Epidemiology of Pennella sp. (Crustacea: Copepoda), in exploited Illex coindetii stock in the NE Atlantic

Abstract

The spatio-temporal distribution of the mesoparasitic copepod Pennella sp. on the short-finned squid Illex coindetii was studied monthly during 1993 in the southeastern North Atlantic (Galician waters, NW Spain). A total of 600 individuals were analysed separately considering two areas (north and west) with different hydrographical characteristics. Six pennellid stages were found: a copepodite, four chalimus stages and the free-living adult male and female. Epidemiology was assessed using the parasite demographic parameters. The results revealed a marked seasonal pattern in the number of parasites in squid samples from the northern area. This seasonal pattern was not detected in squids from the western area. The observed frequency distributions of parasites on the host population were aggregative at each sampling area. Infection values were extraordinarily high when they are compared with published host-parasite records for other representatives of the genus Pennella. Advantages of the parasite aggregation pattern and possible explanations of the seasonality variations in the number of parasites observed in squid samples from the northern area are discussed.