Differential infectivity of Caligus flexispina (Copepoda, Caligidae) in three farmed salmonids in Chile

The ectoparasitic copepod, Caligus flexispina, is causing increasing proble ms in farmed salmonids in southern Chile. Field and experimental approaches were used to assess whether any of the three host species, rainbow trout O ncorhynchus mykiss, atlantic salmon Salmo salar and coho salmon Oncorhynchu s kisutch, is preferentially colonized. Prevalence, abundance, density and developmental stages attained by the parasite in three host species were co mpared. Results clearly revealed that rainbow trout is the most susceptible species: under field conditions, C. flexispina is more prevalent and abund ant and there is a higher proportion of adult stages. No ovigerous females were found in coho salmon. In experimental infestations, rainbow trout were more heavily colonized by infective copepodids, and these were more likely to reach the adult stage. A mixture of factors inherent to each host-paras ite relationship is considered to play a role in these observations because coho salmon is also colonized by copepodids but a low proportion of the pa rasites reach the adult stage. However, atlantic salmon is less suitable fo r colonizing larva. (C) 2000 Elsevier Science B.V. All rights reserved.