Impacts of infestation of Centrocestus sp. on Gills and the Growth of Ornamental Fish Koi Carp (Cyprinus carpio): an Experimental Approach

Abstract

Gill trematode Centrocestus sp. is known to infest many fish species in Sri Lanka. An experimental study was carried out to determine the effect of gill trematode on the gill structure and the growth of ornamental fish koi carp (Cyprinus carpio). Shedding of cercariae was induced by exposing the first intermediate host the snail Melanoides tuberculata to the sunlight. Three aerated tanks with 20 fish in each were treated as experimental tanks and 8 ml of water with approximately density of 4 cercariae μl-1 were introduced to them. Three other tanks were used as control (uninfected). After two months of infection 4 gills of infected fishes were observed and the metacercarial cysts were counted in each gill to observe whether there is any difference in infestation on gills. The standard length (cm) and weight (g) of 30 infested fishes and 30 non-infested fish were measured and condition factor was calculated using the equation K = W/L3 (where K= condition factor, W= weight, L= standard length). Some gills of fish were fixed in Bouin’s solution and processed for histopathological observations. The numbers of parasites infested on each gill were different, but there was no significant difference observed among them (p>0.05). According to the Kruskal Wallis test a significant difference of condition factor between infested and non-infested fish (p = 0.012) was observed. A negative correlation was observed between the parasite density and the condition factor of fish (r = -0.627; p <0.001). The histopathological observations showed distortion of the gill architecture. According to the results it can be concluded that the infestation of metacercarial cysts caused severe damage to the gills and the condition of koi carps which make a considerable impact on the economic value of this ornamental fish species.