Aspects of the biology of the cestode Proteocephalus Filicollis (Rudolphi) from Gasterosteus Aculeatus L.

Abstract

The present study investigated aspects of the biology of the cestode, Proteocephalus filicollis from the three-spined stickleback Gasterosteus aculeatus from Airthrey Loch, Scotland. The population biology study demonstrated that the parasite has an annual cycle of recruitment, which occur mostly in late summer and early autumn. The cestode did not show preference for any sex of the host. Maturation of the cestode also showed a seasonal cycle with the majority of worms maturing in late spring and early summer, but this period may be extended in different generations. Proteocephalus filicollis was overdispersed throughout the year in all sizes of fish, moreover variance to mean ratio always exceeded unity. No severe pathology was observed due to attachment of the worm to the intestine of the fish. The worm population in different sections of the intestine varied according to season and maturity stage. The P. filicollis migrate from the rectum to the anterior intestine as they mature and it is suggested that growth and maturation of the worm is a major stimulus for this migration. Proteocephalus filicollis has a high fecundity as indicated by the higher number of eggs per mm of gravid portion of the strobila and high fertility. Infrapopulation size did not show any relationship with length of worm, percentage gravid portion, number of gravid segments or mean length of gravid segments. Numbers of eggs are correlated to length of the worm, but not to infrapopulation size. Numbers of eggs per mm of the gravid portion are not correlated to length of worm or infrapopulation size. Acanthocyclops robustus was used as an experimental intermediate host. 15-16°C was the optimum experimental temperature for growth and a fully developed larva was formed in 23-27 days at this temperature. No growth was observed at 4°C, growth was slow at 10°C, but rapid at 21-22°C. The eggs are infective for 25 days at 4°C, 10°C and 15-16°C, but for only 15 days at 21-22°C. Prevalence and mortality of copepods are significantly correlated to their exposure time to parasite eggs, but mean intensity of infection did not show any relationship to the exposure time to the eggs. Ultrastructural studies demonstrated that a mature egg is surrounded by at least four embryonic envelopes, the capsule, the outer envelope, the inner envelope, and the oncospheral membrane. All these envelopes originate differently and undergo definite changes during their development.