Seasonal variation of ectoparasite infestation levels of Trachurus picturatus in Bizerte (Tunisia)

Abstract

The blue jack mackerel, Trachurus picturatus, is a commercially important resource in the Mediterranean Sea and the North-East Atlantic. The main aim of this work was to assess the infection levels and diversity of the ectoparasites of the blue jack mackerel. Over a one-year period, between March 2017 and February 2018, 126 specimens of T. picturatus were collected seasonally from the Bizerte coast (Tunisia). The ectoparasite fauna of the examined host was composed of the two monogenean species, Pseudaxine trachuri and Gastrocotyle trachuri and a copepod species, Peniculus fistula fistula. This is the first record of this copepod parasite in Tunisia.

The analysis revealed that the infection levels fluctuated throughout the year. Both monogeneans (P. trachuri and G. trachuri) had high prevalences during the warm season (P% = 87.1, P% = 32.3, respectively).

Additionally, P. trachuri showed some seasonal variations in mean abundance and mean intensity between summer and the other seasons. Furthermore, there was a highly significant variation in the mean abundance of G. trachuri between the summer and autumn-winter seasons. The results of the current study may be explained by the seasonal variations in environmental conditions, the life cycles of the hosts and parasites, the feeding and migratory patterns of the hosts, the chemicals released by the hosts, and the interspecific competition between the two monogenean species.