PREVALENCE OF VIBRIO spp. IN TROPICAL MARINE CAGE-CULTURED FISHES

This study investigates the occurrence of Vibrio in economically important cage-cultured marine fish; seabass (Lates calcarifer), red snapper (Lutjanus spp.) and hybrid grouper (Epinephelus spp.). Sampling was conducted at a commercial floating cage farm, located in Klang, Selangor, Malaysia from December 2016 to August 2017. A total of 25 fish from each species were randomly sampled at monthly interval, where their skin, eye, liver and kidney were sampled for bacterial isolation and identification. The presumptive Vibrio was identified using biochemical methods, molecular approach using gene-encoding protein pyrH and sequencing analysis.

Nine species of Vibrio from cultured fishes were identified, including Vibrio alginolyticus, V. diabolicus, V. harveyi, V. campbellii, V. parahaemolyticus, V. rotiferianus, V. furnissii, V. fluvialis and V. vulnificus. Highest occurrence of Vibrio spp. was found in hybrid grouper (81%), followed by seabass (56%) and red snapper (36%). The associations between Vibrio spp. and P. damselae subsp. damselae with the host fish were not species specific. However, fish mortality and size showed a strong correlation with the presence of some Vibrio spp. On average, 60% of the infected cultured fish exhibited at least one clinical signs. Clinical signs associated with Vibrio include pale and hemorrhagic liver, hemorrhagic kidney and skin lesions. Higher number of large-size hybrid groupers positive with Vibrio exhibit severe skin and fin lesions.

This study suggests that year-long occurrence and abundance of Vibrio in the farmed fish might serve them as potential reservoir of the pathogens. The microbiological monitoring could provide valuable information for managing the health of farmed fish in grow-out cages.