探討日本虎斑猛水蚤在石斑魚虹彩病毒及神經壞死病 毒傳播上的可能角色

Abstract

Grouper aquaculture has been threaten by grouper iridovirus (GIV) and nervous necrosis virus (NNV) for many years, and the insufficient apply of long chain unsaturated fatty acids for grouper metamorphosis development and neural growth, all result in a high mortality rate for grouper fry. Therefore, to culture a high quality grouper fry of specific pathogen free (SPF) becomes an important issue for nowadays grouper aquaculture. Rotifer and artemia nauplius, which are commonly used as live feed organisms are low contents of high unsaturated fatty acids (HUFA), so feeding with these feed organisms effect the successful rate of fry metamorphosis. Although there are many ways of enrichment techniques and products develop to improve these feed organisms, it’s hard to provide proper nutrition composition for grouper fry. The abundant species of copepods, character of appropriate size for grouper fry and high quantity of HUFA all made copepods as the best natural foods for marine fishes fry. However, most of the feeding copepods in grouper cultivation are collected from fish and shrimp culture farm, therefore feeding grouper with these copepods is possible to transport viral pathogens. We had detected the existence of iridovirus from collected copepods in south Taiwan aquatic farm, and showing copepods can be a possible transmission vector for iridovirus. In this experiment, Tigriopus japonicus was used to investigate its possible role of iridovirus and nervous necrosis virus transmission. The results revealed that the best T. japonicus population growth rate was obtained from feeding Isochrysis galbana, then Tetraselmis chui. In addition, T. japonicus can also be cultivated with photosynthetic bacteria and the population growth rate is nearly to that of feeding with Tetraselmis chui. After virus experimental infection and different III periods of fresh seawater culture, PCR, cell titration and transmission electron microscopy were used to check out the existence of viruses in the infected T. japonica.The PCR result shows that GIV can be detected up to 96h in experimental infected T. japonica. The TEM result reveals that some viral like particle can be observed in the digestive tract of copepod. Furthermore, in the experiment of cell titration, both GIV and NNV have been demonstrated viral activity to infect grouper cell, but the viral activity cannot exist over time. It represent that both virus cannot be replicated in T.japonicus, and after periods new fresh seawater culture, the virus can be clean out in copepods. Furthermore, we can get virus-free copepods when T. japonicus is neutralized with anti-virus antibody. Those characteristic can help us to culture SPF copepods for further application.