Parasitic copepods Caligus lacustris (Copepoda: Caligidae) on the rainbow trout Oncorhynchus mykiss in cage aquaculture: morphology, population demography, and first insights into phylogenetic relationships

Herein, data on rainbow trout infections with the copepod Caligus lacustris in cage aquaculture Lake Ladoga is presented. (n = 127 ex.) were collected from a farm housing cage-reared to describe size–age and sex structure of population. Morphological features copepods evaluated according 10 characters terminology proposed by Kabata Gusev (J Linn Soc (Zool) 46(309):155–207, 1966). To determine phylogenetic position C. within genus Caligus, fragments cytochrome c oxidase subunit 1 mitochondrial gene (COI, 645 bp) 18S rRNA (1617 sequenced. An increase parasite prevalence was observed as lake warming up July September. The morphological crustacean’s larval adult stages, characterized specific parameters quantitative traits, are described. Three COI haplotypes only one haplotype identified among five samples. Based analysis (resolution tree poor), we can conclude that clade containing lacustris, aforementioned sister species, appears an early radiation Caligus. development freshwater contributes transfer native farmed trout.