to 11.78, and 4.61‰ to 11.88, respectively. Similarly, their δ¹³C ranged from ?27.36‰ to ?14.89‰, ?27.81‰ to ?13.87‰, ?26.09‰ to ?17.64‰, ?28.80‰ to ?15.47‰, and ?27.21‰ to ?18.79‰, respectively. The trophic levels of S. biddulphi, S. eurystomus, and S. irregularis were 3.19, 2.78, and 2.52, respectively, while those of T. yarkandensis and T. tenuis were 3.44 and 3.55, respectively. The average trophic diversity and feeding sources of Schizothorax were higher than those of Triplophysa, while the trophic level, density of species aggregation, and evenness of species aggregation of Triplophysa were higher than those of S. eurystomus. S. eurystomus is an omnivorous bi-phytophagous fish, whereas S. biddulphi is an omnivorous bi-carnivorous fish. T. yarkandensis and T. tenuis are both carnivorous fish and the top predators of the Kizil River, associated with material endpoints and energy transfer in the basin. The findings presented in this study provide insights into the food web of the Kizil River by exploring the relationships and trophic levels of fish in this habitat. In this study, the mean trophic levels of T. yarkandensis and T. tenuis, among others, are estimated to evaluate their ecological roles in the river ecosystem, improving our understanding of their feeding ecology and providing fundamental data for the conservation and rational use of fish resources in the Kizil River.

Abstract:Tuna is a high-speed swimming species with migratory behavior. As rapid swimming often involves large amounts of energy consumption, the oxygen absorption efficiency of gills is crucial to tuna mobility. However, our current understanding of the histological characteristics of gills is far from sufficient to understand the cost-efficiency of oxygen uptake in tuna. In this study, the microstructure, surface ultrastructure, and internal ultrastructure of juvenile and adult yellowfin tuna in the northern South China Sea were studied using optical microscopy, scanning electron microscopy and transmission electron microscopy. The results showed that the top of the filaments of yellowfin tuna was bent, with different cell types on the surface of gill arch, filament, and gill rake. Surface ultrastructural studies showed that gills had high lamellar density, unique oblique blood flow patterns and gill fusion characteristics, and significant differences between juvenile and adult gills structures. The pavement cells (PVC) covered the filament epithelium and lamellae of the gills, with microvilli or microridges at the top. The gills of adult fish had higher cytoplasmic density than those of juvenile fish. Ionocytes were mainly distributed in the lamellae and the base of the lamellae. The top part of gills of the ionocytes of juvenile fish was comprised of microvilli, and adult fish were pit-shaped. Based on these results, the gills rake of juvenile and adult fish are likely to act as a selective barrier and play a role in predation. Rectangular gill lamella, an oblique blood flow pattern, and gill fusion all enable a greater supply of oxygen for yellowfin tuna, which promotes a high oxygen absorption efficiency, thereby meeting its energy requirements for high-speed swimming. In addition, the two main cells of gill epithelium, the pavement cells and ionocytes, provide a guarantee for the survival, respiration, and energy supply of yellowfin tuna in the ocean environment. Among them, a large number of micro-ridge structures on the surface of pavement cells increase the respiratory surface area of gill lamella and improve the gas exchange efficiency of the gills. A large number of mitochondria in ionocytes produce ATP for ion regulation and self-energy. In conclusion, this study elucidated the histological structure of the gills of juvenile and adult yellowfin tuna, enriching our access to the apparent and microstructure data of yellowfin tuna, as well as providing relevant information regarding the ultrastructure of pavement cells and ionocytes in gills filaments and lamella. Thus, this work provides a basis for the relationship between the specific morphological characteristics of high-speed swimming fish and their high-speed swimming habits.

Abstract:External tagging methods facilitate the study of the spatio-temporal behavior of Apostichopus japonicus at population and individual levels, as well as population dynamics, breeding, and efficient harvesting methods. However, due to the soft body wall and strong exclusion ability of Apostichopus japonicus, the retention rate of traditional invasive tagging methods is low. Moreover, damage caused to the body wall by traditional tagging methods often leads to wound ulceration, which affects the quality of life of Apostichopus japonicus. In this study, a non-invasive identification method for Apostichopus japonicus is developed by processing images using a deep convolutional neural network model to extract features and characterize the unique body texture patterns of individual specimens. After feature extraction and the training of the classifier on consecutive images of Apostichopus japonicus taken in a period of 50 d, the classifier achieved a maximum accuracy of 0.996±0.011 on the test set compared to traditional invasive tagging methods that only achieved an accuracy of up to 0.75. For individual temporal tracking recognition, feature extraction and model training were performed using images taken in a period of 1 to 25 d. The classifier achieved an accuracy of 0.946±0.058 on the test set consisting of images taken in the periods of 26–50 d. These results indicate that the use of the ResNet50 convolutional neural network can effectively predict the categories of Apostichopus japonicus and achieve a better accuracy than traditional tagging methods in the temporal tracking task.

Abstract:Collichthys lucidus is a demersal fish with a high economic value that has demonstrated an ability to adapt to warm water. Many scholars have studied the embryonic and larval development, morphological differences of geographical groups, feeding habits, and genetic structure of Collichthys lucidus. In this study, specimens of Collichthys lucidus larvae and juveniles were collected using a larval net (mouth diameter, 1.3 m; mesh size, 0.5 mm) in the north of Hangzhou Bay between June and July, 2014 to evaluate vertebral column and appendicular skeleton development. A series of wild specimens (body length, 3.3–12.7 mm) were stained for both cartilage and bone. The results showed that the larval notochord did not appear segmented until the first segment was formed by the bone rings gradually growing out from the front to the back. Ossification occurred in an anterior-to-posterior direction. The neural arch also grew in this direction and was completely formed before the ossification of the notochord, while the neural arch of lower fish grew from middle to both ends or from posterior to anterior. Therefore, the growth type of Collichthys lucidus belonged to relatively higher fish. The pectoral fin of fish plays a very important role in swimming, wherein being able to swim and eat freely is a key condition for the evolution from endogenous to exogenous nutrition. The pectoral fin supports of Collichthys lucidus were first to develop among the appendicular skeleton, and the post-temporal had four spines protruding in different directions. The dorsal fin supports first developed in the middle of body, before gradually growing to both ends. Furthermore, the dorsal fin supports in the front of the body were longer than those in the back. The ossification of the caudal fin supports occurred subsequent to that of other appendicular bones, and the lateral inferior caudal bone fused with the bases of two adjacent inferior caudal bones. This type of fusion can enhance the swimming ability of fish. For example, the flying fish Parexocoetus mento mento glides quickly on the surface of the water before taking off, with this type of fusion providing power for the flying action. These findings not only provide a scientific basis for early morphological classification in bone development but also provide insights into the role of bone development in the process of artificial reproduction in Collichthys lucidus.

Abstract:We evaluated the effect of prolonged summer fishing moratorium on the conservation of fishery resources in Bohai Sea from three perspectives (individual, population, and community) by analyzing the dominant species of nekton, the individual mean body weight, and fisheries resources index of nekton and some main fishery populations or biological categories. Data was collected during trawl surveys in August 2012–2016 and 2017–2021, representing the former and prolonged summer fishing moratorium, respectively. The results showed that the individual mean body weight of nekton in the former fishing moratorium was higher than that in prolonged summer fishing moratorium (4.35 g/ind and 3.77 g/ind, respectively). The individual mean body weight of nekton in the prolonged fishing moratorium decreased, mainly as a result of the annual average density of the populations increasing compared to their annual average resource density, indicating that both the number of complementary populations and the fertility of the parents increased significantly. The dominant species of nekton in the early stage of the prolonged fishing moratorium were Engraulis. japonicus, Oratosquilla oratoria, and Setipinna taty, similar to those in the former fishing moratorium. However, several new dominant species appeared in the later stage of the prolonged fishing moratorium, with a low occurrence frequency and a high annual variation. In general, the dominant species composition of nekton fluctuated greatly throughout the whole fishing moratorium. Meanwhile, body size and the trophic level of dominant species in the prolonged fishing moratorium showed an increasing trend. The annual biomass of nekton, pelagic fish, demersal fish, and crustaceans in the prolonged fishing moratorium were generally higher than those in the former fishing moratorium, especially in the first year. However, the biomass of all of the above biological categories in certain years in the prolonged fishing moratorium were lower than those in the corresponding years of the former fishing moratorium. The annual average biomass of the above biological categories in the prolonged fishing moratorium increased by 186.38%, 178.26%, 357.63%, and 132.89%, respectively. The annual biomass ratio of the bottom to middle and upper organisms in the prolonged fishing moratorium was larger than that in the former fishing moratorium, with an interannual increasing trend. The biomass of higher trophic level organisms remained low in the former fishing moratorium but increased sharply in the prolonged fishing moratorium, showing an increasing trend, with an average annual increase of 493.67% compared with that in the former fishing moratorium. In conclusion, the biomass of both lower and higher organisms in the ecosystem of Bohai Sea in the prolonged fishing moratorium was found to increase significantly, consolidating the energy foundation of the ecosystem, optimizing the community structure of fishery resources, and gradually stabilizing the succession of the ecosystem. These findings indicate that the input control measures of the prolonged fishing moratorium had a beneficial ecological effect in the Bohai Sea.

Abstract:Black rockfish (Sebastes schlegelii) and fat greenling (Hexagrammos otakii) are important commercial species in the rocky areas of China. However, in recent years, their resources have declined dramatically due to overfishing. The construction of marine ranching and artificial reefs is undergoing rapid development in China in an attempt to restore fishery resources and the ecological environment and has achieved promising results. Despite an increase in the scale of the artificial reefs and the abundance of fishery resources, the strategy by which fish are captured in the most reasonable and efficient manner in artificial reef areas is yet to be established. At present, the main methods for catching black rockfish and fat greenling include traps, hooks, and gillnets. Traps are characterized by poor size selectivity, whereas hooks have a low catch efficiency. By contrast, gillnets are widely used in coastal fisheries because of their simplicity of operation and suitability for complex bottom conditions. However, due to the small mesh size of gillnets, large numbers of juveniles are often captured. To address this issue, in this study, gillnets with four different mesh sizes (40 mm, 50 mm, 60, and 70 mm) were tested for the capture of black rockfish and fat greenling during sea trials in the artificial reef areas of Beibu Bay, Rongcheng in October 2021. A total of 340 specimens of black rockfish and 415 specimens of fat greenling were caught. The total lengths of black rockfish and fat greenling ranged from 70 to 250 mm and 80 to 250 mm, respectively. Four different selectivity models (normal, lognormal, gamma, and bi-normal) of the SELECT method were fitted to the data sets. The lognormal model provided the best fit for these two species, with the lowest deviance and AIC value. The estimated modal lengths were 114.23 mm, 142.79 mm, 171.35 mm, and 199.90 mm for black rockfish and 129.67 mm, 162.09 mm, 194.51 mm, and 226.92 mm for fat greenling for the corresponding mesh sizes of 40, 50, 60, and 70 mm, respectively. The theoretical mature body length (MBL) of black rockfish and fat greenling was set at 150 mm for analysis. The proportion of juveniles captured decreased with an increasing mesh size. These results indicate that 70 mm and 70 mm are suitable for the capture of black rockfish and fat greenling while protecting juvenile resources in artificial reef areas.