Ectoparasites Recovered from Whole Cage Freshwater Treatment on Cultured Marine Fish Disease Outbreak in Floating Cages
Leong Tak Seng1.
Multi-species marine finfish are farmed in floating cages, with farmers experience frequent fish disease outbreaks. Common symptoms observed are scratches on body surface, scale drop, fin- and tail-rot, head region devoid of scales, eye opaque and blind. Farmers commonly do freshwater
treatment for the infected fish in the whole cage when disease outbreak occurs involving ectoparasites, to prevent further mortality. Monitoring study to identify ectoparasites of disease outbreaks in a Penang fish farm was done between 2014 -2018. During the outbreaks, the whole cage of fish was freshwater treated and the ectoparasites samples were collected for identification and counted under dissecting microscope. Three groups of ectoparasites recovered during these monitoring studies were capsalid monogeneans (Benedenia spp., Neobenedenia spp.), leech, (Zeylanicobdella arugamensis) and caligid copepods (Caligus spp.). The capsalid monogeneans, especially B. lutjani, were the dominant ectoparasites removed from snappers while leech was the dominant parasite in groupers. Observations on initial disease outbreak showed injuries on body surface caused by vast ectoparasites activities. These ectoparasites were considered as the PRIMARY PATHOGENS initiating disease outbreaks in the floating cage culture ecosystem leading to physiological complications, secondary bacterial infection, and fish dying. Freshwater treatment is effective in removing ectoparasites in snappers, but not in groupers. Crimson snappers was mostly infected by capsalid monogeneans and spread the parasites to other species in the floating cage. Groupers, however, are the major contributor of leeches for infecting other fish. Observations on regular freshwater treatment in the crimson snapper’s cage for nine months showed no disease outbreaks. Constant removal and re-infection of the ectoparasites in the cultured fish is a process of natural life vaccination especially during the first year of placement in cages. The affected fish become immune to these infections resulting in fewer disease outbreaks asthe fish grow.
Affiliation:
- Gelugor, Pulau Pinang, Malaysia
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