The outbreak of Red Sea Bream Iridovirous (RSIV) disease in cage farming resulting in the death of fish has been reported again from Kundapur in Udupi district.
It had been reported earlier during the winter season of 2018 and 2019.
Scientists from the Department of Aquatic Animal Health Management, College of Fisheries, Mangaluru, who visited Thallur estuary, near Kundapur, on Sunday, reported that there is a danger of the disease spreading in the estuarine and coastal waters thereby not only affecting cultured fish but also the other fish.
As there is no cure for RSIV, diseased and dead fish should be immediately cleared and buried or burnt in a safe location. The spread of the virus in the waters is difficult to control as the water is free flowing, the college said.
Dean of the college A. Senthil Vel said in a release here on Tuesday that a team comprising Assistant Professor Girisha S.K. and research staff Nithin, Kushala K.B. and Soundarya, visited the site on Sunday and observed large-scale death of sea bass in one particular cage and infected fish in the other cage. They held discussions with the Fisheries Department officials and collected water samples in and around the floating fish cages.
“Dead, moribund and apparently healthy fish samples were collected and brought to the college laboratory for microbial and viral testing. Based on the analysis, it was found that around 2,000 fish of 40-60 grams each in two cages were infected or dead on account of RSIV,” Prof. Vel said and added that internal organ analysis of these dead fish showed enlarged spleen and dull coloration of skin.
The release said that the State government should make it mandatory that fish seeds procured by farmers are only from certified fish seed sellers.
“The possible spread of the virus in these cage culture farms may be on account of high stocking density. Proper housekeeping, sanitation, disease control measures, monitoring needs to be undertaken,” Prof. Vel said.
The release said that apart from high stocking density, cages, during low tide, have very little depth of water thereby increasing stress in fish. The high stocking density and low water-levels during low tide lead to stress thereby becoming a fertile ground for such virus activation.
“The cultured sea bass are highly carnivorous and are fed with trash fish. If proper care is not taken and infected feed is given, chances of such infection with RSIV increases. It is advised that authenticated commercial feed may be provided to these fish,” he said.
The release said that during discussions with fish farmers it was mentioned that the water has high load of pollution level mainly from sewage.
As it had been reported in the winter during the last two years, stocking of seeds can be avoided during these winter months and they can be stocked from late February as this virus subsides during the summer months, the college said.