Effects of replacing fishmeal with fermented and non‐fermented rapeseed meal on the growth,immune and antioxidant responses of red sea bream (Pagrus major)

The effect of rapeseed meal (RM) and Aspergillus oryzae fermented rapeseed meal (RM‐Koji) on red sea bream (Pagrus major) was examined. Three groups of fish (initial weight, 4.5 ± 0.02 g) were fed a basal diet (RM0) and two test diets where half of fishmeal was replaced by RM (RM50) and RM‐Koji (FRM50) for 56 days. The obtained results showed that fish fed RM0 and FRM50 exerted significantly higher growth performance, feed utilization and haemoglobin level but lower triglyceride and cholesterol than RM50 group (p < 0.05). Interestingly, except of antiprotease activity, all the immune parameters including lysozyme, respiratory burst (NBT) and bactericidal activities were significantly increased in fish fed RM0 and FRM50 diets compared to RM50 diet (p < 0.05). In addition, malondialdehyde and reactive oxygen metabolites were significantly reduced in RM0 and FRM50 groups over RM50 group (p < 0.05). The present results suggest that fermented RM induced better growth performance and immune responses than feeding red sea bream with non‐fermented RM and both RM and RM‐Koji improved the antioxidative status of fish, making RM‐Koji an interesting candidate as a functional feed for aquatic animals.     

Effects of dietary taurine levels on epidermal thickness and scale loss in red sea bream,Pagrus major

Taurine is often added to artificial fish diets to compensate for a reduction in fish meal (FM). However, the taurine content of FM‐based diets is typically lower than in diets consisting of raw fish, even in diets where FM is the only protein source. We evaluated the effects of dietary taurine in FM‐based diets on epidermal thickness and scale detachability in red sea bream Pagrus major. We compared the effect of diets containing 0% (control), 0.3% (Tau‐0.3%), 0.6% (Tau‐0.6%) and 1.0% (Tau‐1.0%) taurine. Red sea bream (average body weight, 39 g) were fed these diets for 7 weeks. Taurine supplementation had no effect on growth, feed intake, feeding efficiency, or survival. However, the epidermal thickness was higher in fish in the Tau‐0.6% and Tau‐1.0% groups than in the control and Tau‐0.3% groups. Similarly, scale loss was significantly higher in the control group than in the Tau‐0.6% and Tau‐1.0% groups. Our results suggest that supplementation with >0.6% taurine (1.0% in diet) improves skin condition.     

The effect of demand feeding on swimming speed and feeding responses in Atlantic salmon Salmo salar L., gilthead sea bream Sparus aurata L. and European sea bass Dicentrarchus labrax L. in sea cages

Abstract Using underwater cameras, data were collected on the feeding behaviour and swimming speeds of Atlantic salmon Salmo salar L., gilthead sea bream Sparus aurata L. and European sea bass Dicentrarchus labrax L. in sea cages. Comparisons were made between the behaviours of fish fed on demand using interactive feedback systems and those of fish fed under the standard feeding practice of each farm (control). In all three species, swimming speeds were similar before feeding , but they were significantly higher in the control regimes during feeding. When fed on demand, sea bass had reduced swimming speed just before and during feeding compared with that observed during the non‐feeding periods. Higher proportions of feeding fish were observed in the control regime cages than in fish fed on demand for all three species, indicating a greater feeding intensity during meals in the control regimes. This was further supported by observations of an increase in the density of sea bass in the upper water in the control cages during feeding. The results suggest decreased levels of competition between the on demand‐fed fish during feeding, which might be hypothesized to lead to improved growth and production efficiency in aquaculture.     

Effects of natural feeding stimulants and glutamic acid supplementation on the feed intake,growth performance and digestive enzyme activities of red sea bream (Pagrus major) fed fish meal‐free soy protein concentrate (SPC)‐based diet

Two experiments were conducted for red sea bream (Pagrus major). In experiment 1, the optimum level of glutamic acid and natural feeding stimulants to enhance feed intake were determined and found that glutamic acid level of 0.5% and fish meat hydrolysate (FMH) were effective. In experiment 2, fish were fed with soy protein concentrate (SPC)‐based diet with synthetic feeding stimulants (Basal diet), the Basal diet with FMH (FMH diet), the FMH diet with glutamic acid (FMHG diet) and with fish meal diet (FM diet) as a control until satiation for 8 weeks. Feed intake of FMHG‐fed fish was significantly higher than others (p < 0.05). Specific growth rate and the feed conversion ratio of FMHG were comparable to those of FM‐fed fish (p > 0.05). Relative visceral fat ratio and crude lipid content of any SPC‐based diet‐fed fish tended to be lower than those of FM diet‐fed fish. There were no significant differences in trypsin and lipase activities hepatopancreas among treatments. SPC can be utilized as a sole protein source in a diet for red sea bream. The lower growth performance in SPC‐based diet‐ fed fish was not due to poor digestive enzyme secretion but could be associated with lipid utilization disorder.     

Tributyrin‐supplemented high‐soya bean meal diets of juvenile black sea bream,Acanthopagrus schlegelii: Study on growth performance and intestinal morphology and structure

An 8‐week growth trial was conducted to evaluate the effects of different levels of tributyrin supplementation in a high‐soya bean meal diet on juvenile black sea bream (11.30 ± 0.16 g). The positive control (PC) diet contained 45% fishmeal and 20% soya bean meal, while the negative control (NC) contained 12% fishmeal and 45% soya bean meal. Graded levels of tributyrin were added to the NC diet at 0.05% (TB 0.05), 0.1% (TB 0.1), 0.2% (TB 0.2), 0.4% (TB 0.4) and 0.8% (TB 0.8). Ultimately, the fish fed the PC diet had a higher weight gain and specific growth rate than the fish fed other diets. The fish fed the NC diet had the lowest growth, and TB 0.05–TB 0.2 diets increased growth performance while TB 0.4–TB 0.8 diets caused reduction in growth. Dietary tributyrin supplementation improved protease activity and enhanced antioxidant capacity. Compared with the fish fed the NC diet, the fish fed the tributyrin‐supplemented diets had improved gut morphology and structure, and the results were similar to those of the fish fed the PC diet. Furthermore, the analysis of the dose response with second‐order polynomial regression indicated that the optimum tributyrin supplementation for juvenile black sea bream is 2.24 g/kg in the 45% soya bean meal diet.     

Partial Replacement of Fish Meal by Fermented Soybean Meal in Diets for Black Sea Bream,Acanthopagrus schlegelii,Juveniles

The effect of fish meal (FM) substitution with fermented soybean meal (FSBM) in the diets of the carnivorous marine fish, black sea bream, Acanthopagrus schlegelii, was investigated. An 8‐wk feeding trial was conducted with black sea bream (11.82 ± 0.32 g; mean initial weight) in indoor flow‐through fiberglass tanks (25 fish per tank). Six isonitrogenous and isoenergetic diets were formulated, in which FM was replaced by FSBM at 0% (control diet), 10% (FSBM10), 20% (FSBM20), 30% (FSBM30), 40% (FSBM40), or 50% (FSBM50), respectively. Each diet was fed to triplicate groups of fish twice daily to apparent satiation. The results showed that there was no difference in survival of black sea bream during the feeding trial. Fish fed the FSBM10 or FSBM20 diet showed comparable growth performance compared with fish fed the control diet (P > 0.05), whereas more than 30% replacement of FM adversely affected weight gain and specific growth rate (P < 0.05). Feed intake was significantly lower for fish fed the FSBM50 diet compared with fish fed the control diet. Feed conversion ratio (FCR) tended to increase with increasing dietary FSBM with the poorest FCR observed for fish fed the FSBM50 diet. Protein efficiency ratio and protein productive values showed similar patterns. Apparent digestibility of nutrients significantly decreased with increasing dietary FSBM level. With the exception of protein content, no significant differences in whole body and dorsal muscle composition were observed in fish fed the various diets. Fish fed the FSBM50 diet had significantly lower intraperitoneal ratio than fish fed the control or FSBM10 diet. Hepatosomatic index and condition factor were unaffected by dietary treatments. This study showed that up to 20% of dietary FM protein could be replaced by FSBM protein in the diets of juvenile black sea bream.     

Prebiotics effect on growth performance,hepatic intermediary metabolism,gut microbiota and digestive enzymes of white sea bream (Diplodus sargus)

This study aimed at evaluating the effects of short‐chain fructooligosaccharides (scFOS), xylooligosaccharides (XOS) and galactooligosaccharides (GOS) on growth performance, hepatic metabolism, gut microbiota and digestive enzymes activities of white sea bream juveniles. Four diets were formulated: a control diet with fish meal (FM) and plant feedstuffs (PF) (30FM:70PF) and three test diets similar to control but supplemented with 10 g of scFOS, XOS or GOS per kilo diet, which were fed to fish during 12 weeks. Prebiotics had no effect on growth, feed efficiency or gut microbiota. Plasmatic triglycerides were lower in fish fed XOS than FOS and GOS diets. Malic enzyme activity was lower in fish fed XOS than FOS diet. Fish fed XOS diet had lower fatty acid synthetase (FAS), a key lipogenic enzyme and higher alanine aminotransferase activities. Fifteen days after the start of the trial, an enhancement of total alkaline protease, trypsin and lipase activities was observed in fish fed prebiotics, but such effect disappeared at 12 weeks. In conclusion, scFOS, XOS or GOS seem to have limited applicability in white sea bream feed.     

Effect of phytase supplementation of a plant‐based diet on phosphorus and nitrogen bioavailability in sea bream Sparus aurata

To assess to what extent addition of phytase to a plant‐based diet results in spatio‐temporal changes of phytate, available P, soluble protein, total amino acids and the activity of the main digestive proteases in gilthead sea bream, fish were fed two plant‐based diets with or without phytase. Stomach, proximal intestine and distal intestine contents were monitored for these parameters at 0, 1, 2, 4 and 6 h after feeding. A reduction (P < 0.0001) of the soluble P–IP6 in the stomach when phytase was added to the diet was observed. Within stomach, most of the total P–IP6 was precipitated (86%), possibly due to the low acidification capacity of the sea bream (pH > 4), but 57% of the dietary P–IP6 was dephosphorylated, suggesting that phytase could have the capacity to dephosphorylate insoluble IP6 at such pH. An increment (60%) (P < 0.01) in total gastric protease activity was observed by phytase addition, this being the first demonstration of the in vivo effect of IP6 on the pepsin activity in fish stomach. Gastric pH and residence time of the digesta inside the stomach are critical factors for an efficient phytase action and improve P and N bioavailability in plant‐based diets used in fish aquaculture.     

Combined Effects of Cycled Starvation and Feeding Frequency on Growth and Oxygen Consumption of Gilthead Sea Bream,Sparus aurata

Triplicate groups of gilthead sea bream, Sparus aurata (10.4 g), were distributed among 27 tanks (12 fish per tank) and reared in flow‐through seawater. A factorial experiment (3 × 3) was designed to include a continuously fed control group and two cycled starvation groups: 1 + 3 (starved 1 d, fed 3 d), 1 + 5 (starved 1 d, fed 5 d). Each of the feeding groups was subjected to one of three feeding frequencies (2, 4, and 6 times per day) over the 60‐d experiment duration. The average final weight of fish in 1 + 3 and 1 + 5 groups were significantly lower than that of the control group. Partial compensation was observed in the starved groups subjected to any of the three feeding frequencies. Regardless of the feeding frequency, control fish consumed less feed than the starved groups. The highest body protein content was found in the control group. The rate of oxygen consumption significantly increased 30 min after the feeding and the magnitude of the effect increased with the feeding frequency. These results suggest that the present cycling starvation schedules did not invoke a full compensation in gilthead sea bream.     

Effects of dietary linolenic acid on growth,fatty acid composition,immune function and antioxidant status of juvenile blunt snout bream,Megalobrama amblycephala

A nine‐week feeding trial was performed to determine the dietary linolenic acid (LNA; 18:3n–3) requirements of juvenile blunt snout bream. Six iso‐nitrogenous, semi‐purified diets were prepared with different concentrations of LNA (0–25 g/kg). Dietary LNA had no significant effects on survival rate. However, final fish weight, weight gain (WG), specific growth rate (SGR) and feed efficiency ratio (FER) increased with increasing dietary LNA concentrations up to 20 g/kg. Dietary LNA increased muscle LNA and total n‐3 polyunsaturated fatty acid (PUFA) contents, but decreased total saturated fatty acid content. Fish fed 20 g/kg LNA had the highest plasma alkaline phosphatase activity, total protein, albumin and white blood cell count levels. Additionally, fish fed 20 g/kg LNA had higher triglyceride levels than control fish. Plasma glucose increased with increasing dietary LNA concentrations. Superoxide dismutase and glutathione peroxidase activities significantly increased with increasing dietary LNA concentrations up to 15 g/kg. Based on SGR and FER, the optimal dietary LNA requirements of juvenile blunt snout bream were 17.5 and 15.6 g/kg respectively.     

Evaluation of pea proteins and poultry protein as fish meal alternatives in the diets for juvenile black sea bream,Acanthopagrus schlegelii

The potential of three different protein resources (pea protein isolate, PPI; pea protein concentrate, PPC; enzyme treated poultry protein, ETPP) as fish meal (FM) alternative protein in diets for juvenile black sea bream, Acanthopagrus schlegelii. (initial average weight 7.90 ± 0.13 g) was evaluated. Seven isonitrogenous and isoenergetic diets were formulated to replace FM at 0% (T0, control diet), 8% (designated as T1‐T3) and 16% (designated as T4‐T6) using PPI, PPC and ETPP respectively. Each diet was randomly assigned to triplicate groups of 25 juvenile fish for 8 weeks. At the end of the feeding period, survival rate was not significantly affected by dietary treatments. Growth performance in T6 (16% ETPP) group was significantly inferior to T0 group, however, weight gain and specific growth rate in other treatments showed no significant differences (P > 0.05). Mean feed intake, feed efficiency ratio and protein efficiency ratio were also poorer in fish fed in T6 than those of fish fed with the control diet respectively. Apparent digestibility coefficients (ADCs) of dry matter and crude protein for fish fed ETPP diets were significant lower than those of fish fed with the control diet, whereas ADCs of lipid were unaffected by dietary treatments. ADC's of dietary Leu, Ile, His and Lys was also significantly influenced. There were no marked variations in proximate compositions of dorsal muscle. With regard to plasma characteristics, significant difference was observed in triacylglycerol content. Ammonia concentration in plasma tended to increase in alternative protein diets as substitution level increased. There were significant differences in aspartate aminotransferase activities among groups, but alanine aminotransferase levels were unaffected by treatments. In conclusion, the present study demonstrated that PPI and PPC were potential protein sources for using in juvenile black sea bream diet. However, the substitution level of FM by ETPP should be limited within 16%.     

Extracts of Oliviera decumbens and Satureja khuzestanica as immunostimulants affect some innate immunity indices of Cyprinus carpio against Aeromonas hydrophila infection

In this study, the effect of extracts of two herbs (Oliviera decumbens and Satureja khuzestanica) on immune response of carp was investigated. At the beginning of experiment, fish were divided to two groups including vaccinated (using vaccine developed against A. hydrophila) and non‐vaccinated. Fish in both groups were fed diets containing O. decumbens and S. khuzestanica and combination of two herbal extracts for 5 weeks. Control fish (negative control) and fish vaccinated only (positive control) were fed basal diets without supplements of herbal extracts. Lysozyme activity, antibody titre, complement activity and bactericidal activity in serum were measured. After 5 weeks feeding, fish were infected with A. hydrophila and mortalities were recorded. In both experimental groups, no significant differences were found in terms of alternative haemolytic complement (ACH50) activity and antibody titres of Serum. In non‐vaccinated fish group, lysozyme and bactericidal activity of fish fed S. khuzestanica or combination of O. decumbens and S. khuzestanica was higher compared with control and other experimental treatments. In vaccinated fish group, the lysozyme and bactericidal activity was not significant in all treatments compared with control group. The results of this study showed that feeding non‐vaccinated and vaccinated carp with only S. khuzestanica or in combination with O. decumbens enhance only some immunity indices including lysozyme and bactericidal activity in non‐vaccinated fish and these extracts have no immunological stimulatory role on vaccinated individuals.     

Effects of dietary yeast inclusion and acute stress on postprandial plasma free amino acid profiles of dorsal aorta‐cannulated rainbow trout

In a 4‐week experiment, 15 cannulated rainbow trout were fed three diets based on fish meal (FM), Saccharomyces cerevisiae yeast (SC) and Wickerhamomyces anomalus and S. cerevisiae yeast mix (WA). Fish were fed daily, and blood samples were collected on day 7 of each week at 0, 3, 6, 12 and 24 hr after feeding. In the final week, fish were exposed to a 1‐min netting stressor. All essential and non‐essential plasma amino acid levels except methionine were similar between fish fed diets FM, SC and WA. Plasma methionine and sarcosine were significantly higher in fish fed diets SC and WA, possibly due to the crystalline methionine level, form or feeding regime. Hydroxy‐proline and 3‐methyl‐histidine were higher in fish fed diet FM, which can be explained by the higher levels present in fish meal compared with yeast. In stressed fish, there were no dietary effects on plasma amino acid levels, but significant increases in taurine and cystathionine were found in stressed compared with unstressed fish. These results demonstrate that yeast‐based diets produce similar plasma amino acid profiles to fish meal and suggest that yeast may be a suitable fish meal replacement in diets for rainbow trout.     

Effect of dietary lipid oxidation with vitamin C and E supplementation on fillet quality of red sea bream,Pagrus major (Temminck & Schlegel) during storage

An experiment was conducted to determine the effects of different levels of dietary vitamin C (VC) and E (VE) supplementation on fillet quality of red sea bream fed oxidized fish oil (OFO). Fish with an average body weight of 205.0 g were fed four test diets for 9 weeks. Control diet contained fresh fish oil (FFO) with 100 mg kg^?1 of VE and 500 mg kg^?1 of VC (FFO100E/500C). The other three diets contained OFO with varying levels of VE (mg kg^?1) and VC (mg kg^?1) (OFO100E/500C, OFO200E/500C and OFO200E/1000C). After feeding trial, two fillets from each fish by hand filleting were stored in a refrigerator at 4°C for 96 h during analyses. Results showed that fish fed OFO increased fillet thiobarbituric acid reactive substances (TBARS) and K‐value, and decreased fillet VC and VE concentrations during storage time. Supplementation of VC did not have any detectable effect on fillet quality. Increasing dietary VE supplementation increased fillet VE concentrations, reduced fillet TBARS and K‐value values of red sea bream. Therefore, we suggest that dietary supplementation of 200 mg kg^?1 of vitamin E could improve fillet oxidative stability of red sea bream fed OFO.     

Effect of different feeding strategies on gilthead sea bream (Sparus aurata) demand-feeding behaviour and nutritional utilization of the diet

We have studied the effects of time‐restricted food access and ration restriction on gilthead sea bream demand‐feeding behaviour and nutritional use of the diet (Sparus aurata), and also compared the nutritional efficiency of three different feeding systems: manual, automatic and modulated‐automatic. In the first trial, fish were allowed to feed from self‐feeders under three different conditions: ad libitum, ration restriction, and time‐restricted food access, and their demand‐feeding pattern, diet utilization and body composition were analysed. In the second trial, animals were fed by hand or using an automatic system, either fixed or modulated, and diet utilization and body composition were analysed as before. Restricting the amount of food modifies gilthead seabream self‐feeding behaviour, with fish increasing the number of demands provided these are rewarded with food. However, demand‐feeding activity does not increase if rewards are restricted to a certain time. Feeding gilthead sea bream by hand versus automatically, and distributing the daily food ration in two or three equal or unequal‐size daily meals, have no effect on the animals’ growth, nutritional use of the diet or body composition.     

Effects of Dietary Vitamin C on Blood Chemistry and Nonspecific Immune Response of Juvenile Red Sea Bream,Pagrus major

A trial was conducted to determine the effect of ascorbyl‐2‐monophosphate Na/Ca (AMP‐Na/Ca) on blood chemistry and nonspecific immune response of red sea bream juveniles. Test diets with three levels of AsA (free, 107, and 325 mg/kg diet) were fed to juvenile red sea bream (36.0 ± 1.3 g) two times a day for 3 wk. There were no significant differences in hematocrit, glucose, and blood urea nitrogen. Total cholesterol and triglyceride in plasma of fish fed AsA‐free diet was significantly (P < 0.05) higher than that of fish fed two other diets. There were no significant differences in serum albumin, total bilirubin, and total serum protein. Glutamyl oxaloacetic transaminase in serum of fish fed diets containing 107 and 325 mg of AsA were significantly (P < 0.05) lower than that of fish fed AsA‐free diet. Serum lysozyme activity (LA) of fish fed diets containing 107 and 325 mg of AsA were significantly (P < 0.05) higher than that of fish fed AsA‐free diet. There was no significant difference in mucus LA. The results mentioned above demonstrated that AMP‐Na/Ca is a bioavailable AsA source for red sea bream juveniles. Supplement of more than 107 mg AsA/kg in diets improved blood chemistry and nonspecific immune function of red sea bream juveniles.     

Partial replacement of fishmeal with Clostridium autoethanogenum single‐cell protein in the diet for juvenile black sea bream (Acanthopagrus schlegelii)

Clostridium autoethanogenum protein (CAP) is a single‐cell protein derived from ethanol production and may have potential to become a substitute for fishmeal in aquafeeds. A 70‐day feeding trial was conducted with black sea bream (Acanthopagrus schlegelii) (mean initial weight 6.03 ± 0.09 g) to evaluate partial replacement of fishmeal with CAP in diets. Seven isonitrogenous and isoenergetic diets were formulated with graded levels of CAP (0, 4.85, 9.70, 14.55, 19.40, 38.80 and 58.20%) to replace fishmeal. The inclusion of CAP at all dietary levels tested did not significantly affect the growth performance (p > .05). Fish fed the CAP58.20% diet showed a significantly lower feeding rate, with significantly higher protein efficiency ratio and feed efficiency ratio compared with fish fed the other diets (p < .05). No statistical differences were found in dorsal muscle and whole‐body compositions. Total superoxide dismutase in serum of fish fed CAP58.20% diet was significantly lower compared with that of the control. Malondialdehyde, catalase, total antioxidant capacity and digestive enzyme activities revealed no significant differences among dietary treatments. Phosphorus retention efficiency significantly increased, and phosphorus discharge showed a downward trend with increasing CAP inclusion levels. In conclusion, the results indicated that CAP is a safe and effective alternative protein source, which can replace fishmeal in the diet of black sea bream up to 58.20%, without adverse effects on growth performance, antioxidation and digestive enzyme activity. This study has shown the potential of converting industrial waste into a high protein feed ingredient for aquafeeds.     

The use of preserved copepods in sea bream small‐scale culture: biometric,biochemical and molecular implications

Considering the well‐known problems arising from the use of rotifers and Artemia as live prey in larval rearing in terms of fatty acid deficiencies, the aim of this study was to evaluate a partial or complete replacement of traditional live prey with preserved copepods during the larviculture of gilthead sea bream (Sparus aurata). Sea bream larvae were randomly divided into 4 experimental groups in triplicates: group A larvae (control) fed rotifers followed by Artemia nauplii; group B fed a combined diet (50%) of rotifers–Artemia and preserved copepods; group C fed rotifers followed by preserved copepods; and group D fed preserved copepods solely. Survival and biometric data were analysed together with major molecular biomarkers involved in growth, lipid metabolism and appetite. Moreover, fatty acid content of prey and larvae was also analysed. At the end of 40 days treatment, a stress test, on the remaining larvae, was performed to evaluate the effects of different diets on stress response. Data obtained evidenced a positive effect of cofeeding preserved copepods during sea bream larviculture. Higher survival and growth were achieved in group B (fed combined diet) larvae respect to control. In addition, preserved copepods cofeeding was able to positively modulate genes involved in fish growth, lipid metabolism, stress response and appetite regulation.     

A natural infection by the red sea bream iridovirus‐type Megalocytivirus in the golden mandarin fish Siniperca scherzeri

An outbreak of a Megalocytivirus infection was found in the golden mandarin fish Siniperca scherzeri during September and October 2016, in Korea. Phylogeny and genetic diversity based on the major capsid protein (MCP) and adenosine triphosphatase (ATPase) genes showed a new strain. Designated as GMIV, this strain derived from the golden mandarin fish was suggested to belong to the red sea bream iridovirus (RSIV)‐subgroup I. Additionally, this train clustered with the ehime‐1 strain from red sea bream Pagrus major in Japan and was distinguished from circulating isolates (RSIV‐type subgroup II and turbot reddish body iridovirus [TRBIV] type) in Korea. The infection level, evaluated by qPCR, ranged from 8.18 × 10² to 7.95 × 10⁶ copies/mg of tissue individually, suggesting that the infected fish were in the disease‐transmitting stage. The diseased fish showed degenerative changes associated with cytomegaly in the spleen as general sign of Megalocytivirus infection. The results confirm that the RSIV‐type Megalocytivirus might have crossed the environmental and species barriers to cause widespread infection in freshwater fish.