Adam Bowen and Professor Richard A. Heckmann, Zoology
Argulus, commonly called fish-lice, are crustacean ectoparasites of fish. This study compared three members of the genus Argulus: A. pugetensis from Nanaimo, British Columbia; A. coregoni from Curitiba, Brazil; and A. siamensis from Bangalore, India. It was hypothesized that argulids of different taxons must have morphological variations of commonly held structures. For example, two species of Argulus possess marginal membranes on their suckers, but the membranes should have different quantities and qualities of substructures. To test this hypothesis, all specimens were photographed with the JEOL 6100 scanning electron microscope; the micrographs of A. pugetensis and A. siamensis are the first ever in print. Data from these micrographs were used to compare the three species.
As ectoparasites of farmed and wild fish, Argulus threaten the survival and health of these economically important aquatic animals. Gresty et al. indicated that fish-lice are both vectors and pathogenic pests to international fish stocks. Parasite congregation and feeding habits cause abrasions and irritation to the host’s skin. The former occurs mostly as a secondary symptom from the irritated fish rubbing their bodies against the substrate to de-lice themselves. The fish often die from secondary bacterial and fungal infections of the exposed tissues. The latter symptom, irritation, is primarily caused by toxic secretions from the argulid preoral spine; secretions that also cause hemorrhaging in the host’s skin. Kabata claimed these secretions caused a severe inflammatory response in the host integument where parasites clustered close together.
Cyprinus carpio (common carp) is a favored host of fish-lice. Common sites for infection are around the gills, operculum, mouth, back, and pelvic and pectoral fins. Diagnosis is made by the presence of white or green lumps aggregated on the host’s skin. The adult parasites measure from 2-11 mm in length; females are generally longer and larger than males. Shimura reported infestations in trout reaching populations of 446 parasites per fish.
Like the insect louse, fish-lice migrate from host to host. Parasite migration has necessitated careful introductions of fish to new waterways. Shafir et al. postulated that the argulid manner of reproduction may aid in the high adaptability of this parasite to new niches. Reproduction is accomplished when the female exits the host and lays continuous strings of eggs on rocks or plants in the substrate; eggs, however, are not laid in these strings until the embryos have matured within the clutch. This behavior appears to ensure maximum survival of the young and may, as Shafir suggests, explain the cosmopolitan distribution and success of the genus.
References
- Gresty, K. A. et al. 1993 Phil. Trans. Royal Soc. of Lond B. BioL Sci. 339:119-135.
- Shimura, S. & K. Inoue. 1984 Bull. Jap. Soc. Sci. Fisheries. 50:729
- Kabata, Z. 1970 In: Diseases of Fishes. I. Crustacea as Enemies of Fishes. T.H.F. Publications, New Jersey.
- Shimura, S. 1982 Parasitology. 86:537-552.
- Shafir, A. & J. G. Van As. 1986 J Zool. Soc. of Lond (A). 210:401-414.