In this study we examine differences in the occurrence of life history stages of the destructive fish ectoparasite Argulus foliaceus (L., 1758) on eight fish species (stickleback, rudd, roach, gudgeon, bream, tench, crucian carp and common carp) sampled from a mixed-species recreational fishing lake on nine occasions during late spring and summer. Total numbers of A. foliaceus, as well as the number of larval, juvenile and adult parasite stages, from each fish were recorded along with the fish species. Lice generally exhibited an aggregated distribution approximating a negative binomial distribution. Significant differences in the prevalence, intensity and intensity frequency distribution were observed between life history stages and between host species. In general, all life history stages of A. foliaceus exhibited an over-dispersed distribution. However, larval lice did show some degree of aggregation particularly within the stickleback samples. Infection data for parasite larval stages suggested that sticklebacks are more likely to be infected than other host species. For adult lice, however, carp appeared to be the main host. We propose that A. foliaceus infection characteristics are predominantly determined by the level of host exposure to the parasite and its life history stages (larval, juvenile and adult) rather than by an innate difference in host susceptibility related to individual host factors such as immune responses. We conclude that host exposure is determined by the parasite-host behavioural interplay related to species-specific ecology and behavioural traits such as microhabitat preference and normal swimming speed.
The taxonomic classification of some parasitic isopods of the family Gnathiidae has been revised in the last years. However, their biological cycles have been described only partially or incompletely. Gnathia maxillaris (Montagu, 1804) is one of the most studied species, but certain aspects of its life cycle are still poorly known. A detailed study on the life cycle of G. maxillaris was carried out over several years by sampling larvae from an infestation of large volume aquaria at the Aquarium of Barcelona. At the same time, a system of in vitro cultivation of G. maxillaris was developed, which provided new data to complete the description of its life cycle. Periods of incubation, fertilization, planktonic stages, the attachment site on the fish host and biometric characteristics of larval forms were detailed. The new information may help better control health state of marine fish in aquaculture.