Establishment of preventive measures against viral nervous necrosis (VNN) in finfish hatcheries

Abstract

The establishment of preventive measures against viral nervous necrosis (VNN) at the finfish hatcheries of SEAFDEC Aquaculture Department in Iloilo, Philippines, was instituted primarily to minimize the impact of the viral infection in cultured stocks. Selection of VNN-negative broodstocks was conducted and the detection rate ranged from 25-56%. It was confirmed that all species of broodstocks are already contaminated with the virus with varying percentages. The combination of cell culture and RT-PCR in the detection of the virus proved to be more sensitive than the RT-PCR alone. The trash fish food was suspected as a main source of contamination and tests prove that most of the trash fish species were contaminated with the virus. The effect of chemical treatment was tested and a good result was obtained by using 5 and 7 ppm iodine. Several recommendations were formulated in the prevention and control of VNN in the hatchery phase: VNN-negative broodstocks should be selected by using cell culture and PCR; spawning of the selected broodstocks should be limited to only six times and these fertilized eggs should be used for larval productions; fertilized eggs should be washed and disinfected with iodine; and commercial broodstock feeds should be used instead of trash fish.