Susceptibility of hatchery-reared snubnose pompano Trachinotus blochii to natural betanodavirus infection and their immune responses to the inactivated causative virus
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Mass mortality of snubnose pompano Trachinotus blochii fry exhibiting dark coloration, anorexia, and abnormal swimming behavior was recently documented at the hatchery of the Aquaculture Department of the Southeast Asian Fisheries Development Center, Philippines. Samples of brain tissues were collected from affected fish and processed for RT-PCR amplification and virus isolation in cell culture. Infected E-11 cells exhibited cytopathic effect characteristic of betanodavirus. Histopathology of moribund fish showed pronounced vacuolations in the brain, spinal cord, and retina. An RT-PCR product of approximately 430 bp was amplified from the culture supernatant of betanodavirus-infected E-11 cells and sequenced. Sequencing of the T4 region of the coat protein gene (RNA 2) revealed clustering of the isolated virus within the red-spotted grouper nervous necrosis virus type. The pathogenicity of the isolated betanodavirus in healthy pompano juveniles and fry was determined via intramuscular injection and immersion challenges, respectively. Higher mortality rates were obtained in challenged fish compared with the controls. An inactivated vaccine was subsequently prepared by treating the clarified betanodavirus with formalin. Pompano juveniles intraperitoneally injected with the inactivated vaccine exhibited neutralizing antibodies from days 15 (mean titer 1:240) to 125 (1:560) with the highest titer noted at day 64 (1:2240) post-vaccination. Additionally, pompano fry bath-vaccinated and consequently bath-challenged with betanodavirus at day 35 post-vaccination showed higher survival rate compared with the control, indicating the potential of the inactivated betanodavirus vaccine against VNN in pompano fry and juveniles.
CitationPakingking Jr., R., Mori, K., Bautista, N. B., de Jesus-Ayson, E. G., & Reyes, O. (2011). Susceptibility of hatchery-reared snubnose pompano Trachinotus blochii to natural betanodavirus infection and their immune responses to the inactivated causative virus.
This study was funded by SEAFDEC/AQD (study code: 5203-T-RD FH0507) and the Government of Japan Trust Fund through the Regional Fish Disease Project (study code: 8001-T-FD-FH0507). We would like to thank Dr. Takuma Sugaya of Fisheries Research Agency, Oita, Japan, for the invaluable help on sequencing and phylogenetic analysis and Dr. Felix Ayson for the critical review of the manuscript.
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Larval and early juvenile development of silver therapon, Leiopotherapon plumbeus (Actinopterygii: Perciformes: Terapontidae), reared in mesocosms FA Aya, MNC Corpuz, MA Laron & LMB Garcia -
Acta Ichthyologica et Piscatoria, 2017 - Szczecińskie Towarzystwo NaukoweThe silver therapon, Leiopotherapon plumbeus (Kner, 1864), is an endemic and economically important freshwater food fish in the Philippines. The natural populations of this species have been declining during the past years, mainly due to intense fishing pressure, habitat degradation, and introduction of invasive alien species. At present, it is considered a target species for domestication and conservation efforts. Despite several attempts of artificial reproduction and larval rearing, little is known on larval and early juvenile development of silver therapon. The presently reported study was therefore intended to fill this gap in the knowledge by determining the growth and describing body proportions, pigmentation, and fin formation of this fish. Newly hatched larvae were reared in mesocosm tanks at a mean temperature of 29.5°C. Larvae up to 30 days after hatching were sampled at irregular intervals and preserved in 5% buffered formalin. Early development stages for 245 preserved specimens were described in detail with reference to changes in morphology, growth and body proportions, pigmentation, and fin formation. Five developmental stages of silver therapon were identified: yolk sac larva (1.88 mm TL), preflexion (2.51 mm TL), notochord flexion (4.50-8.27 mm TL), postflexion larva (6.90-12.21 mm TL), and early juvenile (>13.40 mm TL). Growth was isometric for eye diameter and gape size whereas positive allometry was observed for body depth, head length, and preanal length. Some body proportions showed abrupt changes from preflexion to postflexion larvae before it stabilized during the early juvenile stage. Pigmentation in the form of stellate and punctate melanophores increased with developmental stage, with larvae becoming heavily pigmented from postflexion to early juvenile stage. These morphological changes, together with the full complement of fin rays and squamation observed in specimens larger than 13.4 mm TL, suggest the attainment of the juvenile stage of this species. These morphological changes may explain the food and feeding habits during the early life stages of silver therapon which is critical to their survival and recruitment in the wild and in a mesocosm hatchery environment.
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