Frontiers in Marine Science (Nov 2015)
Commercial and game fish from the Dąbie lake (Poland) and their infection of Paracoenogonimus ovatus (Digenea)
Abstract
Paracoenogonimus ovatus is the parasite that infest wide definitive host range (predator birds) and at least two intermediate hosts: molluscs (Viviparus viviparus, V. fasciatus) and freshwater fish from eastern and central Europe. The larvae of the parasite (metacercariae) go to the muscle and connective tissue, and at high intensity of infection to the internal organs and brain of fish. A total of 128 fishes were caught in autumn 2009 and 2014, by fishing boats operating in Lake Dąbie, which is one of the largest lakes in Poland. The species selected reflect the species structure of commercial and recreational catches. They were roach, bream, silver bream, crucian carp (Cyprinidae), ruffe, perch, zander (Percidae) and pike (Esocidae). The fish were filleted, and the skinned muscle was compressed under a trichinoscope, what allowed to see and count metacercariae in the tissues. To facilitate parasite isolation from the cysts, the muscle tissues were subjected to a 0.1 % solution of activated pepsin and 5 % citric acid at a temperature of 20ºC. The free larvae were measured and identified under an Olympus BX 50 microscope coupled with a camera running AxioVs40 V 4.8.2.0 software. Metacercariae are grouped primarily at depths ranging from just beneath the skin to about 50% of fillet thickness. The infection prevalence of P. ovatus metacercariae in the fish analyzed was 78,5%. The density of infection per gram of muscle tissue mass in the fish infected was 8.85 (from 1 to 84 metacercariae). The highest density was noted in roach, bream and white bream (17.09, 11.14 and 9.58, respectively). Metacercariae occurred singly in pike, parasites were not found in the muscles of crucian carp, ruffe, and perch examined. The reason for such differences in infection is the availability and composition of food, as well as the behavior of the fish examined.
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