Infection with digenetic metacercariae of Yellow Grub, Clinostomum sp. (Trematoda, Clinostomidae) in a wild fish population in Sri Lanka

Abstract

Spike tail paradise fish, Pseudophromenus cupanus (Cuvier, 1831) is a freshwater fish found only in Sri Lanka and South India. P. cupanus was sampled using a hand net from a freshwater lake, Dadagamuwa wewa in Gampaha district. Adult fish with length range of 2-5cm (n=210) were examined for parasites by cutting the ventral side from the anal opening to the lower jaw. Large number of internal parasite was observed with the naked eye in the abdominal cavity of P. cupanus that were sampled from May to October 2018. The metacercariae collected from the abdominal cavity were fixed in 70% alcohol and permanent slides were prepared after staining in heamotoxyline and eosin. According to the morphological features observed through binocular microscope, the parasite was identified as Clinostomum sp. The main morphological characters of the metacercaria were stout body, slightly wider in gonadic region; 4000-6000μm long, 2560-3000μm wide. The elongated oval shaped metacercaria possessed small oral and a ventral sucker. Testes arranged in tandem between middle and posterior third of body. Clinostomum sp. has a heterogeneous life cycle and both vertebrates and invertebrates act as hosts and assist them in completing life cycle. Humans may become accidental hosts if they ingest raw freshwater fish containing metacercaria of Clinostomum sp. which causes pharyngitis or laryngitis. This was the first time, metacercarial stage of Clinostomum was recorded in a wild fish population in the country. Further studies are warranted to assess the impact and the pathogenicity of the parasite on native fish varieties in Sri Lanka