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Abstract:Knowledge of fish population ecology is fundamental for understanding population structure, habitat utilization, resource dynamics, and formulating conservation policy for natural fish resources. To date, various technologies have been used to better understand fish population ecology. Among them, otolith microchemistry analysis is one of the most important research approaches. Otoliths (ear bone) are biologically calcified structures in the inner ear of fish, which show continuous growth and are metabolically inert. They usually constitute three pairs of sagittae, lapilli, and asterisci in bony fish. As these hard tissues can record the habitat information that individual fish experience during their lifetime, otoliths are a useful resource for reconstructing the temporal and spatial histories of fish populations. The composition and content of otolith elements (like “fingerprints”) are mainly related to the bioavailability of macro and trace elements (including stable isotopes) in the ambient water and aquatic physical and chemical properties (especially salinity). Increasing scientific evidence has demonstrated that otolith microchemical analysis is a powerful tool to study fish population ecology, revealing the environmental conditions experienced by the organisms and tracing the key habitats (e.g., spawning site, nursery ground, and growing area) throughout their life cycle. Moreover, this approach offers significant advantages in assessing the formation mechanism and spatial structure dynamics of fish stocks. As the ratios of strontium to calcium (Sr/Ca) significantly differ between freshwater and seawater, and among different freshwater tributaries on a fine spatial scale, otolith Sr/Ca ratios are powerful markers for distinguishing freshwater, brackish water, and seawater habitats, and are widely used as a useful tool for revealing the habitat history related to spawning, hatchery, development, and migration of migratory fish. The combined analysis of otolith microchemistry (e.g., otolith line transects of elements) and microstructure (e.g., otolith increment of somatic growth) can be effectively used to quantify the duration and frequency of different habitat requirements by the target fish populations. Otolith microchemistry analysis also provides a good reference for studying population genetics. The core element characteristics of otoliths can separate the different fish sources originating from different spawning sites and obtain more accurate information on population structure. Notably, because of the small size of the fish at early life stages, electronic tags and telemetry technologies are almost impossible to use in life history studies. In contrast, the trace elements assimilated by fish during the ontogeny and growth process are stored in the otolith microstructure, and elemental profiles of the otoliths can indicate habitat clues of fish even at early life stages. The present review highlights the advances in studies on the characteristics of fish otolith elements and the application of otolith microchemistry analysis on fish population ecology, especially of natal origin reconstruction, habitat history inversion, population structure evaluation, and stock connectivity assessment. The limitations of otolith microchemistry analysis and possible solution routes are also discussed. Baseline investigations are suggested to enhance the robustness and interpretability of otolith microchemistry analysis, as several exogenous and endogenous factors may influence the spatio-temporal patterns of otolith chemistry. Additionally, building a multiyear database of otolith chemistry and water elemental signatures is recommended. It is noteworthy that the structure of otoliths in some cartilaginous fish is not suitable for microchemical analysis, and collecting otoliths from endangered or protected fish species is difficult. Alternative hard tissues (e.g., rays, scales, spines, and scutes) can be used to study fish population ecology as non-invasive substitutes of otolith samples. As mentioned, otolith microchemical analysis can accurately distinguish the ecological profiles of migratory fish; if combined analysis of otolith microchemistry and genetic markers is used to reveal the genetic structure and differentiation of fish populations, the results would become more reliable for developing and executing effective management and conservation strategies. At present, with improvements in the otolith microchemistry research, the analysis of otolith microchemistry has been extended to several new fields. The 87Sr/86Sr isotope ratio of otoliths has been utilized to investigate the life history of fish on a wider spatio-temporal scale. Furthermore, the approach of artificial otolith marking by macro and trace elements has strong applicability in the restocking of fisheries and will play a vital role in enhancing commercial and endangered fishery resource in the future.

Abstract:Aquatic products are a general term referring to marine and freshwater fishery organisms and their products. Such products mainly include fish, shrimp, crabs, shellfish, and seaweed. Aquatic products are rich in nutrients such as proteins, vitamins, fatty acids, and minerals. However, the recent illegal counterfeiting of the geographic origin label for aquatic products has become a major problem, receiving increasing attention worldwide. China is the largest producer of aquatic products globally, with a wide variety of aquatic species (especially fish, shrimp, crab, shellfish, sea cucumber, and microalgae). Several of these products are famous, exotic, high-quality, and new or endorsed by protected designations of origin. As an increasing number of consumers pursue better quality aquatic products, many well-known aquatic product brands and the protection of geographical indication products have been established. Consumers prefer aquatic products of well-known origins or famous brands, and are willing to pay higher prices for their quality. It is noteworthy that unscrupulous businessmen frequently fake shoddy products as real ones to earn profits. In addition to adulteration, the unclear origin identification and mislabeling are also rampant. Counterfeit activities inevitably harm the legitimate interests of consumers, producers, and the fishery industry. Using “bathed” Chinese mitten crab to counterfeit the native crabs cultured in the Yangcheng Lake of Jiangsu Province is a typical case of the above-mentioned activities. However, the establishment of traceability systems related to aquatic products remains unaccomplished in China. Thus, it is imperative to accelerate research on the origin traceability of aquatic products, and use scientific and objective methods to identify and confirm the origin of the products. Moreover, accurate and reliable analysis approaches are a prerequisite for effectively solving the adulteration and mislabeling of aquatic products and have special significance for implementing the national policy of rural revitalization. So far, biogeochemical approaches have especially advanced with a set of techniques for traceability of aquatic product origins. In particular, the corresponding mineral elements (e.g., Sr, Ba, Zn, Ca, Na, Cu, Mg, Al, As, Be, Co, Cr, Fe, K, Mn, Ni, P, Ti, and Zn) and stable isotopes (e.g., δ13C, δ15N, δ2H, δ18O, and 87Sr/86Sr) analyses have received increasing attention. The composition and content of mineral elements and ratios of stable isotopes in different habitats of aquatic organisms have individual characteristics and the mineral element/stable isotope “fingerprints” profiles in aquatic products must be different owing to various bioassimilation and bioaccumulation processes of the elements to the organisms from different geographical production regions of either natural or aquaculture water environments. Therefore, chemometric (especially, multivariate statistical authenticity analysis, e.g., discriminant analysis and principal component analysis) models based on the aforementioned “fingerprints” profiles (i.e., multi-elements, multi-stable isotopes, and the combination of multi-element and stable isotope) can be used to discriminate between aquatic products of wild or farmed origin, geographical origin, and species authenticity. This review summarizes the progress of the principles and applications of approaches to multi-mineral elements and stable isotopes traceability in aquatic products. Although the element uptake in fishery organisms may be influenced to some degree by water pollution and artificial diet, the availability of multi-elements/stable isotopes in ambient habitat waters and their bioassimilation/bioaccumulation are the most consistent and prominent factors influencing the biogeochemical “fingerprint” profiles in aquatic products. Advanced chemical analysis techniques can precisely and accurately reveal these profiles; for example, inductively coupled plasma (ICP) optical emission spectroscopy, ICP-atomic emission spectroscopy (ICP-AES), ICP-mass spectrometry (ICP-MS), laser ablation-ICP-MS, single collector quadrupole-ICP-MS, isotope ratio mass spectrometry, and multi-collector-ICP-MS. Successful studies of geographical origin traceability have already been reported in literature involving in many fishery species; e.g., Prochilodus lineatus, Genidens genidens, Eriocheir sinensis, Sepia officinalis, Dosidicus gigas, Ruditapes philippinarum, Mytilus edulis, Mytilus galloprovincialis, Patinopecten yessoensis, Chlamys farreri, Argopecten irradians, Pecten maximus, Salmo salar, Oncorhynchus mykiss, Salmo trutta, Oncorhynchus tshawytscha, Oncorhynchus kisutch, Ictalurus punctatus, Scomber japonicus, Larimichthys polyactis, Theragra chalcogramma, Apostichopus japonicus, Litopenaeus vannamei, Dicentrarchus labrax, Trichiurus haumela, tiger prawns, and several Cyprinidae species. The present article provides the most recent references and important theoretical bases for the development of more effective traceability and authenticity detection technologies for the famous, special, high-quality, and new aquatic products, promoting the implementation of national policies for rural revitalization. In addition, the establishment of local and national level databases is strongly suggested for effective geographical origin traceability of aquatic products in China.

Abstract:The implementation of the 10-year fishing ban in the Yangtze River is an important issue in the 14th Five-Year Plan of China, and the effective tracking and objective evaluation of its effects has become a major national demand. Coilia nasus is a long-distance migratory fish found in the Yangtze River. This fish has suffered from heavy fishing pressure during its spawning migration from the sea to the river, making its populations very vulnerable. The fishing ban on C. nasus in the Yangtze River was launched early in 2019 and has benefited the species for nearly two years; this includes the aforementioned 10-year ban, in place since 2020. Utilizing C. nasus as the representative species, a comparative study on the catch quantities before and after the start of national fishing ban strategies in fixed habitats and similar fishing seasons can undoubtedly effectively track and evaluate the effect of the policy on population recovery in the Yangtze River. Therefore, this study investigated the effects of the aforementioned ban on fishing in the Yangtze River by analyzing catch amount, catch per unit effort (CPUE), and the ratios of anadromous to freshwater resident individuals from the spawning ground and adjacent waters in Poyang Lake. Data were gathered from the same fishing season in the 7-year period before (2014—2018) and after (2019—2020) the fishing ban. The results showed that from 2014 to 2018, the CPUE of anadromous C. nasus was (0.81±1.73) [×10–5, ind./(h·m)], with anadromous individuals comprising only (1.42±2.41)%. In contrast, from 2019 to 2020, CPUE increased to (66.14±69.74) [×10–5, ind./(h·m)], an approximate 82× increase. In this period, the ratio increased to (60.56±40.87)%, an approximate 43× increase compared with 2014—2018. These results indicate for the first time that the quantity of anadromous C. nasus in Poyang Lake shows a tendency towards recovery, benefiting from national fishing ban strategies that have only been in place for two years.

Abstract:Life histories for Coilia nasus in the Kenli section of the Huanghe River were reconstructed using otolith microchemistry. An electron probe microanalyzer (EPMA) was used to analyze the Sr and Ca microchemistry patterns in otoliths of five C. nasus individuals(D1,D2,D4,D5 and D6 collected from Kenli section in May 2016. Results of line transect analysis showed that the life history of C. nasus was complex. All individuals were born in fresh water with a lower Sr/Ca ratio in the core area; however, as they grew, they demonstrated different life histories. After leaving the freshwater habitats, D1 and D4 mainly lived in the estuarine environment rather than seawater, where the salinity is relatively lower; the maximum Sr/Ca ratios of D1 and D4 were 6.1 and 6.2 respectively. D2 moved between the freshwater and brackish water habitats without migrating. The Sr/Ca ratios of D5 and D6 were higher, manifesting the maximum Sr/Ca ratios of 8.44 and 8.63, respectively. However, because of water and sediment discharge regulations, we cannot judge whether the habitat of D5 and D6 had been extended to the sea. All differences were confirmed from the mapping results of the EPMA data. The otolith of D1 and D4 presented a bluish pattern in the core area and greenish pattern in the outer regions. The otolith of D2 showed a multicolored pattern (alternating bluish, greenish, even yellowish). The otolith of D5 and D6 presented a bluish pattern with lower Sr/Ca ratios in the core area; as they grew, a yellowish circle was formed in outer regions adjacent to the bluish central regions. Based on the results, we were able to reconstruct the habitat history of C. nasus in the Kenli section of the Huanghe River. Most of the individuals completed their hatching and early life mainly in freshwater habitat, then entered the estuary or seawater, and leaved to and from the fresh-brackish water habitats for feeding until they were captured. The life history of the freshwater stock represented by D2 is relatively complex, and we speculate that it may enter the Huanghe River because of the water drainage during the flood season in Dongping Lake.

Abstract:To study the feasibility of using the strontium marking method in otoliths to identify the group of released Liza haematocheila, juveniles with a total length of ~5 cm were immersed in four different concentrations (50, 100, 200, and 400 mg/L) of Sr2+ for 48 h to detect the Sr2+ sedimentation effect. A double ring marking experiment was also conducted: L. haematocheila juveniles with a total length of about 3 cm were immersed in seawater with Sr2+concentrations of 200 mg/L, for 96 h. When the length of the first marked juveniles reached 5 cm, half of them were again immersed in seawater with Sr2+ concentrations of 100 mg/L, for 48 h. A significant peak was observed in EPMA (electron probe microanalysis) line transect analysis and a "high strontium marking ring" appeared in EPMA mapping analysis of L. haematocheila otoliths in all the marked treatments. Based on the results of the experiment and the marking efficiency, we suggest that a marking concentration of 50 mg/L Sr2+ could be used for strontium marking on otoliths of L. haematocheila. A well-structured double marking ring was observed in EPMA mapping analysis of L. haematocheila otoliths in double ring marking treatment, and the EPMA line transect analysis result of each ring in double-ring marking juveniles otoliths was the same as that in the corresponding monocyclic ring treatment. These results suggest that it is feasible to identify different groups of released L. haematocheila by changing the strontium marking times.

Abstract:Shrimp plays a key role in the functional group of marine ecosystems, and its biomass is affected by multiple factors. Based on an epidemiological survey of white spot syndrome virus (WSSV) in wild shrimp in the Yellow Sea and the northern East China Sea, the impact of WSSV prevalence on the biomass of shrimp in these regions from 2016 to 2018 was analyzed using the gradient random forest model (GFM) and generalized additive mixed models (GAMM). The results of molecular detection showed that 11 out of 26 species of shrimp obtained in the survey were determined to be WSSV-positive; the percentage of WSSV-positive sites in 2016, 2017, and 2018 was 48.40%, 38.75%, and 21.74%, respectively. The percentage of WSSV-positive samples was 16.86%, 9.60%, and 4.80% in 2016, 2017, and 2018, respectively. The GFM analysis results showed that the explanatory variable "logarithm of the number of positive samples (ln_posi)" showed the highest priority to the response variable "logarithm of the shrimp biomass (ln _Abu)". The GAMM model analysis results showed that the optimal model selected according to the minimum principle of Akaike information criterion (AIC) was ln_Abu ~ WSSV positive rate (P_rate) + ln_posi+longitude (Long), in which the ln_posi and P_rate were crucial factors affecting the biomass of shrimp, and the biomass of shrimp decreased with the increase in WSSV positive rate. The above results revealed that the WSSV was prevalent in the shrimp of the Yellow Sea and the northern East China Sea, and will have a potential impact on the biomass of shrimp.

Abstract:Oratosquilla oratoria is the main catch of drift net fishery in the nearshore area of Haiyang. To achieve sustainable use of resources, it is necessary to study the population status and life history characteristics of this species. During the period from March 2018 to September 2019, O. oratoria samples caught by a drifter in the Haiyang inshore current were analyzed monthly, excluding the months of the summer fishing moratorium. The body length and body weight of the samples were measured, the feeding intensity and ovarian development degree of the females were identified, and the ratio of males to females in the catch was calculated. The results showed that the ratio of males to females was 1: 1.03 over the whole year of catching. There was no significant difference in average body length between male and female samples in April and December (P>0.05), but there were significant differences in other months (P<0.05). The dominant body length of female O. oratoria ranged from 100 to 140 mm, with dominant body weight ranging from 10 to 40 g. The dominant body length of male O. oratoria was 110~150 mm, with a dominant body weight of 20~50 g. Except for December, there were significant differences in body length distribution between male and female samples in all months (P<0.05). The gonad maturity of female O. oratoria samples ranged from stages Ⅰto Ⅳ over the whole year, with individuals in stages Ⅲ and Ⅳ primarily appearing from April to May, and October to January of the following year. May and January represent the 2 peak periods of sexual maturity for females. In October, the empty stomach rate of male and female O. oratoria was the lowest in the whole year, with the highest relative growth rate of body length. The relationship between body length and weight of female O. oratoria was W=5.39×10–5L2.709 8 (R2=0.825 4, P<0.05), while the relationship between body length and weight of male O. oratoria was W=2.62×10–5L2.874 4 (R2=0.798 6, P<0.05). In addition, there were some differences between the male and female group structures.

Abstract:Enclosure experiments were carried out in Sanggou Bay in autumn 2015 to study the effects of high-capacity Patinopecten yessoensis and Gracilaria lemaneiformis culture on physical, chemical, and biological (phytoplankton community) factors of aquatic water within 60 h. The results showed that the concentration of dissolved oxygen (DO) and dissolved inorganic nitrogen (DIN) in water, and the abundance and composition of phytoplankton population can significantly change within 60 h. After 12 h, phytoplankton abundances in the experimental groups of P. yessoensis and G. lemaneiformis were significantly lower than that in the control groups. The filter effects of P. yessoensis on four dominant diatom species (Nseudo-nitzschia delicatissima, Surirella sp., Nitzschia spp., and Synedra spp.) in aquatic water were significantly different, indicating a greater filter effect on P. delicatissima and Surirella sp., than that on Nitzschia spp. and Synedra spp.. The characteristics of photosynthetic pigments in water also revealed the selective feeding effect of P. yessoensis on phytoplankton; that is, P. yessoensis could significantly filter fucoxanthin (characteristic pigment of diatoms) and alloxanthin (characteristic pigment of Cryptphytes) in water. On the contrary, prasinoxanthin (the characteristic pigment of pico-algae) was significantly higher in the scallop groups than in the control groups and the macroalgae groups after 48 h, which indicated that the cultivation of G. lemaneiformis had no significant effect on the biomass of pico-algae.

Abstract:Mudflat in the Yellow River Delta is the main production region of shellfish in Shandong Province. To enable economic development, the mudflat was greatly exploited, natural condition of the mudflat was disturbed, and the shellfish habitat was constantly subjected to changes. Based on remote sensing (RS) data and geographic information system (GIS) technology, the mudflat shellfish habitat in the Yellow River Delta data were obtained, and its spatio-temporal variation over the past 30 years was analyzed. For this study, a collection of Landsat images taken during the lowest tidal levels during 1986—2017 were selected as the data source and six images were used in the study. To extract the mudflat shellfish habitat, we chose the instantaneous waterline as the lower boundary and the reclamation dyke, aquaculture pond, or mean high tide line combined with vegetation line as the upper boundary. The results showed that the shellfish habitat area continued to decline from 1986 to 2017, from 1188 km2 in 1986 to 396 km2 in 2017. The variations were the most obvious during 1993—2001 and 2008—2013, and the average annual reduction area was approximately 34 km2. In terms of space, the Diaokou section showed a drastic variation, and the lower boundary expanded slightly to the sea during 1986—1993. However, the upper boundary moved toward the sea and the lower boundary retreated to the land during all other periods, and the area was greatly reduced. As for the estuary, its upper boundary was stable. At the lower boundary, deposition and erosion alternated due to the dual effects of runoff, sand transportation, and marine dynamic erosion, but the area changed only slightly on the whole. The factors influencing spatio-temporal changes in shellfish habitat were evidently different. Occupation by salt fields, aquaculture ponds, and engineering constructions were the main reasons for the changes in the Diaokou and Laizhou Bay sections. The estuary was mainly affected by changes in runoff, sand transportation, and marine dynamic erosion. However, in the Dongying Harbor and its adjacent section, habitat function was completely lost because of the construction of ports and oilfields.

Abstract:This study was conducted to evaluate the potential of replacing fish meal with ribose protein in juvenile turbot (Scophthalmus maximus L.). A single factor experiment -with six fish meal levels was used. A control diet (D1) was formulated to contain 45% fish meal. In other five diets, 44.5% (D2), 44% (D3), 43% (D4), 42% (D5), and 41% (D6) of the fish meal in the diet control were replaced with ribose protein, respectively. Each diet was randomly fed to triplicate groups of 30 fish per tank. The experimental period was 56 d. The results showed that as the replacement ratio of fish meal by ribose protein increased, the weight gain rate (WG), specific growth rate (SGR), and protein efficiency ratio (PER) showed a trend of first rising and then decreasing, they were all significantly higher in the D3 group than in the D5 and D6 groups (P<0.05). However, the feed conversion ratio reached a minimum in the D3 group. Compared with the control group, the serum IGF-1 and GH contents in the replacement groups were significantly decreased (P<0.05). Trypsin activities of the intestine in D3, D4, and D5 groups were significantly higher than in other groups (P<0.05). Amylase activities in the intestine of the D3 and D4 groups were significantly higher than that in the control group (P<0.05). Lipase activity reached a minimum in the D3 group (P<0.05). The total protein, globulin, and alkaline phosphatase contents in the replacement groups were significantly higher than those in the control group (P<0.05). The lysozyme activity in the D3 group was significantly higher than that in the D6 group (P<0.05). The albumin content and the activity of superoxide dismutase were not significantly different among all the groups (P>0.05), while the serum IL-1β and TNF-α contents were significantly increased (P<0.05). Compared with the control group, the total cholesterol and triglyceride contents in the D4, D5, and D6 groups were significantly decreased (P<0.05). The serum low-density lipoprotein cholesterol content of the D5 and D6 groups was significantly decreased (P<0.05), and the serum high-density lipoprotein cholesterol content of the D4 group was significantly increased (P<0.05). Glucose content first increased and then decreased as the replacement ratio of fish meal by ribose protein increased, and it was the highest in the D3 group (P<0.05). The challenge study showed that the D2 group had a lower cumulative mortality rate than other groups after 48 hours (P<0.05). It can be concluded that the optimum level of replacing fish meal in turbot diet with ribose protein is 1% based on growth performance, and simultaneously considers the indices of digestion and specific immune, and disease resistance in S. maximus under this experimental condition.

Abstract:Turbot (Scophthalmus maximus) is an economically important marine fish species in northern China. With the unceasingly amplification of farming scale and great improvement of intensivism in recent years, turbot diseases have been occurring frequently. Bacillus cereus YB1 could be used as a candidate probiotic strain, which has animal safety for turbot at a certain concentration. The present study aimed to investigate the effect of B. cereus (YB1) on growth performance, liver immune enzyme activity, intestinal digestive enzyme activity, and intestinal tissue structure of juvenile S. maximus, and would provide new probiotic strains for turbot aquaculture. A total of 720 healthy juveniles with an average body weight of (3.6±0.7) g were randomly divided into 4 groups with 3 replicates per group and 60 fish per replicate. The fish in the 4 groups were fed diets containing YB1 at a viable count of 0 (control), 105, 106, and 107 CFU/g at (21±2)℃, respectively, and the experiment lasted for 50 days. Results showed that the weight gain rate (WGR) and specific growth rate (SGR) were significantly higher in juvenile turbot fed diet supplemented with 107 CFU/g of YB1 than those of the fish fed the control diet (P<0.05). The amount of protease and amylase increased by 57.86% and 82.37%, respectively in 106 CFU/g group, and were significantly higher than those in the control group (P<0.05). Lipase content of fish in 107 CFU/g was significantly higher than that of the control group (P<0.05). Catalase activity in fish fed diets supplemented with YB1 was not significantly different from fish in the control group. Malondialdehyde content of juveniles fed 106 CFU/g YB1 dietary supplement was decreased by 42.03%, and was significantly lower than that in the control group (P<0.05). SOD activity of fish fed YBI increased compared with that of the control, however, the increase was not significant (P>0.05). YB1 led to a significant increase in the height and number of folds in the intestinal mucosa of turbot (P<0.05). Intestinal muscularis thickness was significantly increased in the 106 CFU/g YB1 dietary supplement group than in the control group; it was 68.91% higher than that of the control group at the end of the experiment. In this study, B. cereus (YB1) could promote the growth of juvenile turbot, improve the activities of digestive and liver immune enzymes in their intestine, and improve the structure of intestine. This study shows that B. cereus (YB1) can be used in turbot aquaculture, with a recommended dosage of 106 CFU/g.

Abstract:This study aimed to determine the optimal stocking density for juvenile Megalobrama pellegrini. Meanwhile, enzymology and molecular biology analyses were performed to analyze the effects of stocking density on the intestinal antioxidant enzyme activities and the expression of stress-related genes in this fish species. 5 density treatments groups, including 0.15 kg/m3 (50 tails/barrel), 0.24 kg/m3 (80 tails/barrel), 0.34 kg/m3 (110 tails/barrel), 0.42 kg/m3 (140 tails) /Barrel), 0.50 kg/m3 (170 tails/barrel) were set up in triplicate. The experimental period was 42 days. The results showed that fish growth performance (weight gain rate and specific growth rate) increased as the stocking density increased from 0.15 kg/m3 to 0.34 kg/m3, but no significant differences were found among the groups (P>0.05). When stocking density continued to increase, fish growth performance decreased, and significantly lower growth was found in fish reared at a stocking density of 0.50 kg/m3 compared with the 0.34 kg/m3 group (P<0.05). Meanwhile, the highest density group (0.50 kg/m3) had a significantly higher feed conversion ratio compared with the low and medium stocking density groups (0.15 kg/m3, 0.24 kg/m3, 0.34 kg/m3) (P<0.05), which indicated that the higher stocking density had side effects on fish growth and feed utilization. The results also showed that increasing the stocking density did not significantly affect the survival rate of M. Pellegrini (P>0.05), and the survival rate of each group was very high (>97%). The crude protein and crude fat content of the whole-body in the fish of the 0.34 kg/m3 group were significantly higher than those in other experimental groups (P<0.05). The intestinal antioxidant enzymes and other related indexes of fish were significantly affected by stocking density. Specifically, the 0.24 kg/m3 and 0.34 kg/m3 groups had significantly higher total antioxidant capacity than the lowest-density group (0.15 kg/m3) and the higher-density groups (0.42 kg/m3, 0.50 kg/m3) (P<0.05); the activities of intestinal superoxide dismutase and catalase were lowest at 0.50 kg/m3, while content of malondialdehyde was the highest (P<0.05); the highest value of glutathione content appeared in the 0.34 kg/m3 group and was significantly higher than that of other experimental groups (P<0.05). The lowest density experimental group, 0.15 kg/m3, had the lowest intestinal CYP1 A gene expression, but a significant difference was only found between the 0.42 kg/m3 experimental group (P<0.05). Fish in the 0.50 kg/m3 group had significantly higher relative expression levels of the Nrf2 gene and significantly lower relative expression levels of MnSOD compared with the 0.34 kg/m3 density treatment group (P<0.05), which indicated that the intestinal oxidative stress response was induced when the stocking density was too high. The results of this study indicated that M. Pellegrini at the weight of 0.45~1.36 g could be cultured at a density of 0.34 kg/m3, which will provide a theoretical basis for improving breeding efficiency and promoting the restoration of the resources of M. Pellegrini.

Abstract:This study aimed to investigate the effects of yeast hydrolysate on the growth performance, immunity, oxidation resistance, and anti-Streptococcus agalactiae activity of genetically improved farmed tilapia (GIFT). Five experimental diets were prepared by adding 0 (control group), 0.5%, 1.0%, 1.5%, and 2.0% yeast hydrolysate to the basic diet of these fish. GIFT with an initial weight of (25.80±0.45) g were randomly divided into five groups and were cultured for 8 weeks. After the breeding test, 12 fish from each group were selected for the S. agalactiae challenge test. Each fish was injected intraperitoneally with 0.2 mL bacterial solution at a concentration of 8.3×105 CFU/mL, and the cumulative mortality was counted for 14 days. The results showed that the final body weight and specific growth rate (SGR) increased significantly at first (P<0.05) and then decreased with the increase in the concentration of yeast hydrolysate. Regression model analysis showed that the most suitable dietary yeast hydrolysate level reached the highest SGR at 1.29%. The activities of nitric oxide synthase, phenol oxidase, acid phosphatase, catalase, and superoxide dismutase increased (P<0.05) at first and then decreased under the increased dietary yeast hydrolysate level; the peak was reached on supplementation with 1.5% yeast hydrolysate. Dietary yeast hydrolysate significantly influenced the resistance of GIFT to S. agalactiae (P<0.05). Except for the 0.5% yeast hydrolysate test group, the cumulative mortalities of the other test groups (1.0% yeast hydrolysate supplementation or more) were significantly lower than the cumulative mortality of the control group (P<0.05). In this study, the addition of yeast hydrolysates to the diet of GIFT significantly improved their growth performance, immunity, and disease resistance, and the 1.5% yeast hydrolysate-supplemented test group showed the best results.

Abstract:This study explored the effects of dietary palmitic acid/(docosahexaenoic acid [DHA] and eicosapentaenoic acid [EPA]) on the anti-oxidative capacity and muscle quality of large yellow croaker (initial weight: 30.51 ± 0.16 g). Fish meal and soybean meal were used as the main dietary protein sources. DHA rich oil, EPA-rich oil, palmitic acid, and lecithin were used as the main dietary lipid sources. Three isonitrogenous (43 % crude protein) and isolipidic (11 % crude lipid) experimental diets were formulated to have 1∶5, 1∶1, and 5∶1 palmitic acid/(EPA+DHA) ratios, and called P0, P50, and P100, respectively. The feeding trial lasted for 10 weeks. Results showed that there was no significant difference in the growth rate among the three groups (P>0.05). Compared with the P100 group, the hardness, adhesiveness, cohesiveness, and chewiness of muscle in large yellow croaker fed P0 and P50 were significantly higher (P<0.05). Muscle polyunsaturated fatty acid (PUFA) content in the P0 group was significantly higher than that in the P50 and P100 groups (P<0.05). The saturated fatty acid (SFA) content of the P100 group was significantly higher than that in the P0 and P50 groups (P<0.05). The expression levels of superoxide dismutase 2 gene (SOD2) and catalase gene (CAT) in the muscle of the P100 group were significantly higher than those in the P0 and P50 groups (P<0.05). The gene expression level of muscle nuclear factor E2-related factor 2 gene (Nrf2) in the P0 group was significantly higher than that in the P50 group (P<0.05); however, there was no significant difference either between the P100 and P0 groups or between the P100 and P50 groups (P>0.05). There was no significant difference among the three groups in the expression level of superoxide dismutase 1 gene (SOD1) in muscle (P>0.05). The total anti-oxidative capacity (T-AOC) of muscle in the large yellow croaker fed P50 was significantly lower than that in the P0 and P100 groups (P<0.05). The activities of total superoxide dismutase (T-SOD) and CAT, and malondialdehyde (MDA) content of muscle showed no significant differences among all the groups (P>0.05). In conclusion, higher antioxidative capacity was found in muscle when large yellow croaker juveniles were fed with higher levels of dietary palmitic acid or (EPA+DHA). Higher dietary palmitic acid levels decreased the texture parameters in muscle.

Abstract:Cobia (Rachycentron canadum) is an important marine fish with marked potential for aquaculture in China. Skeletal malformations are fundamental problems that severely decrease the production efficiency and profitability of cobia aquaculture by affecting external morphology, growth, and survival. In this study, we documented the skeletal deformities in tank-reared cobia juveniles (25 days after hatching; n=180). Based on observations of cleared and double-stained specimens, skeletal deformities have been described. Overall, 72 of 180 fish were deformed (with a deformity rate of 40.00%) and 22 types of skeletal malformations were identified: Meckel’s cartilage deformity, basihyal deformity, basihyal allotopia, lowered hyoid arch, lordosis, vertebral deformity, bifurcated neural spines, bifurcated haernal spines, haernal spine fusion, cartilage redundancy, epural deficiency, epural fusion, epural deformity, hypural deficiency, hypural and parhypural fusion, hypural deformity, bifurcated pterygiophore, pterygiophore deformity, pterygiophore redundancy, pterygiophore allotopia, anal fin ray redundancy, and dorsal fin spine deficiency. Malformations were most common in the cranium (17.22% of specimens) and caudal fin (15.56%), and the skeletal deformities with the highest incidence were Meckel’s cartilage deformity (12.22%) and epural deficiency (7.78%). All fish with these skeletal deformities showed no visible morphological changes. In addition, a significant difference in total length (TL) was found between normal fish and all deformed individuals (P<0.01), individuals with cranial deformities (P<0.01), and individuals with caudal fin malformations (P<0.01). The TL of individuals with dorsal and anal fin deformities was significantly different to that of individuals with cranial (P<0.05) and caudal fin malformations (P<0.05). These results provide insights into the skeletal developmental process for optimizing cobia rearing conditions.

Abstract:In the present study, six isoforms of melatonin receptor 1 (Mtnr1) were cloned from grass carp (Ctenopharyngodon idella) using RACE technology and bioinformatic analysis. The distribution pattern of the six paralogs in different tissues was detected using real-time quantitative polymerase chain reaction (RT-qPCR). The full-length cDNAs of the six isoforms (Mtnr1Aa, Mtnr1Ab, Mtnr1Alike, Mtnr1Ba, Mtnr1Bb, and Mtnr1C) were 2045, 2036, 2031, 2799, 2535, and 2477 bp, with open reading frames (ORF) of 1053, 1056, 1035, 1071, 1044, and 1086 bp, encoding 350, 351, 344, 356, 347, and 361 amino acids, respectively. All of the proteins contain 7 transmembrane domains (TM), an NRY motif, a CYICHS motif, a NAXXY motif, conserved residues interacting with G-proteins in the TM3, asparagine-linked glycosylation sites, and several phosphorylation sites. The six Mtnr1 proteins are composed of 20 amino acids and are stable hydrophobic proteins. Protein sequence identity analysis showed that the six Mtnr1 isoforms share 93.1%-99.4%, 84.8%-95.2%, 82.8%-96.8%, 90.1%-97.5%, 79.7%-98.3%, and 90.6%-95.6% identities with their respective counterparts in other fishes. Phylogenetic analysis revealed that six grass carp Mtnr1 paralogs were clustered into the Cyprinidae clade, sharing a close relationship with those of Danio rerio, Cyprinus carpio, and Carassius auratus. In addition, the expression of the six Mtnr1 isoform genes was detected in the liver, heart, gill, brain, muscle, forgut, midgut, hindgut, and kidney tissues. Results showed that Mtnr1Aa and Mtnr1Ba were highly expressed in the brain and kidney, suggesting that they might play a vital role in nervous system regulation and the immune response in grass carp, respectively.

Abstract:Thirteen morphological traits: Total length (X1), body length (X2), carapace length (X3), carapace width (X4), carapace height (X5), first abdominal segment length (X6), first abdominal segment width (X7), first abdominal segment height (X8), sixth abdominal segment length (X9), sixth abdominal segment width (X10), sixth abdominal segment height (X11), tail segment length (X12), and tail fan length (X13) were measured to explore the relationship between the morphological traits and body weight (Y) of Trachypenaeus curvirostirs. The relationship between the traits was studied using path analysis and gray correlation analysis. The results showed that the biological indicators values of females were greater than those of males. There was a highly significant positive correlation between the traits of females and males (P<0.01), and the correlation coefficients of X2 to Y were the highest (0.972 and 0.969, respectively). Path analysis and determination coefficient analysis showed that X2 had the highest direct effect (path coefficients: 0.443 and 0.519, respectively) and direct determination coefficient on Y for the females and males, X7 (sum of indirect determination coefficients = 0.750) and X12 (0.887) had the highest indirect effect on Y for the females and males respectively. The co-determination coefficient of X2 and X5 was the highest (0.167) for the females, while that of X1 and X2 was the highest (0.248) for the males. The stepwise regression method was used to establish multiple regression equations for morphological traits and Y in both female and male populations. The equations were Y1＝–14.563+0.133X2+0.374X7+0.282X5+0.225X13 (R2=0.978) and Y2＝–7.947+0.092X2+0.309X4+0.203X10+0.036X1–0.087X12 (R2=0.980), respectively. The average correlation coefficient of morphological traits to Y for females was between 0.868 and 0.941, and that of the males was between 0.793 and 0.906. For the same morphological traits, the average value of the correlation coefficient and Y for the females was greater than that of the males. The correlation degree was the highest between X2 and Y for the males and females. The results of the path analysis and gray correlation analysis were not exactly the same. A comprehensive comparative analysis showed that during T. curvirostirs breeding, X2 can be used as the main selective trait for males and females. X5 and X7, X4 and X1 can be used as assisted selective traits for females and males, respectively.

Abstract:The ridgetail white prawn Exopalaemon carinicauda belongs to the suborder Pleocyemata, in the family Palaemonidae, and is one of the most economically important pond-reared shrimp. At present, most of the egg-carrying broodstock are harvested from natural sea areas, which considerably restricts the development of E. carinicauda aquaculture. Thus, artificial propagation methods are required to enhance the productivity of E. carinicauda in aquaculture systems. To develop these systems, there is a need for a greater knowledge base encompassing the mechanism of ovarian and embryonic development of E. carinicauda. Ubiquitin C-terminal hydrolases (UCHLs) are a subset of deubiquitinating enzymes that are involved in numerous physiological processes. Many studies have shown that the UCH family of deubiquitinating enzymes plays an important role in reproduction. In this experiment, the full-length cDNA of UCHL5 was identified and characterized using an approach that combines transcriptome data and rapid amplification of cDNA ends (RACE). The expression profile of UCHL5 in different developmental stages of the ovary and various tissues was determined using real-time quantitative PCR. The pET32a-UCHL5 prokaryotic expression recombinant plasmid was constructed and induction expression was carried out. The cloned UCHL5 gene was 1440 bp in length, encoding 329 amino acids. Isoelectric point (pI) of UCHL5 protein was 5.51, and molecular weight was 37.57 kDa Homology and phylogenetic analysis showed that the deduced amino acid sequence of UCHL5 shared high homology in different species and the highest conservation with Litopenaeus vannamei (83%). Real-time quantitative PCR results indicated that the expression quantity of UCHL5 was the highest in the gill tissue of E. carinicauda, followed by that in the ovary. The expression quantities of UCHL5 at different ovary developmental stages (Ⅰ~Ⅳ) were progressively upregulated, and the expression of UCHL5 was the lowest in stageⅤ. The fusion protein UCHL5 obtained through prokaryotic expression was 52 kDa. From the results of this study, we may conclude that UCHL5 is possibly playing an important role in the ovarian development of E. carinicauda.

Abstract:Chlorella pyrenoidosa is widely used in aquaculture as a living food, water adjusting agent, and functional feed additive. It is thus important to study the methods of effectively maintaining cell activity and nutritional quality, and extending shelf life in the concentrated products of C. pyrenoidosa. At present, the commonly used preservation method for microalgae is cryopreservation. In this study, we used concentrated algal paste (8×1010 cells/mL) and concentrated algal fluid (1×108 cells/mL) of C. pyrenoidosa prepared by centrifugation and resuspension as the research objects, and systematically evaluated the effects of pasteurization and temperature (25℃ and 4℃) on the relative cell activity and nutrient retention rates under short-term storage without light exposure. Our results showed that pasteurization treatment caused the browning of both C. pyrenoidosa concentrates, and storage at room temperature accelerated the decay of concentrated products. Thus, the concentrated products could be stored directly at a low temperature of 4℃ for 15 days without pasteurization treatment. The total chlorophyll, carotenoids, and protein content in the concentrated C. pyrenoidosa paste reached 97.20%, 100.00%, and 98.20% of the levels before preservation, respectively; in the concentrated C. pyrenoidosa fluid all levels were 100.00% of those before preservation. This study also established the optimal conditions of the fluorescent probe method for cell viability detection: cell density of 2.6×105 cells/mL, working concentration of 60 μmol/L of fluorescein diacetate, and staining time of 30 min. The results indicated that the relative cell viability of the concentrated C. pyrenoidosa paste and fluid directly stored at 4℃ were 48.26% and 61.36%, respectively, before preservation. The cryopreservation technology established in this study for the concentrated products of C. pyrenoidosa provides a critical technology support for the downstream aquaculture applications of fresh concentrated products of microalgae.

Abstract:The breeding of snails is indispensable in Guangxi agriculture. The snail powder industry in Liuzhou City, Guangxi, reaches 8 billion yuan per year. With the improvement of living standards, people's demand for aquatic products is increasing, and their nutritional and safety requirements are becoming more stringent. In order to analyze the nutrient content of the muscles of Cipangopaludina cathayensis and the pollution of heavy metals, we tested the muscle content of conventional nutrients, amino acids, fatty acids, and some heavy metals in C. cathayensis snails from Luchuan County, Yulin, Guangxi. The amino acid score (AAS) and chemical score (CS) were used to evaluate muscle amino acid levels, while the single factor pollution index (I), comprehensive pollution index (P), and target risk factor (THQ) were used to evaluate safety. The results showed that the crude protein, moisture, crude fat, and crude ash content of C. cathayensis were 13.89%, 76.52%, 0.57%, and 5.21%, respectively; 16 amino acids were detected in the muscle; the total amount was 106.2 mg/g, including 8 human essential amino acids, accounting for 36.8% of the mass; the essential amino acid index (EAAI) was 248.2, and delicious amino acids accounted for 48.2%. A total of 19 fatty acids were detected, including 8 saturated fatty acids (SFA), accounting for 43.8%, and 11 unsaturated fatty acids, accounting for 56.2%. The EPA+DHA content reached 9.77%, and the atherosclerosis index (IA) and thrombosis index (IT) were 0.08 and 0.12, respectively. The contents of lead, cadmium, chromium, and copper in the muscle were 0.897, 0.0055, 0.214, and 4.62 mg/kg, respectively, all of which met the national health standards. The pollution index for lead was 0.897, while that for all others were below 0.15. The comprehensive pollution index was 0.66, which is relatively clean. The THQ evaluation results show that copper has the lowest risk, and lead has the highest risk. The total hazard coefficient (TTHQ) of a single heavy metal THQ and compound heavy metal was less than 0.3. In summary, C. cathayensis has high protein and low fat content, is rich in EPA and DHA, with no risk of heavy metal exposure, and has high nutritional and aquaculture development value. This study explored the nutritional value and safety of C. cathayensis and could therefore, provide some reference for the rational development and utilization of C. cathayensis resources in China.

Abstract:To determine the nutritional value of three different sizes of Ammodytes personatus, basic nutrient, amino acid, fatty acid, and inorganic element composition were systematically analyzed. The results showed that the lower the weight of A. personatus, the higher the content of moisture, ash, and crude protein and the lower the content of crude fat. Glutamate, aspartate, lysine, and leucine were the most abundant among the 17 kinds of alternative amino acids in A. personatus. The lower the sample weight, the higher the total amount of hydrolyzed and essential amino acids. According to the result of amino acid scoring (AAS) analysis, the first limiting amino acid of A. personatus was valine, and the second limiting amino acid was isoleucine. According to the result of chemistry scoring (CS) analysis, the first limiting amino acids were sulfur-containing amino acids (Met+Cys), and the second limiting amino acid was valine; the essential amino acid indices were 90.75, 85.74, and 86.04, respectively. The fatty acid compositions of the samples with different specifications were significantly different. According to the three samples of small, medium and large weight, saturated fatty acid contents were 41.71 mg/g, 60.68 mg/g, and 69.31 mg/g respectively; monounsaturated fatty acid contents were 31.81 mg/g, 65.03 mg/g, and 103.91 mg/g respectively; and polyunsaturated fatty acids (PUFA) contents were 83.17 mg/g, 110.71 mg/g, and 109.39 mg/g respectively. The larger the specification, the higher the proportion of eicosapentaenoic acid and the lower the proportion of docosahexaenoic acid in PUFA. A. personatus was found to be rich in a variety of inorganic elements needed by the human body; the contents of Na and K were the highest among the major elements, and the contents of Fe and Zn were the highest among the trace elements. This study have shown that A. personatus is a high-quality fish with high nutritional value and delicious taste.