The best known species of gill maggot is S. californiensis. It was originally confined to salmonid fishes of the genus Oncorhynchus in streams emptying into the northern Pacific Ocean, but has recently moved eastwards in the US, e.g., to Missouri and Arkansas (Hoffman 1984) and subsequently to Iowa, New Jersey, and West Virginia (Sutherland and Wittrock 1985).
Sutherland and Wittrock (1985) reported the parasite from an aquaculture site in Iowa, stating a prevalence of 83% and a mean intensity of 4.6 female copepods. Infections were associated with hyperplasia of gill filaments caused by female copepods and atrophy or growth inhibition of affected gill filaments.
The above authors also noticed a harmful effect of chalimus larvae, such as hyperplasia and sometimes fusion of the basal elements of adjacent gill filaments. Gall et al.
(1972) found evidence of the influence of S. californiensis on the reproductive performance of a domesticated strain of rainbow trout. Johnson and Heindel (2001) reported problems with high numbers of S. californiensis in broodfish of chinook salmon, O. tshawytscha, and they described a method for their manual removal.
Another significant species from the same genus is Salmincola edwardsii, a parasite specific to Arctic charr, Salvelinus alpinus, and brook trout, Salvelinus fontinalis. This parasite inflicted health problems in fishes cultured in Quebec and New Brunswick, Canada (Parissa Irani-Bunin, pers.
comm.). Salmincola salmoneus is specific for Atlantic salmon, Salmo salar. Heavy infestations with this parasite of salmon broodstock kept in hatcheries in the Maritime Provinces of Canada were reported by McGladdery and Johnston (1988).
Salmincola carpionis was reported from central Japan infecting cultured brook trout and whitespotted charr, Salvelinus leucomaenis (cf. Nagasawa et al. 1997 1998). Salmincola stellatus were recently reported in Hokkaido, Japan in the buccal cavity of cultured taimen, Hucho perryi, with intensities ranging from 10 to 50 individuals per fish (Nagasawa et al. 1994).
The closest relatives of Salmincola spp. are representatives of Achtheres. The latter genus differs from the former one in having a prominent genital process. According to Kabata (1969), there are 6 valid species of this genus.
Achtheres percarum which occurs in Europe on perch (Perca fluviatilis) and zander (Sander lucioperca) can be pathogenic to fish. Because of its attachment to gill filaments, it can trigger epithelial hyperplasia, which fuses gill lamellae, and cause partial or total loss of gill filaments.
Prevalences often reach 100%, and the number of Achtheres females can reach 40 per fish (Kozikowska et al. 1957). The highest observed number of all stages of the parasite in zander was 117 (Piasecki 1993b) and 81 individuals in perch (Piasecki and Wo oszyn 1991). The life cycle of A. percarum includes 7 stages: nauplius, copepodid, 4 chalimus stages, and adults (Piasecki and Ku´ zmi´ nska 1996).
Basanistes huhonis is another“cousin”of Salmincola. It looks similar to Salmincola spp. but is covered with 12 prominent humps or outgrowths. It infects Danube salmon, Hucho hucho, and broodstock may host very high numbers of this parasite (Ivaska 1951, Witkowski and B achuta 1980).
The least known freshwater lernaeopodid genus is Tracheliastes (Fig. 4), and the most-pathogenic species within this genus is T. maculatus. This copepod has a very slim appearance, it is slightly longer than Lernaea, and its bulla attaches permanently to the scales of common bream.
Its presence is initially associated with focal inflammation about its feeding area, with pronounced congestion of the skin and extravasations of blood.
With heavy infections, diffuse inflammation of the skin can be observed and even extensive perforation of the scales (Fig. 5) to which the parasite , bullae are attached. There are 2 documented cases of extreme infection levels of this parasite on bream.
The 1st was in Jamno Lake, Poland and was associated with fish mortalities. The intensity reached 56 individuals per fish (Grabda and Grabda 1958). The other mass infection occurred in Pierzcha y Lake, Poland with an intensity of 61 individuals per fish (Piasecki 1991).
The life cycle of T. maculatus consists of 7 stages: premolt nauplius, infective copepodid, 4 chalimus stages, and adults (Piasecki 1989). Sea lice or fish lice of the family Caligidae (Siphonostomatoida), pathogenic to marine fishes cultured in cages, have only 1 freshwater representative, Caligus lacustris.
This copepod has caused only 1 known outbreak in cultured salmonids (Rokicki 1987) but may have the potential to negatively affect freshwater aquaculture operations.
Authors:
Wojciech Piasecki, Andrew E. Goodwin, Jorge C. Eiras, Barbara F. Nowak
