Abstract
Parasitism leads to severe economic losses to marine fish exports in Sri Lanka. Swordfish is a seasonal species with high demand both locally and internationally. Presence of a parasite in their flesh confuses the suppliers with zoonotic Anisarkis spp. This study is aimed to identify the plerecercoid parasitic larvae found in swordfish and establish a feasible method of diagnosis at fish processing factories. Parasites buried in frozen swordfish ( Xiphias gladius ) muscles were isolated and stored in cold sea water. Samples were washed with normal saline water and observed under bright field light microscope at 40x and 100x magnifications, and the parasites were identified based on their morphological features. For further confirmation, confocalmicroscope was used to record scolex parameters. Total length of the parasites was 1.7 cm– 3.5 cm (2.27 cm). Presence of the elongated, acraspidote scolex (length 6.23 mm, width at pars bothridialis 2.4 mm) with four tentacular armature and curved, apically inverted, thick edged bothridia confirmed the parasitic larvae belonged to the Order Trypanorhyncha. Corona of falciform hooks in the basal armature and the heteromorphous hooks in a half spiral arrangement at metabasal armature are characteristics of the genus Molicola . This is the first record of the Trypanorhynch plerocercoid larvae (genus: Molicola ) isolated in swordfishes from Sri Lanka. This study emphasizes that morphological examination of the parasite scolex using bright field microscopy will be helpful to distinguish the parasitic genera and feasible to use in the fish processing factories.
Highlights
Capture fisheries is a major source of protein for the majority of the people in the world
Sample collection Parasitic larvae were extracted from swordfishes (Xiphias gladius) that were captured from the FAO zone 57 of the Indian Ocean by multi-day boats and received at frozen state from a fish processing company
Parasites fixed in 10% formalin were observed for scolex morphology under the bright field microscope (Olympus, CX22LED, USA) and one parasite with complete morphology was stained in bromophenol blue and observed under confocalmicroscope (Fluoview FV1200, Olympus, USA) to measure the structures in the scolex
Summary
Capture fisheries is a major source of protein for the majority of the people in the world. As an island situated in the Indian Ocean, Sri Lanka has a long history of capture fisheries. Fisheries sector in Sri Lanka has a great impact on the economic and social life contributing about 1.8% to the gross domestic production (GDP) and earns over US$ 94.3 million with a production over 0.4 million tonnes of fish annually Improving postharvest practices can upgrade the quality of fish, infestation with parasites is an inevitable cause for their rejection by the consumers. The intermediate and definitive host specificity are generally lacking. Most of these parasites have a life cycle with very long larval stages within intermediate hosts. Many consumers concern about the parasites in fish because of the potential zoonotic species. The most abundant zoonotic parasite is a nematode belonging to the family
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