Aspects of the Ecology and Natural History of Paraergasilus Rylovi (Copepoda, Ergasilidae) Parasitic in Unionids of Finland

Abstract

The distribution of Paraergasilus rylovi in 17 populations of unionids was investigated. In 1 unionid population, the parasite was studied regarding host age, size, sex, and the reproductive period (occurrence of egg sacs). Results from pooled material from the years 1987--1989 and 1996 (southern Finland, 11 populations) indicated that Anodonta piscinalis (n = 1,359) is the main host (total mean prevalence 71% and intensity +/-SE of infection 16.4+/-0.6). Pseudanodonta complanata (n = 106) was infected occasionally (3% and 1.3+/-0.3), whereas Unio pictorum (n = 108) and U. tumidus (n = 17) were not infected. Results from 17 A. piscinalis populations showed that P. rylovi occurs in southern Finland but not in northern Finland. In A. piscinalis, the mean intensity of infection was higher in lake populations than in river populations. Both host age and length had a negative relationship with the intensity of P. rylovi infection. Host sex did not affect the intensity of infection. Egg sacs of P. rylovi were found from June to August. There was a tendency for higher intensities of infection in autumn. Infection by the digenean Rhipidocotyle fennica had no effect on the intensity of P. rylovi infection.

Burrowing behaviour affects Paraergasilus rylovi abundance in Anodonta piscinalis

“…We found that P. rylovi was better adapted to its local host population in a reciprocal transplant experiment (Saarinen and Taskinen, 2005 b). Our field observations (Saarinen and Taskinen, 2004) and experimental results (Saarinen and Taskinen, 2005 b) indicated clear habitat-dependence in abundance of P. rylovi, probably due to variation in exposure rate in different habitats.…”

“…Clams were allowed to take a new burrowing position freely and to become infected naturally by P. rylovi. The reproductive period of P. rylovi is between June and August (Saarinen and Taskinen, 2004), and new infections are established in August (Saarinen and Taskinen, 2005 a). After 17 days, on 29 August 2005, burrowing depths were marked by a diver as described above and the clams collected and transported to the laboratory where they were examined and measured.…”

“…Paraergasilus rylovi is an ergasilid copepod. Adult females of P. rylovi parasitize the gills of clam, and are specific to one host species, A. piscinalis (Saarinen and Taskinen, 2004). The virulence of P. rylovi in A. piscinalis is not known, but the ergasilids of fish feed on gill tissues and blood (Bush et al 2001).…”

Long-lasting effect of stress on susceptibility of a freshwater clam to copepod parasitism

“…Ergasilid parasites of fishes feed on gill tissues and blood, and may cause deformation or necrosis of the gill filaments (Bauer, Musselius & Strelkov, 1973). According to Saarinen & Taskinen (2004) the parasite was specific to A. piscinalis in the present study areas, and the annual reproductive period of the parasite was between June and August.…”

“…The parasite, an ergasilid copepod Paraergasilus rylovi Markewitsch (sensu Chernysheva & Purasjoki, 1991), has been observed only in north-east Europe, in gills of A. piscinalis (Chernysheva & Purasjoki, 1991 ;Saarinen & Taskinen, 2004). Ergasilid parasites of fishes feed on gill tissues and blood, and may cause deformation or necrosis of the gill filaments (Bauer, Musselius & Strelkov, 1973).…”