Journal of Fisheries and Life Sciences

Author(s): Sumuduni B. G. D., Munasinghe D. H. N. and Arulkanthan A.

Abstract: The infestation of cercariae larvae of Centrocestus sp. make considerable impact on Koi carp culture and it is important to understand the parasite behavior in order to apply control measures. The Infested snails, Melanoides tuberculata by Centrocestus sp. were induced for shedding cercaria larvae for the estimation of larval survivability. Observations were recorded at two hourly intervals. After emerging from the snail, the cercariae lived for 26 hours by maintaining a plateau period and thereafter became immotile and died after 26-32 hours. The transmission rate of the cercaria larvae to early fingerlings of koi carps (Cyprinus carpio) (total length 2 cm - 2.5cm) was recorded at every 02 hours until reached to zero.The transmission rate of the cercariae to the fish host was 9.34% just after the emerging from snail and this rate was increased up to 70% after two hours and remained at the constant level until an abrupt decrease in the ability to infest after 24 hours of the emergency. The estimated lethal number of parasites that infested on fish fry (total length 0.8 cm -1cm) revealed that there was a positive relationship between the cercariae concentration and the mortality of the fish.The median lethal number of parasites for fish fry was estimated as 1467cercariae/L.The results indicated that cercariae larvae of Centrocestus sp. not only infested on gills but under heavy exposures parasite infestation can be observed on head region, body (skin) and fins of the fish which may be one of the reasons cause for mass mortalities in the koi carp culture systems.