Abstract
This study was done to describe the morphology and morphometric characters of the life cycle stages of the digenean gill parasite, Centrocestus sp. that infests Koi carp (Cyprinus carpio) at Rambadagalle and Ginigathhena ornamental fish breeding centres of Sri Lanka and to identify the species of the parasite. The snail, Melanoides tuberculata (Muller, 1774) that inhabited the earthen ponds with Koi carps were induced to shed cercariae and 45 days old Koi carps were experimentally infested by them. The infected fish with mature metacercariae were fed to chicks (Gallus gallus) and eggs of the parasite released with faeces and adult stages of the parasite developed in the intestine were recovered. After keeping the eggs in water for several days ciliated miracidia were observed by application of tactile pressure. Infested snails were dissected and the morphometric characters of sporocyst and redia stages were recorded. The eggs were operculated, oval shaped, yellowish brown in colour with lattice design on the shell surface. The ciliated miracidi, was the infective stage to snails. The sporocyst was sac like and the redia was tubular and curved. The cercaria had an oral and a ventral sucker, two eye spots and a tail. The encysted metacercaria was oval in shape with ‘X-shaped excretory bladder’. Excysted metacercaria was elongated and narrower at the anterior end being similar to adults. The adult worm was small and oral sucker was surrounded by 32 circumoral spines arranged in two alternated rows. Acetabulum located in the middle of the body. The excretory bladder opened to a terminal excretory pore. The morphology and morphometric characters of the life cycle stages of the Centrocestus sp. that infests Koi carp at Rambadagalle and Ginigathhena ornamental fish breeding centres were compared with published literature and the parasite was identified as Centrocestus formosanus (Nishigori, 1924), which has not been documented in Sri Lanka earlier.
Highlights
The digenean parasite Centrocestus sp. belongs to the Family Heterophyidae, which was considered to be native to Asia (Salgado-Maldonado et al, 1995; Scholz and Salgado-Maldonado, 1998)
Balasuriya (1988) had stated that metacercarial stage of Centrocestus sp. that infest food fish in certain areas of Sri Lanka (Dambulla, Polonnaruwa, Muruthawela, Udawalawa) was C. armatus. His conclusions was based on morphometric characters of the parasitic stage found on fish; and the complete life cycle of the parasite had not been studied and documented under local conditions
When compared with published reports, the measurements obtained for the different body parts of the adult Centrocestus sp. in the present study showed intermediate ranges for ovary and oral sucker, while the eggs, pharynx and body length have shown higher values as pointed out in the study of Wongsawad et al, (2013)
Summary
The digenean parasite Centrocestus sp. belongs to the Family Heterophyidae, which was considered to be native to Asia (Salgado-Maldonado et al, 1995; Scholz and Salgado-Maldonado, 1998). It is an important etiological agent that causes gill lesions and respiratory difficulties in infested fish leading to significant economic losses in the aquaculture industry (Mitchell et al, 2005). It is a zoonotic pathogen and humans get the infestation by ingestion of raw or partially cooked fish (Chai et al, 2013). That infest food fish in certain areas of Sri Lanka (Dambulla, Polonnaruwa, Muruthawela, Udawalawa) was C. armatus. His conclusions was based on morphometric characters of the parasitic stage found on fish; and the complete life cycle of the parasite had not been studied and documented under local conditions
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