Aquaculture Research

It is of great significance for bivalve aquaculture to promote the growth through nutritional strategy. Phosphatidic acid (PA) is a potential growth-promoting nutraceutical that targets for mammalian target of rapamycin (mTOR) in vertebrates, but its role in invertebrates remains largely unknown. Here, the effects of PA on mTOR and metabolic pathways in bivalve mollusk Sinonovacula constricta were determined by intramuscular injection with di-18 : 2 PA and di-16 : 0 PA. PA (both di-18 : 2 and di-16 : 0 PA) was found to increase the glycogen concentration in the muscle of S. constricta. Di-16 : 0 PA decreased the triglyceride concentration from 0.143 ± 0.04 mmol/g protein to 0.040 ± 0.018 mmol/g protein. The concentration of Asp, Glu, Ala, Cys, Val, Met, Ile, Leu, Phe, Arg, and Pro was reduced by di-18 : 2 PA or/and di-16 : 0 PA. PA increased the mRNA level of mTOR and the phosphorylation levels of eIF4E binding protein 1 and p70S6 kinase 1. Furthermore, PA decreased the protein level of microtubule-associated protein 1 light chain 3 Ⅱ/Ⅰ and the mRNA level of AMP-activated protein kinase. The mRNA expressions of two key enzymes of glycolysis (pyruvate kinase and glucokinase) were also upregulated by both PA, while the mRNA level of glucose transporter 1 was increased by di-18 : 2 PA. Di-16 : 0 PA decreased the mRNA level of phosphoenolpyruvate carboxykinase. The mRNA levels of sterol responsive element binding protein, fatty acid synthase, and acetyl-CoA carboxylase were increased by both PA. The mRNA level of stearoyl-CoA desaturase was increased by di-18 : 2 PA. Both PA species increased the mRNA levels of key enzymes involved in tricarboxylic acid cycle (citrate synthase and NADP-isocltrate debydrogenase). Our results indicated that PA activated mTOR signaling pathway, subsequently leading to the increase of anabolism and the inhibition of catabolism in S. constricta.

In recirculating aquaculture systems (RAS), off-flavors can accumulate in fish muscle tissue. They are problematic for consumer acceptance and the reputation of farmed fish products. Although off-flavors are not toxic at low concentrations, they often give fish muscle earthy, muddy, or other unwanted flavors. Traditionally, the study of off-flavors in fish focused on muddy and earthy off-flavors caused by geosmin (GSM) and 2-methylisoborneol (MIB), but other unwanted flavors and compounds have also been identified. In this study, the selected off-flavors were chemically quantified in fish from a RAS-rearing rainbow trout (Oncorhynchus mykiss) and in different stages of depuration. A group of trained panelists with experience in sensory evaluation was specifically trained in analyzing rainbow trout samples. The panelists evaluated the fish with a sensory profile of 29 sensory attributes (12 odor, 5 taste, and 12 flavor properties). Overall, the concentrations of all the studied off-flavor compounds decreased, some to below the limit of detection and others (e.g., octanal, octanoic acid, phenylacetaldehyde, and acetoin) to a certain low level. Moldy, earthy, and musty odors and flavors especially decreased during depuration compared to fish in RAS. This study shows the consistency of the chemical analysis and sensory profiling. It also provides important information about the effects of the depuration period in RAS and on the chemical and sensorial quality of rainbow trout.

Melanoma differentiation-associated gene 5 (MDA5) and the laboratory of genetics and physiology 2 (LGP2) are family members of retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs), which play important roles in the immune response against pathogens invasion. In the present study, MDA5 and LGP2 genes were identified in largemouth bass (Micropterus salmoides), a fish species with a great economic value. The two proteins contained similar conserved domains and motifs as their counterparts of other vertebrates, including the DExDc domain (the DEAD/DEAH box helicases domain), HELICc domain (helicases superfamily domain), and regulatory domain (RD). Real-time qPCR revealed that the two genes were constitutively expressed in tissues of healthy fish and could be induced in the spleen by polyinosinic and polycytidylic acid (polyI:C) challenge in vivo. Also, selective pressure analysis revealed that the negative selection had roles in the evolutions of the two genes. Furthermore, the dsRNA binding mechanism of msLGP2 and msMDA5 were analyzed by the molecular docking strategy. The amino acids of msLGP2 involved in dsRNA binding were V604, N663, L682, and L684, which were located in the regulatory domain (RD) of msLGP2. The amino acids of msMDA5 involved in dsRNA binding were G429, H434, L842, and L845, which were located in the DExDc domain and the RD domain of msMDA5. These results indicated that fish LGP2 and MDA5 might share similar functions and ligand binding mechanism as their mammalian counterparts.

Vibriosis causes a major setback in the marine aquaculture industry. In controlling vibriosis, vaccination of the broodstock could help in transferring the initial immunity to the fry and perhaps giving immunity to them during the culture period. This study determines the efficacy of three live-attenuated Vibrio harveyi vaccine (LAVh) derivatives on zebrafish broodstock in providing immunological protection to their offspring against pathogenic Vibrio spp. Zebrafish were vaccinated intraperitoneally with full effective dose (ED80) and monitored for 14 weeks. On week 6, the specimens were intraperitoneally (i.p.) challenged with pathogenic 10⁷ CFU/ml of Vibrio spp., and subsequently another batch was left to spawn. Thereafter, the antibody level of larvae was monitored for 4 weeks post-hatching. Groups of juvenile zebrafish were given booster vaccination via immersion (1 × 10⁷ CFU/mL) with vaccines similar to their predecessor. The fish were sampled weekly for four weeks to determine their antibody profile and pro-inflammatory gene expression. Finally, at week 3, the juvenile fish were challenged with pathogenic strains of Vibrio spp. Results of antibody profiling in the adult zebrafish model indicated that freeze-dried and stale LAVh delivers a longer immunological protective duration, while the FKVh vaccination group failed to provide immunological protection against V. alginolyticus. However, the gene expression of pro-inflammatory interleukin 1β (IL-1β) in the FKVh vaccinated group was elevated longer than that in the freeze-dried LAVh vaccinated group. Nevertheless, the relative percent survival (RPS) of both vaccination groups against pathogenic Vibrio spp. displayed 100% immunity. Overall, the freeze-dried LAVh vaccine was found to confer maternal immune protection for its offspring, provide a long duration of immunological protection and cross-protection coverage against pathogenic Vibrio spp., and have a longer shelf life. It is proposed to be commercially available for farmers to protect against Vibrio spp. infection.

Red king crab (RKC) has become a valuable resource, and most of this fishery operates in a quota-regulated area (QRA) east of 26°E. West of the QRA, a free fishery area (FFA) is established to limit further migration. Today, juvenile RKCs from the FFA are not utilized. This study investigated morphological and quality parameters in adult RKCs (≥800 g) after live holding (LH) of 23 months starting from juveniles (on average 500 g). During the LH, the RKCs were kept in two separate tanks, one at ambient seawater temperature (AST) and one at elevated seawater temperature (AST-E). The RKCs were fed ad libitum. Both tanks were divided into two sections, one with a sand tray. After 23 months, the RKCs were processed and analyzed. The hepatosomatic index, abdomen index, meat content, cluster yield, moisture, whiteness index, and instrumental chewiness differed significantly ( P < 0.05 ) between the wild RKCs and the RKCs from one or both LH groups. The availability of sand indicated improved habitat conditions as several parameters were positively affected. Also, lower variation in morphology and quality parameters of the processed muscle was observed in RKCs from the subgroups with access to sand than those without sand.

Alpha-monolaurin is reported to exhibit strong antiviral and antibacterial effects. This paves the way for its use as a new generation of feed additives. The experiment was carried out to examine the effects of the inclusion of alpha-monolaurin as a feed additive for Nile tilapia (Oreochromis niloticus) growth and immune response. Four diets were formulated to include alpha-monolaurin at 0, 2, 4, and 6 g alpha-monolaurin kg⁻¹ diets and fed to the Nile tilapia (initial weight, 3.19 ± 0.11 g) for 70 days. Compared to those of the control group, the final body weight, weight gain rate, specific growth rate, and efficiency of feed of fish fed 4 and 6 g alpha-monolaurin kg⁻¹ diets were (P ≤ 0.05) higher. The diet supplemented with a 2 g alpha-monolaurin kg⁻¹ diet (P ≤ 0.05) improved endogenous amylase and lipase more than other treatments. The intestinal villus length, width, and goblet cell number were increased (P ≤ 0.05) in fish fed a 6 g alpha-monolaurin kg⁻¹ diet. The same treatment displayed decreased (P ≤ 0.05) AST and ALT and increased total protein, albumin, and globulin. The highest levels of IgG and IgM were also noted in fish fed a 6 g alpha-monolaurin kg⁻¹ diet. The highest values of hematocrit, hemoglobin, and red blood cell and white blood cell counts were seen in fish fed either a 4 or 6 g alpha-monolaurin kg⁻¹ diet. The highest levels of thyroxine, triiodothyronine, and growth hormone were recorded in fish fed a 6 g alpha-monolaurin kg⁻¹ diet. Likewise, the same treatment recorded the highest levels of SOD, CAT, GSH, and GPx but the lowest MDA value. Diets supplemented with 4 g or 6 g alpha-monolaurin kg⁻¹ displayed the highest gene expressions of IFN-γ and IL-1β; however, HP70 genes were downregulated. In summary, the study showed that monolaurin may exert immunostimulatory effects on the immune system of the Nile tilapia by modulation of the host immune response and through metabolite production.

Global warming is a challenge facing the aquaculture industry, and mitigating its effects on aquatic animals’ productivity is mandatory. Hence, the present study investigated the alleviation of heat stress impacts on the performances of striped catfish by dietary allicin. For 60 days, striped catfish were fed dietary allicin at 0, 0.5, 1, 2, and 4%, and then the fish were exposed to 35°C. The results indicated that dietary allicin remarkably enhanced the growth performance (FBW, WG, and SGR) and feed utilization (FCR and PER) in striped catfish in a dose-dependent manner. Further, striped catfish fed allicin at 1 and 2% before heat stress, and those fed on 1% after heat stress had the highest lipase, amylase, and protease activities. The intestinal villi of allicin-treated fish showed increased length and branching. Before heat stress, the AST value was not affected by dietary allicin, but after heat stress, the AST was markedly reduced in fish fed on allicin at 1, 2, and 4%. Significantly, T-CHO and triglycerides were higher after heat stress than before with or without allicin. The blood proteins, albumin, and globulin were markedly lower after heat stress than before heat stress. The glucose and cortisol levels were increased after heat stress, either with or without dietary allicin. Heat stress reduced lysozyme activity, and the best activity was seen in fish fed 2% allicin. In addition, the phagocytic activity before and after heat stress was increased by dietary 1, 2, and 4% allicin. The activities of superoxide dismutase, catalase, and glutathione peroxidase were increased by dietary allicin before and after heat stress. The regression analysis illustrated that the best performances of striped catfish could be achieved by using 1.89–2.28% dietary allicin, leading to high resistance to heat stress.

The marble goby (Oxyeleotris marmoratus) is a valuable food fish, but its aquaculture production is often hampered by poor growth performance associated with starvation at an early stage. The objective of this study was to investigate the effects of delayed initial feeding on the growth performance and nutritional condition of the marble goby. Six different first feeding times were examined: 0, 12, 24, 36, 48, and 60 hours after the first feeding (HAFF), and their impacts on growth performances were evaluated based on larval final total length (mm) and survival (%), while nutritional condition was evaluated based on body morphometric changes, gut epithelium height (μm), and gut condition. The experiment was conducted for 15 days. All parameters were measured after larvae were collected at different sampling times, except survival and growth, which were measured at the end of the experiment. The results showed that the onset of the first feeding was 36 h after hatching (hAh) and that a short delay in the first feeding by 12, 24, 36, 48, and 60 HAFF significantly reduced the growth performance of the larvae and severely affected the larval nutrition condition with noticeable shrinkage in body morphometry and gut epithelium height. This study concluded that the onset of first feeding in marble goby occurs at 36 hAH and that first feeding beyond 36 hAH significantly worsens the nutritional condition and growth performance of the larvae.

This study investigated the antimicrobial activity of polyvinylpyrrolidone-capped silver nanoparticles (PVP-AgNPs) in vitro against two antibiotic-resistant isolates of Aeromonas hydrophila and A. caviae. Solid crystal silver nanoparticles were synthesized by the chemical reduction approach employing polyvinylpyrrolidone (PVP) as a neutral stabilizer, glucose as a reducing agent, and sodium hydroxide as a catalyst. The crystallinity and purity of the prepared PVP-AgNPs were investigated using the X-ray diffraction spectrometer (XRD). Transmission electron micrograph analysis demonstrated the formation of irregular spherical shapes PVP-AgNPs with average crystallite size diameters ranging from 5.07 to 9.74 nm. By phenotypic and gene sequence analysis, A. hydrophila and A. caviae isolates were identified from diseased Nile tilapia. Our findings showed that all A. hydrophila and A. caviae isolates were multidrug-resistant (MDR) and showed resistance to four antimicrobial classes. The PVP-AgNPs displayed 15 mm and 14 mm clear inhibition zones for A. hydrophila and A. caviae, respectively. In addition, the minimum inhibitory concentrations for PVP-AgNPs were estimated to be 6.25 μg/ml and 7.5 μg/ml for A. hydrophila and A. caviae, respectively. The chemically synthesized PVP-AgNPs were found to possess a strong antimicrobial effect against A. hydrophila and A. caviae with the possibility to be used as a commercialized antimicrobial agent in the aquaculture industry.

Two four-week feeding trials were conducted with fingerlings of Eurasian perch (Perca fluviatilis, 3.52 ± 0.08 g) and rainbow trout (Oncorhynchus mykiss, 1.49 ± 0.05 g) fed with graded levels of dried (DWD) and fermented (DWF) duckweed meal (Spirodela polyrhiza). The purpose of these two trials was to evaluate DWD and DWF as replacements for fishmeal. Fishmeal protein was substituted by 12%, 24%, and 35% of duckweed protein and compared to control diets containing 40% (for perch) and 35% (for rainbow trout) fishmeal and no duckweed. The performance of the fish (growth, feed conversion, and protein and lipid utilization) and their whole-body composition were evaluated and compared with the control. While even the lowest inclusion level, regardless of its form (dried or fermented), resulted in significantly reduced performance in Eurasian perch, rainbow trout were able to utilize feed containing duckweed meal considerably well. Compared to the control, at a 12% inclusion level, rainbow trout showed an equal or comparable percent weight gain (PWG; DWD: 377%, DWF: 373%), specific growth rate (SGR; DWD: 4.37%/day, DWF: 4.33%/day), feed conversion ratio (FCR; DWD: 1.11, DWF: 1.12), and protein productive value (PPV; DWD: 21.5%, DWF: 21.2%). Increasing the inclusion levels above 12% of both DWD and DWF resulted in reduced performance in rainbow trout, with the most pronounced effects observed in the DWD35 group. All experimental diets, including control, affected the whole body composition of perch, most notably reducing the lipid content compared to initial fish. Compared to initial, control and DWD rainbow trout increased whole-body protein, lipid, and ash contents. In conclusion, for rainbow trout, fermented and dried S. polyrhiza duckweed meal appears to be a promising feed ingredient when used at a maximum inclusion level of 12%, while for Eurasian perch, it should not be considered as a feed ingredient.

The current study aimed to explore the intestinal fungal community characteristics of grass carp and black carp and their correlation with cultured water fungi. Grass carp, black carp, and their cultured water samples were collected from the same reservoir. Based on the Illumina HiSeq 2500 high-throughput sequencing platform, the fungal internal transcribed spacer (ITS) region sequences of each sample were determined and analyzed. The results showed that a total of 1,193,261 valid sequences with an average length of 235–251 bp were detected in the three groups of samples, which included 9 phyla, 27 classes, 65 orders, and 288 genera. Ascomycota, Basidiomycota, Mortierellomycota, and Chytridiomycota were the dominant phyla. Mortierella, Thermoascus, and Thermomyces were the main genera. Compared with cultured water samples, the abundance of major phyla and genera was significantly different from grass carp and black carp samples, but there was no significant difference between grass carp and black carp samples. Surprisingly, Ascomycota was enriched in CY and QY samples. In conclusion, the dominant fungi in grass carp, black carp, and cultured water samples were similar, but the relative abundance was significantly different compared with cultured water samples. The results will provide a basis for the tolerance of fish with different feeding habits to colonize water and provide a theoretical basis for the regulation and improvement of aquaculture water quality and the realization of healthy and green aquaculture of fish.

To explore the effect of nitric oxide (NO) on Enterocytozoon hepatopenaei (EHP) invading the shrimp, sodium nitroprusside was used as an exogenous NO donor to investigate the effects of different concentrations (0 μg/L (control group), 0.3 μg/L, 0.6 μg/L, and 0.9 μg/L) of sodium nitroprusside on the EHP copy number and the structure in the hepatopancreas of Exopalaemon carinicauda infected by EHP. The results showed that the EHP copy number in the sodium nitroprusside group was significantly lower than that in the control group, and the hepatopancreas in the sodium nitroprusside injection group had less structure damage than the control group. Additionally, superoxide dismutase (SOD) activity in the control group and 0.3 μg/L groups increased and then decreased, while alkaline phosphatase (AKP) activity decreased and then increased, with the same trend, and, the inducible nitric oxide synthase (iNOS) activity in the haemolymph of the 0.3 μg/L group was significantly higher than that of the control group at 3 days (P<0.05). The NO content the 0.3 μg/L group was also higher from 1 to 4 days than that in the control group and significantly higher than that in the control group at 3 days (P<0.05). The injection of NO could reduce the EHP copy number in infected E. carinicauda and slow down the pathological changes in the hepatopancreas structure, which might be related to the increase in NO content.

Shell colors that exhibit a positive relationship with excellent traits can be employed as marker colors for breeding new varieties of bivalves. The clam Cyclina sinensis is an economically important marine bivalve that has three main colors: black, white, and purple. In the present study, we cloned and analyzed the full-length cDNA of the tyrosinase gene (TYR), which is the key gene for melanin synthesis, to explore the formation mechanism of black shells. The full-length cDNA of TYR was cloned by RACE-PCR, and the results showed that the full-length cDNA of TYR was 2993 bp, including a 2262 bp open reading frame encoding 753 amino acids. The results of functional domain prediction showed that deduced TYR protein contains a typical functional domain of tyrosinase, the common central domain. Phylogenetic analysis was conducted using neighbor-joining and maximum likelihood methods, and the results indicated that the evolutionary positions of C. sinensis and Meretrix meretrix were closest. The qRT‒PCR results showed that TYR mRNA was highly expressed in the outer edge of the mantle, which suggested that TYR was involved in the synthesis of melanin in the mantle of C. sinensis and might play an important regulatory role in the formation of melanin in black clam shells.

This study investigated the capability for fin regeneration in zebrafish larvae with the mechanism of FCS isolated from green and purple sea cucumbers Apostichopus japonicus (G-FCS and P-FCS). HPGPC determined that mean molecular weight of purified G-FCS and P-FCS is 19.5 and 18.8 kDa, and the FT-IR spectrum displayed similar characteristic absorption peaks. AFM images presented that G-FCS was shown as a spherical polysaccharide, while P-FCS molecules exhibited elongated chains. For the regeneration examination, FCS increased the regrowth area of the larval fin at 48 hours postamputation with enhanced locomotor behaviors, and the transcription levels of regeneration-related genes (Wnt10a, msx1b, fgf20a, bmp2a, bmp4, and igf2b) were upregulated. Moreover, FCS promoted the mRNA expression of inflammatory factors (iNOS, TNF-α, IL-6, IL-10, and IFN-γ) and TLR/NF-κB pathway-related genes (TLR3, TLR4a, NF-κb, and MyD88). The Western blot analyses of TNF-α and IL-1β supported that FCS enhanced immune response. ELISA results indicated that FCSs increased the contents of NO, CAT, SOD, and G6PD. Summarily, the present results suggested that FCS was a potential regeneration enhancer by elevating immunomodulatory and antioxidative processes in zebrafish.

The major goal of the study is to determine the potential use of poppy seed oil as a main lipid source in common carp diets. To investigate this, five different experimental diets (PO0, PO25, PO50, PO75, and PO100) with various proportions of fish oil and poppy seed oil blended as oil sources were provided and supplied to common carp for 90 days. In triplicate groups of 60 fish, 300 common carp weighing 1.15 ± 0.06 g were randomly placed in 100 L aquariums. At the end of the feeding trial, blood and tissue samples were collected from the fish after gravimetric measurements of the fish. The growth and feed utilization performance of the fish were calculated by gravimetric measurements, and tissue samples were examined by hematological, micromorphometric, and histopathological methods. According to the results, poppy seed oil enhanced the quantity of linoleic acid (18 : 2 ω−6) in the diet, and fish fed with the diet consisting completely of poppy seed oil (PO100) had the significantly greatest growth and feed utilization performance ( P < 0.05 ). Furthermore, no significant differences in hematological or liver pathology were detected between all groups that were fed with experimental diets ( P > 0.05 ). However, as compared to the control group, the digestive system micromorphometry and histomorphometric measurements of the fish fed with PO100 group diets showed a significant increase ( P < 0.05 ). In conclusion, it was determined that the carp fed with feeds produced by using only poppy oil as the main fat source improved their digestive system, growth, and feed utilization performance without any negative effects.

Dietary supplementation with fermentation products of Astragalus can enhance the immune function of aquaculture animals. We explored the synergistic effects of Lactobacillus plantarum and Bacillus coagulans on the solid-state fermentation of Astragalus to investigate whether feeding fermentation products to crucian carp can improve disease resistance. The optimal ratio of Astragalus + (L. plantarum + B. coagulans) (ALB), temperature, and number was 3 : 3, 37°C, and 1.0 × 108 CFU/g, respectively. After 48 h mixed fermentation, the number of probiotics increased to 2.2 × 109 CFU/g, pH decreased to 3.2, and high molecular weight proteins disintegrated into small molecular weight or soluble proteins. In addition, several holes appeared on the Astragalus surface. Compared with unfermented Astragalus, the content of Astragalus polysaccharide and calycosin increased by 3.82- and 1.31-fold, respectively, on fermentation and that of total Astragalus saponins decreased by 0.77-fold. Furthermore, on Cyprinid herpesvirus 2 (CyHV-2) and Aeromonas veronii (A. veronii) challenges, the cumulative survival rates of crucian carp fed common feed and ALB were 80.00% and 65.00%, respectively. Overall, feeding mixed fermentation products to crucian carp positively impacted their health and disease resistance. We believe that our results provide theoretical guidance for developing effective plant-based agents to prevent diseases in crucian carp.

Intestinal steatosis, called lipid malabsorption syndrome (LMS) in severe cases, is a common condition in farmed Atlantic salmon, associated with choline deficiency causing low lipid transport in enterocytes, excessive lipid accumulation, and increased mucosal weight. A previous dose-response study supplying a plant-based diet with choline chloride indicated that 3.4 g/kg choline prevents LMS in Atlantic salmon. However, no similar documentation exists using phosphatidylcholine (PC) as a choline source. The present study therefore aimed to determine the ability of PC from krill meal (KM) and krill oil (KO) towards reducing steatosis in Atlantic salmon. Two diets with suboptimal PC levels (1.5 and 2.6 g/kg) were tested against two control diets, a choline-deficient diet with no supplementation (0.6 g/kg), and a high choline (4.0 g/kg choline chloride) diet. After 8 weeks of freshwater feeding, growth was significantly higher in KM and KO groups, at both PC levels, in comparison to the choline-deficient group. However, growth was significantly higher only in the KM and KO diets with 2.6 g/kg of PC when compared to the positive control. This indicated that suboptimal levels of PC from KM and KO satisfied choline needs for growth. A clear dose-dependent effect on the decreasing pyloric intestine (PI) somatic index was observed for KM and KO diets, with no significant difference between KM and KO diets (2.6 g/kg choline) and high choline reference diet. Accordingly, PC from both KM and KO significantly reduced lipid accumulation in the PI and liver when added to a choline-deficient diet. However, histological and lipid analyses also indicated that the optimal dietary choline requirement for full elimination of lipid accumulation in PI is higher than 2.6 g/kg with KM and KO as supplementary sources.

The excessive use of chemical fertilizers causes many problems for which solutions are being sought in a variety of agricultural production systems. From the perspective of paying attention to the health requirements of aquatic animals in terms of water quality, this study investigated the impact of chemical fertilizer application on water quality in a rice (Oryza sativa L.; Cultivar “Qingxiangruangeng,” accession number: 2014004)–eel (Monopterus albus) coculture system in Shanghai, China. Chemical fertilizer was applied four times—as base fertilizer, rejuvenated fertilizer, tiller fertilizer, and ear granule fertilizer—during the production process of a rice–eel coculture system (June to October 2020). Changes in the water quality parameters of rice field’s surface water and ring ditch water in the regular chemical fertilizer group (RF) and no chemical fertilizer group (NF, the control) were compared before and at 24 h, 48 h, and 72 h after the chemical fertilizer application. The results for the analyzed physical and chemical indexes of each water area before and after four fertilizations revealed several consistent trends. First, the pH, dissolved oxygen (DO), water temperature (T), and chemical oxygen demand (COD) of either water area were similar between the NF and RF groups, whereas their total nitrogen (TN), total ammonia nitrogen (TAN), and total phosphorus (TP) levels differed significantly. After adding the above fertilizer containing nitrogen and phosphorus, 24 h later, the TN, TAN, and TP content had already increased significantly in comparison with the control. The maximum average content of TAN and nitrite nitrogen (NO2−-N) in the ring ditch water reached 12.30 mg/L and 0.37 mg/L, respectively, at 24 h after the chemical fertilizer application. Nonlinear regression analysis results showed that there was a significant positive relationship TN (δTN) and TAN (δTAN) vis-à-vis the nitrogen content of the fertilizer. The results of this study provide a timely empirical reference and data support for improving fertilizer management in rice–eel coculture systems.

A feeding experiment was conducted to study the effects of dietary lipid sources and L-carnitine on the growth performance, body component, muscle fatty acid composition, and antioxidant enzyme ability of average weight of 0.28 g dog conch larvae, Laevistrombus canarium. Three sources of lipid: fish oil, soybean oil, and beef tallow were tested in combination with two levels (0 and 0.5%) of L-carnitine. The dog conch larvae fed diets containing fish oil with L-carnitine supplementation exhibited the highest weight gain. After air exposure challenge, the liver tissue of dog conch fed the diets containing soybean oil and beef tallow without supplemented L-carnitine had lower levels of superoxide dismutase (SOD, U min−1), phenoloxidase (PO, U min−1), and glutathione peroxidase (GPx, mU/mL) activity. The activity of SOD, PO, and GPx of dog conch larvae increased with increasing levels of dietary L-carnitine. In particular, dog conch larvae fed the diet containing fish oil supplemented with L-carnitine exhibited significantly ( P < 0.05 ) enhanced antioxidant responses. The thiobarbituric acid reactive substances (TBARS) in the muscle tissue of dog conch larvae fed the diet containing fish oil without L-carnitine supplementation showed significantly ( P < 0.05 ) higher activity. It was concluded that dietary administration of L-carnitine can enhance resistance against beta-oxidation, and the administration of fish oil in the diet was the best strategy to promote growth due to high nutritional availability.

This study aims to provide a quantitative analysis of the amino acids (AAs) and fatty acids (FAs) found in by-products of the Patagonian marine polychaete Abarenicola pusilla. Samples of polychaetes were taken in different seasons and processed to generate three by-products: eviscerated whole body, press cake, and press liquid. The results showed a clear seasonal difference, with essential nutrients decreasing significantly in winter. For example, from eviscerated whole body specimens, essential fatty acids, eicosapentaenoic acid (EPA), and arachidonic acid (ARA) maintained a relationship of 1 in summer, 1.24 in winter, and 1.5 in spring and autumn. In comparison, docosahexaenoic acid (DHA) was undetected in some extracts in winter. However, the fatty acid content in press liquid resulted in high variation, with the lowest content during the autumn. In contrast, the press liquid and press cake responded similarly. DHA decreased from spring to winter (from 0.1 to 0.08), whereas EPA resulted in high variation along the seasons (from 0.57 to 0.03) from summer to autumn. The highest protein values were observed in the spring and summer. In contrast, lipid values remained under 10% constant throughout all seasons, unless in the eviscerated carcass, where 5 to 3% higher lipids were found, indicating that A. pusilla uses protein more efficiently than lipids as an energy source. The most abundant EAAs were lysine (LYS) and leucine (LEU), while glycine (GLY), glutamic acid (GLU), and alanine (ALA) were the most abundant NEAAs. Finally, A. pusilla harvest conditions and the type of extract recommended to produce a valuable ingredient for marine aquafeeds are discussed.

Australian abalone aquaculture is characterised by a prolonged culture period and slow and variable growth, and abalone is cultured in fluctuating water temperatures ranging between 10 and 25°C with distinct seasons. Temperature is a crucial environmental factor influencing abalone’s physiology and energetics, leading to a change in nutritional requirements. However, feeds are generally formulated to match the nutritional requirements at their optimal temperature. Hence, there is a need to optimise dietary protein levels to match temperature-specific requirements during extreme conditions (winter and summer). Given this, a growth trial evaluating five experimental feeds consisting of graded protein inclusion levels (320, 350, 380, 410, and 440 g·kg−1) was conducted on subadult hybrid abalone (Haliotis rubra × H. laevigata) at three different temperatures reflecting winter (12°C), summer (22°C), and the annual average water temperature (17°C) for 143 days. At lower water temperature (12°C), there was a marginal improvement in growth performance as dietary protein levels increased from 320 to 440 g·kg−1. However, at higher water temperatures (when the culture water temperature is above 17°C), there was a significant improvement in growth performance as dietary protein levels increased from 320 to 440 g·kg−1 as evidenced by an improved weight gain, specific growth rate, and feed conversion ratio. Furthermore, increasing dietary protein levels did not compromise the nutritional quality of the abalone tissue at all three tested temperatures. Therefore, during periods of higher water temperatures, feeding Australian hybrid abalone with a relatively high dietary protein level (410 g·kg−1) is expected to result in improved growth, shorter culture duration, and profit maximisation.

We investigate the early developmental characteristics of the skeletal system in Miichthys miiuy larvae using a double staining method on the whole larval skeletons (aged 1–30 days). We systematically observed and described the morphological development of both the spinal vertebrae and appendicular skeleton. The results showed that there were 25 spinal vertebrae in M. miiuy, which consist of 12 abdominal vertebrae and 13 coccyges; The development of spinal vertebrae began at 12 days after hatching (dah), with the emergence of ossified neural and haemal arches, where ossification appeared at 17 dah; and the appendicular skeletons were developed from the pectoral fins to ventral fins. The coracoid-scapula cartilage was clearly observable at three dah, and fin rays were clearly differentiated at 21 dah. The cartilage of appendicular of the ventral fins was formed until 19 dah, and the ventral fins were completely ossified at 21 dah. Subsequently, the caudal, dorsal, and anal fins appeared at 10, 13, and 14 dah, respectively. Additionally, the appendicular skeleton associated with the movement of M.miiuy was completely developed by 28 dah. Finally we observed that there are four types of spinal vertebrae abnormalities during the early development of M.miiuy, which included spinal bulging, splitting of vertebrae, and supernumerary and bifurcated haemal and neural spines. Skeletal length and age (in days) were highly correlated (r2 = 0.942). There was a strong relationship between total length and skeletal length (r2 = 0.979) and between body length and skeletal length (r2 = 0.9779).

Black soldier fy (Hermetia illucens) larvae (BSFL) production will likely increase to meet the growing demand for sustainable protein and lipids. A by-product is "frass," which is a mixture of mostly larval excrement but also chitin. Tis mineral-richby-product could be a valuable aquaponic supplement, but the information is limited. Te aim of this study was twofold to determine if BSFL frass additions could enhance the production, mineral composition, and chlorophyll content of collard greens (Brassica oleracea var. viridis) after 10 weeks as well as the infuence of culturing collard greens with or without media. Each aquaponic system contained 20 channel catfsh (Ictalurus punctatus; initial mean weight of 128 g) that were fed twice daily to apparent satiation. Results showed that dissolved nitrogen, pH, and dissolved oxygen were unafected (p > 0.05) by BSFL frass additions. Tere was a signifcant media and BSFL frass efect (p < 0.05) on total weight, individual weight, and total height of collard greens where the media/frass treatment led to a ninefold increase in weight compared to the no media/no frass treatment. Moreover, both media and BSFL frass signifcantly increased (p < 0.05) the total chlorophyll content while extensive chlorosis was observed in the no media/no frass group. Manganese in collard greens was signifcantly increased (p < 0.05) by BSFL frass. Te best combination for collard green growth and preventing any chlorosis was the media/frass treatment, which may be due to an increase in various nutrients that were more accessible by biomineralization in the media.

Dietary n-3 highly unsaturated fatty acids (HUFAs), which are low in vegetable oils (VO), are natural ligands of fatty acid-binding protein (fabp) genes, which function in molecular n-3 HUFAs metabolism in fish. Low water temperature (LWT) also affects fish fatty acid (FA) metabolism. Therefore, in this study, we investigated mRNA expression levels of fabp genes in European seabass (Dicentrarchus labrax) reared in LWTs. For this purpose, we cloned and characterized open reading frames of 10 fabp genes. Changes in the expression of fabp genes to VO-based diets for 60 days and fish oil (FO)-based diet for 30 days were determined. The present study's results suggest the following: (1) D. labrax fabp genes are orthologues of vertebrate fabp/FABP genes. (2) fabp1b.1/fabp1b.2 and fabp7a/fabp7b are retained in the D. labrax genome most likely because of the subfunctionalization. (3) The variation in tissue-specific expression of fabp10a/fabp10b and fabp11a/fabp11b paralogues also provides evidence of subfunctionalization; however, nutrigenomic results did not support this observation. Therefore, more detailed promoter analyses are needed to better understand their retentions in the D. labrax genome. (4) Feeding D. labrax with a FO-based diet following feeding with VO-based diets is insufficient for molecular FA metabolism recovery. This study is the first report on the characterization and nutritional regulation of fabp genes by dietary FAs in D. labrax reared in LWTs and suggests that transcriptional control of fabp genes by agonists would be helpful to maintain lipid homeostasis, protect fish health and increase fish welfare for sustainable aquaculture production.

The present study was conducted to evaluate the growth, immunity, haematology, antioxidant components and resistances to Aeromonas hydrophila infection in the common carp, Cyprinus carpio fed quercetin (QUR) enriched diet. A number of 360 fish (30.5 ± 1.5 g) were distributed into 12 tanks (30 fish/tank) in three replicates and fed experimental diets containing 0% (control), 0.1% (1 g/kg diet), 0.5% (5 g/kg diet) and 1% (10 g/kg diet) QUR for 60 days. Based on the results, the survival and growth performance (weight gain [%], specific growth rate and feed conversion ratio) improved in response to dietary QUR (p < 0.01). The analysis of fish body composition indicated higher content of protein in 0.5% and 1% QUR‐supplemented fish compared to others (p < 0.01). The plasma (complement activity, IgM content, lysozyme activity, bactericidal activity, total protein, total albumin) and mucus (IgM content, lysozyme activity) immune components significantly increased almost all in the supplemented fish compared to those in the control group; however, the highest values were observed in group of 1% QUR (p < 0.01). The mucosal protease and alkaline phosphatase increased only in fish fed 1% QUR (p < 0.01). The expression of the immune‐related genes (C3, Lyz and IgM) significantly increased in response to 0.5 and 1% QUR compared to control (p < 0.01). The expression of the inflammatory genes, tumour necrosis factor‐α (TNF‐α) and interleukin‐8 (IL‐8) significantly declined in fish fed 1% QUR compared to supplemented fish. The activity of liver antioxidant enzymes [superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT)] was also increased by QUR supplementation. The highest liver antioxidant enzyme activity was found in group of 1% QUR (p < 0.01). The QUR supplementation also affected haematology of the fish. In this regard, the values of RBC, Hct and WBC significantly elevated in response to dietary QUR (p < 0.01). The MCHC and MCH indices significantly increased in fish fed 0.5 and 1% QUR compared to other diets (p < 0.01). As an indicator of oxidative stress, the levels of malondialdehyde (MDA) showed no significant differences between the experimental groups (p > 0.01). The fish supplemented with 0.5 and 1% QUR significantly showed higher survival rate after challenge with A. hydrophila compared to other experimental groups (p < 0.01). In conclusion, QUR at optimal dietary level improved the growth, antioxidant and immune responses and resistance to Aeromonas hydrophila infection in the common carp.

The study was conducted to investigate the apparent digestibility coefficients (ADC) of nutrients in commonly used protein sources for largemouth bass. A reference diet and test diets with 70% reference diet and 30% feedstuff were formulated with yttrium oxide as a digestibility indicator. Overall, the ADC of dry matter of tested protein ingredients was 69.5%–96.4%, and the ADC of dry matter in animal protein sources was significantly higher than in the other five plant protein sources. The ADC of crude proteins ranged from 89.1% to 97.3% for all tested feedstuffs. The ADC value of total amino acids in the tested ingredients is consistent with that of the protein. The ADC of crude lipid of tested ingredients ranged from 45.4% to 96.2%, and the lowest and highest values were observed in porcine haemoglobin powder and pet‐grade poultry by‐product meal, respectively. The ADC of total phosphorus of animal protein ingredients, except porcine haemoglobin powder, was significantly higher than that of plant protein ingredients, except fermented soybean meal. The results revealed the difference in availability of nutrients in plant and animal protein sources for largemouth bass, which could provide a theoretical basis for the selection of protein sources of commercial feed for largemouth bass.

Vibrio are known opportunistic pathogens of pond‐cultured fish and shrimp. This study determined the presumptive Vibrio count (PVC) and percentage composition of “beneficial” sucrose‐fermenting vibrios (SFVs) and “pathogenic” non‐SFVs in the water, sediment, gills and intestines of healthy tilapia Oreochromis niloticus collected every 2 weeks from Days 30 to 120 post‐stocking in brackish water earthen ponds. PVCs in water and sediment ranged from 102–104 CFU/ml/CFU/g while in tilapias' gills and intestines, PVCs ranged from 103–106 CFU/g and 102–106 CFU/g, respectively, with SFVs dominating in water, sediment, gills (≥50%), and intestines (≥80%) of tilapia. Because use of tilapia‐conditioned green water (TCGW) for shrimp's grow‐out culture has been reported effective against acute hepatopancreatic necrosis disease outbreaks caused by V. parahaemolyticus, PVC, SFVs/non‐SFVs (%), and V. parahaemolyticus count (VPC) in the recycled TCGW and Litopenaeus vannamei's hepatopancreas were also examined from stocking until 105 days of culture (DOC) in earthen ponds. PVCs ranging from 102–103 CFU/ml and 103–104 CFU/g were noted in water and shrimp's hepatopancreas, respectively. While non‐SFVs population in water varied, a downward trend typified by an abrupt 50% reduction was noted in hepatopancreas at DOC 42, and remained or further dropped until DOC 105. VPCs in water likewise varied (undetectable–102 CFU/ml) while in hepatopancreas, counts dropped to undetectable level from DOC 70 onwards. Current data illustrate that remarkable shift of SFVs' dominance in the water and concomitantly in shrimp's hepatopancreas, plays a pivotal role in regulating non‐SFVs proliferation in shrimp's hepatopancreas via competitive exclusion.

Piracanjuba, Brycon orbignyanus, is an important rheophilic species for aquaculture studies on genetic diversity, spermatogenesis, semen cryopreservation and taxonomy. Due to anthropic actions its population has been declining, resulting in the loss of natural stocks, thus pushing the species to near extinction. No stereological analysis of spermatogenesis in piracanjuba has been performed. The present study aimed to evaluate spermatogenesis in B. orbignyanus using stereological analysis to quantify the number of germ cells and Sertoli cells, spermatogonial generations, spermatogenesis yield, meiotic index and the percentage of cell death. Testes of five 1‐year‐old B. orbignyanus specimens were collected, fixed in 2.5% glutaraldehyde and 4% paraformaldehyde and processed for light microscopy. Three types of spermatogonia were identified. Based on the number of B spermatogonia per cyst, it was estimated that spermatogonia underwent approximately nine mitotic divisions before differentiating into primary spermatocytes. Three types of spermatids were identified. In the final spermatid cyst, there were 1204 germ cells, indicating a spermatogenic yield of 58%. An increase in germ cells resulted in a subsequent increase in the number of Sertoli cells, with growth halted at the spermiogenic phase. Thus, stereological analysis of spermatogenesis is essential for better understanding of the reproductive processes in this species.

An 8 week experiment was conducted to assess the effect of dietary thiamin on meat quality of grass carp. Totally, 540 fish were randomly distributed into 18 cages (1.4 m × 1.4 m × 1.4 m) each containing 30 fish in three replicates. Test fish were fed with respective diets for four times daily: 0.12 (thiamin un‐supplemented diet), 0.43, 0.83, 1.25, 1.62 and 2.04 mg thiamin/kg diet. Results revealed that optimum dietary thiamin improves grass carp flesh quality in five aspects: (1) increased nutritional quality (fillet protein, lipid contents) was associated with increasing target of rapamycin and casein kinase 2 expression, (2) improved flesh flavour via increasing the flavour amino acids contents (Glu, Asp, Gly, Ala, Leu and Ile), (3) elevated fillet healthcare components contents (especially docosahexaenoic acid and eicosapentaenoic acid contents), (4) improved sensory characteristics (pH, firmness, water‐holding capacity) of flesh and (5) enhanced flesh antioxidative capacity by elevating the activities and expression of antioxidant enzymes, which was involved in elevating Nrf2 expression and down‐regulating Keap1a and Keap1b expression. Dietary thiamin affected fish flesh quality correlated with changes in muscle flavour, healthcare components, sensory characteristics, antioxidant capacity, target of rapamycin and Nrf2 expression.

Heavy metal lead (Pb) is a primary pollutant that pollutes aquatic environments and can be enriched in aquatic animals. Here, the effects of waterborne Pb on grass carp (Ctenopharyngodon idella) within 96 h of exposure were detected, and the association between microbiota alterations in the intestines and water was analysed. Results revealed that the intestinal barrier was damaged, including the intestinal morphology change, the structure‐related genes (villin‐1 and Claudin‐7) expression down‐regulation, the antioxidant (GST and GSH‐Px) and immune‐related genes (TNF‐α and IL‐8) expression up‐regulation. The MiSeq sequencing data revealed a decrease in diversity and an increase in microbiota richness in the intestines and water after Pb exposure. Linear discriminant analysis (LDA) results revealed an increase in the dominant bacteria (P_proteobacteria and C_Gammaproteobacteria) in the water, which enriched bacteria in the intestines. Canonical correlation analysis (CCA) found that there were correlations between intestinal microbiota and water microbiota, intestinal structure morphology and immune factors. Based on these results, we speculated that the effects of Pb on the grass carp intestinal barrier may be related to changes in the intestinal structure of grass carp and the water microbial community. These findings improve our understanding of the effects of heavy metals on the fish–microbe relationships after polluting aquatic habitats.

Oyster (Ostrea gigas thunberg) has high nutritional and economic values. We analysed bimonthly nutrient‐level variations in Rushan oyster (Crassostrea gigas) to establish a basis for the analysis of the nutritional quality of oysters. The contents of the proximate composition, fatty acids, amino acids, minerals and non‐volatile taste substances were measured using Pacific oysters collected between March 2019 and May 2020; this was followed by comparing the impact of seasonal fluctuations on oyster composition. The findings demonstrated that the contents of crude protein and amino acids with seasonal features were higher in the summer and decreased in the winter and spring. Moreover, crude fat and fatty acid content were found to be higher in the winter and spring and decrease in the summer. Winter and spring have greater EUC values and several taste components than summer and autumn. In conclusion, Crassostrea gigas are more nutritious and delectable from March through May. These findings are useful in determining the ideal season for harvesting and consuming oyster products.

Dietary n‐3 highly unsaturated fatty acids (HUFAs), which are low in vegetable oils (VO), are natural ligands of fatty acid‐binding protein (fabp) genes, which function in molecular n‐3 HUFAs metabolism in fish. Low water temperature (LWT) also affects fish fatty acid (FA) metabolism. Therefore, in this study, we investigated mRNA expression levels of fabp genes in European seabass (Dicentrarchus labrax) reared in LWTs. For this purpose, we cloned and characterized open reading frames of 10 fabp genes. Changes in the expression of fabp genes to VO‐based diets for 60 days and fish oil (FO)‐based diet for 30 days were determined. The present study's results suggest the following: (1) D. labrax fabp genes are orthologues of vertebrate fabp/FABP genes. (2) fabp1b.1/fabp1b.2 and fabp7a/fabp7b are retained in the D. labrax genome most likely because of the subfunctionalization. (3) The variation in tissue‐specific expression of fabp10a/fabp10b and fabp11a/fabp11b paralogues also provides evidence of subfunctionalization; however, nutrigenomic results did not support this observation. Therefore, more detailed promoter analyses are needed to better understand their retentions in the D. labrax genome. (4) Feeding D. labrax with a FO‐based diet following feeding with VO‐based diets is insufficient for molecular FA metabolism recovery. This study is the first report on the characterization and nutritional regulation of fabp genes by dietary FAs in D. labrax reared in LWTs and suggests that transcriptional control of fabp genes by agonists would be helpful to maintain lipid homeostasis, protect fish health and increase fish welfare for sustainable aquaculture production.

This study evaluated how the feeding frequency impacts growth performance, haematological parameters, fatty acid profile and liver histology in meagre (Argyrosomus regius). Fish (15.48 ± 0.11 g) were fed to satiation with a diet formulated according to the nutritional requirements of the species (48% crude protein and 18% crude lipid) for 12 weeks in six different feeding frequencies; 1, 2, 3, 4, 5 times in 24 h (F1, F2, F3, F4, F5) and 2F1 as one day feeding-one day fasted. The final mean weight (FMW) and specific growth rate (SGR) of the F3, F4 and F5 were significantly higher than the F1 and 2F1 groups. Viscerosomatic index (VSI) of the F1 and F3 groups was markedly different from the 2F1. Moreover, packed cell volume (PCV) and haemoglobin (Hb) counts in the F3 and F5 groups were higher than in the 2F1 group. The liver lipid vacuolization was found at more than moderate and also high levels for the groups of F3, F4 and F5 compared to the other groups in histological analysis. The fish in the 2F1 feeding frequency application was negatively impacted by growth performance, feed conversion, condition factor and haematological parameters. Although more feed is consumed in the F4 and F5 groups, the F3 group has a higher economic profit index (EPI). It has been concluded that a higher growth rate and improved health status can be achieved by feeding three times a day (F3) in the practice of mariculture of meagre.

A 60- day feeding trial was conducted to evaluate the growth, survival, physio- metabolic and haemato- biochemical responses of Anabas testudineus reared in (ISW) of varying salinity. Fingerlings (initial weight 6.55 ± 0.08 g) were randomly stocked in triplicate in five treatment groups viz., T1 (0 ppt), T2 (3 ppt), T3 (6 ppt), T4 (9 ppt) and T5 (12 ppt) following a completely randomized design (CRD) with 40/m2 stocking density. No mortality of fish was recorded in any of the treatments during the experimental period. Growth parameters such as weight gain (WG), percentage weight gain (PWG), specific growth rate (SGR) and protein efficiency ratio (PER) were highest (p < 0.05) at 3 ppt salinity followed by 6 and 0 ppt and lowest at 9 and 12 ppt, respectively. Lowest (p < 0.05) feed conversion ratio (FCR) and highest feed efficiency ratio (FER) were observed at 6 ppt salinity with no significant difference from fish at 0 and 3 ppt, respectively. Lowest (p < 0.05) moisture and highest protein and lipid contents were recorded at 3 ppt salinity. Digestive enzyme (protease and amylase) and oxidative stress enzyme (superoxide dismutase, SOD and catalase, CAT) activities were significantly (p < 0.05) higher in high saline groups (T4 and T5). Haemoglobin (Hb), haematocrit (Hct), erythrocytes and leukocytes were higher (p < 0.05) up to 6 ppt (T3) and reduced thereafter. Highest (p < 0.05) serum protein and globulin were recorded at 0 ppt salinity. T5 (12 ppt) group exhibited the highest (p < 0.05) serum glucose, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activity. The present study concluded that A. testudineus can be reared in ISW within an acceptable range of 0– 12 ppt salinity. However, salinity above 6 ppt had a negative effect on growth, feed utilization and various physiological parameters related to the well- being of the fish. Therefore, it can be opined that A. testudineus can be safely considered as a potential cultivable species for inland saline aquaculture up to a salinity of 6 ppt.

Macrobrachium nipponense, an important economic aquaculture species in China, is experiencing degradation of shrimp germplasm resources. Hybridization is a means of genetic improvement and can contribute to overcoming this serious problem. However, the molecular mechanisms of heterosis resulting from hybridization is unknown. In this study, LC–MS/MS combined with TMT tags were used for comparative proteomics analyses of the broodstock populations (Dianshan, DS) and hybrid offspring (DS ♀ × CD [Changjiang, CJ ♂ × Dongting, DT ♀], SCD) in M. nipponense. A total of 57 differentially expressed proteins (DEPs) were identified, of which 35 proteins were up‐regulated and 22 proteins were down‐regulated. The results showed that the 57 differential proteins correspond to three functional types, including 431 biological processes, 458 cellular components and 762 molecular functions. KEGG pathway analyses identified growth‐ and immunity‐related pathways, including alanine, aspartate and glutamate metabolism (ko00250), arginine biosynthesis (ko00220), arginine and proline metabolism (ko00330), hippo (ko04390), apoptosis (ko04215), p53 (ko04115) and complement system (ko04610). The expression of genes encoding the differentially expressed proteins were verified using real‐time quantitative PCR, and the results showed that the hybrid population was superior to the parent population in terms of growth and immunity. This study provided important data for genetic and breeding research of Macrobrachium nipponense.

Real‐time quantitative PCR (RT‐qPCR) is the most advanced and commonly used method for quantification of gene expression levels because of its high sensitivity, specificity and accuracy. The analytical capability of RT‐qPCR, on the other hand, is dependent on precise normalization by using the most stable reference genes. The present study was undertaken to find the best‐suited reference gene for normalization of qPCR data for ontogenetic studies of striped murrel. Four commonly used and constitutively expressed genes, namely beta‐actin (β‐actin), glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH), elongation factor 1‐alpha (EF1α) and 18 S ribosomal protein (18 S RNA) were screened and evaluated for their expression stability in developing larvae from 1 to 35 days post hatch (dph). The stability and suitability of these genes were determined by using four different algorithms; namely, delta Ct, BestKeeper, geNorm and NormFinder. The four algorithms together generated a comprehensive ranking EF1α being the most stable, followed by GAPDH and β‐actin as the least stable gene. This is the first report evaluating the most suitable reference gene for mRNA expression studies in C. striata, in the context of ontogenetic development.

The quality of pearls is related closely to the position where the nucleus is inserted. The visceral mass of freshwater pearl mussels has the physiological condition for the culture of pearls, but the appropriate position for inserting the nucleus has not been determined. In this study, the physiological responses and cultured pearl biology were used to explore the most suitable of five positions in the visceral mass for inserting the nuclei (I: the front end axe foot visceral mass, II: the central axe foot visceral group, III: near the gonad department, IV: near the stomach and V: near the kidney). Overall, kidney damage (urea nitrogen/BUN, urine creatinine/Cr, uric acid/UA) and calcium metabolism indicators were in decline, whereas liver damage indicators (aspartate aminotransferase/AST, alanine aminotransferase/ALT) rose. Enzyme activity index was determined by enzyme‐linked immunosorbent assay. These results indicated that the insertion caused metabolic disorders and immune inflammation. The axe foot visceral group was not significant that compared with the control group, so it was suitable for nucleation. The peak of granulocytes and hyalinocytes in the blood cells appeared on day 10 (thd) and exerted an early immune defence function. Furthermore, the granulosa synthesized by the epidermal cells of the pearl capsule was in the mature stage of normal nacre secretion, thus forming a thicker deposit of pearls. This study filled the gaps in knowledge of visceral mass cultivating pearls and provided a theoretical basis for artificial pearl breeding.

Black soldier fly (BSF, Hermetia illucens) meal is a prominent ingredient to keep up with the increasing demand of protein sources for aquafeeds. This study evaluated the digestibility of defatted BSF larvae meal (DBSFL) by indirect method, growth performance, haematological parameters, and carcass composition of tambaqui (Colossoma macropomum) fed diets containing DBSFL. The apparent digestibility coefficient of protein from DBSFL was 84.2%, corresponding to 42.9% of digestible protein. For the feeding trial, juvenile tambaqui (3.25 ± 0.01 g) were randomly distributed in 18 experimental units (100 L; n = 3; 27 fish/tank) in a recirculation system. Fish were fed to apparent satiation for 60 days with isoproteic and isocaloric diets containing 0%, 6%, 12%, 18%, 24% or 30% of DBSFL meal. At the end of feeding trial, fish length and weight were recorded; blood samples were drawn from caudal vein of three fish per tank, and three fish from each replicate were euthanized for analysis of carcass proximate composition. The inclusion of up to 30% DBSFL meal did not impair tambaqui growth performance and fish body composition. The blood cholesterol level of the fish fed diet with 30% DBSFL inclusion was higher, but within the limits recorded for that species. DBSFL meal seems to be an interesting and safe protein source for tambaqui farming. The use of this ingredient as protein source can encourage the circular economy by promoting environmental sustainability.

An 8‐week feeding trial was conducted to determine the optimal dietary protein requirement for tinfoil barb (Barbonymus schwanenfeldii) fry. Six isocaloric practical test diets (17 kJ g−1 gross energy) were formulated to contain 25%, 30%, 35%, 40%, 45% and 50% protein. Fry (0.40 ± 0.03 g) were randomly stocked in eighteen 60 L glass aquaria at 25 fish per aquarium. Each aquarium was fitted with an individual recirculation system. Each test diet was randomly assigned to three aquaria (triplicates), and the fish were fed twice a day until satiation. The results showed that survival was not significantly affected by the protein level. Weight gain was significantly higher at 50% dietary protein compared with those of lower levels. Fish fed with 50% protein also showed a significantly higher (p < 0.05) specific growth rate than fish fed with 25%–40% protein. Feed efficiency improved with the increase in dietary protein level. Feed conversion ratio (FCR) was 1.29 when fry were fed 50% dietary protein, whereas fry fed 25%–35% protein had FCR of 1.7–2.0. No histopathologic changes in the liver and intestine were observed among all dietary treatments. The results indicated that tinfoil barb fry required a high 50% protein for best growth performance and feed efficiency.

High temperature is considered to be one of the important causes of mass mortality of diploid and triploid oysters in summer. In order to compare the tolerance adaptability of diploid and triploid oysters to heat stress, the activities of superoxide dismutase activity (SOD), catalase activity (CAT) and contents of malondialdehyde (MDA) and the expression of Hsp70 and metallothionein (MT) genes in diploid and triploid oysters under acute and chronic heat stress were studied. The results showed that the survival rate of diploid oysters was significantly higher than that of triploid oysters under acute and chronic heat stress (p < 0.05). Under acute heat stress, the SOD levels in gills of both diploid and triploid oysters increased significantly from hour 3 (p < 0.05), but there was no significant difference in SOD levels between diploid and triploid oysters at all time points. The SOD level in hepatopancreas of triploid oysters was significantly higher than that of diploid oysters at all time points except 48 h (p < 0.05). The CAT level of diploid and triploid oysters decreased sharply at 48 h and that of diploid oysters was significantly higher than that of triploid oysters (p < 0.05). Under acute heat stress, the increase in MDA content in triploid oysters was significantly higher than that in diploid oysters (p < 0.05). Under acute heat stress, the expression levels of Hsp70 in the gills and hepatopancreas were significantly increased in diploid and triploid oysters (p < 0.05), but increased varies between gills and hepatopancreas. The expression levels of MT in the gills and hepatopancreas were significantly decreased in diploid and triploid oysters (p < 0.05). The results obtained in this study provide physiological and immunological evidence to explain differences in high‐temperature tolerance between diploid and triploid oysters and help us better understand the mass mortality of oysters that occurs during high temperatures in summer.

This study investigated the effects of the traditional Chinese medicines (TCMs) Huoxiangzhengqi decoction (HXZQD), Xiaochaihu decoction (XCHD) and Yinchenhao decoction (YCHD) on the biochemical parameters, antioxidant capacity and heat shock protein expression in rainbow trout (Oncorhynchus mykiss) under heat stress. The results showed that before stress, the serum glutathione peroxidase (GSH‐Px), catalase (CAT), hepatic heat shock protein 70 (HSP70) and heat shock protein 90β (HSP90β) mRNA expression levels in the trout were increased in the TCM groups, but the serum glucose (GLU), triglyceride (TG) and cholesterol (CHO) levels were decreased. Under heat stress at 20°C, the fishfed TCMs showed significantly decreased serum TG, CHO, creatinine (CRE) and alanine transaminase (ALT) levels (p < 0.05) and significantly increased serum CAT levels and hepatic HSP70 and HSP90β mRNA expression (p < 0.05). The AST level in the HXZQD group was significantly lower than that in the other groups (p < 0.05). Under heat stress at 25°C, the serum GLU, TG, CHO, aspartate aminotransferase (AST) and ALT concentrations were significantly lower in all the TCM groups than in the control group (p < 0.05). The CRE levels in the XCHD and HXZQD groups were significantly lower than those in the control group (p < 0.05), and the CAT activity in the HXZQD group was significantly higher than that in the control group (p < 0.05). The serum GSH‐Px activity and liver HSP70 and HSP90β mRNA expression in the fishfed TCMs were significantly higher than those in the control fish (p < 0.05). In conclusion, dietary supplementation with these TCMs could improve the physiological response, antioxidant capacity and the expression of two HSPs. The HXZQD group showed the best resistance to heat stress.

High‐density fingerling rearing of pengba was conducted for 90 days in biofloc system (BFS) to study the effect of stocking density on growth, feed utilization, water quality, water use efficiency and health of animals. The study was conducted in 12 continuously aerated tanks (50 m3), grouped into four treatments T‐1, T‐2, T‐3 and T‐4, which were stocked with pengba fry (1.25 ± 0.05 g, 4.74 ± 0.70 cm) at 50, 60, 70 and 80 m−3, respectively. Supplementary feed (1 mm floating pellet) was fed twice daily, each time for 30 min duration. Molasses and urea were supplemented to maintain suitable C:N ratio at 15:1. No water exchange was given, except monthly compensation of evaporation loss. While water quality and most of the growth attributes in T‐1 and T‐2 remained similar, T‐3 at 70 m−3 density showed better water quality, higher survival and growth than T‐4. Body composition remained consistent across treatments despite impaired feed digestion and utilization associated with higher densities. The non‐specific immune responses in fingerlings increased from T‐1 to T‐3, but further density rise showed compromised immune in T‐4. Such results suggested 70 m−3 to be an ideal density for production of healthier fingerlings. But T‐4 produced 13.5% more fingerlings than T‐3, and fingerlings (7.56 ± 0.50 cm; 5.43 ± 0.09 g) were within acceptable size range for grow‐out stocking. T‐4 also showed the lowest total water use and the highest water implicating 80 fry m−3 to have more applicability. Thus, the study recommends 70–80 m−3 as ideal range for fingerling rearing of pengba in BFS.

Sperm motility is an important character for the assessment of milt quality and indicator to the expected rate of fertilization. Many factors can affect the sperm motility, including nature of water used as sperm activator medium after stripping the milt from the male fish. The aim of this study was to gain motility to spermatozoa and improve sperm kinematic parameters by applying a non‐chemical method. The effects of magnetic field on samples of hatchery water exposed to magnetic field of 2.71, 4.51 and 8.11 mT for the duration of 12, 24 and 36 hours on Salmo trutta labrax sperm motility were investigated with computer‐assisted sperm analysis (CASA) system; 4.51 mT exposure for 36 hours (A2H3) was greater in motility kinematic parameters (p < 0.05) and progressive kinematic parameters (VAP, VSL and VCL) with values of (93.1244 ± 37.222, 88.6111 ± 36.137, 96.8378 ± 35.396 μm/s) and (102.9167 ± 32.546, 100.9767 ± 31.894, 105.8778 ± 30.401 μm/s) respectively. But there was no (p ≥ 0.05) in the slow phase just in the VCL parameter had (p ≤ 0.05) (35.8789 ± 39.127 μm/s) among other parameters. There was (p ≤ 0.05) in starting motility time until vibration point (s) for 4.51 mT in 12 hour (A2H1) (27.3333 ± 1.527 s), but total time of motility was greater for 4.51 mT in 36 hour (A2H3) with (p ≤ 0.05) (49.6667 ± 2.081 s) compared with other treatments.

This study examined the performance and suitability of two tropical anguillid eels, Anguilla bicolor pacifica and A. marmorata, under cage culture conditions. Juvenile eels (1.73 ± 0.14 g body weight) of each species were stocked in triplicate hapa net cages (1 × 1 × 1.5 m; 30 eels/cage) suspended in outdoor tanks. Growth, feed utilization, biochemical composition and blood chemistry of the two species were compared after 210 days. Except for survival, mean final body weight (FBW), weight gain percentage (WG), specific growth rate (SGR) and yield of A. bicolor pacifica (64.51 ± 13.07 g, 3514 ± 690%, 2.14 ± 0.12%/day, 1534 ± 380 g/m3) were significantly higher than that of A. marmorata (7.77 ± 2.90 g, 356 ± 125%, 0.89 ± 0.16%/day, 178 ± 89 g/m3). In comparison with A. bicolor pacifica, significantly lower feed intake (FI), feed efficiency (FE) and protein efficiency ratio (PER) observed in A. marmorata suggest the need to develop eel diets with feeding stimulants to improve feed acceptance. Biometric indices, body proximate and amino acid composition were not significantly different between the two species. However, serum glutamic oxaloacetic transaminase (GOT), glutamic pyruvic transaminase (GPT) and total protein (TP) in A. bicolor pacifica were significantly higher than that in A. marmorata. These findings suggest that the differences in growth performance and feed utilization between the two anguillid eel species are related to feed palatability, and that A. bicolor pacifica appears to be a suitable species for cage culture because of its faster growth.

Dabry's sturgeon (Acipenser dabryanus) is critically endangered in China. However, the lack of research on the feeding strategy of this species is detrimental to its conservation management. The present study evaluated the effects of feeding frequency (1, 2, 3, 4 and 5 times per day) on the growth performance, feed transit and digestive enzyme activity of juvenile Dabry's sturgeons (initial weight 0.42 ± 0.09 g) in a continuous flow culture system at a water temperature of 18.2–18.5°C. Single‐meal and normal‐feeding (1, 2, 3, 4 and 5 times per day) experimental methods were adopted to assess the effect of different feeding frequencies on feed transit. The fish in each treatment of the normal‐feeding experiment were fed normally according to the original feeding frequency (1, 2, 3, 4 and 5 times per day). The optimum feeding frequency for juvenile Dabry's sturgeons was determined to be 4 times per day based on the growth performance, feed conversion rate and digestive enzyme activity. The results of the single‐meal experiment demonstrated that changes in daily feeding frequency modified residence time in the stomach (S1–S5: 27.2–10.4 h) and intestine (S2–S5: range from 14 to 29.85 h). However, the obtained gastric emptying time varied significantly depending on the experimental approach. The single‐meal experiment approach resulted in a longer gastric emptying time of fish fed 1 and 2 times per day (S1: >35 h; S2: 35 h) than those in the normal‐feeding experiment (N1: 16 h; N2: 24 h), demonstrating that the single‐meal method might change the gastrointestinal emptying strategy of fish. Furthermore, the digestive enzyme activity had daily rhythmic changes and the average digestive enzyme activity was affected by feeding frequency. The average digestive enzyme activity of the fish in N3 or N4 was higher than those of fish in other groups (p < 0.05). In summary, this study provides much useful information for the healthy farming of juvenile Dabry's sturgeons and towards the understanding of digestive physiology, which is of great significance for the protection of Dabry's sturgeon.

Climate change poses increasing risks to global aquaculture in general and clam farming in particular. In Vietnam, clam farming has often encountered massive clam mortalities and the main reasons for that are weather‐related extreme events. This study, therefore, aims to assess risks and then propose mitigation solutions for clam farms in Northern Vietnam in the context of climate change. Five categories of risks for clam farms were identified and categorized, including (i) physical risks of nature, (ii) operational and technical risks, (iii) financial and market‐related risks, (iv) social and political risks (v) liability and consumer‐related risks. Each risk type was assessed for probability and consequence on a 5‐point scale. A risk matrix was used to define the level of risk as negligible, low, moderate, high or extreme. Results showed that clam farms in Northern Vietnam were at high or extreme risk from tropical cyclones and floods, severe temperature and salinity, environmental pollutants, infectious diseases and predators. The other risks ranged from negligible to moderate, except for the low quality of seeds, high stocking densities and unstable markets defined as high risk at some farms. Remarkable physical risks of nature detected in the present study indicate that greater awareness of risk management for clam farming is required if this activity is to be sustainable under climate change.

The present trial was conducted to investigate the effect of inclusion dried periphyton in Nile tilapia diets on growth, digestive enzymes activity, hematological, oxidative stress, and intestinal morphometric parameters. Five isoproteic (32%), isolipidic (5%) experimental diets were formulated, to comprise graded levels of dried periphyton (0, 2.5, 5, 7.5, and 10 g kg-1 diet). At the end of the feeding trial, the highest (P < 0.05) performance, feed utilization and survival rate were noticed in fish fed diet contained 7.5 and 10 g dried periphyton kg-1 diet. Also, intestinal amylase and lipase activity were markedly (P < 0.5) higher in fish fed 7.5 and 10 g dried periphyton kg-1 diet. Fish fed 10 g dried periphyton kg-1 recorded the highest (P < 0.05) value of hemoglobin, hematocrit, red, white blood cells, neutrocyte, lymphocytes, monocytes, and eosinophil count. The lowest level of ALT, AST and AP were observed in fish fed 10 and 7.5 g dried periphyton kg-1 diet. Serum total protein, albumin, globulin, phosphorus, and calcium were higher (P ≤ 0.05) in fish fed diets 5, 7.5 and 10 g dried periphyton kg-1 diet. However, the lowest (P < 0.05) content of creatinine, cholesterol, triglycerides, and LDL-C was noted in fish fed diets 7.5 and 10. Higher (P < 0.05) values of SOD and CAT were observed in fish fed diet contained 10 g dried periphyton kg-1 diet compared with other treatments. The lowest (P < 0.05) content of MDA content was attained by fish fed diets contained 7.5 and 10 g dried periphyton kg-1 diet. The current feeding trial showed the suitability of periphyton as a dietary supplement and its supplementation up to 7 g kg-1 diet in tilapia for improving growth, digestive enzyme, serum biochemical, antioxidant response and intestinal morphometric in Nile tilapia.

The Nile tilapia (Oreochromis niloticus) industry represent the 71% of aquaculture total world production and demands for novel feeds and better proteins. In this sense, Pacific thread herring (Ophistonema libertate) contains high-quality proteins suitable to produce protein hydrolysates (PH) with antioxidant activity for tilapia feeds. In this study, two Alcalase herring muscle PH were prepared at 10% and 30% degree of hydrolysis (DH) and were supplemented on two formulated feeds, FH10 and FH30 respectively. One hundred eighty tilapia juveniles were fed with the experimental and a control feed (CF) for 6 weeks and then submitted to an acute stress by temperature increment for 24 hours. The results revealed that organisms fed with the FH10 shown the highest (p < 0.05) weight increment compared to the other feeds, showing a better protein yield. The enzymatic activity of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) measured in Nile tilapia livers was influenced by the experimental feeds, the organisms fed with FH10 exhibited the highest activity in SOD and CAT and the best productive performance, while the tilapias fed with FH30 showed an elevated GPx activity, suggesting that herring muscle PH in feeds are a suitable option to bring a potential benefit for Nile tilapias.

Grass carp, a native Chinese freshwater fish species, has been widely introduced and established worldwide for different purposes (protein source, weed control agent, and sport fish). This species can be very effective in controlling aquatic plants. A few countries, such as Afghanistan, Myanmar, Laos and Vietnam, have cultured grass carp as human food for decades. In contrast, other countries, such as Bangladesh, India, and Iran, initially cultured grass carp as weed control agents and later transitioned to using them as food fish. The uncontrolled population of grass carp and the adverse ecological effects cause concern. Grass carp are a source of nutrients, including essential omega-3 fatty acids, eicosapentaenoicacid (EPA) and docosahexaenoic acid (DHA), which greatly benefit human health. Farming and consuming low trophic-level fish is more sustainable than relying on high trophic-level fish. A sustainable polyculture system yields positive social, economic, ecological and aquaculture outcomes. It involves culturing grass carp together with filter-feeding fish of different ecological requirements, feeding habits and behaviours in the same pond. The application of sustainable feeding materials (e.g., food processing waste and food waste-based fish feed pellets) may significantly improve sustainable aquaculture. It might mitigate the adverse ecological impacts experienced by some countries.

Black tiger shrimp (Penaeus monodon) is a commercially important species. It is reported to have low reproductive maturation rates in captivity. To improve the production of this species via sustainable aquaculture, genetic techniques are required to improve its maturation rates. However, to date, reports on P. monodon reproduction at a transcriptional level are limited. To address this, we conducted transcriptome sequencing of the ovaries and testes of P. monodon using high‐throughput sequencing to identify sex‐related pathways and genes. A total of 75.74 Gb of clean data were generated from nine gonadal tissue libraries. We obtained 62,276 unigenes with a mean length of 1452 bp and N50 of 2423 bp. A total of 11,411 significantly differentially expressed genes (DEGs) were identified between the testis and developed ovaries. Enrichment analysis of the DEGs identified 415 significantly enriched GO terms and 106 enriched KEGG pathways. Genes related to the P. monodon ovaries were enriched in the steroid biosynthesis, mRNA surveillance, nucleocytoplasmic transport, oxidative phosphorylation and DNA replication pathways. Five upregulated and five downregulated ovarian genes were confirmed using RT‐PCR. This investigation has thus identified important sex‐related functional genes, GO terms and pathways in P. monodon. In particular, we identified several important genes and pathways related to gonadal development, such as GnRH/GnRHR‐like, Hsp90, PCNA, cathepsin L, Wnt signalling pathway and ovarian steroidogenesis pathway, which provide important insights into the mechanism analysis and sex regulation of shrimp gonadal development. The results will provide reference data for future research into the reproductive biology of shrimp, which will aid in improved black tiger shrimp breeding in captivity.