Prevalence, risk factors and transmission of nervous necrosis virus in a hatchery producing hybrid grouper (Epinephelus lanceolatus × Epinephelus fuscoguttatus) fry

This study investigates the prevalence, risk factors, and transmission of nervous necrosis virus (NNV) in a hatchery producing hybrid grouper (Epinephelus lanceolatus × Epinephelus fuscoguttatus) fry. The eggs and sperm of giant grouper (GG) and tiger groupers (TG) that were collected for breeding purposes within the 12-month study period were sampled to detect NNV. At the same time, three breeding attempts of different NNV status of broodstocks, which were NNV-positive GG × NNV-positive TG, NNV-positive GG × NNV-negative TG and NNV-negative GG × NNV-negative TG were conducted. The produced hybrid grouper (HG) fry was then sampled at 5, 10, 20, 30, 40, 60, 90, and 120 days post-hatched to detect the presence of NNV. The fresh fish, live feed, and commercial fish pellet that were used to feed the broodstocks or HG fry throughout the study period were also sampled for NNV detection. The water’s physico-chemical parameters during each sampling were determined. The results revealed that the broodstocks had a low prevalence to NNV. However, when at least one of the broodstocks was NNV-positive, all batches of the fry were NNV-positive at high prevalence. There were consistent associations of ammonia and iron with the presence of NNV in both broodstocks and fry. Phylogenetic tree indicates the possible horizontal and vertical transmissions of NNV in the hatchery culture system. Understandings the epidemiology of NNV in a real hatchery condition can provide significant information for control and prevention of the disease

The presence of vibrionaceae, betanodavirus and iridovirus in marine cage-cultured fish: role of fish size, water physicochemical parameters and relationships among the pathogens

The study determines the presence of Vibrionaceae, Betanodavirus and Iridovirus in marine cage-cultured fish, while identifying the roles of fish size, water physicochemical parameters and relationships among the pathogens itself. Cultured grouper and snapper were randomly sampled from a commercial fish farm between February and December 2014. The total body weight and length of individual fish were measured. The kidney, liver and spleen were sampled for bacteria isolation, while for viral identification, the sample of brain, eye, kidney and spleen were used. Water physicochemical parameters during the sampling activities were also determined. Laboratory results revealed isolations of multiple pathogens including Vibrio alginolyticus, V. vulnificus, Photobacterium damselae subsp. damselae (PD), Nervous Necrosis Virus (NNV) and Iridovirus (IV) at low to high prevalence throughout the study period. The weight of affected groupers ranged between 98 g and 719 g, while snappers between 67 g and 982 g. There was a weak and moderate negative correlation between the grouper’s weight and the presence of NNV (R = −0.3684; P 0.05) difference was noted in the rate of isolated pathogens between groupers and snappers, and between the pathogens affecting snappers. However, detection of IV in groupers was significantly (P < 0.05) higher than V. alginolyticus, V. vulnificus and PD. Isolations of V. vulnificus in groupers showed strong and moderate positive correlations with isolations of PD (R = 0.7069; P < 0.05) and IV (R = 0.6665; P < 0.05), respectively. In snappers, there was strong positive correlation between isolation of V. alginolyticus and NNV (R = 0.7526; P < 0.05). Multivariate analyses showed that water temperature, dissolved oxygen, ammonia, iron and nitrite were the most significant water physicochemical parameters associated with presence of these pathogens

Persistent detection of Tilapia lake virus in wild tilapia and tinfoil barbs.

Background and Aim: One of the emerging viral diseases in freshwater fish is Tilapia lake virus (TiLV), which infects all stages of fish and results in mass mortalities. Previously, a TiLV case was detected in the wild environment in Malaysia that involved tilapia and tinfoil barb. Hence, this study aimed to determine the presence of TiLV in wild tilapia (Oreochromis niloticus) as well as tinfoil barbs (Barbonymus schwanenfeldii) at the similar lake after the initial outbreak in year 2017. Materials and Methods: Both fish species were sampled from this lake at a month interval for two years and subjected to TiLV detection using reverse transcriptase-polymerase chain reaction and cell culture isolation. Concurrently, bacterial isolation and water quality measurements were performed to deduce their correlation with TiLV occurrence. Other wild fish species and mollusk were also occasionally sampled during the fish inventory activity at this lake. The fish’s weight, length, and associated clinical signs were noted throughout the entire study period. Results: Mortality was not observed throughout the whole study period, and results indicated a moderate to high prevalence of TiLV infection in both tilapia and tinfoil barbs. There was no correlation between TiLV infection with the isolation rate of opportunistic bacteria such as Aeromonas spp., Plesiomonas spp., and Edwardsiella spp. in the study site. At the same time, the Pearson correlation test revealed a moderate negative correlation between the water pH with the presence of TiLV (R=−0.4472; p<0.05) and a moderate positive correlation between the water iron content with the monthly detection of Aeromonas spp. in wild tilapia. This is contrary to tinfoil barbs, where there was a moderate negative correlation between the water iron content with the monthly isolation of Aeromonas spp. (R=−0.5190; p<0.05). Furthermore, isolation of TiLV on cell culture-induced viral invasion was resulted in the cytopathic effects. Conclusion: Our results suggest that the wild fish may harbor TiLV for an extended period following a massive die-off event in 2017 without any obvious clinical signs and mortality. The persistency of viruses in the wild may need continuous and effective control as well as prevention strategies. Keywords: Malaysia, Tilapia lake virus, tinfoil barbs, wild tilapia

The presence of Vibrionaceae, Betanodavirus and Iridovirus in marine cage-cultured fish: Role of fish size, water physicochemical parameters and relationships among the pathogens

The study determines the presence of Vibrionaceae, Betanodavirus and Iridovirus in marine cage-cultured fish, while identifying the roles of fish size, water physicochemical parameters and relationships among the pathogens itself. Cultured grouper and snapper were randomly sampled from a commercial fish farm between February and December 2014. The total body weight and length of individual fish were measured. The kidney, liver and spleen were sampled for bacteria isolation, while for viral identification, the sample of brain, eye, kidney and spleen were used. Water physicochemical parameters during the sampling activities were also determined. Laboratory results revealed isolations of multiple pathogens including Vibrio alginolyticus, V. vulnificus, Photobacterium damselae subsp. damselae (PD), Nervous Necrosis Virus (NNV) and Iridovirus (IV) at low to high prevalence throughout the study period. The weight of affected groupers ranged between 98 g and 719 g, while snappers between 67 g and 982 g. There was a weak and moderate negative correlation between the grouper’s weight and the presence of NNV (R = −0.3684; P < 0.05) and V. vulnificus (R = −0.6451; P < 0.05), respectively. No significant (P > 0.05) difference was noted in the rate of isolated pathogens between groupers and snappers, and between the pathogens affecting snappers. However, detection of IV in groupers was significantly (P < 0.05) higher than V. alginolyticus, V. vulnificus and PD. Isolations of V. vulnificus in groupers showed strong and moderate positive correlations with isolations of PD (R = 0.7069; P < 0.05) and IV (R = 0.6665; P < 0.05), respectively. In snappers, there was strong positive correlation between isolation of V. alginolyticus and NNV (R = 0.7526; P < 0.05). Multivariate analyses showed that water temperature, dissolved oxygen, ammonia, iron and nitrite were the most significant water physicochemical parameters associated with presence of these pathogens

The presence of Vibrionaceae, Betanodavirus and Iridovirus in marine cage-cultured fish: Role of fish size, water physicochemical parameters and relationships among the pathogens

The study determines the presence of Vibrionaceae, Betanodavirus and Iridovirus in marine cage-cultured fish, while identifying the roles of fish size, water physicochemical parameters and relationships among the pathogens itself. Cultured grouper and snapper were randomly sampled from a commercial fish farm between February and December 2014. The total body weight and length of individual fish were measured. The kidney, liver and spleen were sampled for bacteria isolation, while for viral identification, the sample of brain, eye, kidney and spleen were used. Water physicochemical parameters during the sampling activities were also determined. Laboratory results revealed isolations of multiple pathogens including Vibrio alginolyticus, V. vulnificus, Photobacterium damselae subsp. damselae (PD), Nervous Necrosis Virus (NNV) and Iridovirus (IV) at low to high prevalence throughout the study period. The weight of affected groupers ranged between 98 g and 719 g, while snappers between 67 g and 982 g. There was a weak and moderate negative correlation between the grouper’s weight and the presence of NNV (R = −0.3684; P < 0.05) and V. vulnificus (R = −0.6451; P < 0.05), respectively. No significant (P > 0.05) difference was noted in the rate of isolated pathogens between groupers and snappers, and between the pathogens affecting snappers. However, detection of IV in groupers was significantly (P < 0.05) higher than V. alginolyticus, V. vulnificus and PD. Isolations of V. vulnificus in groupers showed strong and moderate positive correlations with isolations of PD (R = 0.7069; P < 0.05) and IV (R = 0.6665; P < 0.05), respectively. In snappers, there was strong positive correlation between isolation of V. alginolyticus and NNV (R = 0.7526; P < 0.05). Multivariate analyses showed that water temperature, dissolved oxygen, ammonia, iron and nitrite were the most significant water physicochemical parameters associated with presence of these pathogens