In recent years, fishmeal supply has surpassed market demand, leading to consistently high prices. To alleviate market pressure and reduce farming costs, it is crucial to investigate economical plant protein alternatives in feed. In this study, we examined the feasibility of incorporating mixed plant proteins into diets for juvenile Chinese longsnout catfish and determined appropriate inclusion levels. Six isonitrogenous and isolipidic diets were formulated using a mixed plant protein source (fermented soybean meal to rapeseed meal ratio of 4:1) to replace fishmeal in a basal diet at levels of 0%, 10%, 20%, 30%, 40%, and 50% (V0, V10, V20, V30, V40, and V50, respectively). Juvenile catfish were fed these diets for 8 weeks, after which growth performance, serum biochemistry, liver antioxidant activity, lipid content, and liver morphology were assessed. The results showed that substituting 50% of dietary protein with vegetable protein sources significantly reduced (P<0.05) the specific growth rate (SGR), whereas the V50 group exhibited a significantly higher feed conversion ratio that of other groups (P<0.05). Blood total cholesterol initially decreased and subsequently increased, reaching its lowest level in V10 (P<0.05). Similarly, both aspartate aminotransferase and alanine aminotransferase displayed decreasing-then-increasing trends, with lowest levels in V30 and V20, respectively (P<0.05). Liver malondialdehyde showed a decreasing-then-increasing trend, with significantly lower values in V10 and V20 groups than those of other groups (P<0.05). Total antioxidant capacity demonstrated an increasing-then-decreasing pattern, peaking at V10. Catalase activity showed a decreasing trend, with the V40 group showing significantly higher activity than that of the V50 group but lower than that of other groups (P<0.05). Histological analysis revealed progressive hepatic steatosis beginning at V30, accompanied by blurred hepatocyte membrane boundaries. Lipid droplet quantity exhibited a decreasing-then-increasing trend, reaching its lowest level at V20 (P<0.05). Under experimental conditions, moderate mixed vegetable protein supplementation improved juvenile Chinese longsnout catfish liver health. SGR was achieved with 37.47% fishmeal replacement by mixed vegetable protein; however, based on liver health indicators, a lower replacement level may be warranted.

Schistura scaturigina, endemic to the lower reaches of the Yarlung Zangbo River, holds considerable ecological and economic value. In this study, we presented the first systematic report on its embryonic and early larval development under artificial breeding conditions to clarify its developmental chronology and characteristics. These findings fill a critical research gap and provide important implications for the conservation and sustainable utilization of this species. We conducted experiments in April 2024. Hormonal induction was performed using a mixture of luteinizing hormone-releasing hormone analog (LHRH-A₂), human chorionic gonadotropin (HCG), and domperidone (DOM). Females received a two-injection protocol: the first injection consisted of LHRH-A₂ (3 μg/kg)+DOM (2 mg/kg), followed 12 h later by a second injection of LHRH-A₂ (10 μg/kg)+DOM (8 mg/kg)+ HCG (2000 IU/kg). Males received a single injection at the time of the female's second injection, at half the female dosage. Approximately 2,000 fertilized eggs were obtained via artificial dry fertilization, yielding average fertilization and hatching rates of 95.60% and 90.40%, respectively. Over 1,700 healthy larvae were ultimately obtained. The results showed that mature eggs were spherical, light yellow, and lustrous, with slight adhesiveness and a tendency to sink upon contact with water. Egg diameter measured 1.08±0.03 mm, expanding to (2.34± 0.08) mm after water absorption. At a water temperature of (20.0±1.0) ℃, fertilized eggs completed intra-membrane hatching in 49 h 20 min, requiring an accumulated temperature of 986.65 h∙℃. Embryonic development was divided into 33 phases across seven stages: fertilized egg, cleavage, blastula, gastrula, neurula, organogenesis, and hatching. Newly hatched larvae measured (4.18±0.30) mm in total length, exhibiting transparent bodies and no pigmentation on the eyes or skin. Distinct pigmentation appeared across the body at 2 days post-hatching. The yolk sac was nearly absorbed at 5 days post-hatching, coinciding with the development of an oval, vacuole-like, and membranous swim bladder. At 10 days post-hatching, a pair of small spherical bony swim bladders had formed, exhibiting a dumbbell-like shape. Functional organs were essentially fully developed at 15 days post-hatching. Overall growth and development of early larvae demonstrated an increasing trend, albeit with stage-specific variations in developmental rate. Our findings reveal that while embryonic developmental chronology of S. scaturigina aligns with that of phylogenetically close species, specific traits observed in its organogenesis progression and newly hatched larval morphology may reflect adaptations to the unique torrential environment of the lower Yarlung Zangbo River. Given its current restricted distribution, enhanced management within protected areas is recommended. Future efforts should prioritize systematic resource surveys and long-term monitoring to provide a scientific foundation for basin-wide conservation strategies.

The family Myctophidae plays a crucial role in marine pelagic fish communities. Ceratoscopelus townsendi, as a member of the genus Ceratoscopelus, is an important food source for numerous oceanic economic fish. It also serves as a biological pump connecting the upper and lower ocean layers, playing a key role in the active oceanic carbon cycle and food web of the Northwest Pacific. However, genomic research on this species is limited. To enrich the Myctophidae genomic database and improve species identification accuracy, we sequenced, assembled, and annotated the complete C. townsendi mitochondrial genome and conducted a phylogenetic analysis. The results showed that the total mitochondrial genome length was 17780 bp, containing 37 coding genes and 1 non-coding region. These genes were distributed across light (L) and heavy (H) strands, with gene overlaps and intergenic regions. Its genome structure was consistent with that of other Myctophidae species. Base composition analysis revealed an AT bias, with the top five most frequent codons being CCC (P), CCU (P), CUC (L), CUU (L), and CAC (H). The total length of protein-coding genes accounted for 57.9% of the genome, with codon usage preferences and distinct base biases across genes. tRNA genes were distributed on both H and L strands, with some duplications, while rRNA genes occupied specific regions with characteristic base compositions. Ka/Ks ratios of 13 protein-coding genes in the mitochondrial genomes of Myctophidae were all lower than 1, indicating purifying selection. Phylogenetic analysis showed that C. townsendi clustered closely with C. maderensis and was closely related to Bolinichthys, thereby clarifying its phylogenetic position within Myctophidae. This study enriches mitochondrial genomic information for Myctophidae, providing important data to support future research on species identification, phylogenetics, and biodiversity within this family.

To optimize the multi-trait synergistic breeding strategy for Marsupenaeus japonicus, this study was based on a G3 selected population. Twenty-eight full-sib/half-sib G4 families were constructed through fluorescent marker mixed culture and natural mating. A combination of linear mixed and generalized linear models was used to systematically evaluate genetic parameters of body length, body weight, and ammonia nitrogen tolerance traits at 120, 180, and 240 days of age, and to assess genotype-environment interaction effects under indoor and outdoor conditions. The results showed that growth traits exhibited moderate heritability, with body length ranging from 0.2992 to 0.4390 and body weight from 0.1324 to 0.3718. The heritability of ammonia nitrogen tolerance traits was low, ranging from 0.0914 to 0.1731. Genetic (0.8501~0.9145) and phenotypic (0.9001~0.9819) correlations between growth traits at different ages were all extremely significantly positive (P < 0.01), indicating that early selection can simultaneously improve phenotypes across multiple growth stages. Genetic correlations between growth and ammonia nitrogen tolerance traits ranged from –0.1957~0.0362 and those between growth and phenotypic correlations ranged from –0.0975~0.0955, with neither being significant (P>0.05), thereby suggesting regulation by independent genetic mechanisms. Genetic correlations of body length and body weight traits between indoor and outdoor environments were –0.017±0.176 and 0.136±0.185, respectively, both<0.8, indicating significant genotype-environment interaction effects on M. japonicus body length and body weight under different breeding conditions. Therefore, to achieve simultaneous improvement of growth and ammonia nitrogen tolerance traits, breeding values for both traits should be estimated, while a comprehensive selection index calculated to realize multi-trait synchronous improvement. Meanwhile, different breeding schemes should be tailored to specific indoor and outdoor breeding environments. The findings of this study provide a theoretical basis for designing efficient breeding programs for M. japonicus.

In this study, we investigated the effects of acute handling stress on serum biochemical indicators, antioxidant capacity, gill morphology, and surface slime microbial community of Seriola aureovittata. The experiment was conducted using S. aureovittata individuals (body weight: 463.86 ± 63.86 g). During the experiment, crowding-air exposure was repeated 10 times. Samples were collected before acute handling stress (C0, control group) and at 0, 3, 6, 12, and 24 h after stress. The results showed that acute handling stress significantly increased serum cortisol levels (P < 0.05). With the extended recovery time, cortisol levels initially increased and subsequently decreased, peaking at 3 h and returning to baseline at 12 h. Superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) activities and malondialdehyde (MDA) content followed a similar trend to that of cortisol; however, they peaked at 6 h after handling stress. After 24 h of recovery, only CAT activity and MDA content returned to their initial levels. In addition, acute handling stress caused bending and swelling of gill lamellae, cell vacuolation, and disordered epithelial arrangement. After 24 h of recovery, gill filament morphology had not fully returned to its original state. Moreover, acute handling stress exacerbated slime microbiota dysbiosis on the body surface, significantly increasing pathogenic bacteria abundance, including Vibrio splendidus, Tenacibaculum soleae, and Tenacibaculum dicentraci (P<0.05). In conclusion, S. aureovittata requires more than 24 h to fully recover from acute handling stress. The optimal window for stress-alleviating interventions occurs within the first 6 h post-handling stress. Regulating slime microbiota balance on the body surface may represent a promising strategy for mitigating acute handling stress.

Dominant species are essential components of ecological communities. Continuous and periodic surveys are critical for analyzing the spatio-temporal variation characteristics of dominant species. These variations in abundance are central to understanding succession characteristics and interspecific relationships. In this study, we investigated the succession characteristics and coexistence relationships of dominant zooplankton species in Xiangshan Bay through monthly surveys conducted over one year. Succession patterns were clarified by analyzing monthly changes in abundance and succession rates, combined with species ecological features. Coexistence relationships among dominant species were examined from a niche perspective by utilizing niche breadth values, niche overlap values between species pairs, and feeding habits. The results showed that the ecological group was singular, with cold-water species comprising 96.43% of the total abundance of dominant species from January to May. Warm-water species accounted for 79.14% from June to December, with the ecological group becoming more diverse. This pattern resembled that of other subtropical sea areas, where ecological groups of zooplankton were temperature-driven and successively shifted from warm-temperate to subtropical species. Abundances of Acartia pacifica, Canthocalanus pauper, and Centropages abdominalis peaked in July (summer), October (autumn), and January (winter), respectively. These peaks coincided with the peak times of the unimodal models of total and average abundance of dominant species in summer, autumn, and winter, respectively. Notably, the outbreak time of C. abdominalis occurred earlier than that in a similar study area in past research, likely reflecting thermal discharges from power plants and global warming. The succession rate of dominant species between adjacent months was generally above 50%. The Cochran and Friedman tests revealed extremely significant differences in species composition and dominant species abundance (P<0.01). Coexistence relationships among dominant species followed the niche differentiation theory: in resource-limited environments, similar species would compete intensely, and without niche separation, disadvantaged species would be eliminated. Herbivorous (Calanus sinicus, Paracalanus parvus, and Subeucalanus subcrassus) and carnivorous (Labidocera euchaeta and Calanopia thompsoni) species (with the same feeding habits) became dominant in different months. Species within the genera Tortanus, Paracalanus, and Centropages also alternated dominance across months. Spatial niche overlap among C. dorsispinus, L. euchaeta, and A. pacifica was moderate (0.6≥Q_ik≥0.3), whereas their temporal niche overlap was high (Q_ik>0.6). Temporal and spatial niche overlap among C. thompsoni, C. pauper, S. subcrassus, and P. aculeatus was high (Q_ik>0.6); however, they differed in food types and particle sizes. Overall, the findings indicated that succession of dominant zooplankton species was relatively frequent, while dominant species coexistence followed the niche differentiation theory. The findings of this study provide fundamental data for understanding interspecific coexistence and community assembly mechanisms of zooplankton in Xiangshan Bay.

This study explored a feeding strategy for the indoor mass culture of high-quality and uniform-size Artemia and clarified the crucial stages for morphological changes in Artemia in high-density culture. First, Artemia franciscana cysts from the Great Salt Lake, USA, were hatched and cultured in 100 L conical tanks for 4 days at an initial density of 1 ind./mL. Freshly cultured microalgae Isochrysis galbana was used as the basic diet. Subsequently, Artemia were transferred to 10 L conical tanks at an initial density of 0.5 ind./mL and fed shrimp feed with a size of 25–30 μm. Feeding was conducted at three levels, with total feed amounts of 3.33 g, 6.70 g, and 10.02 g, and three replicates were performed. The results showed that with total feeding amounts of 6.70 g and 10.02 g, the body length and biomass of Artemia were significantly higher than those with a total feeding amount of 3.33 g (P < 0.05). During the culture process, the overall variation trends of ${\rm{NO}}_2^ - - {\rm{N}}$, ${\rm{NH}}_4^ + - {\rm{N}}$, and total nitrogen (TN) contents were consistent. The ${\rm{NO}}_2^ - - {\rm{N}}$ and ${\rm{NH}}_4^ + - {\rm{N}}$ contents in each group remained at a low level (0.01– 0.04 mg/L and 0–0.12 mg/L, respectively). However, the variation trends of ${\rm{NO}}_3^ - - {\rm{N}}$ differed. With a feeding amount of 3.33 g, the content of ${\rm{NO}}_3^ - - {\rm{N}}$ increased from 0.33 mg/L to 0.53 mg/L; with a feeding amount of 6.70 g, the content of ${\rm{NO}}_3^ - - {\rm{N}}$ increased from 0.33 mg/L to 0.39 mg/L; and with a feeding amount of 10.02 g, the content of ${\rm{NO}}_3^ - - {\rm{N}}$ decreased from 0.33 mg/L to 0.28 mg/L. At the end of culture, the contents of TN in the groups with feeding amounts of 3.33 g, 6.70 g, and 10.02 g reached 7.46 mg/L, 8.69 mg/L, and 15.95 mg/L, respectively. Subsequently, the feeding amount of 6.70 g per 10 L group was applied to the culture of Artemia in a 1-ton water column for 13 days. Two critical stages, namely, the appendage development period and the second antenna degeneration period, were identified during the culture process, which was characterized by a sudden drop in survival rate. On day 13, the survival rate of Artemia was 72.3%, the average body length was 7.24 mm, and the total biomass reached 2230 g. The crude protein content of the biomass was 52.28% dry weight, the crude fat content was 17.64% dry weight, and the eicosapentaenoic Acid (EPA) content was 7.56 mg/g dry weight, all of which were higher than those of biomass collected from Bohai Bay salt ponds. In conclusion, using microalgae with a small size and easy digestibility in the early stage of Artemia culture, followed by an appropriate amount of formulated feed, can achieve a stable biomass yield. Artemia density changes should be closely monitored at the critical stages during the culture process. The results of this study not only provide strategic guidance for the indoor mass Artemia culture but also offer a methodological reference for obtaining a stable number of healthy Artemia in scientific research when using Artemia as experimental animals.

Heterosis, or hybrid vigor, is a cornerstone of modern aquaculture; however, the molecular mechanisms underlying this phenomenon, particularly during the critical early developmental stages, remain poorly understood. Hybrid snakehead (Channa maculata ♀ × C. argus ♂) displays marked growth superiority over its parents, making it an ideal model for dissecting the genetic basis of heterosis. In this study, we aimed to identify key regulatory genes and molecular pathways driving the early growth advantage in hybrid snakehead through comparative transcriptomic analysis against its maternal parent, C. maculata. Specifically, we constructed 12 cDNA libraries from whole-body samples at 13 days post-hatching (dph) and muscle tissues at 43 dph for both hybrid and parental groups. High-throughput RNA sequencing yielded approximately 500 million high-quality clean reads, with Q30 percentages consistently above 93.76% and mapping rates to the C. maculata reference genome (GCA_020496755.1) ranging from 68.73% to 95.90%, thereby confirming dataset reliability. Principal component analysis revealed distinct transcriptional profiles between hybrid and parental groups at both developmental stages, with the first principal component (PC1) accounting for 54.70% (13 dph) and 88.80% (43 dph) of total variance, indicating significant, stage-specific transcriptional reprogramming in the hybrid. Differential expression analysis, using a threshold of |log₂ (Fold Change)|≥1 and false discovery rate<0.05, identified 721 differentially expressed genes (DEGs; 427 up- and 294 down-regulated) at 13 dph and 385 DEGs (168 up- and 217 down-regulated) at 43 dph in hybrid group. Venn analysis revealed 23 core DEGs shared between both stages, suggesting their sustained importance in growth regulation. Gene ontology enrichment analysis highlighted a dynamic shift in biological functions: at 13 dph, DEGs were predominantly enriched in foundational processes—such as "metabolic process," "cellular process, " "binding," and "catalytic activity" —suggesting an early metabolic priming for rapid growth in hybrid group; at 43 dph, the functional landscape significantly shifted towards "developmental process", "multicellular organismal process", and "transporter activity", reflecting a transition to active tissue construction and morphological development. Kyoto Encyclopedia of Genes and Genomes pathway analysis further emphasized the enrichment of pathways associated with neuro-regulation, feeding behavior, muscle development, and energy metabolism. Ten core candidate genes, including npy, slc25a5, ugp2, obscn, ache, coro1ca, tuba, lmod2, nr4a1, and trim33, were selected, and their expression patterns were successfully validated via qPCR. Notably, the consistent upregulation of neuropeptide Y (npy), a potent appetite stimulator, suggests enhanced feeding motivation. Moreover, the upregulation of genes involved in energy metabolism, such as UDP-glucose pyrophosphorylase 2 (ugp2) and solute carrier family 25 member 5 (slc25a5), indicates an optimized energy supply chain for fueling growth. Concurrently, the downregulation of growth inhibitors—such as tripartite motif-containing 33 (trim33)—may relieve myogenic inhibition. Furthermore, genes crucial for muscle structure and remodeling, including leiomodin-2 (lmod2) and coronin-1A (coro1ca), showed differential expression, underscoring active muscle development. In conclusion, our findings demonstrate that early growth heterosis in hybrid snakehead is not governed by a single master gene but constitutes a complex trait orchestrated by the synergistic action of multiple genes across diverse biological pathways. We propose a model where enhanced neuroendocrine-driven feeding motivation, highly efficient energy metabolism, and accelerated muscle development collectively underpin growth superiority in hybrid group. Our findings provide novel insights into the molecular basis of fish heterosis and establish a scientific basis for marker-assisted selection, genetic improvement, and sustainable aquaculture of snakehead.

The Chinese sturgeon (Acipenser sinensis), a flagship species of the Yangtze River and national first-class key wild protected animal, currently relies on stock enhancement and release as the most effective and direct means of population conservation. However, juveniles from full artificial propagation exhibit weaker physical conditions than those from wild populations, including slow growth, low feeding efficiency, and poor stress resistance. To investigate the effects of dimethyl-β-propiothetin (DMPT) supplementation on growth, serum immunity, intestinal digestive enzyme activities, and gut microbiota composition of Chinese sturgeon juveniles, a 5-week feeding trial was conducted with sub-adult second-generation juveniles (initial body weight: 300.88 ± 17.64 g). DMPT was added to the basal diet at 0, 400, 800, and 1600 mg/kg (CK, A1, A2, and A3 groups, respectively), with 3 replicates per group and 10 fish per replicate. The results showed that weight gain and specific growth rate (SGR) in groups A1, A2, and A3 were significantly higher than those in the CK group. The feed conversion ratio in group A3 was significantly lower than that in the CK group. The contents of serum immunoglobulin M (IgM), complement C3, complement C4, and lysozyme activity increased progressively with increasing DMPT levels, with values significantly higher in groups A2 and A3 than those in the CK group. Serum superoxide dismutase activity was significantly lower in all treatment groups than that in the CK group, while alkaline phosphatase activity was significantly higher in groups A2 and A3. Digestive enzyme activities exhibited a trend of initially increasing and subsequently decreasing with increasing DMPT levels. Protease and lipase activities in groups A1 and A2 were significantly higher than those in the CK group, while amylase activity in all treatment groups was significantly higher than that in the CK group. No significant differences were observed in ACE, Chao1, Shannon, or Simpson indices among the treatment and control groups; however, the phylogenetic diversity whole tree (PD_whole_tree) index in groups A2 and A3 was significantly higher than that in the CK group. At the phylum level, Fusobacteria was the absolute dominant gut phylum across all groups, followed by Proteobacteria and Firmicutes; Fusobacteria relative abundance initially decreased and subsequently increased with increasing DMPT levels. At the genus level, Cetobacterium was the absolute dominant genus, with relative abundance progressively increasing with higher DMPT supplementation. The secondary dominant genera in groups CK and A2 were Plesiomonas and Escherichia-Shigella, while those in A1 and A3 groups were Plesiomonas and Bacteroides. Liver gene expression of growth hormone receptor (GHR) in groups A2 and A3 and insulin-like growth factor-1 (IGF-1) and IGF-2 in group A3 were significantly higher than that in the CK group, with GHR, IGF-1, and IGF-2 expression increasing progressively with DMPT dosage. In conclusion, appropriate DMPT supplementation significantly improved growth performance, immune capacity, and digestive capacity in juvenile Chinese sturgeon. Among the four addition gradients (0, 400, 800, and 1600 mg/kg) established in this study, 1600 mg/kg was optimal for promoting growth and health. This dosage can effectively enhance liver growth-related gene expression, thereby promoting the growth of the fish; simultaneously, its key immune indicators were significantly superior to those of the control and low-dose groups. Although DMPT supplementation did not affect species richness or diversity of intestinal flora, it increased the relative abundance of dominant phyla and genera, thereby contributing to improved growth, intestinal health, and disease resistance.

Acanthocephalans are important intestinal parasitic helminths of the large yellow croaker (Larimichthys crocea), and their infections can be detrimental to host growth and health. In this study, we systematically assessed seasonal infection dynamics and their association with host biological traits to enhance understanding of epidemiological characteristics and host-parasite interactions. Specifically, we aimed to elucidate prevalence patterns and establish a scientific basis for disease prevention and control. Accordingly, we conducted a year-long survey on L. crocea cultured in Sanduao Bay, Ningde, Fujian Province. The results showed that Longicollum pagrosomi (Yamaguti, 1935) displayed an aggregated distribution within the host population. Infection significantly reduced host condition factor (P<0.05), indicating that parasitism-induced physiological stress may impair host growth, reproduction, and disease resistance. Temporal analysis revealed significant monthly variations in L. pagrosomi prevalence (P<0.05), with maximum prevalence in August (90.0%) and minimum in September (18.2%). Mean intensity was highest in June (9.0) and lowest in December and March (1.0), indicating infections were concentrated in summer (June-August). These seasonal fluctuations are likely driven by environmental factors, such as water temperature, as elevated summer temperatures may accelerate the parasite life cycle and enhance transmission efficiency. Ontogenetic analysis showed prevalence increased with host body length, reaching a maximum in the 35–40 cm group (F, 66.7%), likely due to increased food intake and prolonged exposure in larger individuals. In contrast, mean intensity followed a bell-shaped pattern, peaking in the 25–30 cm group (D, 7.1), potentially reflecting dietary shifts during host development. A significant positive correlation was detected between L. pagrosomi abundance and host body length (r=0.25, P=0.004). Collectively, these findings demonstrate distinct seasonal and ontogenetic patterns in L. pagrosomi infection, establishing a scientific basis for targeted aquaculture management strategies, including intensified monitoring during summer and among specific size classes. This study advances understanding of marine parasite ecology by highlighting the roles of both abiotic (e.g., temperature) and biotic (e.g., host size) factors in shaping infection dynamics. Future research should elucidate the molecular mechanisms underlying host-parasite interactions across seasons and developmental stages and assess the effects of environmental change on these patterns.