Life history characteristics of Argulus foliaceus L. (Crustacea : Branchiura) populations in central Finland

Life history characteristics of a common fish ectoparasite Argulus foliaceu s, poorly studied in the northern part of its range, were investigated. Fie ld data on the seasonal occurrence, host preference, sex and size of Argulu s foliaceus populations from interconnected lakes in Central Finland were a nalyzed together with experimental data on egg laying, hatching, and mating behaviour. Demographic characteristics of A. foliaceus from a commercial f ish farm thigh host density) with a water supply from the same lake system differed significantly from those of the lake population where the hosts ar e scarce. Extended periods of egg laying and hatching were documented in th e lake population which possibly prevented the appearance of summer peaks i n juveniles that were observed in the farm. The elevated activity of the ma les, which was most clearly observed in their high attachment/detachment ra tes, is suggested to result in lower survival and growth than in females. T he flexibility, in both behaviour and life cycle strategy, allows A. foliac eus to utilize a broad spectrum of habitats of differing host abundance.