Immunization regimen in Asian sea bass (Lates calcarifer) broodfish: A practical strategy to control vertical transmission of nervous necrosis virus during seed production
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Outbreaks of viral nervous necrosis (VNN) in Asian sea bass (Lates calcarifer) at the larval stages via vertical transmission of nervous necrosis virus (NNV) from asymptomatic broodfish remain as a major deterrent during seed production. A five-year study was conducted to produce NNV-specific-free sea bass broodfish reared in land-based tanks through an annual immunization regimen with the formalin-inactivated NNV. We primarily immunized (intraperitoneal injection) sea bass juveniles (5 g) and monitored the neutralizing antibody (Nab) titers in the sera of these fish at scheduled intervals post-immunization. Nab titers in the sera of immunized fish peaked at Month 2 (titer: 1:4480 ± 1185) but thereafter gradually declined and significantly dropped (1:260 ± 83) at Month 12 post-primary immunization. Booster immunization of these fish at Month 12 post-immunization led to abrupt increases in Nab titers in booster immunized (B-Im) fish at Month 1 (1:12800 ± 6704) but thereafter declined and dropped at Month 12 (1:480 ± 165) post-booster immunization. The annual booster injections with the inactivated vaccine or L-15 (Unimmunized [U-Im]) were consecutively conducted for 4 years until the fish became sexually mature. Mature fish from both groups were successively induced to spawn twice (1-month interval) via intramuscular injection with luteinizing hormone-releasing hormone analogue (LHRH-a; 100 µg/kg BW). NNV was not detected by RT-PCR in oocytes and milts, and spawned eggs of B-Im fish. In contrast, oocytes and milts, and spawned eggs of U-Im fish were NNV positive. Spawned eggs of B-Im broodfish exhibited Nab titers ranging from 1:192 ± 34 to 1:240 while such was not detected (<1:40) in eggs of U-Im fish. Taken together, current data clearly demonstrate that annual immunization regimen with inactivated NNV vaccine is a pragmatic approach for sustaining immunocompetent sea bass broodfish reared in land-based tanks and circumvent the risk of vertical transmission of NNV from asymptomatic broodfish to their offspring under stress of repetitive spawning.
CitationPakingking Jr., R., de Jesus-Ayson, E. G., Reyes, O., & Bautista, N. B. (2018). Immunization regimen in Asian sea bass (Lates calcarifer) broodfish: A practical strategy to control vertical transmission of nervous necrosis virus during seed production.
Immunization; Vaccines; Polymerase chain reaction; Viruses; Disease transmission; Seed production; Culture tanks; Epidemics; Oocytes; Sea bass; Necrosis; Lates calcarifer; Luteinizing hormone-releasing hormone; Inactivated vaccines; Viral nervous necrosis; Booster immunization; experiment; Immunoglobulins
This study was funded by Government of Japan Trust Fund V through the Regional Fish Disease Project (study code: FH02-F2010-T) and in part by SEAFDEC/AQD. We express our heartfelt gratitude to Dr. Takuro Shibuno and Dr. Chihaya Nakayasu, former and current GOJ-TF managers, respectively, and the Marine Fish Hatchery staff especially Mr. A. Gamuza.
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Protective immunity against viral nervous necrosis (VNN) in brown-marbled grouper (Epinephelus fuscogutattus) following vaccination with inactivated betanodavirus R Pakingking Jr., NB Bautista, EG de Jesus-Ayson & O Reyes -
Fish and Shellfish Immunology, 2010 - Academic PressViral nervous necrosis (VNN) caused by betanodaviruses has been recently implicated in serious mortalities of groupers in the grow-out culture system. A safe and effective vaccine against this disease is urgently needed. This study demonstrates that a single intramuscular vaccination with formalin-inactivated Philippine strain of piscine betanodavirus (genotype: redspotted grouper nervous necrosis virus; RGNNV) induces potent immune responses and substantial protective immunity against an intramuscular challenge with the homologous virus in brown-marbled grouper, Epinephelus fuscogutattus, a highly susceptible marine fish species to VNN. Seroneutralization assay conducted on sera of vaccinated fish revealed the occurrence of substantial neutralizing-antibody titers from Days 15 (mean titer 1:800) to 190 (1:400) with the highest titer observed at Day 60 post-vaccination (1:5120). When vaccinated fish were challenged with the homologous virus at Days 15, 30 and 75 post-vaccination, significantly higher survival rates were obtained in these fish compared with their corresponding controls (L-15 injected fish). Abrogation of virus multiplication in all vaccinated survivors was indicated by undetectable virus titers in the brains and kidneys paralleled by significantly high levels of neutralizing antibodies in the sera of these fish. Consecutively, replicates of vaccinated fish that survived betanodavirus challenge at Days 15 and 75 post-vaccination were maintained in flow-through aquaria and rechallenged with the homologous virus 3 and 5 months later, respectively. A significant drop in neutralizing-antibody titers of 3 and 8 folds, respectively, were observed in the sera of Days 15 and 75 post-vaccinated fish assayed before the virus rechallenge. Interestingly, reversion in the levels of neutralizing antibodies to significantly high levels (8–15 folds) were noted in these fish after the virus rechallenge. Taken together, our current data clearly demonstrate that a single administration of the inactivated Philippine strain of betanodavirus vaccine can effectively mount a specific anamnestic response and concomitant long-term protection against VNN in grouper at the grow-out culture system.
BookLD de la Peña - 2010 - Aquaculture Department, Southeast Asian Fisheries Development Center
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Aquaculture, Aquarium, Conservation and Legislation, 2012 - BiofluxA 12-week (September to December 2009) feeding trial was conducted to evaluate theimmunostimulatory effects of different substances administered orally through the diet in the brown-marbled grouper, Epinephelus fuscoguttatus. Five experimental diets containing either onion, ginger, β–glucan, or vitamin C and a control diet (without immunostimulants) were fed to the fish weighing about 44 g for 12 weeks. Onion-fed fish showed significantly increased weight gain, hematocrit, and total Ig compared to the control group; however, leukocyte differential count and ROS production were unaffected. Ginger-fed fish likewise significantly increased total Ig, ROS production and lysozyme activity. However, it did not affect growth and hematocrit value. β-glucan significantly increased growth and total Ig but had no effect on the other parameters. Vitamin C significantly increased hematocrit, total Ig and ROS production but did not increase growth. Upon challenge with a bacterial pathogen Vibrio harveyi, mortality was significantly reduced in the onion, ginger and vitamin C-fed fish but not in the β–glucan-fed fish. This study demonstrated that onion and ginger could positively affect the innate immune responses and protect grouper against Vibrio harveyi infection.