POPULATION BIOLOGY OF POMPHORHYNCHUS-LAEVIS IN BROWN TROUT FROM 2 LAKES IN THE WEST OF IRELAND

Since Ireland is the only country in which Pomphorhynchus laevis (Acan thocephala) uses brown trout (Salmo trutta) as its preferred definitiv e host, the population biology of the parasite in this host was invest igated thus enabling a comparison to be made with data collected on P. laevis from other hosts, particularly the cyprinids, chub and barbel. Over a period of 12 months, 549 brown trout were caught from two lake s, Lough Feeagh and Bunaveela Lake, in the Burrishoole River system, C o. Mayo, Ireland. The parasite component community was dominated by a single species, P. laevis. Fifty eight percent of the trout sample wer e infected with the acanthocephalan and the mean abundance (+/- SD) wa s 3.1 +/- 5.1. The relationships between the prevalence and abundance of P. laevis and season and site of host capture and host age and sex were explored. As single factors none of these parameters emerged as s ignificant contributors to changes in parasite abundance although some interaction terms proved to the significant. A random sample of over 700 P. laevis parasites were subjected to further investigation and th eir size, position in the intestine and maturity status are described. Parasites attained an average weight of 7 mg and occupied the posteri ad positions within the fish intestine (77%). Parasites from this samp le of Irish brown trout attained a similar average size to those found in chub and barbel from England. 42.3% of the total parasites examine d contained ovarian balls only and 17% contained fully mature acanthor s. Therefore only a moderate proportion of female worms contained matu re acanthors in these trout whereas the majority of worms recovered fr om a sample of chub were gravid. Utilizing a logistic regression model , parasite size, season, and site of host capture emerged as particula rly significant factors which contribute to whether a parasite contain s mature eggs.