Current infestation status of Atlantic salmon with Anisakis simplex larvae in the river Ponoi (the Murmansk region)

The infestation of Atlantic salmon with larvae of nematode Anisakis simplex has been studied in recreational catches in the River Ponoi of the Murmansk Region by using data from field research. The level and dynamics of infestation of autumn Atlantic salmon in 2009-2016 have been determined in comparison with the historical data. The results of research have shown that the proportion of salmon infested with parasite (extensiveness of infestation) varied from 2,1 to 59,8 % and a number of parasites in a single fish (intensity of infestation) - from 0-1 to 0-28. Indexes of infestation have varied also among different groups of autumn salmon but related neither with a number of years salmon spent at sea nor with salmon run timing into the river. The Red Vent Syndrome (RVS) has never been confirmed for Ponoi Atlantic salmon. The larvae of nematode have been found only in the mesentery and on the internal organs of the abdominal cavity of salmon and never in the muscles. Observations of the behavior of parasite larvae found in the abdominal cavity of the salmon have shown that when storing unbetted fish during the day at different ambient temperatures, migration of larvae to muscle tissue has not been observed. These findings have an important practical application as larvae of nematode Anisakis simplex are infective to humans and cause Anisakidosis. After having analyzed the data on dynamics of salmon infestation the assumption has been made that the level of Atlantic salmon infestation with Anisakis simplex larvae depends mostly on the role of different salmon food species in the parasite life cycle and their availability in different years of salmon feeding migration in ocean.