Experimental study on the influence of paper and pulp mill effluent on the gill parasite communities of roach (Rutilus rutilus)

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Abstract
SUMMARY: Roach (n= 81) caught on 23 May, 1992 from oligotrophic, unpolluted Lake Peurunka were kept in cages over a 2-week period before moving half of the fish to nearby Lake Vatia, which is influenced by pulp mill effluents. Before moving the fish gill parasites were examined from 9 fish; 5Dactylogyrusspecies,Gyrodactylussp. andParadiplozoon homoionwere found, the main components of the infracommunities being dactylogyrids. Afterwards, 5 fish from each lake were studied weekly between 1 July and 17 August. Metazoan parasites were recorded from gill arches divided into 4 sections along the dorso-ventral axis.D. crucifer, D. nanus, D. micracanthusandD. suecicusoccurred in both lakes throughout the study.Gyrodactylussp., Ergasilus briani andP. homoionoccurred in low numbers in both lakes. Differences between the lakes were seen in the prevalence ofD. micracanthuswhich was higher in Lake Vatia and significantly increased abundances ofD. crucifer, D. nanusandD. micracanthusin Lake Vatia. Abundances of otherDactylogyrusspecies remained, on average, at the same level in both lakes. No change during the experiment was recorded in the location of the two most common species,D. cruciferandD. nanus, on the host gills in either of the lakes, both species favouring the 2nd and 3rd gill arches and especially the inner parts of the gills. The apparent lack of competition between the 2 most commonDactylogyrusspecies indicates that no limitation of resources on roach gills occurred. This was also confirmed by the increased overlapping indices with increasing abundances between the two most common species in Lake Vatia.