Red Sea Bream Research Articles

Molecular characteristics, expression analysis and antiviral activity against RSIV of red sea bream IRF3 and IRF7

Interferon regulatory factor (IRF) 3 and IRF7 are important innate immune-related genes that induce type I interferon (IFN). In this study, PmIRF3 and PmIRF7 were identified from red sea bream (Pagrus major) infected by red sea bream iridovirus (RSIV), and expression and functional analyses were performed. PmIRF3 and PmIRF7 consisted of 465 and 436 amino acids, respectively, and contained a well-conserved IRF domain, IRF3 domain, and serine-rich domain (SRD). PmIRF3 and PmIRF7 are ubiquitously expressed in the liver and gills in normal fish, and with a high expression being recorded in kidney and spleen during RSIV infection. In P. major fin cells (PMF cells), pAcGFP-PmIRF3 and pAcGFP-PmIRF7 were localized to the cytoplasm, and overexpression of PmIRF3 and PmIRF7 using the pcDNA3.1 vector induced type I IFN. In addition, in the experiment in vitro, PMF cells overexpressed with PmIRF3 or PmIRF7 exhibited antiviral activity against RSIV and significantly reduced viral genome copies and virus titer. Therefore, PmIRF3 and PmIRF7 may have antiviral activity through the induction of type I IFN against RSIV infection of red sea bream.

Effects of sodium chloride treatment and short-term aging on the amount of taste-related compounds in meat of red sea bream <i>Pagrus major</i>

Effects of sodium chloride treatment and short-term aging on the amount of taste-related compounds in meat of red sea bream <i>Pagrus major</i>

Chronic effects of environmental concentrations of antifoulant diuron on two marine fish: Assessment of hormone levels, immunity, and antioxidant defense system

The presence and toxicity of waterborne diuron in aquatic environments pose a severe threat to non-target organisms. However, the chronic impact of diuron in marine fish has been poorly investigated. In this study, we report the chronic effects (30 and 60 days) of environmentally relevant concentrations of diuron (0.1, 1, and 10 μg L−1) on economically important marine fish, red seabream (Pagrus major), and black rockfish (Sebastes schlegelii) by evaluating several parameters, including hormone levels, immunity, hepatic function, and antioxidant defense. Significant decreases in 17β–estradiol and 11–ketotestosterone levels and gonadosomatic index were observed on day 60 in fish exposed to 10 μg L−1 diuron. Parameters of immunity, such as alternative complement activity, lysozyme activity, and total immunoglobulin levels, were significantly lowered by 60-day exposure to 10 μg L−1 diuron in both fish. Significant decreases in the hepatic enzyme activities of alanine transaminase and aspartate transaminase were observed with an induction of cortisol on day 60 in fish exposed to 10 μg L−1 diuron. Intracellular malondialdehyde and glutathione levels were significantly increased by 10 μg L−1 diuron at day 60 with an increase in the enzymatic activities of catalase and superoxide dismutase. Overall, black rockfish were more sensitive to diuron than red seabream. These results suggest that consistent exposure to environmentally relevant concentrations of diuron is detrimental to the reproduction, immunity, and health of marine fish.

Electrical Stunning Has the Potential to Delay Fillet Degradation Post-Harvest in Red Seabream (Pagrus major)

Ensuring the humane harvest of farmed fish without compromising the quality of the fresh product is paramount to the welfare of fish and in meeting consumer demands. Electrical stunning is a quick and effective way to render fish unconscious and it has emerged as the suggested harvest method by EFSA and OIE. The present study evaluated the effects of electrical stunning on the biochemical processes that lead to fillet degradation postmortem, in the red seabream (Pagrus major). Two distinct electrical stunning conditions (low and high) were compared along with the conventional harvest method (an ice slurry). The activity patterns of calpain, collagenase, and cathepsin B and L were assessed and compared to stereological changes in white muscles at different time points up to 13 days post-harvest. Histological examinations, independent of the harvest technique, revealed a progressively declining trend in fiber volume density and increasing interfibrillar spaces over time, indicative of degradation activity within and between the muscle fibers. Strong correlations between the stereological measures and the individual protease activities were recorded. The higher current condition (electric field 1.8 V/cm and velocity 1.6 m/s) consistently exhibited the lowest protease activity levels and the slowest pace of stereological changes, making it the suggested method of all harvest methods explored.

Generation of monoclonal antibodies against heterologously expressed major capsid protein of infectious spleen and kidney necrosis virus (ISKNV)

Infectious spleen and kidney necrosis virus (ISKNV) is one of the detrimental viruses causing economic losses in several fish species including Asian sea bass (Lates calcarifer). In this study, monoclonal antibodies specific to major capsid protein (MCP) of ISKNV were generated. The MCP encoding gene of ISKNV genotype II was cloned into pGEX-6P-1 and transformed into E. coli. After induction, a glutathione-S-transferase (GST)-MCP fusion protein was produced and used for immunization of Swiss mice for monoclonal antibody (MAb) production. Five MAbs specific to MCP were obtained after selection against naturally ISKNV-infected Asian sea bass by dot blotting, Western blotting and immunohistochemistry. All MAbs showed no cross-reaction with fish tissues, fish viruses including tilapia lake virus (TiLV), nervous necrosis virus (NNV), scale drop disease virus (SDDV) and eight bacterial species commonly found in diseased fish. The detection sensitivity of MAbs was inferior to that of one step PCR. However, a combination of two MAbs enhanced the detection limit about two-fold. The intense immunoreactivity staining could be observed in liver, kidney, gill, intestine, stomach, and spleen tissues from ISKNV-infected fish by immunohistochemical analysis. All five MAbs can be used to detect naturally ISKNV-infected fish from two different farms and phylogenetic tree analysis based on MCP gene sequences demonstrated ISKNV genotype I infection in diseased fish. In addition, all MAbs displayed immunoreactivity to red sea bream iridovirus (RSIV) in the GF cell culture fluid by dot blotting. Therefore, the generated MAbs could be used for detection of ISKNV infection by various immunological assays and might be able to detect RSIV infection as well.

Wild fish and seafood species in the western Mediterranean Sea with low safe mercury concentrations

A total of 1345 specimens belonging to 58 different species of wild fish and seafood from the western Mediterranean Sea were analyzed to assess total mercury levels and to estimate which species meet the EU recommendations for human consumption (0.5 μg g−1 ww) in all cases. All fish species were caught off the Mediterranean coasts and intended for human consumption. All specimens were collected from local markets located in Spain, Italy and France that sell fish caught by local fishermen (Eivissa, Menorca, Mallorca, Alacant, L'Ampolla, Ametlla de Mar, Marseille, Genoa, Civitavecchia, Alghero) at different time periods. Mercury concentrations were measured by thermal decomposition-gold amalgamator-atomic absorption spectrometry.Only thirteen species were found that did not exceed 0.5 μg g−1 ww in any specimen analyzed. These safe species were sardines (Sardina pilchardus), anchovies (Engraulis encrasicolus), blue whiting (Micromesistius poutassou), picarel (Spicara smaris), blackspot seabream (Pagellus bogaraveo), gilthead seabream (Sparus aurata), pearly razorfish (Xyrichtys novacula), surmullet (Mullus surmuletus), painted comber (Serranus scriba), brown meagre (Sciaena umbra), salema (Sarpa salpa), common dolphinfish (Coryphaena hippurus) and squid (Loligo vulgaris). These species occupy different trophic levels, have different lengths and average weights, but show a low mercury concentration than others living in the same environments.Potential human consumption of these species as sole source of fish would imply estimated weekly intakes representing between 49% and 70% of the recommended provisional tolerable weekly intake of methylmercury in the worst case.Health authorities should pay specific attention to species that do not meet EU thresholds and make appropriate precautionary health recommendations, especially for pregnant women and children.

A case report of interspecies transmission of nervous necrosis virus (NNV) between red seabream brood (Pagrus major) and juvenile Pacific cod (Gadus macrocephalus)

The viral infectious disease called viral nervous necrosis (VNN) or viral encephalopathy and retinopathy (VER) is a particularly lethal virus for larvae and juvenile fish, and seven genotypes have been reported thus far. These viruses are capable of both vertical and horizontal transmission. In this study, molecular biological and histopathological analyses were performed to determine the cause of mass mortality in juvenile Pacific cod (Gadus macrocephalus), which began to feed on red seabream (Pagrus major) eggs. Vacuolization, one of the characteristic symptoms of VNN, was confirmed in the brain and eyes of brood red seabream (P. major) and juvenile Pacific cod (G. macrocephalus). In addition, the inclusion body-like structure was confirmed in the electron microscopic analysis of the gonads and eggs of brood red seabream (P. major). In molecular biological analysis, the target bands were also found in the brain, kidney, liver, spleen, gonad (P. major brood only), and egg (P. major brood only). This vertical/horizontal interspecies transmission needs to be controlled with particular care when producing seedlings, considering that seedlings can be produced for release for the creation or recovery of aquatic resources in addition to aquaculture.

Identification and functional analysis of histone 1.2-like in red sea bream (Pagrus major)

Histone H1 acts as an essential chromatin component and participates in the formation of higher chromatin structures together with core histones. In addition, H1 also has important functions in physiological processes such as gene expression regulation, DNA repair, and the immune response. In this study, the histone homologous protein Pm-H1.2-like was identified from the transcriptome database of Pagrus major we studied previously. Conservatism of evolution was investigated by sequence alignment and phylogenetic analysis. Transcripts of Pm-H1.2-like were detected in P. major tissues. The highest expression level was found in gill and skin tissues. Consistent with the data from the transcriptome database, we observed that the expression of Pm-H1.2-like was rapidly induced in nonspecific cytotoxic cells (NCCs) infected with inactivated Vibrio anguillarum. Gene silencing of Pm-H1.2-like by RNAi significantly suppressed the expression of NK-lysin and GZMB in NCCs at 12 h after pathogen stimulation, but had no significant effect on IFN-γ expression. Next, we obtained the fusion proteins rPm-H1.2-like and rPm-H1.2-like (36–80) through prokaryotic expression. ELISA showed that rPm-H1.2-like bound to oligonucleotide (ODN) in a concentration-dependent manner, while no binding activity of rPm-H1.2-like (36–80) with ODN was observed. This study confirmed that Pm-H1.2-like actively participates in the immune response of NCCs to bacterial infection, deepening the understanding of the immune features of histone H1 in fish.

Development and Validation of a Quantitative Polymerase Chain Reaction Assay for the Detection of Red Sea Bream Iridovirus

The analytical and diagnostic performances of methods for detecting red sea bream iridovirus (RSIV), which infects marine fish, have not been evaluated. As disease management and transmission control depend on early and reliable pathogen detection, rapid virus detection techniques are crucial. Herein, we evaluated the diagnostic performance of a TaqMan-based real-time polymerase chain reaction (PCR) assay that detects RSIV rapidly and accurately. The assay amplified the RSIV, infectious spleen and kidney necrosis virus, and turbot reddish body iridovirus genotypes of Megalocytivirus and the detection limit was 10.96 copies/reaction. The assay’s performance remained uncompromised even in the presence of nine potential PCR inhibitors, including compounds commonly used in aquaculture. The variation of the cycle threshold values between assays performed by three technicians was evaluated using a plasmid DNA containing the major capsid protein gene sequence. The variation between replicates was low. The diagnostic sensitivity and specificity of the developed assay were evaluated using fish samples (n = 510) and were found to be 100% and 99.60%, respectively. Two technicians evaluated the reproducibility of the assay using fish samples (n = 90), finding a high correlation of 0.998 (p < 0.0001). Therefore, the newly developed real-time PCR assay detects RSIV both accurately and rapidly.

Red Sea Bream Iridovirus (RSIV) Kinetics in Rock Bream (Oplegnathus fasciatus) at Various Fish-Rearing Seawater Temperatures.

Simple SummaryRed sea bream iridoviral disease (RSIVD) generates serious economic losses by causing mass mortality events of rock bream during the season with high water temperature in the Republic of Korea and other Asian countries. However, very few studies have investigated RSIV kinetics in rock bream under various rearing water temperatures. In this paper, we investigated the viral load shedding of RSIV into seawater after artificially infecting rock bream (Oplegnathus fasciatus) with the virus. Overall, our data suggest that the viral load shedding of RSIV into seawater varies depending on water temperature and virus inoculation concentration. Our results reveal the potential of non-invasive virus detection approaches, such as the utilization of environmental DNA in fish farms. In addition, we showed that the quantitative analysis of seawater viruses can indirectly improve our understanding of disease progression in fish, potentially contributing to enhanced disease control.Red sea bream iridoviral disease (RSIVD) causes serious economic losses in the aquaculture industry. In this paper, we evaluated RSIV kinetics in rock bream under various rearing water temperatures and different RSIV inoculation concentrations. High viral copy numbers (approximately 103.7–106.7 RSIV genome copies/L/g) were observed during the period of active fish mortality after RSIV infection at all concentrations in the tanks (25 °C and 20 °C). In the group injected with 104 RSIV genome copies/fish, RSIV was not detected at 21–30 days post-infection (dpi) in the rearing seawater. In rock bream infected at 15 °C and subjected to increasing water temperature (1 °C/d until 25 °C) 3 days later, the virus replication rate and number of viral copies shed into the rearing seawater increased. With the decrease in temperature (1 °C/d) from 25 to 15 °C after the infection, the virus replicated rapidly and was released at high loads on the initial 3–5 dpi, whereas the number of viral copies in the fish and seawater decreased after 14 dpi. These results indicate that the number of viral copies shed into the rearing seawater varies depending on the RSIV infection level in rock bream.

Dietary Supplementation of Bacillus sp. PM8313 with β-glucan Modulates the Intestinal Microbiota of Red Sea Bream (Pagrus major) to Increase Growth, Immunity, and Disease Resistance.

A 56-day feeding trial was conducted to determine the effect of dietary supplementation with Bacillus sp. isolated from the intestines of red sea bream on the growth performance, immunity, and gut microbiome composition of red sea bream. Three diets (a control diet and two treatments) were formulated without Bacillus sp. PM8313 or β-glucan (control, CD), 1 × 108 CFU g−1 PM8313 (BSD), and 1 × 108 CFU g−1 PM8313 + 0.1% β-glucan (BGSD). At the end of the experiment, the weight, specific growth rate, feed conversion ratio, and protein efficiency ratio of the fish in the BSD and BGSD diet groups were significantly improved than those of the control group (P < 0.05). Additionally, amylase and trypsin activities were significantly higher (P < 0.05) in both groups compared to the control. Superoxide dismutase and lysozyme activity, which are serum non-specific immune responses, only increased in the BGSD group. The two treatment groups exhibited a marked difference in the intestinal microbiota composition compared to the control group. Furthermore, the treatment groups exhibited an upregulation of IL-6 and NF-κb, coupled with high survival rates when challenged with Edwardsiella tarda. Therefore, dietary supplementation with PM8313 improved the growth performance, digestive enzyme activity, non-specific immunity, and pathogen resistance of red sea bream, in addition to affecting the composition of its intestinal microflora.

Analysis of metabolites of red seabream (Pagrus major) from different geographical origins by capillary electrophoresis time-of-flight mass spectrometry.

Red seabream (Pagrus major), a migratory fish, is characterized by high protein levels in the muscle. South Korean and Japanese red seabreams have a general distribution pattern; however, distinguishing them based on their geographical origin is difficult. In this study, we used capillary electrophoresis time-of-flight mass spectrometry (CE-TOF/MS) to analyze the red seabream muscle metabolome to investigate how can distinguish the origin of the fish. The metabolites were extracted using 50% acetonitrile in water. Chromatographic separation was successfully used to classify the metabolite profiles of Japanese and South Korean red seabream. Principal component analysis and hierarchical cluster analysis showed good ability to categorize the samples according to their origin. Amino acids showed the greatest quantitative difference in South Korean and Japanese muscle samples. Specifically, the L-alanine, L-glutamic acid, L-isoleucine, dimethylglycine, and L-valine levels in Japanese red seabream samples were significantly higher than those in South Korean samples. In contrast, the levels of trimethylamine N-oxide and inosine monophosphate in South Korean muscle samples were significantly higher than those in Japanese red muscle samples. The monitored metabolite profiles suggest that South Korean and Japanese red seabreams can be identified on the basis of amino acid levels.

Whole-genome analysis of red sea bream iridovirus spread in 2021 in Japan provided epidemiological and viral traits insight.

Red sea bream iridovirus (RSIV) is the pathogen that causes red sea bream iridoviral disease. It causes a huge loss to the Japanese aquaculture industry. In 2021, outbreaks of red sea bream iridovirus occurred in South Japan. This study analysed nine whole-genome sequences of RSIV isolated in Oita and Ehime Prefectures in 2021 using a short-read next-generation sequencer. Nine isolates had highly uniform sequences, and there was no variant depending on locations or host species. Phylogenetic analyses with other reported megalocytivirus isolates showed that RSIV isolated in 2021 was genetically different from RSIV previously isolated in Oita and Ehime Prefectures in 2017-2019. These results suggest that RSIV isolated in Oita and Ehime Prefectures in 2021 might spread from a common ancestor different from the recent one. Additionally, it was found that RSIV isolated in 2021 had sequence mutations on protein-coding sequences that may be involved in viral pathogenicity and infectivity.

Red sea bream interleukin (IL)-1β and IL-8 expression, subcellular localization, and antiviral activity against red sea bream iridovirus (RSIV)

Interleukin-1 beta (IL-1β) is transcribed by monocytes, macrophages, and dendritic cells in response to activation of toll-like receptors (TLRs) by pathogen-associated molecular patterns (PAMPs) or cytokine signalling and causes a rapid inflammatory response to infection. IL-8, also known as chemokine C-X-C motif ligand (CXCL)-8, is regulated by IL-1β and affects the chemotaxis of macrophages and neutrophils upon pathogen infection. In healthy red sea bream, rsbIL-1β is most highly distributed in the liver, and rsbIL-8 is most highly distributed in the head kidney. In response to RSIV infection, rsbIL-1β and rsbIL-8 mRNA are significantly upregulated in the kidney and spleen. This may be because the primary infection targets of RSIV are the kidney and spleen. In the gills, both genes were significantly upregulated at 7 days after RSIV infection and may be accompanied by a cytokine storm. In the liver, both genes were significantly downregulated at most observation points, which may be because the immune cells such as macrophages and dendritic cells expressing rsbIL-1β or rsbIL-8 migrated to other tissues because the degree of RSIV infection was relatively low. Using a GFP fusion protein, it was confirmed that rsbIL-1β and rsbIL-8 were localized to the cytoplasm of Pagrus major fin (PMF) cells. RsbIL-1β overexpression induced the expression of interferon gamma (IFN-γ), myxovirus-resistance protein (Mx) 1, IL-8, IL-10, TNF-α, and MyD88, while rsbIL-8 overexpression induced the expression of IFN-γ, Mx1, rsbIL-1β and TNF-α. In addition, overexpression of both genes significantly reduced the genome copies of RSIV and significantly reduced the viral titers. Therefore, rsbIL-1β and rsbIL-8 in red sea bream play an antiviral role against RSIV through their normal signalling.

Identification of a rabbit Ig light chain recombinant protein bound to serum immunoglobulins from different marine fish species

The structures of fish serum immunoglobulin differ among different fish species. In this study, we accidently isolated a rabbit immunoglobulin (Ig) light chain bound to serum immunoglobulin from different marine fish species using phage display. Fish Ig was separated using a protein A column. The phage library was generated from variable regions of rabbit spleen B cells immunized with bluefin tuna Thunnus orientalis Ig. Fish Ig–specific phages were enriched using two rounds of bio-panning with yellowtail Seriola quinqueradiata serum Ig, followed by two rounds of bio-panning with red seabream Pagrus major serum Ig. The enriched phages demonstrated an increase in binding specificity to the tuna, yellowtail, and red seabream Igs compared to the phages listed in the unpanned library. A recombinant protein of a single clonal phage, which encodes the rabbit Ig light chain, was produced, and the binding specificities to fish Igs were analyzed using enzyme-linked immunosorbent assay (ELISA) and western blotting. The recombinant protein exhibited binding properties to fish Igs in the ELISA. However, the recombinant protein that bound to serum protein(s), but not IgM, was detected via western blotting. The recombinant protein may provide a novel information on the common structural feature in the fish immunoglobulins.

CRISPR/Cas Genome Editing—Can It Become a Game Changer in Future Fisheries Sector?

Fisheries and aquaculture are the fastest-growing food-producing sector and rapidly becoming an important element for the global food security since they are the primary source of seafood and high animal protein in the human diet. Genome editing offers new possibilities such as the clustered regularly interspaced palindromic repeats (CRISPR)/CRISPR-associated protein (Cas9) technology, which has the potential to accelerate the sustainable genetic improvement in fisheries and aquaculture. The CRISPR/Cas9 system has four key components, namely, target DNA, Cas9, the protospacer adjacent motif sequence, and the guide RNA or single-guide RNA. CRISPR/Cas is cheaper, easier, and more precise than the other genome editing technologies and can be used as a new breeding technology in fisheries and aquaculture to solve the far-reaching challenges. The attributes like high fecundity, external fertilization, short generation interval, the established method of breeding, and the larval rearing of most aquaculture species have advantages for CRISPR/Cas9 genome editing applications. CRISPR/Cas9 has recently been applied to the traits valued in some aquaculture species (almost &amp;gt;20 species), targeting the main traits of traditional genetic improvement initiatives like growth, disease resistance, reproduction, sterility, and pigmentation. Genome editing can fast forward the breeding process with precision where changes occur in the targeted genes. The probability of desired changes occurring and passing the trait in the next generation is high, so it takes 1-3 generations to establish a breed. Moreover, CRISPR/Cas genome editing rapidly introduces favorable changes by disrupting genes with targeted minor changes, in contrast to transgenesis, which introduces foreign genes into the host genome and thereby alleviates major public concerns on safety. Although the CRISPR/Cas technology has a tremendous potential, there are several technical challenges and regulatory and public issues concerning the applications in fisheries and the aquaculture breeding sector. Nonetheless, the exciting point in the CRISPR/Cas9 genome editing is that two CRISPR-edited fish, namely, red sea bream and tiger puffer developed by the Kyoto-based startup got approval and are now on the market for sale, and another fish, FLT-01 Nile tilapia developed by the AquaBounty, is not classified under genetically modified organism regulatory. However, there is still a way to go before it revolutionizes and becomes viable in commercial aquaculture as the new breeding technology for aquaculture-important traits and species.

Specific importance of low level dietary supplementation of Lypomyces starkeyi CB1807 yeast strain in red sea bream (Pagrus major)

Abstract Most probiotic yeast supplement in fish exhibit beneficial effect at ≤1% of the dietary proportion. This study aimed at evaluating the specific effects of Lypomyces starkeyi CB1807 yeast strain supplemented at ≤1% of dietary proportion on the performance of juvenile red sea bream (Pagrus major, 1.9 ± 0.04 g). Five diets were supplemented with yeast at graded levels of 0% (control diet ‘CD1’), 0.05% (D2), 0.1% (D3), 0.5% (D4), and 1.0% (D5). After 45 days of feeding trial, significant (P&lt;0.05) improvement was detected on final body weight (FBW) and body weight gain (BWG) in fish fed D3 and D5 compared to control. Low values of total cholesterol (T-Cho) and aspartate aminotransferase (AST) were recorded in fish groups fed on D2, D4, and D5, respectively. Fish fed on D3, D4 and D5 diets showed high (P&lt;0.05) values of serum, mucus and liver lysozyme compared to control. Fish fed on D5 showed high values of total immunoglobulin (Ig) compared to control. Fish fed on D2 showed strong correlation with biological antioxidant activity (BAP), superoxide dismutase (SOD) and catalase activity (CAT). The biological antioxidant potential (BAP) activity in fish fed on D2 was significantly higher compared to control (P&lt;0.05). The reactive oxygen metabolites (d-ROM) were significantly lower in fish fed on D2 and D3 compared to CD1 (P&lt;0.05). Peroxidase activity was improved significantly (P&lt;0.05) in fish fed on D3, D4 and D5 compared to control. The tolerance ability (LT50) of fish fed on D5 against low salinity stress was significantly higher compared to control (P&lt;0.05). It was concluded that dietary benefits of spent L. starkeyi yeast at ≤1% showed considerable improvement in antioxidant capacity in red sea bream, P. major.

Effect of oral administration of a single bolus of six different protein sources on digestive physiology of red seabream Pagrus major juveniles.

To reveal direct effects of various protein sources on digestive physiology of red seabream, Pagrus major (38.5 ± 0.4g), six different protein sources of fishmeal (FM), soybean meal (SBM), corn gluten meal (CGM), soy protein concentrate (SPC), poultry by-product meal (PBM), and poultry-feather meal (PFM) were orally administered to fish (2mg protein/g body weight) and sampled at 1.5h and 3h after administration. Gallbladder weight of fish administered FM, PBM, and PFM decreased after administration (p < 0.0001), while no difference was observed in the other ingredients compared to a non-protein sham control group, indicating that animal protein sources could more strongly stimulate bile secretion than plant protein sources in red seabream. Trypsin and chymotrypsin activity in the intestinal content markedly increased by the FM, SBM, and PFM administration (p < 0.0001). Lipase and amylase activity was also increased by FM and SBM but also by CGM for lipase and by PBM and PFM for amylase (p < 0.0001). These indicate that stimulation effect of the secretion of digestive enzymes is largely different among the protein sources. This might be due to the absorptive capacity of the protein source since intestinal absorption parameter genes (anpep, cpa, ggt1, and atp1a2) also increased by the FM, SBM, PBM or PFM (p < 0.05). In addition to the secretion levels of bile and digestive enzymes, gene expression levels of bile related genes (cyp7a1, cyp8b1, and shp) and digestion-regulating genes (casr and cck) were increased by the FM, SBM, PFM, and/or PBM administration, suggesting that animal proteins and SBM could be potent digestive stimulants compared to CGM and SPC. This study first revealed that single protein sources directly influence digestive enzyme secretion and bile secretion in fish. Information about the direct effect of each single source on digestive physiology could help to design feed formulation with less fishmeal.

Complete genome sequence and phylogenetic analysis of red seabream iridovirus isolated from a cage-cultured small yellow croaker (Larimichthys polyactis) in China.

Iridoviruses are emerging pathogens that are widespread in diverse environments and hosts. Numerous members of the family Iridoviridae are known to cause severe disease in freshwater and marine organisms. Here, we report the complete genome sequence and phylogenetic analysis of iridovirus strain LPIV-ZS-2021, isolated from a small yellow croaker (Larimichthys polyactis) in China. The genome sequence comprises 110,560 bp with a G+C content of 53.42%, has 104 putative open reading frames (ORFs), and shares the highest sequence similarity with red seabream iridovirus (RSIV) isolated in Japan (98.61%). Phylogenetic analysis revealed that it belongs to RSIV clade 1. This is the first fully sequenced RSIV genome from a small yellow croaker. The host range expansion of members of the genus Megalocytivirus warrants further attention to determine its potential economic and ecological impact.

Bioavailability of porcine blood meal as a fish meal substitute in the diet for red sea bream ( Pagrus major , Temminck &amp; Schlegel) fingerling

We replaced fish meal (FM) with porcine blood meal (BM) in red sea bream (Pagrus major) diets to examine the influence on growth performance. Four experimental diets were prepared to be isonitrogenous and isolipidic by replacing 0%, 10%, 20% and 30% FM protein with BM (BM0, BM10, BM20 and BM30, respectively). After the 8-week feeding trial, the final mean body weight, weight gain, specific growth rate, daily feeding rate, condition factor and survival rate were not significantly different among the treatments (p > 0.05). However, feed efficiency tended to lower linearly as the dietary BM level increased, and no significant difference was observed between the BM20 and BM0 groups (p < 0.05). The protein digestibility in the BM20 and BM30 groups decreased significantly compared with that in the BM0 group (p < 0.05). Fat digestibility decreased significantly in the BM30 group than in other treatment groups (p < 0.05). The total serum protein and total cholesterol concentrations in the BM30 group were the highest among all treatment groups. In conclusion, BM can replace up to 20% of FM in the red sea bream diet without adversely affecting growth performance.