Evaluation of the parasitic degree and the effects caused on the commercial fish stocks at the Romanian Black Sea coast

Abstract

This paper presents the results of the parasitological research on parasite infestation at the main fish species of commercial interest on the Romanian Black Sea coast: Sprattus sprattus - sprat, Engraulis encrasicholus - anchovy, Trachurus mediteraneus ponticus - horse mackerel, Psetta maxima maeotica - turbot. The investigations were carried out between 2016 and 2017, on fish collected from Sulina to Vama Veche. The following species of ectoparasites were identified: the ciliate - Trichodina domerguei, and the flat worm - Mazocraes alose and the endoparasites: Contracaecum aduncum, Contracaecum sp., Anisakis sp., Porrocaecum sp. and the flat worm Botriocephalus scorpii were found. Ectoparasites, including those outside the body affecting fish species, especially the substrate of skin, fins, gills and eyes were rather low in number. Trichodinina domerguei affected fish outside the body, fins and gills and Mazocraes alose affected only the gills. Specific analysis made to evaluate the effects of nematode worm parasites on the status of fish populations revealed high values of prelevance (percentage of infested fish), mean infestation intensity and abundance of parasites being higher in larger specimens compared to the smaller ones. Thus, for sprat, the larger specimens, 10-11 cm in length, reached 80% and anchovy 11-12 cm length reached 100%, while the specimens under these lengths were 40-70% infested. The flat worm Botriocephalus scorpii, found in turbot stomach in very large numbers, caused severe lesions, especially inflammations, wounds, desquamation of the damaged epithelium. Toxic substances released by the worms are absorbed and produce whole body intoxication. The presence of these parasites in natural fish populations may represent a real danger to the state of existing stocks, but also to their evolution.