E. sieboldi
Schäperclaus (1954) described a case of a single, 36-cm-long tench that harbored some 3600 specimens of E. sieboldi on its gills.
This heavily infected fish had a condition factor of only 0.88. Similarly, intensive infection of peled (Coregonus peled) was reported by Abrosov and Bauer (1959 1961) from Pskov Lake, Russia.
Heinemann (1934) found 5431 specimens of E. sieboldi on a single tench that died of asphyxia. Severe infection with E. sieboldi can result in heavy losses in the yield of tench.
In Lake Scharmuzel, Germany, the yield of tench dropped from 5000 kg before the appearance of E. sieboldi to 350 kg after its unwanted introduction.
In 2 other small German lakes, the yield of tench dropped from 31-47 to 16.5 kg ha-1 after the invasion of this parasite and with copepod prevalences of only 50%. In Lake Grimiz, Germany, the yield of tench between 1926 and 1931 declined from 4583 to 111 kg (Schäperclaus 1992), again a reduction apparently related to Ergasilus infections.
The 2nd most common host of E. sieboldi is the pike. Pike deaths attributed to E. sieboldi infections were described from 2 Pomeranian lakes in Germany by Lehmann (1924) and Rumphorst (1924). Deaths of whitefish (Coregonus wartmanni) in Zugersee, Germany were described by Baumann (1913).
A very extensive account on aspects of E. sieboldi occurrence in different hosts was published by Grabda (1963b). Ergasilus sieboldi causes mass fish-kills not only of tench but also of perch, Perca fluviatilis in W odawa Lake, Poland (Kocy owski 1954), whitefish in Cugersk Lake in the USSR, and bream in a number of lakes (Markevi 1956).
In Southeast Asia, Ergasilus sp. occurs on the gills of cultured fishes including Osteophilus hasselti, O. gouramy (in Indonesia), Ctenopharyngodon idella (in Malaysia), and on Oxyelotris marmoratus (in Thailand).
The parasite has the potential to adversely affect aquaculture in this region, but so far, no major outbreak attributed to Ergasilus sp. has been reported. (Kabata 1985). Another ergasilid, Sinergasilus major, may have importance in Central Asian aquaculture, including the former Soviet republics and China regarding the host Ctenopharyngodon idella (cf. Bauer and Babaev 1964).
Sinergasilus lieni is another important parasite, affecting Hypophthalmichthys molitrix (cf. Musselius 1973). In Japan, Nakajima and Egusa (1973) found Pseudoergasilus zacconis on gills of cultured ayu, Plecoglossus altivelis. In spite of this record, Egusa (1992) saw no serious threat by ergasilids to Japanese freshwater aquaculture.
Traditional treatment of ergasilosis included the use of organophosphate compounds, pesticides, or a mixture of copper sulfate and ferric sulfate. It has been observed that well-developed aquatic vegetation helps reduce infection levels. It apparently limits movements of small bream that otherwise spread this parasite all over the lake (Schäperclaus 1992).
Another important group of freshwater parasites is the family Lernaeopodidae (Siphonostomatoida). The freshwater branch of this family is represented by the 7 genera of Salmincola, Achtheres, Coregonicola, Basanistes, Tracheliastes, Pseudotracheliastes, and Cauloxenus (cf. Kabata 1979).
This group is characterized by their relatively large size, comparable to that of Lernaea. Their lernaeopodid attachment mechanism is unique, however, and seems to inflict less damage than that associated with Lernaea or Ergasilus spp.
The body of a lernaeopodid female can be divided into 3 major parts: the large genital trunk (responsible for reproduction), the elongate and movable cephalothorax surmounted with mouth appendages, and finally a pair of more or less powerful “arms”, which are transformed 2nd maxillae.
The maxillae are fused to a mushroom shaped anchoring structure known as a bulla. The bulla, a product of the frontal gland, is attached to the host.
From an aquaculture perspective, the most important lernaeopodid genus is Salmincola with 16 valid species (Kabata 1969). The vernacular name for Salmincola spp. is the gill maggot, and the genus has a circumpolar distribution in the northern hemisphere.
Gill maggots may occur in high intensities and create serious problems for fish kept at high densities in cages and other aquaculture facilities (Kabata 1970, Vaughan and Coble 1975, Kabata and Cousens 1977, Sutherland and Wittrock 1985). In natural fish populations, the prevalence and intensity of infection are usually low and have little impact on fish (Black 1982, Black et al. 1983, Bowen and Stedman 1990, Amundsen et al. 1997).
The life cycle of the gill maggot, S. californiensis, was described by Kabata and Cousens (1973). It consists of 6 stages: the copepodid (free-swimming infective stage), 4 chalimus stages (which attach to a host by the frontal filament), and adults (the adult female attaches to a host by a bulla, while the male remains mobile).
Authors:
Wojciech Piasecki, Andrew E. Goodwin, Jorge C. Eiras, Barbara F. Nowak
