Juvenile Grouper Research Articles

Effect of Amorphous Halomonas-PHB on Growth, Body Composition, Immune-Related Gene Expression and Vibrio anguillarum Resistance of Hybrid Grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatu ♂) Juveniles.

Poly-β-hydroxybutyrate (PHB) is a bacterial metabolite produced by bacteria such as Halomonas sp. that serves as a carbon and energy storage compound for bacteria under nutrient-limited conditions. Two experiments were conducted to investigate the effects of dietary supplementation with Halomonas-PHB on hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatu ♂). In experiment I, juvenile groupers were fed basal diets supplemented with 3% Halomonas-PHB (3% HM-PHB) containing 1.4% PHB and 3% Halomonas (3% HM) without PHB, as well as a control diet, for seven weeks. The results showed no significant difference in survival rate, weight gain, and crude fat content between the 3% HM-PHB group and the control group; however, the crude protein of the 3% HM-PHB group was significantly lower than that of the control group. Furthermore, supplementation with 3% HM-PHB increased the fatty acids content in fish muscles, including long-chain unsaturated fatty acids C18:1n9, EPA, and DHA. In experiment II, groupers were fed a basal diet supplemented with 6.5% Halomonas-PHB (6.5% HM-PHB) containing 3% PHB and 6.5% Halomonas (6.5% HM) containing no PHB, as well as a basal diet (Control). After seven weeks of rearing, the fish were challenged with Vibrio anguillarum for 48 h. Although no significant difference in survival rate and growth was observed among different groups, the dietary supplement of 6.5% Halomonas-PHB improved the survival rate of V. anguillarum challenged grouper and significantly increased the gene expressions of catalase (CAT) and superoxide dismutase (SOD) in blood, interleukin 1 (IL1) and interleukin 10 (IL10) in the liver, spleen, head kidney, and blood (p < 0.05). In conclusion, dietary supplementation of Halomonas-PHB had no significantly positive effect on fish growth performance but increased the content of fatty acids, including long-chain unsaturated fatty acids C18:1n9, EPA, and DHA in fish muscle; it also improved the V. anguillarum resistance, possibly through increasing immune-related gene expression in different tissues and organs. Our findings offer compelling evidence that Halomonas-PHB can be utilized as a feed additive in intensive grouper farming to enhance the groupers' resistance to Vibrio.

Effects of dietary fish oil replacement with rice bran oil on growth performance, serum biochemical index, antioxidant capacity, lipid metabolism and inflammatory response of large yellow croaker (Larimichthys crocea) juveniles

Fish oil (FO) replacement has become a top priority with the increasing growth of aquaculture and the decline of FO production. Dietary rice bran oil (RBO) has been marked with good application prospects and development potential in humans and terrestrial animals. Hence, this study was geared towards ascertaining the effects of replacing dietary FO with RBO in fish feeds. In this study, a 74-day feeding trial was conducted with large yellow croaker (Larimichthys crocea) juveniles to ascertain the effects of dietary FO replaced by different levels (0%, 25%, 50%, 75% and 100%) of RBO. Each diet was randomly fed to triplicate groups of large yellow croaker juveniles (120 fish per group) with an initial mean body weight of 13.02 ± 0.02 g. Fish fed with dietary RBO 25% showed significantly higher final body weight, weight gain rate, specific growth rate, and feed intake compared to other treatments. Also, fish fed diets with RBO showed significantly higher antioxidant capacity compared to the control. Interestingly, fish fed with RBO 25% diet showed a significantly improved serum lipid profile when compared to the control. Moreover, the hepatic mRNA expression of sterol regulatory element-binding protein-1 (srebp-1), and fatty acid synthase (fas) was significantly upregulated in RBO 25% replacement, while peroxisome proliferator-activated receptor α (pparα), was significantly suppressed in fish fed RBO 100% compared to the control. Furthermore, fish fed RBO 100% had significantly increased Interleukin-1β (il-1β), Tumour necrosis factor-α (tnf-α), and Interferon-γ (ifn-γ), and significantly decreased transcript levels of Interleukin-10 (il-10). Therefore, the results of the present study showed that RBO could promote the performance of large yellow croaker juveniles, by improving the growth indexes, serum biochemical properties, antioxidant capacity, and alleviating liver inflammation.

The toxic effects of tetracycline exposure on the physiological homeostasis of the gut-liver axis in grouper

Antibiotic residues, such as tetracycline (TET), in aquatic environments have become a global concern. The liver and gut are important for immunity and metabolism in aquatic organisms. In this study, juvenile groupers were subjected to 1 and 100 μg/L TET for 14 days, and the physiological changes of these fish were evaluated from the perspective of gut-liver axis. After TET exposure, the liver showed histopathology, lipid accumulation, and the elevated ALT activity. An oxidative stress response was induced in the liver and the metabolic pattern was disturbed, especially pyrimidine metabolism. Further, intestinal health was also affected, including the damaged intestinal mucosa, the decreased mRNA expression levels of tight junction proteins (ZO-1, Occludin, and Claudin-3), along with the increased gene expression levels of inflammation (IL-1β, IL-8, TNF-α) and apoptosis (Casp-3 and p53). The diversity of intestinal microbes increased and the community composition was altered, and several beneficial bacteria (Lactobacillus, Bacteroidales S24-7 group, and Romboutsia) and harmful (Aeromonas, Flavobacterium, and Nautella) exhibited notable correlations with hepatic physiological indicators and metabolites. These results suggested that TET exposure can adversely affect the physiological homeostasis of groupers through the gut-liver axis.

Feeding frequency affects liver health in largemouth bronze gudgeon Coreius guichenoti: Implications for lipid metabolism, oxidative stress, and inflammation response

In artificial breeding, feeding frequency is crucial for maintaining the liver health status in largemouth bronze gudgeon (Coreius guichenoti). Nevertheless, the underlying mechanism governing this relationship remains unclear. The present study aimed to elucidate the effects of feeding frequencies (2 T/D, 2 times day-1; 3 T/D, 3 times day-1) on the liver health of Coreius guichenoti. Groups of juveniles (60 fish group-1) with an initial body weight of 4.91 ± 0.11 g were randomly assigned to 6 tanks. Fish were fed with 2 T/D and 3 T/D for 8 weeks at a feeding rate of 3%. The results showed that the SGR and FER of the 3 T/D were higher than those of the 2 T/D (P < 0.05). Compared with the 2 T/D, the hepatic TG and glucose concentrations in the 3 T/D were decreased, but the hepatic TC, TBA, and lipase activity were increased (P < 0.05). Moreover, the relative areas of hepatic vacuoles and lipid droplets in the 3 T/D were decreased (P < 0.05). Furthermore, the hepatic activities of FAS and ACC1, and the mRNA levels of srebp1 in the 3 T/D were down-regulated (P < 0.05), while the mRNA levels of apoa1 and apoe2 were up-regulated. For liver antioxidant status, the hepatic GSH, SOD, and CAT levels in the 3 T/D were higher than those in the 2 T/D, while the hepatic MDA and ROS levels were lower (P < 0.05). For hepatic inflammation and apoptosis, the hepatic mRNA level of tgfβ1 was up-regulated in the 3 T/D, while the hepatic mRNA levels of tnfα, il1β, and caspase8 were down-regulated (P < 0.05). In conclusion, the 3 T/D improves the liver health of Coreius guichenoti by reducing hepatic lipid accumulation, oxidative stress, and inflammatory response. This improvement enhances feed utilization efficiency, resulting in better growth performance.

Dietary sodium butyrate positively modulated intestinal microbial community, but did not promote growth of largemouth bass (Micropterus salmoides).

This study investigated the effects of dietary sodium butyrate (NaB) on growth, serum biochemical indices, intestine histology, and gut microbiota of largemouth bass (Micropterus salmoides). A basal diet was formulated and used as the control diet (Con), and five additional diets were prepared by supplementing NaB (50%) in the basal diet at 2.0, 4.0, 8.0, 12.0, and 16.0 g/kg inclusion (NaB-2, NaB-4, NaB-8, NaB-12, and NaB-16 diets). Then, the six diets were fed to triplicate groups of largemouth bass juveniles (2.4 ± 0.1 g) for 8 weeks. NaB supplementation linearly and quadratically affected weight gain (WG) and feed intake (FI) (P < 0.05). The NaB-16 group displayed lower WG (- 6.8%) and FI than the Con group (P < 0.05), while no differences were found in WG and feed conversion ratio between the other NaB groups and Con group (P > 0.05). Serum alkaline phosphatase and lysozyme activities were higher in the NaB groups (P < 0.05), and D-lactate content was lower in the NaB-12 group (P < 0.05) than the control. Intestinal lipase activity in NaB-2, NaB-4 group, and villi width in NaB-8 group were also higher than those in the Con group (P < 0.05). Compared to the Con group, the intestinal abundances of Firmicutes and Mycoplasma were increased and the abundances of Proteobacteria, Achromobacter and Plesiomonas were decreased in NaB-4 and NaB-16 groups (P < 0.05). In conclusion, dietary NaB did not promote the growth of juvenile largemouth bass, but positively modulated the intestinal microbial community.

Identification of candidate SNPs and genes associated with resistance to nervous necrosis virus in leopard coral grouper (Plectropomus leopardus) using GWAS

The leopard coral grouper (Plectropomus leopardus), which has become increasingly popular in consumption due to its bright body color and great nutritional, holds a high economic and breeding potential. However, in recent years, the P.leopardus aquaculture industry has been impeded by the nervous necrosis virus (NNV) outbreak, leading to widespread mortality among fry and juvenile grouper. However, the genetic basis of resistance to NNV in P. leopardus remains to be investigated. In the present study, we conducted a genome-wide association analysis (GWAS) on 100 resistant and 100 susceptible samples to discover variants and potential genes linked with NNV resistance. For this study, 157,926 high-quality single nucleotide polymorphisms (SNPs) based on whole genome resequencing were discovered, and eighteen SNPs loci linked to disease resistance were discovered. We annotated six relevant candidate genes, including sik2, herc2, pip5k1c, npr1, mybpc3, and arhgap9, which showed important roles in lipid metabolism, oxidative stress, and neuronal survival. In the brain tissues of resistant and susceptible groups, candidate genes against NNV infection showed significant differential expression. The results indicate that regulating neuronal survival or pathways involved in lipid metabolism may result in increased resistance to NNV. Understanding the molecular mechanisms that lead to NNV resistance will be beneficial for the growth of the P. leopardus breeding sector. Additionally, the identified SNPs could be employed as biomarkers of disease resistance in P. leopardus, which will facilitate the selective breeding of grouper.

Establishment of a TaqMan probe-based qPCR assay for detecting microsporidia Enterospora epinepheli in grouper.

Enterospora epinepheli is an intranuclear microsporidian parasite causing serious emaciative disease in hatchery-bred juvenile groupers (Epinephelus spp.). Rapid and sensitive detection is urgently needed as its chronic infection tends to cause emaciation as well as white faeces syndrome and results in fry mortality. This study established a TaqMan probe-based real-time quantitative PCR assays targeting the small subunit rRNA (SSU) gene of E. epinepheli. The relationship between the standard curve of cycle threshold (Ct) and the logarithmic starting quantity (SQ) was determined as Ct = -3.177 lg (SQ) + 38.397. The correlation coefficient (R2 ) was 0.999, and the amplification efficiency was 106.4%. The detection limit of the TaqMan probe-based qPCR assay was 1.0 × 101 copies/μL and that is 100 times sensitive than the traditional PCR method. There is no cross-reaction with other aquatic microsporidia such as Ecytonucleospora hepatopenaei, Nucleospora hippocampi, Potaspora sp., Ameson portunus. The intra-assay and inter-assay showed great repeatability and reproducibility. In addition, the test of clinical samples showed that this assay effectively detected E. epinepheli in the grouper's intestine tissue. The established TaqMan qPCR assays will be a valuable diagnostic tool for the epidemiological investigation as well as prevention and control of E. epinepheli.

Oleic acid as modulator of oxidative stress in European sea bass (Dicentrarchus labrax) juveniles fed high dietary lipid levels

Although the benefits of oleic acid (OA) have been established in mammals, its effects on fish remain understudied. The aim of this study was to evaluate the antioxidant potential of OA in the liver, intestine, and muscle of European sea bass juveniles fed diets containing different lipid levels. For that purpose, six diets with 16 or 22% lipids and 0, 1, and 2% OA were formulated and triplicate groups of European sea bass juveniles (21.4 g) were fed with these experimental diets for 9 weeks. Increasing dietary lipid levels or OA supplementation did not affect antioxidant enzyme activity in the liver and muscle. Superoxide dismutase (SOD) activity in the intestine increased with both the dietary lipid and OA levels, while glucose 6 phosphate dehydrogenase (G6PDH) activity increased only with dietary OA supplementation. Reduced glutathione (GSH) and total glutathione (tGSH) content were higher in the liver and intestine of fish fed the low-lipid diets, while in the high-lipid diets it was lower in the muscle than in the liver and intestine. Present findings suggest that OA plays a role in the antioxidant defense mechanisms of European sea bass, particularly at the intestine level, but additional research is required to further assess the potential benefits of incorporating OA into the diets.

Environmentally relevant concentrations of Mn2+ disrupts the endocrine regulation of growth in juvenile Yunlong groupers (Epinephelus moara♀×Epinephelus lanceolatus♂)

Even though manganese is a bioelement essential for metabolism, excessive manganese levels in water can be detrimental to fish development and growth. Therefore, the aim of this study was to evaluate the effects of Mn2+ (0, 0.5,1, 2, and 4 mg·L−1) exposure for 30 d on the growth performance, growth hormone/insulin-like growth factor (GH/IGF) axis, hypothalamic-pituitary-thyroid (HPT) axis, and monoaminergic neurotransmitters of Epinephelus moara♀×Epinephelus lanceolatus♂(Yunlong grouper). Compared with the control and low Mn2+concentration groups of (0.5 and 1 mg·L−1), the high concentration of Mn2+ (4 mg·L−1) significantly reduced body weight (BW), body length (BL), weight gain rate (WGR), and specific growth rate (SGR), increased the feed coefficient rate (FCR) and mortality of Yunlong groupers (P < 0.05). Further, the levels of GH and IGF, along with the expression of ghra and ghrb were significantly reduced after exposure to 2 and 4 mg·L−1 Mn2+for 30 d, whereas the expression of sst5 was significantly up-regulated after exposure to 2 and 4 mg·L−1 Mn2+for 20 and 30 days. Moreover, Mn2+exposure increased thyroid hormone (T3) and thyroid stimulating hormone (TSH) contents, accompanied by increased mRNA levels of dio1 and dio2, however, the T4 level was decreased. Finally, dopamine (DA) and serotonin (5-HT) levels significantly decreased after long-term exposure to higher concentrations of Mn2+, and the levels their metabolites changed as well, suggesting that the synthesis and metabolism of DA and 5-HT were affected. Accordingly, changes in the GH/IGF and HPT axes-related parameters may be the cause of growth inhibition in juvenile groupers under Mn2+ exposure, indicating that the relationship between endocrine disorder and growth inhibition should not be ignored.

Growth performance and gene expression of FAS, CPT1, G6P, and HK in juveniles of the freshwater prawn, Macrobrachium acanthurus, fed diets with different levels of protein, lipids, and carbohydrates

AbstractA feeding trial with Macrobrachium acanthurus juveniles was performed to determine growth performance and utilization of diets varying in protein, lipid, and carbohydrate level. Twelve diets were formulated with three levels of protein (P) and supplemented with different proportions of lipids (L) and carbohydrates (C): P30‐L20‐C8, P30‐L15‐C19, P30‐L12‐C25, P30‐L10‐C31, P35‐L20‐C3, P35‐L15‐C15, P35‐L10‐C26, P35‐L5‐C38, P40‐L15‐C8, P40‐L10‐C19, P40‐L5‐C31, and P40‐L1‐C40. Lipids and carbohydrates were added allowing an overall energy content limit of 400 kcal per 100 g of diet. Each diet was fed to triplicate groups of juveniles with an initial weight of 60.9 ± 10.9 mg (mean ± SD) for 60 days. Overall growth performance and gene expression of fatty acid synthase (FAS), carnitine palmitoyltransferase 1 (CPT1), glucose‐6‐phosphatase (G6P), and hexokinase (HK) in the hepatopancreas were assessed. Highest weight gain values and specific growth rates were observed in prawns fed diets with 35% of protein inclusion. Expression of FAS was downregulated when fed 30% of protein. Results indicate M. acanthurus use protein as their primary source of energy and when this is low in the diet, lipids are used to spare the energy from proteins. Suggested inclusion of protein, lipids, and carbohydrates in diets for M. acanthurus should be 35%, 15%, and 15%, respectively.

Studies of fish breeding biological and genetic parameters of stellate sturgeon (Acipenser stellatus Pallas, 1771) offspring obtained using native and cryopreserved sperm

Comparative results of experimental work on the study of stellate sturgeon offspring obtained using cryopreserved (experimental) and native (control) sperm, carried out at the scientific and experimental complex of aquaculture “BIOS” of the Volga-Caspian branch of VNIRO (CaspNIRKH) in this article were presented. Molecular genetic studies of cryopreserved sperm, females and males from the brood stock of the complex were carried out. In order to select the optimal parental pairs, calculations of genetic relationship of fish spawners were made. The scheme of the experiment was developed. The technological process of working with stellate sturgeon spawners was described: obtaining mature reproductive cells, insemination, incubation of caviar. Holding and breeding of the studied groups of stellate sturgeon juveniles up to standard weight was carried out. Each stage of the research work was subjected to comparative analysis. The genetic diversity of juveniles was studied. As a result of the work carried out, it was found that the group of fish obtained using of cryopreserved sperm had higher weight indicators, compared with the juveniles of the control group obtained from males from the brood stock of “BIOS”, by an average of 16%. In addition, the experimental group had a higher homogeneity compared to the control group, as evidenced by the values of the coefficients of variation. The survival rate of juveniles of the experimental group of fish was higher than the control group by an average of 10%. The stellate sturgeon obtained using cryopreserved sperm was characterized by higher values of the total number of alleles and the absence of a deficit of heterozygotes compared to the control group of juveniles, which is especially important for preserving the diversity of this valuable sturgeon species. The results of the research work carried out will help develop proposals for the formation of artificially created sturgeon brood stocks by replenishing them with juveniles obtained using cryopreserved sperm and having higher fish breeding biological and genetic indicators. This will allow the herd to have a stock of working material from different generations of sturgeon species, which is a promising factor for the conservation of aquatic biological resources and selection in commercial aquaculture.

Effect of replacing a portion of fish meal with unfermented and/or fermented soybean meal on the growth performance, antioxidant and immunity capacity and related gene expression in juvenile Coho Salmon, Oncorhynchus kisutch

AbstractThis study investigated the effect of replacing a portion of fish meal with unfermented and/or fermented soybean meal in juvenile coho salmon (Oncorhynchus kisutch). Four groups of juveniles (initial weight 110.31 ± 3.12 g) in triplicate were fed for 90 days on four different iso‐nitrogen and iso‐lipid diets. The G0 diet comprised 28% fish meal protein (control group). In the other three diets (G1, G2, and G3), 10% of the fish meal protein was replaced with unfermented and/or fermented soybean meal protein. The main results were: Compared with G0, the WGR, SGR, CF; the contents of GLU, TP, ALB, T‐CHO, and T‐AOC, the activities of AKP, CAT, SOD, GST, GSH‐PX, O2·‐CR, OH·‐CR, and GSH and the expressions of SOD, GSH‐PX, GST, CAT, and Nrf2 genes of juvenile coho salmon in G3 were significantly (p &lt; 0.05) increased, However, the FCR, HSI, the content of MDA, and the expressions of TNF‐α and IL‐6 genes of juvenile coho salmon in G3 were significantly (p &lt; 0.05) decreased. There was no significant effect (p &gt; 0.05) of diet on their survival rate (SR). In conclusion, the fermented soybean meal in the juvenile coho salmon diet can replace 10% of the fish meal protein.

Effect of dietary protein, lipid and carbohydrate ratio on growth, digestive and antioxidant enzyme activity of prawn Macrobrachium acanthurus postlarvae

Macrobrachium acanthurus is a freshwater prawn with aquaculture potential. However, little is known about its nutrient requirements, particularly regarding protein and lipid-carbohydrate ratio interactions in the diet. To assess the effect of these macronutrients in growth performance and the activity of digestive and antioxidant enzymes, a 2 × 3 factorial design experiment was conducted using two different levels of protein (P35 and P40) and three lipid-carbohydrate ratios (L:C ratio): 2:1 (20 % L and 10 % C), 1:2 (10 % L and 20 %) and 1:6 (5 % L and 30 % C). Each diet was fed to triplicate groups of juveniles with an initial mean weight of 0.075 ± 0.015 g for 60 days. No significant differences in growth performance were found. Although treatment P35 LC 1:2 showed the highest values of weight gain and specific growth performance, survival rate in this diet was lowest among treatments. Interaction between protein and L:C ratio influenced trypsin, chymotrypsin, leucine aminopeptidase and amylase activities, but protein content alone affected the alkaline proteases. Lipase did not differ among treatments. Catalase, glutathione peroxidase, total antioxidant capacity, phenoloxidase and prophenoloxidase activities were also influenced by protein and lipid-carbohydrate interaction; however, super oxide dismutase activity was only affected by dietary protein level. The highest activities of phenoloxidase and prophenoloxidase were observed in prawns fed diet P40 and L:C ratio 1:6 which suggests oxidative stress. These results suggest that 35 % dietary protein and 10 % lipids and 20 % carbohydrates (L:C ratio 1:2) are optimal for growth performance and activity of digestive and antioxidant enzymes. However, measures should be taken to avoid cannibalism and increase the survival rate.

Growth Performance, Antioxidant and Immunity Capacity Were Significantly Affected by Feeding Fermented Soybean Meal in Juvenile Coho Salmon (Oncorhynchus kisutch)

This study aims to investigate the effects of partial dietary replacement of fish meal with unfermented and/or fermented soybean meal (fermented by Bacillus cereus) supplemented on the growth performance, whole-body composition, antioxidant and immunity capacity, and their related gene expression of juvenile coho salmon (Oncorhynchus kisutch). Four groups of juveniles (initial weight 159.63 ± 9.54 g) at 6 months of age in triplicate were fed for 12 weeks on four different iso-nitrogen (about 41% dietary protein) and iso-lipid (about 15% dietary lipid) experimental diets. The main results were: Compared with the control diet, the diet with replaced 10% fish meal protein with fermented soybean meal protein supplementation can significantly (p < 0.05) influence the expression of superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase, nuclear factor erythroid 2-related factor 2, tumor necrosis factor α and interleukin-6 genes, the growth performance, the serum biochemical indices, and the activity of antioxidant and immunity enzymes. However, there was no significant effect (p > 0.05) on the survival rate (SR) and whole-body composition in the juveniles among the experimental groups. In conclusion, the diet with replaced 10% fish meal protein with fermented soybean meal protein supplementation could significantly increase the growth performance, antioxidant and immunity capacity, and their related gene expression of juveniles.

Antiviral immunity of grouper MAP kinase phosphatase 1 to Singapore grouper iridovirus infection

Singapore grouper iridovirus (SGIV), with various mechanisms for evading and modulating host, has inflicted heavy economic losses in the grouper aquaculture. MAP kinase phosphatase 1 (MKP-1) regulates mitogen-activated protein kinases (MAPKs) to mediate the innate immune response. Here, we cloned EcMKP-1, an MKP-1 homolog from the orange-spotted grouper Epinephelus coioides, and investigated its role in the infection of SGIV. In juvenile grouper, EcMKP-1 was highly upregulated and peaked at different times after injection with lipopolysaccharide, polyriboinosinic polyribocytidylic acid and SGIV. EcMKP-1 expression in heterologous fathead minnow cells was able to suppress SGIV infection and replication. Furthermore, EcMKP-1 was a negative regulator of c-Jun N-terminal kinase (JNK) phosphorylation early in SGIV infection. EcMKP-1 decreased the apoptotic percentage and caspase-3 activity during the late stage of SGIV replication. Our results demonstrate critical functions of EcMKP-1 in antiviral immunity, JNK dephosphorylation and anti-apoptosis during SGIV infection.

Effects of prior acclimation on the survival, feed intake and salinity preference of a freshwater-adapted euryhaline crab

Abstract In estuarine systems, salinity changes by freshwater inflows and tides affect the survival and behaviour of euryhaline species. Juvenile Chinese mitten crabs, Eriocheir sinensis, are considered to live in fresh water during their complex life history, whilst some are found in coastal wetlands. To understand how juveniles disperse in estuarine residence, we investigated their survival, feed intake and salinity preference after acclimating in three different water situations (i.e., fresh water, salt water and alternation between fresh water and salt water). We supposed that behavioural alternation and salinity preference would play an essential role in their acclimation. Results showed no significant difference in survival and feed intake amongst the three groups of juveniles () in acclimation trials. However, the feed intake of crabs in each group was declining after changing water every three days. In the salinity preference experiment, crabs from fresh water preferred 0 and 12, whereas those from salinity and alternation treatments showed no preference. The salinity preference seemed to be modified by prior acclimation as well, and juvenile crabs could therefore survive and disperse in the different salinities. Our study helps to explain the complex distribution of juveniles in estuaries and provides arguments for the feasibility of Chinese mitten crabs being reared in low salinity waters.

Glycerol Monolaurate Alleviates Oxidative Stress and Intestinal Flora Imbalance Caused by Salinity Changes for Juvenile Grouper.

Groupers with an initial body weight of 9.10 ± 0.03 g were selected to investigate whether dietary addition of 0 (G0) and 1800 mg/kg glycerol monolaurate (GML, G1800) could alleviate the oxidative stress response and intestinal flora imbalance after 0, 6, 12, and 24 h of salinity change in grouper. Experimental results show that the dietary addition of GML significantly reduced the liver MDA content and increased the SOD activity of grouper. The gene expression of CAT and SOD increased and then decreased with time after adding 1800 mg/kg GML, and the highest values were significantly higher than those of the control group. Salinity change had a slight effect on the top four intestinal flora composition of grouper at 0, 12, and 24 h, with changes occurring only at 6 h when Cyanobacteria replaced Actinobacteria. The addition of dietary GML slowed down the intestinal flora disorder, inhibited the colonization of harmful bacterium Vibrio, and promoted the abundance of beneficial bacterium Bacillus. In conclusion, dietary GML significantly reduced the oxidative damage caused by sudden changes in salinity, improved the antioxidant capacity, and alleviated the intestinal flora imbalance in juvenile grouper.

Unraveling site fidelity and residency patterns of sperm whales in the insular oceanic waters of Macaronesia

Knowledge of the distribution and residency of pelagic marine megafauna, particularly deep-diving species, is scarce due to their high mobility over difficult-to-access oceanic areas and long periods underwater. However, the threatened status of many of these species, such as the sperm whalePhyseter macrocephalus, increases the need to obtain quantitative data to support conservation measures. In the warm temperate waters of Macaronesia (Eastern North Atlantic), sperm whales occur year-round in a set of island systems (the Azores, Madeira, and the Canaries), mainly in social groups of females and juveniles with the occasional visits of mature males. Although it is known that they perform inter-archipelago movements, information on site fidelity and residency times is still scarce. Here, based on photographic-identification data, site fidelity and residency times of sperm whales were estimated for subareas of the Azores and the Madeira archipelagos, with a preliminary assessment for a subarea of the Canaries. The Azores and Madeira subareas presented similar proportions of individuals with recaptures (~25%), mainly inter-annual, while in the subarea of the Canaries, only &amp;lt;10% of the individuals were recaptured. Standardized Site Fidelity Indexes showed very low values (&amp;lt;0.01) for both the Azores and Madeira subareas. Lagged identification rates based on models including emigration and reimmigration estimated that an average of 44.8 individuals (SE=4.9) spent 12.9 days (SE=1.5) in the Azores before leaving for 99.1 days (SE=12.5), while 8.4 individuals (SE=16.1) spent 0.8 day (SE=6.6) in Madeira before leaving for 8.6 days (SE=6.9), with a very low mortality rate. This study i) indicates a degree of residency of about ¼ of the identified individuals for the Azores and Madeira subareas and ii) supports that these oceanic archipelagos constitute an important habitat for a Vulnerable species in the Atlantic. Moreover, it also highlights the importance of combining data from opportunistic and dedicated surveys and joint national and international efforts toward the conservation of marine megafauna.

Acute lethal toxicity of dried garlic (Allium sativum) powder on orange-spotted grouper (Epinephelus coioides) juveniles under static exposure

The present study was carried out to assess the toxic effect and determine the lethal concentration of dried garlic (Allium sativum) powder on the orange-spotted grouper (Epinephelus coioides) juveniles. Laboratory static bioassays were conducted to determine the 96-h LC50 of different concentrations of garlic (0, 30, 60, 90, 120, 150 and 180 mg L-1) on grouper juveniles (mean weight, 35.4±6.18 g and mean length, 13.2±0.51 cm). The 96-h LC50 was 74.78 mg L-1 with lower and upper confidence limits of 62.8 and 89.06 mg L-1, respectively. All fish exposed to 30 to 180 mg L-1 exhibited rapid movement, faster opercular activity and erratic swimming whereas at higher concentrations (90 mg L-1 to 180 mg L-1) fish showed additional behavioral changes such as loss of balance, lethargy, gulping for air and respiratory distress. Water quality parameters were within the recommended acceptable limits. This LC50 value can be used as a baseline reference to generate an effective concentration of garlic for future prophylaxis and treatment for parasitic, viral and bacterial infection in grouper.

Effects of the Replacement of Dietary Fish Meal with Defatted Yellow Mealworm (Tenebrio molitor) on Juvenile Large Yellow Croakers (Larimichthys crocea) Growth and Gut Health.

Simple SummaryFish meal is the most common protein source in aquatic feeds. The decline of fishery resources and the increased demand have led to a shortage of fish meal resources in recent years. To ensure the sustainable development of the aquaculture industry, it is crucial to find a low-price, high-quality protein source to replace fish meal. In this study, substituting fish meal of large yellow croakers (Larimichthys crocea) diets with defatted yellow mealworm (Tenebrio molitor) test was carried out. The results showed that the dietary fish meal could be replaced by 15% defatted yellow mealworm in feeds containing 40% fish meal without adversely affecting the growth of large yellow croakers, and to some extent improving the immunity of the organism. Substitution levels of 15% or more are beneficial for digestive enzymes. In addition, the moderate addition of defatted yellow mealworm improves intestinal health by improving the structure and microbial composition of the gut.This study was conducted to investigate the effects of Tenebrio molitor meal (TM) replacement for fish meal (FM) on growth performance, humoral immunity, and intestinal health of juvenile large yellow croakers (Larimichthys crocea). Four experimental diets were formulated by replacing FM with TM at different levels—0% (TM0), 15% (TM15), 30% (TM30), and 45% (TM45). Triplicate groups of juveniles (initial weight = 11.80 ± 0.02 g) were fed the test diets to apparent satiation two times daily for eight weeks. There was no significant difference in final body weight (FBW) and weight gain rate (WG) among TM0, TM15, and TM30, while TM45 feeding significantly reduced the FBW and WG. Compared with TM0, AKP activity in serum was significantly decreased in TM45, while the TM15 group remarkably increased LZM activity. TM30 showed significantly higher serum C3 levels compared to the TM0 group, while the TM addition groups decreased the C4 levels significantly in the serum. In terms of intestinal histology, the addition of TM increased the height and thickness of the intestinal villus and also increased the thickness of the intestinal muscles significantly. The addition of TM significantly reduced the serum DAO and D-lactate concentrations. The results of 16S rRNA gene sequencing showed that the addition of TM significantly enhanced the relative abundance of Bacilli and Lactobacillus and contributed to the decrease in the relative abundance of Plesiomonas. In addition, the TM30 and TM45 groups significantly reduced the abundance of Peptostreptococcaceae. Overall, our results indicated that TM could be a viable alternative protein source, 6.7% TM supplantation (replacing 15% FM) in large yellow croaker feed improved humoral immunity and intestinal health with no adverse effects on growth. Furthermore, the replacement of FM with 30% and 45% TM adversely affects growth and humoral immunity.