Gyrodactylus derjavini infections in four salmonids:comparative host susceptibility and site selection of parasites

Abstract

The susceptibility of 4 salmonids [rainbow trout Oncorhynchus rnykiss, brown trout Salmo trutta, a Baltic (Iijoki) and an Atlantic (Conon) strain of Salmo salar] to infect~on with a Danish isolate of Gyrodactylus derjavinj was tested in the laboratory (12 to 13°C). Initial parasite attachment numbers did not differ between species, but parasite populations increased significantly faster and to a higher level in rainbow trout compared to the other salmonids, with S. trutta exhibiting an intermediate position. The 2 strains of S. salar became only slightly infected during the following weeks despite a heavy infection pressure. The parasites' selection of microhabitat on the hosts also differed between species and changed over time on the same host species. The tail fin was the preferred site in all salmonids although the pectoral, pelvic and anal fins were important sites in the initial period of the 6 wk investigation. It is notable that the cornea1 surface, especially in the Baltic salmon, became increasingly more heavily infected in the later stages of the infection period. Explanations for the differing degrees of susceptibility are suggested and some of these were investigated. Lysozyme activity in the fin epithelia and the density of mucous cells in the fins from the hosts were compared. Marked lysozyme activity was detected in tail fins from the 4 salmonids, but the activity was not associated with host resistance to infection. In contrast, the density of superficial mucous cells, which showed regional variation on the tail fins, was negatively correlated with susceptibility to infection. Thus, fish with high density of epithelia1 mucous cells showed the lowest susceptibility to infection, and this finding is discussed in relation to host resistance.

Population increase of Gyrodactylus derjavini on rainbow trout induced by testosterone treatment of the host

“…Changes in site selection of gyrodactylids on the hosts during a period of infection were previously noted by Harris (1988) and Cone & Cusack (1989). Later findings of this phenomenon have been interpreted as being an escape of parasites from localized immune reactions in the skin (Richards & Chubb 1996, Buchmann & Bresciani 1997, Buchmann & Uldal 1997. Acquired immunity to infection was indeed clearly demonstrated in the donor fish used for the cohabitation in the present study.…”

“…Water quality monitoring, internal recirculation, pose fin, dorsal fin, pectoral fins, pelvic fins, anal fin, water exchange and aeration were performed as corpus surface, head and the cornea1 surface were regdescribed previously (Buchmann & Uldal 1997).…”

“…Similarly, as Pickering (1977) described a decline in mucous cell concentrations in the epidermis of spawning male trout, this parameter has been suggested to influence host resistance to infection with external parasites. Further evidence of a protective role of high mucous cell densities in salmonids against G, derjavini infections was presented by Buchmann & Uldal (1997) and Buchmann & Bresciani (1997). Therefore, the present investigation was undertaken to elucidate whether testosterone levels in rainbow trout Oncorhynchus mykiss are associated with population densities of G. derjavini on the host.…”

Gyrodactylus derjavinoides sp. nov. (Monogenea, Platyhelminthes) on Salmo trutta trutta L. and G. derjavini Mikailov, 1975 on S. t. caspius Kessler, two different species of Gyrodactylus — combined morphological and molecular investigations

“…In 1972, the species was also found on S. t. trutta in natural water and on farmed Oncorhynchus mykiss (Walbaum), Salvelinus alpinus (L.) and S. fontinalis (Mitchill). Since then specimens of the species have been documented from many different Skóra Stefañski Göran Malmberg et al 90 OEl¹ski Gyrodactylus species combined morphological and molecular investigations localities and areas (Table I; Malmberg 1991, 1993), and in Denmark, the species became an important experimental organism (see e.g., Buchmann et al 1995;Buchmann 1997Buchmann , 2004Buchmann and Uldal 1997).…”

Seasonal population dynamics of the monogeneans Pseudorhabdosynochus coioidesis and P. serrani on wild versus cultured groupers in Daya Bay, South China Sea

“…It is still not known whether monogenean infrapopulational growth is reduced by unsuitable water temperature, enhanced immunity or some other reason. It is known that the infrapopulational growth and infection duration of monogeneans often differ between related host species (e.g., Mo, 1997;Boeger et al, 2005;Moen & Stockwell, 2006;Olstad et al, 2007), and the chemical structure of the epidermis and mucus of related fish can differ substantially (Buchmann & Uldal, 1997). This may explain different abundances of P. coioidesis and P. serrani on E. coioides, E. awoara and E. bruneus in the present study.…”