Prevalence and abundance of helminth parasites in an intensively fished population of brook trout (Salvelinus fontinalis) at a small subarctic lake

Abstract

1991. Prevalence and abundance of helminth parasites in an intensively fished population of brook trout (Salvelinus Jontinalis) at a small subarctic lake. Can. J . Zool . 69: 69 1 -697. Brook trout from a 5-ha lake near Schefferville, Quebec, were intensively sampled by small-mesh gill nets during 2 successive years to study patterns of helminth parasite occurrence in relation to changes in the age and size class structure of the fish population. Nearly 1800 brook trout were removed from the lake, of which all were measured and weighed, 568 were aged by otolith readings, and 36 1 were examined for parasites. The digeneans Crepidostomumfurionis, Phyllodistomum umblae, and Diplostomum sp. and the cestode Eubothrium salvelini were present in more than 50% of the necropsied fish, and the prevalence and (or) abundance of all species except C . furionis increased from the first to the second year of the study. The fish catch in the first year was dominated by the 3+ year class and older fish, whereas by the second year I + and 2+ fish were proportionately more abundant, and the importance of older cohorts declined. This change in brook trout population structure, resulting from gill net selectivity, appears to have had the effect of improving per capita food availability for members of the residual stock. After the initial year of intensive fishing, the fish that remained fed more upon both benthic and planktonic invertebrates and their acquisition of parasites was intensified. ALBERT, E., et CURTIS, M. A. 199 1. Prevalence and abundance of helminth parasites in an intensively fished population of brook trout (Salvelinus fontinalis) at a small subarctic lake. Can. J . Zool. 69 : 691 -697. Des Ombles de fontaine (Salvelinus fontinalis) ont eti echantillonn6s pendant 2 annkes const!cutives au moyen de filets maillants, dans un lac de 5 ha situe pres de Schefferville, Quebec; cet ichantillonnage intensif a permis d'ktudier les variations des populations d'helminthes en fonction des variations de la structure de la population de poissons quant a 1'Age et a la taille. Pres de 1800 ombles ont ete captures dans le lac; tous ont ete mesures et, 568 peses ont ete soumis 2 i une lecture de ]'Age sur les otolithes et les parasites ont ete inventories chez 36 1 d'entre eux. Les digeniens Crepidostomum farionis, Phyllodistomum umblae et Diplostomum sp. et le cestode Eubothrium salvelini ont it6 trouves chez plus de 50% des poissons examines et la prevalence et (ou) l'abondance de toutes les especes sauf C . farionis a augmente entre la premikre et la deuxieme annees de I'etude. Les echantillons recueillis la premiere annee etaient dominees par les poissons de la classe d'ige 3+ et les poissons plusAges, alors que les kchantillons de I'annke suivante contenaient plus de poissons des classes 1 + et 2 + et l'importance des cohortes plus Agkes avait decline. Ce changement dans la structure de la population d'ombles, resultat de la sklectivitk de I'engin de capture, semble avoir eu I'effet d'ameliorer la disponibilite per capita de la n...

Effects of Eubothrium salvelini (Cestoda) on the behaviour of Cyclops vernalis (Copepoda) and its susceptibility to fish predators

“…Watson & Lawler, 1965 ;Marcogliese & Esch, 1989); their prevalence in their copepod intermediate host is usually much less than 1-2 %. On the other hand, prevalence of E. salvelini infection in brook trout definitive host can be greater than 50 % (Albert & Curtis, 1991). In addition, some fish are infected by large numbers of these cestodes (Albert & Curtis, 1991); for instance, a few of our wild caught trout harboured more than 40 adult E. salvelini.…”

“…On the other hand, prevalence of E. salvelini infection in brook trout definitive host can be greater than 50 % (Albert & Curtis, 1991). In addition, some fish are infected by large numbers of these cestodes (Albert & Curtis, 1991); for instance, a few of our wild caught trout harboured more than 40 adult E. salvelini. Boyce (1974) listed a few possible explanations for the marked discrepancy between the prevalence of infection in copepods and fish; among them, he mentioned the possibility that infection alters the copepods' behaviour and leads to a much greater proportion of infected individuals among the ones detected by fish.…”

Major drivers of biodiversity loss and their impacts on helminth parasite populations and communities

“…These results parallel those above in that removal of a top predator reduced the abundance of a parasite with a complex life cycle. In another study that examined the effects of exploitation of a fish stock on parasitism, two of three trophically transmitted helminths increased in an intensively-fished population of brook trout ( Salvelinus fontinalis ) in northern Quebec, Canada (Albert & Curtis, 1991). This increase in parasite recruitment may have been due to increased feeding of younger fish cohorts due to competitive release following selective removal of an older cohort of fish (Albert & Curtis, 1991).…”