Introduction Data on rainbow trout infection with the copepod Caligus lacustris in cage aquaculture on Lake Ladoga is presented.
Materials and MethodsCaligus lacustris (n=127 ex.) were collected from a farm in Lake Ladoga housing cage-reared rainbow trout to describe the size-age and sex structure of the copepod population. Morphological features of the copepods were evaluated according to 10 characters with terminology proposed by Kabata, Gusev (1966). To determinate the phylogenetic position of C. lacustris within the genus Caligus, fragments of the cytochrome c oxidase subunit 1 mitochondrial gene (COI, 645 bp) and 18S rRNA gene (1617 bp) were sequenced.
ResultsAn increase of parasite prevalence was observed as the lake was warming up from July to September. The morphological features of the crustacean's larval and adult stages, characterized by specific parameters of quantitative traits, are described.Three COI haplotypes and only one 18S rRNA haplotype of C. lacustris were identified among five samples. Based on 18S rRNA analysis (resolution of the COI tree was poor) we can conclude that the clade containing C. lacustris, and the aforementioned sister species, appears as an early radiation of the genus Caligus.
ConclusionsThe development of freshwater aquaculture contributes to the transfer of the native parasite Caligus lacustris to farmed rainbow trout.
Changes in the numbers of 10 species of parasites belonging to 5 classes of roach and Siberian dace were investigated in the transect "Selenga River -Delta -Lake Baikal" in 2001Baikal" in -2006. The numbers either increased along this transect (myxosporea Myxobolus bramae, monogeneans of genus Dactylogyrus, diplostomatids metacercariae and Rhipidocotyle campanula, parasitic copepodes Ergasilus sieboldi and E. briani) or decreased (myxosporea Myxidium rhodei, cestoda Caryophyllaeides fennica, trematoda Allocreadium isoporum). Differences in the infection rates of fishes in the transect are explained by features of the parasite morphology and biology, and by levels of water contamination.
Myxobolus talievi Dogiel, 1957 was originally described from the eyes, skeletal muscles and body cavity of endemic cottoid fish from Lake Baikal. In the present study, we supply new information on the myxospore morphology and histopathology of M. talievi; furthermore, we complete the original species description by Dogiel and Bogolepova (1957) with 18S ribosomal DNA (rDNA) sequence data. Histopathological analysis showed that the plasmodium was encapsulated by a thin layer of connective tissue and located in the intermuscular connective tissue among muscle cells. No inflammation was observed. Phylogenetic analysis revealed that M. talievi clustered with Myxobolus sp. 2 (NCBI Acc. No. U13830), an unidentified Myxobolus species from cottoid fish studied by Smothers et al. (1994), and located in the sister clade of Myxobolus spp. developing spores in the nerves of salmonids.
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