Health Risks Associated with Freshwater Fish Consumption

Aims: To determine the prevalence and density of the larval digenean trematode Paracoenogonimus ovatus in fish muscle tissue. To determine larval survival under selected thermal conditions.

Place and Duration of Study: Division of Hydrobiology, Ichthyology and Biotechnology of Breeding, West Pomeranian University of Technology, Szczecin, October 2009 and 2014.

Methodology: Twelve fish species from Lake Dąbie (Poland) that are exploited by both commercial and recreational fisheries were selected. Samples of muscle tissue were weighed and then viewed under a trichinoscope where encysted P. ovatus larvae (metacercariae) could be counted. Then, they were subjected to artificial digestive juice (0.1% activated pepsin and 5% citric acid) to facilitate isolating the cysts from the muscle tissues. The parasites that were isolated were removed from their shells, and the species was identified. Further, ten freshwater bream fillets with encysted larvae were placed under refrigeration (4ºC) and frozen (-18ºC); larval viability was checked after 24, 48, and 78 h.

Results: The prevalence of P. ovatus larvae increases (76.5% in 2009 and 80.5% in 2014). The highest density was noted in roach (Rutilus rutilus), freshwater bream (Abramis brama), and white bream (Blicca bjoerkna). It was confirmed that metacercariae are resistant to decreases in temperature to 4ºC, but that further reducing the temperature to -18ºC results in larval death in 24 h.

Conclusion: Many species of freshwater fishes are infected by P. ovatus metacercariae. Eating improperly prepared fish and fisheries products may provide serious health problems. Further studies are needed to neutralize the living metacercariae in raw materials and food products.