Monthly occurrence of parasites of the chaetognath Sagitta friderici off Mar del Plata, Argentina

Abstract

During a 1-year study period between March 2000 and 2001, 195 (6%) out of 3236 Sagitta friderici were found to be parasitized by metacercariae of digenean species and metacestodes. Parasites belonged to Derogenes sp., Ectenurus virgulus, Monascus filiformis, Lepocreadiidae, Parahemiurus merus and tetraphyllidean metacestodes. Among the chaetognaths parasitised, 178 (91%) harboured one parasite, and the remaining 17 (9%) showed two or three parasites of the same or two different species. The highest prevalences for most of the species occurred in autumn-winter (April-August), except for E. virgulus, which had maximum values in summer (December-January). Species richness varied during the year, reaching a peak in May and June 2000 with six species. The metacercariae of Lepocreadiidae were present in autumn, winter and summer at all maturity stages of S. friderici, with higher prevalence values for stages 0 and I, whereas the rest of the digeneans were absent in stage 0, with higher prevalences for the more advanced maturity stages II and III. The different types of metacercariae did not seem to induce castration in the host. Copepods (Corycaeus amazonicus) were observed attached to the body of chaetognaths or partially digested in their gut. No nematodes, internal parasitic copepods or polychaetes were found.