Fishes, Volume 9, Issue 4 (April 2024) – 39 articles

Aquaculture’s role in addressing food security has grown, with a spotlight on Asian carp species. Polyculture, i.e. cultivating multiple fish species in a single system, is being increasingly adopted for its resource efficiency and economic benefits. This practice for Asian fish for food and ornamental purposes is gaining traction in Europe despite their invasive potential. Rising temperatures due to climate change offer an opportunity for thermophilic Asian carps (Hypophthalmichthys molitrix and Aristichthys nobilis). Using GIS modeling (Maxent), we identified the possible settlement of Asian carp in Northern Europe amidst climate change. We analyzed carp global distribution centers, assessed the potential carp spread in Europe, and evaluated their potential suitability for polyculture systems. By 2050, H. molitrix may extend its range to 58–62° N latitude, with a potential 1.7-fold habitat increase, while A. nobilis, which are more heat-tolerant, may move north to 52–58° N latitude, with a 1.3-fold potential increase. Despite the slight ecological differences in their native habitats, niche modeling indicates that these carp can occupy similar niches in Europe (proven statistically). The eventuality of using Asian species for polyculture in Europe presents both opportunities and challenges in the face of a changing climate as long as invasion risks are prevented. Envisaging such polyculture, yet very carefully for the protection of ecosystems, can help food security. Full article

The diverse freshwater fish fauna of the Japanese archipelago is distributed among four main island landmasses, which include Hokkaido in the north, with many diadromous species. One relatively well-preserved river drainage along the southern coast of Central Hokkaido is the Mukawa River. Fish fauna surveys in the Mukawa River were mostly in downstream areas and the fish diversity is not well-documented among the upper, lower river, and coastal environments. Fish communities in the river, estuary, and sea were sampled using eDNA analysis to evaluate upstream and downstream species detections, and tidal and spatial detection variation near the river mouth. The number of species was higher at the river mouth and nearshore sites compared to the river and offshore. Fish detections reflected life history categories (freshwater resident, diadromous, brackish, or marine) and the environments. Similarity analysis showed that fish species compositions were divided into (1) upstream and midstream, (2) downstream and river mouth, (3) adjacent shore, and (4) offshore. Salmonid, cyprinid, loach, and sculpin species were detected in the river, compared to a mixture of species downstream and along the coast. This rapid assessment type study demonstrated that eDNA survey methodology would be effective for multiple river comparative surveys, seasonality studies, or evaluating possible effects of cross-river weirs or dams. Full article

Global marine fish harvests have reached a plateau over the last decade, and efforts to increase aquaculture tend to face limitations in terms of water resources and contamination problems. Of the current fish harvest, at least 50% is discarded as waste. The current situation requires efforts to process, preserve, and utilize the fish capture to minimize waste. Chemical and microbiological contamination limit the utilization of harvested fish. There is a need to improve fish preservation to minimize spoilage and to process them into more appealing products. Instead of resorting to individual food-processing methods, the efficiency of processing could best be increased by a combination of conventional and modern processing methods or by combinations of modern processing methods. Fish waste is a rich source of oils containing essential fatty acids, polypeptides, and amino polysaccharides that could be utilized through the upscaling of current scientifically proven methods to new processing technologies. The separation of collagens, gelatins, bioactive peptides, edible fish oils, and chitosan form the primary stages in the utilization of fish waste. The products need purification to meet food quality and safety standards and to have desirable industrial characteristics. The diversity of information and products generated through new methods require advanced data handling and prediction systems, such as artificial intelligence, to address food safety and to derive the best out of fish processing and utilization. Full article

One way to approach the nutritional requirements of native shrimp, necessary to consolidate their culture, is to know their biochemical composition. The effect of feeding two levels of lipids (4 and 12% L) and four levels of proteins (30, 35, 40 and 45% P) in M. tenellum females was evaluated with respect to the biochemical composition of their eggs (EG), larvae (LR), gonad (GO) and hepatopancreas (HP). Total protein (TP), total carbohydrate (TC) and total lipid (TL) were estimated. In EG, L and P levels influence TP and TL; TP increases in diets higher than P35. In LR, there are no differences (p > 0.05) in TP and in TL, only diets L4P40 and L12P30 were different (p < 0.05). In GO, there is no trend in TP differences; in TC there was variation in the range of the data and TL was higher in L4P30 and L4P35. In HP, the diets with L4 obtained the highest TP values (p < 0.05); the L12 diets were higher in TL (p < 0.05). In general, diets with an inclusion of L12 showed the highest TP, TC and TL means, within this lipid level the P30 diet stood out; therefore, it is recommended to use a diet with L12P30 in the formulation of balanced feed for the species. Full article

The Chinese mitten crab (CMC) also known as Eriocheir sinensis has great significance in the aquaculture industry. The bacterial communities inhabiting the CMC’s gut may differ depending on the host habitat and can aid in their normal biological functioning. These microbes are also known to have certain effects on their flavor. In this study, we utilized MiSeq high-throughput sequencing technology to explore the diversity of bacterial communities in the gut of CMCs from three different geographical locations in Korea: the Geum (GD), Han (HD), and Tamjin (TD) rivers. Although most of the environmental parameters were similar at the three sites, significant differences in conductivity (CDS), dissolved oxygen (DO), and salinity were observed. The results show that CMCs sampled from these locations exhibited distinct microbial composition and abundance. For example, the genus Candidatus Hepatoplasma displayed significantly higher abundance in CMCs from HD than those in the other locations, suggesting nutritional stress. Similarly, the crabs collected from TD showed a higher abundance of pathogenic Helicobacter than those from HD and GD sites. We also observed differences in the amino acid, nucleotide, and lactic acid concentrations between different tissues such as the muscle, hepatopancreas, and testis of CMCs. However, only small differences were observed when these characteristics were compared in CMCs from different locations. Our results offer important insights into the intestinal bacterial composition in CMCs which in turn may help in designing better culturing strategies for these important species of crabs. Full article

Fish health is of significant ecological and economic importance. In response to public observations of parasite-like structures in a popular edible fish, this study aimed to characterize nematode larvae commonly found in the muscle and body cavity of Saurida tumbil (Bloch, 1795), a commercially important fish species inhabiting the Persian Gulf and Oman Sea. This fish, locally known as Hasoom, holds substantial culinary importance, being a staple in the diets of millions residing in countries around the Persian Gulf. A total of 458 Saurida tumbil specimens were obtained from fish markets between June 2022 and May 2023. Subsequent examination revealed the presence of a total of 6132 nematode larvae. Nematodes found in the body cavity were identified as belonging to the genus Hysterothylacium sp., family Raphidascarididae, while those in the muscle were identified as Anisakis sp. larval type, family Anisakidae. Histopathology results suggested that these parasites may have adverse health impacts on their fish host. Notably, both nematode genera were found in the third larval stage, which is known to be the infective stage for anisakidosis. Given the reported cases of anisakidosis among people living in the study region, it is strongly recommended that fish be properly cooked before consumption to mitigate health risks. Full article

Changes in the number, structure, and function of mitochondria during the early life stages of animals can play an important role for an organism’s metabolic rate, growth, and health. Previous studies have shown that juvenile brown trout (Salmo trutta) subjected to elevated temperatures during the embryonic stage respond phenotypically with a reduced metabolic rate. The aim of this study was to explore if embryonic temperature affects the mitochondria content of young brown trout and as such explains the previously found differences in metabolic rates. Here, we optimize a quantitative PCR (qPCR) method for the mitochondria cytochrome c oxidase subunit I gene, and then use the method as a proxy for mitochondrial DNA content. We hypothesize that young trout subjected to elevated temperatures during the embryonic stage respond phenotypically with a reduced mitochondrial DNA content. To test this hypothesis, we subjected brown trout to either control ambient (4.4 ± 1.5 °C) or elevated temperatures (7.1 ± 0.6 °C) during embryogenesis. Subsequently, we extracted DNA from liver and white muscle tissue of juvenile brown trout from the two different incubation temperature treatments and successively optimized qPCR for mitochondrial DNA. We found that the amount of mitochondria DNA in liver tissue was 18 times higher than in white muscle tissue, but there was no significant difference in mitochondria content in liver or muscle tissue between brown trout exposed to elevated and ambient control temperatures during embryogenesis. We conclude that reduced metabolic rate is not likely associated with mitochondria DNA content. We also suggest that qPCR is a simple and cost-effective method to quantify mitochondria DNA in frozen and partly degraded tissue from different treatment groups and a useful proxy for identification of differences in mitochondria number. Full article

In order to study the muscle quality of different crustaceans, we aim to provide a comprehensive assessment of their muscle quality characteristics as a theoretical reference. In this work, seven major species of farmed and consumer crustaceans were selected, including crayfish (Procambarus clarkii), freshwater prawns (Macrobrachium rosenbergii), pacific white shrimp (Litopenaeus vannamei), black tiger shrimp (Penaeus monodon), kuruma prawns (Penaeus japonicus), river prawns (Macrobranchium nipponense), and Chinese shrimp (Penaeus chinensis). Their morphometric parameters, nutritional composition, textural properties, and physical and chemical indexes were comparatively analyzed. The results showed that the meat content (MC, about 14.78%) of crayfish was significantly lower than that of the other six species. By contrast, pacific white shrimp had the highest MC, although the MCs of black tiger shrimp, kuruma prawns, and Chinese shrimp are greater than 40%. All seven crustacean species were high in protein and low in fat, while pacific white shrimp had the highest crude protein, crude lipid, and crude ash content compared to the other crustaceans. The content of threonine (Thr) was the highest in crayfish. The content of methionine (Met) and lysine (Lys) was the highest in freshwater prawns. The content of isoleucine (Ile), leucine (Leu), and non–essential amino acid (NEAA) was the highest in pacific white shrimp. C18:2n-6 (linoleic acid, LA) was the highest in freshwater prawns and pacific white shrimp; C18:3n-3 (linolenic acid, LNA), C20:4n-6 (arachidonic acid, AA), unsaturated fatty acids (UFA), and monounsaturated fatty acids (MUFA) were all the highest in crayfish; and polyunsaturated fatty acids (PUFA) was the highest in freshwater prawns, but the content was not significantly different from crayfish, pacific white shrimp, black tiger shrimp, and Chinese shrimp. Pacific white shrimp had the highest values for hardness, cohesiveness, gumminess, and chewiness. The redness values of crayfish, black tiger shrimp, and Chinese shrimp were significantly higher than those of the other three species except kuruma prawns. Compared to other crustaceans, river prawns had the highest drip loss and cooking loss. Black tiger shrimp and Chinese shrimp had the lowest cooking loss rates. The research shows that the tail muscle of the seven species of crustaceans is rich in protein, essential amino acids, unsaturated fatty acids and low in fat, representing a high-quality protein. Among these crustaceans, the main essential amino acids and essential fatty acids in the tail muscle of pacific white shrimp, freshwater prawns, and crayfish are higher in content and better in nutritional value. Full article

Green terror cichlid (Aequidens rivulatus) is a popular tropical freshwater ornamental fish. In 2021, an unknown disease was observed in cultured A. rivulatus in Tianjin, China, with a cumulative mortality rate of 25% within 7 days of onset. The main clinical signs were scale loss, skin ulceration, and slight bleeding. Histopathological observation revealed obvious damage to the liver, spleen, and kidney of diseased fish. In addition, abundant granulomas were observed in the spleen and head kidney of the diseased fish. To define the potential pathogens from A. rivulatus, bacteria were isolated from the visceral tissue of diseased fish with conventional methods. An artificial infection experiment was carried out to prove the pathogenicity of the isolated bacteria. The strains HG-2021-1 and HG-2021-3 were isolated from diseased fish and identified as being responsible for the disease. They were identified as Streptococcus iniae based on physiological and biochemical tests, lctO gene detection, and 16S rRNA gene sequence analysis. According to the result of multilocus sequence typing (MLST), HG-2021-1 and HG-2021-3 belong to different genotypes of S. iniae. Furthermore, they were found to contain the virulence genes pgmA, scpI, cpsD, and pdi, and the median lethal dose (LD₅₀) for A. rivulatus was 1.8 × 10⁶ Colony-Forming Units (CFU)/mL and 6.6 × 10⁶ CFU/mL, respectively. To our knowledge, this is the first report of fish coinfected by two genotypes of S. iniae. Full article

Natural food available in ponds can complement formulated feed in fed aquaculture. This study elucidated the natural food intake and its contribution to tambaqui (Colossoma macropomum) growth in fertilized and unfertilized ponds, using stable isotope and stomach contents analyses. Additionally, it described the impact of fertilization management on natural food availability, fish performance, and production costs. Tambaqui juveniles (93.8 ± 15.0 g) were stocked (0.55 fish/m²) in fertilized (Fert) and unfertilized (NoFert) ponds (600 m²) for a culture period of 10 months in quadruplicate. A lower food conversion ratio was observed in Fert ponds. The main natural food items ingested by tambaqui were insects, vegetables, and cladocerans. Plankton contributed 39.4% and 10.7% of muscle formation in Fert and NoFert ponds, respectively. Pond fertilization (2.45 g of nitrogen and 0.80 g of phosphorus per square meter every two weeks) did not significantly affect fish growth, survival, or productivity but had a slightly influence on water quality parameters. However, fertilization increased the zooplankton density (through phytoplankton) in the water, thereby increasing autochthonous food availability for tambaqui consumption. This species demonstrates the ability to alternate between natural food sources and commercial feed without compromising its development. Consequently, tambaqui exhibits suitability for farming within restorative and integrated aquaculture systems as well as intensive systems reliant on commercial feed. Full article

An 8-week feeding experiment aimed to investigate the effects of fermented soybean residue in diets on the growth performance, serum antioxidant parameters, intestinal digestive capacity, and microbial composition of the hindgut of Furong crucian carp. The feeds were formulated to contain 0%, 6%, 12%, 18%, and 24% fermented soybean residue (CON, FSR6, FSR12, FSR18, and FSR24, respectively), respectively, to form five diets (crude protein: 33%; crude lipid: 5%). The results showed that incorporating 6% fermented soybean residue into the diet significantly increased the weight gain rate (WGR) and specific growth rate (SGR) and decreased the feed coefficient rate (p < 0.05). Through regression analysis of WGR and SGR, the optimal levels of the dietary fermented soybean residue of Furong crucian carp were determined to be 6.78% and 7.06%. Incorporating fermented soybean residue into the diet decreased the lipid content of the whole body and the levels of glucose, total cholesterol, and triglyceride in the serum of Furong crucian carp. The inclusion of 6% and 12% fermented soybean residue in the diet markedly increased the antioxidant capacity, intestinal amylase activity, and intestinal villous height of Furong crucian carp (p < 0.05). At the 6% level, fermented soybean residue significantly increased the abundance of Romboutsia and Clostridium_sensu_stricto_1 while significantly decreasing the abundance of Vibrio (p < 0.05), indicating that a 6% level of fermented soybean residue was beneficial for intestinal health. In conclusion, incorporating 6–7% fermented soybean residue into the diet of Furong crucian carp was recommended. Full article

While benthic characteristics of coral reef habitats are a major driver of the structure of coral reef fish assemblages, non-reef habitats adjacent to coral reefs (e.g., mangroves, seagrass beds, and macroalgal beds) can affect reef fish assemblages. Here, we investigate how reef fish assemblages respond to local-scale benthic habitats within a coral reef and larger-scale adjacent seascape features (habitats within 500 m of coral reefs) on Siquijor Island in the Philippines. We examined an abundance of species for the entire reef fish assemblage and within the assemblages of parrotfishes (subfamily Scarinae) and wrasses (family Labridae). Five distinct habitat types were identified in a cluster analysis, which incorporated benthic characteristics within coral reefs and habitats adjacent to coral reefs. We found that the diversity and structure of coral reef fish assemblages were affected by benthic characteristics within coral reefs and also by benthic habitat types adjacent to coral reefs. Individual species responses and juveniles of certain species demonstrated uniquely high abundances in habitat clusters characterized by the non-reef habitats surrounding coral reefs. Considering coral reef habitats and adjacent non-reef habitats as a holistic, interconnected seascape will provide better estimations of the drivers of the structures of coral reef fish assemblages. Full article

The southern red snapper, Lutjanus purpureus, is one of the primary fishery resources of the Amazon continental shelf. Due to the demand for specimens of less than 900 g in weight, increased fishing effort focusing on this size class has led to a drastic decrease in catches. The present study was based on the analysis of cellular structures in the female gonads (formation of oocytes and other reproductive tissues) to identify reproductive processes and evaluate the effectiveness of current fishery management practices. The presence of postovulatory follicles (POFs) peaked in April, which was interpreted as a period of intense spawning. In addition to POFs, hydrated oocytes peaked in July, indicating either reproductive continuity or a second peak, based on the presence of atretic oocytes and atresia. Given that the local snapper fishery preferentially targets very young individuals, an extension of the closed season from March to July would be recommendable to guarantee the reproductive potential of the spawning stock. Full article

Ascidian biofouling generates significant challenges to bivalve aquaculture. Their rapid spread across almost every available surface leads to increased maintenance costs and reduced yields in shellfish farming. In addition, ascidians may introduce pathogens or toxins, further compromising the health and marketability of bivalve stocks and thereby necessitating strict management strategies to manage these impacts. The aim of this study was the evaluation of different management practices for eliminating ascidian fouling and the identification of the best method for Mytilus galloprovincialis (Lamarck, 1819) aquaculture farms. The effects of different anti-fouling treatments as well as their interactive outcomes were examined by conducting two experiments. Various experimental procedures were applied, including the temporally differential washing of mussels, air exposure and immersion in 50 ppt and 70 ppt salinity solutions, as well as the combination of these applications. All treatments reduced the number of ascidian colonies on mussel socks but at varying proportions. Immersing mussel socks in a 70 ppt salinity solution followed by air exposure for 1 day was the most efficient method and led to a 93% eradication. Full article

Shrimp feed formulations have moved towards less fish meal and more of the readily available and cheaper plant proteins. To counteract the lower attractiveness and palatability of plant proteins, feeds are supplemented with ingredients known to have chemoattractive properties that will increase feed intake. This study investigated the putative chemoattractive effect of Calanus finmarchicus hydrolysate, when used as a dietary supplement in shrimp feeds. C. finmarchicus is a zooplankton species native to the northern Atlantic Ocean and is a novel and sustainable raw material for shrimp feed products. Diet attractiveness was evaluated in a 24-day feeding trial with whiteleg shrimp (Litopenaeus vannamei) by measuring the intake of 12 diets with various levels of fish meal, calanus hydrolysate, and krill (Euphausia superba) meal. Higher inclusion rates of both ingredients resulted in increased feed intake, and supplementing the high fish meal diet with calanus hydrolysate gave a statistically significant higher feed intake. Low molecular weight peptides, chemoattractive amino acids, and the water-soluble nature of the hydrolysate could explain the chemoattractive properties observed in the study. Full article

The accurate labeling of species and size of specimens plays a pivotal role in fish auctions conducted at fishing ports. These labels, among other relevant information, serve as determinants of the objectivity of the auction preparation process, underscoring the indispensable nature of a reliable labeling system. Historically, this task has relied on manual processes, rendering it vulnerable to subjective interpretations by the involved personnel, therefore compromising the value of the merchandise. Consequently, the digitization and implementation of an automated labeling system are proposed as a viable solution to this ongoing challenge. This study presents an automatic system for labeling species and size, leveraging pre-trained convolutional neural networks. Specifically, the performance of VGG16, EfficientNetV2L, Xception, and ResNet152V2 networks is thoroughly examined, incorporating data augmentation techniques and fine-tuning strategies. The experimental findings demonstrate that for species classification, the EfficientNetV2L network excels as the most proficient model, achieving an average F-Score of 0.932 in its automatic mode and an average F-Score of 0.976 in its semi-automatic mode. Concerning size classification, a semi-automatic model is introduced, where the Xception network emerges as the superior model, achieving an average F-Score of 0.949. Full article

This study evaluated the disparities in growth performance and nutritional composition between two common Chinese mitten crab varieties, “Jianghai 21” and “Changjiang 2”, cultured in Jiangxi Province. Over the breeding period, parameters such as body weight, height, carapace length and width, and lengths of the second and third legs exhibited increases. Growth indices of “Jianghai 21” surpassed those of “Changjiang 2” during the intermediate and late breeding phases. While “Changjiang 2” demonstrated significantly higher crude lipid content than “Jianghai 21”, the latter exhibited markedly higher levels of total amino acids (TAAs), essential amino acids (EAAs), and delectable amino acids. Although overall nutrient composition did not significantly differ, TAA and EAA contents in the hepatopancreas were notably greater in “Jianghai 21” than in “Changjiang 2”. Moreover, a total of 901 differentially expressed genes (DEGs) were identified between the two varieties, with 560 upregulated and 341 downregulated. These DEGs were primarily associated with pathways related to fatty acid degradation, metabolism, and growth regulation. The observed variances in growth performance and nutrient composition between “Jianghai 21” and “Changjiang 2” suggest potential regulation by relevant genes. In summary, the results showed that the growth performance of “Jianghai 21” is greater than that of “Changjiang 2”, offering valuable insights for the selection of aquaculture varieties in the region. Full article

The Aeromonas salmonicida is responsible for causing furunculosis in various fish species. Furunculosis is a ubiquitous disease that affects the aquaculture industry and causes the mass mortality of turbot. Vibrio vulnificus is a pathogen that causes skin ulcers and hemorrhagic septicemia in fish, resulting in significant mortality in aquaculture. In this study, we have established a bivalent inactivated vaccine against A. salmonicida and V. vulnificus with Montanide™ ISA 763 AVG as an adjuvant. This bivalent inactivated vaccine was used to immunize turbot by intraperitoneal injection, and the relevant immune indexes were detected. The results demonstrate that the bivalent inactivated vaccine exhibited a relative percent survival (RPS) of 77% following A. salmonicida and V. vulnificus intraperitoneal challenge. The vaccinated group exhibited higher levels of acid phosphatase activity and lysozyme activity compared to the control group. ELISA results showed a significant increase in serum antibody levels in immunized turbot, which was positively correlated with immunity. In the kidney tissue, related immune genes (TLR5, CD4, MHCI and MHCII) were up-regulated significantly, showing that the vaccine can induce cellular and humoral immune responses in turbot. In conclusion, the bivalent inactivated vaccine against A. salmonicida and V. vulnificus was immunogenic, efficiently preventing turbot from infection, which has the potential to be applied in aquaculture. Full article

This article proposes a mechanism that triggers first maturation and spawning in coral reef (bony) fish, which allows for predicting their length at first maturity. Thus, mean lengths at first maturity (L_m) and the corresponding maximum lengths (L_max) in 207 populations of 131 species of coral reef fish were assembled and used to test the hypotheses that (a) there is, in coral reef fish, a single value of a size-related parameter acting as a trigger for their maturation and eventual spawning, and (b) that this single value is statistically the same as that published previously for other bony fish. The results, based on the assembled L_m and L_max data and on estimates of the parameter D, which link the length of fish with the relative surface of their gills, covered 44 families and L_max values ranging from 1.8 to 181.6 cm and confirmed that the threshold in (a) exists. Also, we assessed (in b) that this threshold value, i.e., L_max^D/L_m^D = 1.35 (±0.02), is not statistically different from similar estimates for other groups of teleosts, notably semelparous salmonids, cichlids, sturgeons and Chinese and Turkish freshwater and marine fish. One implication is that given ocean warming and deoxygenation, coral reef fish will not only be smaller than they currently are, but also mature and spawn at smaller sizes, and thus produce fewer, smaller eggs. Full article

Vitamin C (VC) can be used to increase disease resistance in practice in intensive aquaculture. But it is still unconfirmed whether VC could alleviate inflammation and what dosage is suitable. This study investigated the effects of dietary VC on the immunity and enteritis of juvenile blunt snout bream (Megalobrama amblycephala) challenged with Aeromonas hydrophila. The fish were fed with VC levels ranging from 25.35 to 2231.98 mg/kg for 60 days. After that, fish fed with 150.65 mg/kg, 573.79 mg/kg, and 2231.98 mg/kg VC were challenged with A. hydrophila orally to simulate enteritis. The results showed that 285.39 and 573.79 mg/kg dietary VC significant improved growth performance and feed utilization. Dietary VC (573.79 and 1133.79 mg/kg) significantly enhanced the serum immune parameters, antioxidant enzymes’ activities, and relative gene expressions of ikbα and cat in the liver in the 60-day feeding trail. The survival rate was significantly higher in 573.79 mg/kg dietary VC group than the other two treatments. Cytokines were activated after the bacteria challenge. Dietary 573.79 mg/kg VC caused significantly higher TNF-α level at 12 hpi and maintained a high level of IL-8 at 48 to 72 h compared to other treatments. In conclusion, more than 500 mg/kg VC was needed to maintain the health of blunt snout bream juveniles. Suitable VC would activate cytokines to increase disease resistance along with antioxidant enzymes. Full article

This study aimed to evaluate the growth, mortality parameters, and exploitation rate of Pontic shad, Alosa immaculata Benett, 1835, in the Danube River, Romania (km 169–197). The sampling collection started with the first signs of Pontic shad migration, on 4 March 2023, and continued weekly until the beginning of June 2023, when the last specimens were caught in the nets. The estimation of the growth, mortality parameters, and exploitation rate was done in FiSAT (FAO-ICLARM Stock Assessment Tools). The von Bertalanffy growth equation was estimated at L_∞ = 36.75 cm, the growth coefficient was k = 0.68 year⁻¹, and the theoretical initial age was t₀ = −0.67 year⁻¹. The total mortality rate (Z) estimated was 2.76 year⁻¹, with a natural mortality rate (M) and fishing mortality rate (F) of 0.89 year⁻¹ and 1.87 year⁻¹, respectively. The Z/k ratio was found to be 4.11 and the exploitation rate (E) was estimated at 0.68 year⁻¹, indicating the overexploitation of Alosa immaculata stocks. In conclusion, this study provides valuable insights into the population dynamics of Pontic shad in the Danube River, Romania. The assessments of the growth parameters, mortality rates, and exploitation rates highlight a level of overexploitation of Alosa immaculata stocks. These findings underscore the importance of applying effective fishery management strategies to ensure the sustainability and conservation of this valuable fish species in the Danube River ecosystem. Full article

The objective of this study was to assess the impact of concentrated cottonseed protein (CPC) as a substitute for fishmeal (FM) in juvenile hybrid culter (Erythroculter ilishaeformis ♀ × Ancherythroculter nigrocauda ♂). A total of 360 fish with an initial body weight of 10.0 ± 0.5 g were randomly allocated into 12 indoor culture tanks, with each tank containing 30 fish. Four diets were formulated in which fish meal (FM) was replaced by CPC at different inclusion levels: 0% (T0), 15% (T15), 30% (T30), and 45% (T45). The corresponding amounts of CPC included were 0, 61, 122, and 182 g/kg, respectively. At the end of the 10-week feeding trial, the findings revealed an inverse correlation between the proportion of CPC replacing FM and both final body weight (FBW) and weight growth rate (WG) in hybrid culter. Specifically, the T30 and T45 groups exhibited significantly lower FBW and WG compared to the T0 group (p < 0.05). No significant differences in crude protein and ash contents were observed among all groups (p > 0.05). However, the crude lipid content was highest in hybrid culter fed the T45 diet and lowest in the T0 group (p < 0.05). There were no significant differences in muscle amino acid composition among all treatment groups (p > 0.05). The contents of total protein (TP) and albumin (ALB) declined slightly as the proportion of FM substituted by CPC increased, yet this decline did not reach statistical significance (p > 0.05). Serum alanine aminotransferase (ALT) activity elevated with increasing dietary CPC, and the T45 group exhibited significantly higher ALT activity compared to the T0 group (p < 0.05). The hepatic activities of superoxide dismutase (SOD) and catalase (CAT) were significantly lower in the T45 group than in the T0 and T15 groups (p < 0.05). Furthermore, there was a decrease in intestinal villi length with an increasing replacement ratio of FM by CPC, and the villi length in the T45 group exhibited a significant reduction when compared to that in the T0 group (p < 0.05). It is concluded that replacing 15% FM with CPC does not exert obviously detrimental effects on growth performance, serum biochemical indices, intestinal morphology, muscle amino acid profile, or antioxidant performance of juvenile hybrid culter. Full article

Already a multibillion-dollar global industry, shrimp aquaculture, is growing all the time. The intensive method, which is the most common method in shrimp aquaculture, remains commercially challenged due to the expenditures associated with environmental pollution abatement. Although the comprehensive understanding of this intricate aquaculture environment has been advanced using mathematical modeling, recent attempts to improve the model’s structure have not yielded enough results. This work upgraded the previous method to a three-dimensional hydrodynamic ecosystem model with the effects of shrimps being replaced by approximation equations for the environmental assessment of a shrimp aquaculture pond in Kyushu District, Japan. Our approach was successful, as demonstrated by the high consistency of the simulation results when compared to observation data and the previous results. Additionally, we first revealed the impacts of stratification and confirmed the notable daily variation in the water quality. Our case study offers significant practical information on the characteristics of intensive shrimp aquaculture, implications for long-term sustainable operations, and future research priorities on local-scale ecosystem modeling. Full article

Natural environmental change, anthropogenic development, and inter-annual variability can affect the ecology of estuarine fish and invertebrates. Yaquina Bay, Oregon, a well-studied estuary, has undergone intense development, as well as deep-draft dredging during the latter half of the 20th century, resulting in the alteration of ~45% of the lower estuary’s natural shoreline. In 1967, the United States Environmental Protection Agency (USEPA) conducted a 21-month survey of Yaquina Bay to characterize the demersal fishes and epibenthic crustaceans that occupy the bay. From 2003 to 2005, we conducted a 25-month survey to replicate that work and provide a comparative snapshot of the demersal fish and epibenthic crustacean community in the bay. A comparison of the trawl survey datasets reveals a 91% decline in total catch per unit effort (CPUE) between surveys, as well as a decline in multiple measures of biodiversity. Furthermore, the fishes and crustaceans of Yaquina Bay have experienced a shift in species dominance from demersal fishes in the late 1960s to epibenthic crustaceans in the 2000s, marked most notably by a nine-fold increase in the Dungeness crab CPUE. While this work does not establish a causal relationship between changes in the demersal communities of this West Coast estuary and human or natural events, it does document substantial changes in both the diversity and total abundance of animals in that community over a three-plus decade period of development and environmental variability. Hence, this forms a second baseline for continued long-term monitoring. Full article

Japanese anchovy (Engraulis japonicus) is a small pelagic fish with commercial and ecological importance. In spite of its importance, in recent years, specific research on anchovy in the Shandong Peninsula area has been relatively scarce and outdated. This study aims to estimate the age and growth characteristics of anchovy through year-round seasonal sampling from 2016 to 2017, utilizing length–frequency and otolith microstructure analysis. The higher coastal abundance and larger size observed in the spring and summer suggest a potential peak spawning period for anchovies dominated by larger-sized individuals. Based on otolith analysis, anchovies range in age from 0 to 4 years, with a limited presence at age 0 and dominance in the age-1 group. The length–weight relationship (LWR) equation shows hyper-allometric growth for each season, with a mean relative condition factor (K_n) of 1.025 ± 0.005, indicating good health. Additionally, the von Bertalanffy growth equation of can be expressed as L_t = 154.40 [1 − e^{−0.604 (t + 0.965)}], suggesting a medium growth rate (K = 0.604). These findings contribute to the understanding of anchovy age and growth patterns, emphasizing the continuous need for research and monitoring to support rational and sustainable fisheries management and conservation efforts. Full article

To investigate the effect of prickly ash (Zanthoxylum bungeanum) seed kernel oil (PASO) on the lipid metabolism of grass carp (Ctenopharyngodon idellus) under a high-fat diet, PASO were added into two lipid-level (4 g/kg and 8 g/kg) diets to form four isonitrogenous diets: soybean oil (SO), PASO, high-fat soybean oil (HSO), and high-fat prickly ash seed oil (HPASO). A total of 216 healthy grass carp (9.43 ± 0.82 g) were randomly divided into four groups and fed with the four diets, respectively, for 56 days. The result showed that the viscerosomatic index (VSI) and the content of the crude lipid in the hepatopancreas and muscle was significantly higher by oil levels (p < 0.05). The linolenic acid content in the body of the fish significantly increased in PASO and HPASO compared to that in SO and HSO (p < 0.05). The fatty acid composition of the hepatopancreas, intraperitoneal fat, and muscle in four dietary groups was significantly similar to the fatty acid composition in the diets (p < 0.05). More significant fat infiltration and nuclear translocation in the hepatopancreas of fish was found in the HSO group but was decreased in the HPASO group. The adipocyte size in the intraperitoneal fat tissue in the PASO group was significantly lower than that in the SO group (p < 0.05). The relative mRNA expression of the lipogenesis-related genes ppar-γ, cebp-α, and srebp-1c was significantly down-regulated in the PASO group compared with the SO group (p < 0.05), and the mRNA expression of lipolysis-related genes ppar-α and cpt-1 were significantly up-regulated in the PASO group (p < 0.05). In conclusion, dietary PASO showed the function of reducing lipid accumulation in the fish. This reduction might be attributed to the inhibition of the lipogenesis-related genes and the stimulation of the lipolysis-related genes, which were probably modulated by the high content of linolenic acid in PASO. Full article

The catch composition of a coastal gillnet fishery in the Eastern Mediterranean Sea was analyzed through a two-year experimental fishing survey. Seven fish species occurred regularly in the hauls. Surmullet, Mullus surmuletus, which is the most valuable demersal fish in Greek waters and the intended target of the gillnets in small-scale fisheries, was the most abundant and systematically caught species. Almost all surmullets were larger than their minimum conservation reference size. However, three commercially exploited species (Diplodus annularis, Pagellus acarne, and P. erythrinus) were caught systematically as undersized individuals. In addition, these three species were caught mostly as immature individuals. Moreover, the operational season of the surveyed métier overlapped completely with the reproductive period of five commercially exploited species (D. annularis, M. barbatus, M. surmuletus, Sphyraena sphyraena, and Trachurus trachurus). Improvements and the establishment of additional technical measurements should be considered for the small-scale gillnet fisheries in the studied area to attenuate their detrimental effects and achieve a better compromise between sustainable exploitation of the local multi-species fish resources and the need for an economically sustainable practice. Full article

The genus Dichichthys was resurrected for five species previously allocated to the genus Parmaturus in the family Pentanchidae. Supraorbital crests on the chondrocranium distinguish Dichichthys from Parmaturus and other members of the family Pentanchidae. A new family, Dichichthyidae, has been proposed to contain Dichichthys. The sequence of the NADH2 mitochondrial gene confirms the placement of Dichichthys outside of the Pentanchidae family, as well as separate from the Atelomycteridae and Scyliorhinidae families. Dichichthys albimarginatus was described using a holotype collected off the coast of New Caledonia. A second juvenile specimen collected off the coast of Papua New Guinea was tentatively assigned as D. cf. albimarginatus. Dichichthys bigus is known from the holotype collected in the Coral Sea off the coast of Queensland, Australia. A new, parasite-afflicted underwater observation was reported further north of Queensland. The type species Dichichthys melanobranchus, previously only known from juvenile specimens, was redescribed based on adult specimens. Dichichthys nigripalatum is known from the holotype collected off Sumbawa, Indonesia, and a tentatively identified photo record from West Java. Dichichthys satoi n. sp. is described from the West Norfolk Ridge and off the North Island of New Zealand. Members of the genus Dichichthys have unique curved egg cases which have pliable ridges made up of numerous fibres and long coiled tendrils on the posterior end. Full article

Insulin-like growth factors (IGFs) play central roles in the growth and development of vertebrates. Blotched snakehead (Channa maculata), an economically significant fish, exhibits obvious sexual dimorphism and achieves sexual maturity in one year. However, the role of IGFs in C. maculata remains unknown. Three IGF genes were identified in C. maculata, designated as CmIGF1-1, CmIGF1-2, and CmIGF2. The cDNA sequences of these genes are 1184, 655, and 695 bp, encoding putative proteins of 168, 131, and 215 amino acids, respectively, and all three proteins contain a conserved IGF domain. Quantitative real-time PCR (qPCR) revealed the predominant expression of CmIGFs in the liver of adult fish, with higher expression levels observed in males. Notably, CmIGF1-1, CmIGF1-2, and CmIGF2 displayed analogous expression profiles in the liver across various developmental stages, peaking at 365 days after hatching (dah). Subsequently, 600 individuals at 75 dah, at an early developmental stage, were randomly divided equally into six groups and reared in aerated 2 m × 2 m × 2 m cement ponds at 26.0 ± 1.0 °C. Following a one-week acclimatization period, fish without observed abnormalities were intraperitoneally injected with either 17α-ethynylestradiol (EE₂) or 17α-methyltestosterone (MT) at a dose of 10 μg/g body weight. Three groups underwent short-term hormone treatment, and the remaining three groups underwent long-term hormone treatment, which included five injections at two-week intervals over ten weeks. The analysis of CmIGFs expression levels in the liver under different hormone treatments revealed that EE₂ suppressed the expression of CmIGF1-1 and CmIGF1-2 while promoting CmIGF2 expression. In females, MT up-regulated the expression of CmIGF1-1 and CmIGF2 in a time-dependent manner, but consistently inhibited CmIGF2 expression. In males, MT promoted the expression of CmIGFs in a time-dependent manner, reaching peak levels for CmIGF1-1, CmIGF1-2, and CmIGF2 after 8, 10, and 2 weeks of injection, respectively. Additionally, CmIGF1 and CmIGF2 might exhibit a complementary relationship, with a compensatory increase in CmIGF2 expression in response to low CmIGF1 concentration. These findings highlight the potential key role of IGFs upon growth and their regulation by sex steroid hormones in C. maculata, providing a crucial foundation for future research aimed at elucidating the molecular mechanisms underlying the growth dimorphism between female and male blotched snakeheads. Full article

The Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis, YFP) possesses the ability to detect distance through echolocation signals, and its sonar signal signature is adjusted to detect different targets. In order to understand the vocal characteristics of YFPs in different behavioral states and their differential performance, we recorded the vocal activities of YFPs in captivity during free-swimming, feeding, and nighttime resting and quantified their signal characteristic parameters for statistical analysis and comparison. The results showed that the number of vocalizations of the YFPs in the daytime free-swimming state was lower than that in the feeding and nighttime resting states, and the echolocation signals emitted in these three states showed significant differences in the −10 dB duration, −3 dB bandwidth, −10 dB bandwidth, and root-mean-square (RMS) bandwidth. Analysis of the resolution of the echolocation signals of the YFPs using the ambiguity function indicated that their distance resolution could reach the millimeter level. These results indicate that the echolocation signal characteristics of YFPs present diurnal differences and that they can be adjusted with changes in their detection targets. The results of this study can provide certain scientific references and foundations for the studies of tooth whale behavioral acoustics, and provide relevant scientific guidance for the conservation and management of YFPs. Full article