Monthly and inter-annual variations of Opechona sp. (Digenea: Lepocreadiidae) parasitizing scyphomedusae off southern Brazil

Abstract

Monthly and inter-annual variations of prevalence (P) and intensity of infection (I) of Opechona sp. metacercariae were analyzed in the two most common scyphomedusae from south Brazil (~25.5°S, 48.4°W), between November 1997 and December 2004. Chrysaora lactea was highly parasitized (n = 817; P ≈ 41 %; I = 1–35), while Lychnorhiza lucerna hosted few metacercariae (n = 968; P ≈ 3 %; I = 1–3). Prevalence remained around 40 % in all size classes of C. lactea, and I positively correlated with its BD (bell diameter; Pearson, r = 0.34, p 20 cm. Overall annual P and I remained in similar levels among different years for both scyphomedusae, although peaking not exactly in the same month every year. Chrysaora lactea was parasitized throughout the year, but between July and December P reached the highest values (>40 % and up to 78 %). Lychnorhiza lucerna´s P was typically higher between July and November and lower or absent in the other months. Seasonality of the infection apparently was related to host availability and population dynamics; whenever the host was more abundant and/or larger, the infections tended to be higher. The high P and I in C. lactea indicate this medusa is a regular secondary host of Opechona sp., thus an important vector of this parasite to the final fish hosts. This relationship indirectly suggests feeding interactions between medusae and fish. A thorough literature review of metacercariae parasitizing scyphomedusae indicates that Semaeostomeae are the most studied (21 out of 28 records) and lepocreadiids the most common parasites.