The effect of octopaminergic compounds on the behaviour and transmission of Gyrodactylus

BACKGROUND

The high transmission potential of species belonging to the monogenean parasite genus Gyrodactylus, coupled with their high fecundity, allows them to rapidly colonise new hosts and to increase in number. One gyrodactylid, Gyrodactylus salaris Malmberg, 1957, has been responsible for devastation of Altantic salmon (Salmo salar L.) populations in a number of Norwegian rivers. Current methods of eradicating G. salaris from river systems centre around the use of non-specific biocides, such as rotenone and aluminium sulphate.Although transmission routes in gyrodactylids have been studied extensively, the behaviour of individual parasites has received little attention. Specimens of Gyrodactylus gasterostei Gläser, 1974 and G. arcuatus Bychowsky, 1933, were collected from the skin of their host, the three-spined stickleback (Gasterosteus aculeatus L.), and permitted to attach to the substrate. The movements of individual parasites were recorded and analysed.

RESULTS

The behaviour patterns of the two species were similar and parasites were more active in red light and darkness than in white light. Four octopaminergic compounds were tested and all four inhibited the movements of parasites. Treatment ultimately led to death at low concentrations (0.2 μM), although prolonged exposure was necessary in some instances.

CONCLUSIONS

Octopaminergic compounds may affect the parasite's ability to locate and remain on its host and these or related compounds might provide alternative or supplementary treatments for the control of G. salaris infections. With more research there is potential for use of octopaminergic compounds, which have minimal effects on the host or its environment, as parasite-specific treatments against G. salaris infections.

A review of the biology of the parasitic copepod Lernaeocera branchialis (L., 1767) (Copepoda: Pennellidae)

This review concerns the parasitic marine copepod Lernaeocera branchialis (L., 1767) and provides an overview of current knowledge concerning its biology and host-parasite interactions. The large size and distinctive appearance of the metamorphosed adult female stage, coupled with the wide exploitation and commercial importance of its final gadoid hosts, means that this species has long been recognised in the scientific literature. The fact that the Atlantic cod, Gadus morhua L., is one of its key host species, and has itself had a major impact on the social and economic development of many countries bordering the North Atlantic for more than 10 centuries is also a factor in its widespread recognition. L. branchialis is recognised as a pathogen that could have major effects on the aquaculture industry and with gadoid (especially cod) farming expanding in several North Atlantic countries, there is considerable potential for this parasite to become a serious problem for commercial mariculture. The main subject areas covered are the parasite's taxonomy; the life history of the parasite including its life cycle, reproduction and host associations; parasite physiology; parasite seasonality and distribution; and the pathogenic effects of the parasite on its host.

Inhalation teratology and two-generation reproduction studies with 1,1-dichloro-1-fluoroethane (HCFC-141b)

HCFC-141b is one of the chemicals being considered as a replacement for CFC 11 in solvent and foam-blowing applications. Teratology studies were conducted in both rats and rabbits and a two-generation reproduction inhalation toxicity study was conducted in rats. The pregnant rabbits were exposed to levels of 0 (control), 1400, 4200 and 12,600 ppm HCFC-141b from day 7 to day 19 of gestation (6 hr/day). There was no evidence of developmental or teratogenic effects on the foetuses. The pregnant rats in the teratology study were exposed to levels of 0 (control), 3200, 8000 and 20,000 ppm from days 6 to 15 of gestation (6 hr/day). In the 20,000 ppm exposure group, there was an increase in implantation losses; furthermore, in this group, foetal weights tended to be lower than controls. As with the rabbits, there was no evidence of a teratogenic effect. The reproduction study was conducted at exposure levels of 0, 2000, 8000 and 20,000 ppm, 7 days/wk starting approximately 10 wk before the first pairing. Adult rats exposed at 20,000 ppm (and, to a lesser extent, those exposed to 8000 ppm) showed increases in water intake, slight increases in food consumption, and decreases in body weight. Following the mating of the F0 parents, there were fewer litters in the 20,000 ppm exposure level group than in controls. When these parents were then paired with different partners, again, the number of litters was lower in the 20,000 ppm group, although most of the animals that did not produce litters the first time mated successfully the second time. When the F1 animals were mated to produce the second generation, the number of litters was comparable for all groups. In the second F0 mating and the F1 mating, the number of pups per litter was lower at 20,000 ppm; although birth weights were comparable, body weight gain tended to be slower in the high-level exposure group. Survival was good in all groups. At 8000 ppm no significant effects were observed in the pups and only minimal signs in the adults. The 2000 ppm exposure level represented a clear no-observed-effect level for all indices.