Field evaluation of palm oil adjuvanted feed-based streptococcosis vaccine efficacy in red hybrid tilapia

Vaccination plays an important role in the aquaculture industry to prevent disease outbreaks, thereby ensuring an economically viable industry. A field trial was conducted in Pedu Lake, Kedah, to determine immunoglobulin M (IgM) progression in red hybrid tilapia following oral vaccination with palm oil adjuvanted streptococcosis vaccine. A total of 6,000 tilapias of 60 ± 20 g were selected and divided into three groups of single booster, double booster, and control group in duplicate. The single booster group was vaccinated orally at weeks 0 and 2, while fish of the double booster group were vaccinated at weeks 0, 2, and 6. Fishes from the control group were not given any vaccine throughout the experimental period. Samples of eye, brain, and kidney were collected at two weeks intervals for sixteen weeks cumulative to isolate the bacteria, while serum samples were collected to determine the antibody level. Throughout the study period, no outbreaks of streptococcosis were recorded, and none of the groups studied showed the presence of Streptococcus agalactiae. Very low mortality of single booster, double booster, and control group was noted at 2.1 ± 8.5 %, 1.3 ± 2.8 %, and 1.5 ± 7.1 %, respectively. Both vaccinated groups showed significant (p<0.05) increases in IgM antibody levels following immunization of first and booster doses before going down below the cut-off value six weeks post-vaccination in the single booster group. However, IgM antibody levels in the fish from the double booster group remained high until the end of the trial. In conclusion, oral vaccination with palm oil adjuvanted feed-based streptococcosis vaccine stimulates an adequate systemic immune response, which can confer possible protection against streptococcosis

Retrospective identification of bacterial depository revealed that Streptococcus iniae was responsible for some of the streptococcosis cases in cultured red tilapia in Malaysia since 2006

This paper reports the identification of Streptococcus iniae from a large collection of isolates previously identified as Streptococcus sp., Lactococcus lactis subsp. lactis or Leuconostoc sp. A total of 204 bacterial isolates recovered either from the brain, eye, or kidney of red tilapias in previous disease outbreaks and disease monitoring in Malaysia from 2006 to 2008 were used. PCR identification revealed that 34 (16.7%) of the isolates were confirmed as S. iniae. Our records showed that S. iniae-infected fish exhibited lethargy, exophthalmia, and erratic swimming patterns. Pathological lesions including generalised congestion of the internal organs, splenic infarction with soft and oedematous brain. Histopathological examination revealed multifocal encephalitis as one of the major findings. However, 44% and 26.5% of the tilapias from which S. iniae was isolated did not manifest any clinical sign and pathological lesion, respectively. This study revealed that S. iniae was responsible for streptococcosis in cultured red tilapia in Malaysia since 2006

Current status and advances of fish vaccines in Malaysia

Fish diseases have a significant negative influence on the Malaysian aquaculture industry. Since the 1980s, the sector has grown in size, which has resulted in a rise in the prevalence of infectious outbreaks affecting both freshwater and marine cultured fish species. Demand for commercially available fish vaccinations is predicted to increase as infectious disease outbreaks continue to occur. In Malaysia, aquaculture vaccine research and development (R&D) are still in its infancy, with most efforts concentrating on producing vaccines against bacterial infections, most notably streptococcosis, vibriosis, andmotile Aeromonas septicemia. Despite several attempts, no homegrown vaccine has been effectively introduced into the manufacturing pipeline to date. At the moment, only three imported aquatic vaccines have received full permission, a far cry from the 314 and 60 vaccines licensed in the poultry and porcine industries, respectively. This review will describe recent findings regarding the development of aquaculture vaccines for certain fish species and diseases in Malaysia. In our opinion, R&D on fish vaccines is critical to the aquaculture industry’s viability

On-farm epidemiological surveillance of genetically improved farmed tilapia (gift) cultured at floating net cages in Pahang, Malaysia

Incidence of streptococcosis, parasitic infestation and Tilapia Lake Virus (TiLV) outbreaks in tilapia aquaculture were reported worldwide, affecting the production and poses a significant threat to sustainable aquaculture. There is limited information on genetically improved farmed tilapia (GIFT) strain with regard to its susceptibility against these diseases. Thus, eight months of farm-level epidemiology surveillance was conducted at a private tilapia farm from August 2017 to March 2018, to determine the prevalence of bacterial, parasite and TiLV in GIFT cage-culture. Throughout the study, a total of 205 tilapias were sampled and subjected to bacteriology, parasitology, and TiLV detection. Water quality parameters, fish weight and length, and associated clinical signs were noted. Mortality of cultured GIFT was recorded at 24.8% from initial stocking, where high mortality was observed in early four months of the culture period. Low prevalence of Streptococcus agalactiae (10.3%) was detected throughout the sampling period. S. agalactiae was successfully isolated in September (32%), October (4%), December (4%) and March (28%). Among other bacteria species that were isolated include Aeromonas hydrophila (4.6%), Staphylococcus spp. (5.1%) and Plesiomonas shigelloides (1.7%). Low prevalence (4-12%) of Cichlidogyrus spp. and Trichodina spp. was also observed during post-mortem. Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR) analysis on all pooled sample of the liver, spleen, and brain showed negative TiLV reaction. This finding suggests that the localized risk in GIFT culture is minimal. However, much attention should be directed to reduce the severity of factors affecting fish health

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

Feed-based vaccination regime against streptococcosis in red tilapia, Oreochromis niloticus x Oreochromis mossambicus

Background: Streptococcosis is an important disease of tilapia throughout the world. In Malaysia, streptococcosis outbreak was commonly reported during the 3-month period of high water temperature between April and July. This study describes the duration of protection following single and double booster dose regimes against streptococcosis in tilapia using a feed-based vaccine containing formalin-killed Streptococcus agalactiae. A total of 510 tilapias of 120 ± 10 g were selected and divided into 3 groups. Fish of Group 1 were vaccinated at weeks 0 and 2 (single booster group) while fish of Group 2 were vaccinated at weeks 0, 2 and 6 (double booster group) with a feed-based vaccine against streptococcosis. Fish of Group 3 was not vaccinated. Serum samples were collected weekly to determine the antibody level while samples of eye, brain and kidney were collected for bacterial isolation. At week 10, all fish were challenged with live S. agalactiae and the survival rate was determined. Results: Both vaccinated groups showed significant (p < 0.05) increase in the antibody levels following the first booster dose, which lasted until week 6. Group 2 showed consistent high level of antibody following the second booster dose at week 6 and remained high until week 12. Challenge trial at week 10 resulted in 45 %, 70 % and 0 % rate of survival for Groups 1, 2 and 3, respectively. Conclusion: Double booster regime is most suitable to be applied for feed-based vaccination against streptococcosis prior to the start of the hot season

On-farm epidemiological surveillance of genetically improved farmed tilapia (GIFT) cultured at floating net cages in Pahang, Malaysia

Incidence of streptococcosis, parasitic infestation and Tilapia Lake Virus (TiLV) outbreaks in tilapia aquaculture were reported worldwide, affecting the production and poses a significant threat to sustainable aquaculture. There is limited information on genetically improved farmed tilapia (GIFT) strain with regard to its susceptibility against these diseases. Thus, eight months of farm-level epidemiology surveillance was conducted at a private tilapia farm from August 2017 to March 2018, to determine the prevalence of bacterial, parasite and TiLV in GIFT cage-culture. Throughout the study, a total of 205 tilapias were sampled and subjected to bacteriology, parasitology, and TiLV detection. Water quality parameters, fish weight and length, and associated clinical signs were noted. Mortality of cultured GIFT was recorded at 24.8% from initial stocking, where high mortality was observed in early four months of the culture period. Low prevalence of Streptococcus agalactiae (10.3%) was detected throughout the sampling period. S. agalactiae was successfully isolated in September (32%), October (4%), December (4%) and March (28%). Among other bacteria species that were isolated include Aeromonas hydrophila (4.6%), Staphylococcus spp. (5.1%) and Plesiomonas shigelloides (1.7%). Low prevalence (4-12%) of Cichlidogyrus spp. and Trichodina spp. was also observed during post-mortem. Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR) analysis on all pooled sample of the liver, spleen, and brain showed negative TiLV reaction. This finding suggests that the localized risk in GIFT culture is minimal. However, much attention should be directed to reduce the severity of factors affecting fish health

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

Assessment of antibacterial activity of fresh garlic juice extract against Vibrio spp. isolated from hybrid grouper (Epinephelus fuscoguttatus x Epinephelus lanceolatus): An in vitro study

We assessed the antibacterial activity of fresh garlic juice extract against Vibrio spp. isolated from hybrid grouper (Epinephelus fuscoguttatus x Epinephelus lanceolatus). The disc diffusion method was conducted to evaluate five concentrations of fresh garlic juice extract against Vibrio alginolyticus, Vibrio vulnificus, and Vibrio parahaemolyticus. The tested concentrations are 20%, 40%, 60%, 80%, 100%, and oxytetracycline (OTC) antibiotic as a positive control, while absolute ethanol as a negative control. Results from the disc diffusion study revealed 100% and 80% garlic juice extract have higher inhibition zone against V. alginolyticus and V. vulnificus compared to OTC. The inhibition zone against V. parahaemolyticus was slightly less when 100% garlic juice extract gave an equal inhibition zone with OTC and smaller in other concentrations. Minimum inhibition concentration (MIC) and minimum bactericidal concentration (MBC) were also studied, which resulted in the lowest MIC value was V.alginolyticus (0.011%) followed by V.vulnificus (0.023%) and the highest is V. parahemolyticus (0.045%). Similarly, the lowest MBC value was V. alginolyticus (0.023%) followed by V. vulnificus (0.045%) and the highest is V.parahemolyticus (0.09%). The results revealed that fresh garlic juice extract was effective against the test bacteria and showed the potential of using fresh garlic juice extract treatment as an antibacterial agent to treat vibriosis in hybrid grouper fish