Bathymetric segregation of two species of merizocotyline monogeneans (Monocotylidae), across species of skates (Rajidae) inhabiting the northern Argentine Sea and comments on haptoral abnormalities

IRIGOITIA, M.M.; CANTATORE, D.M.P.; INCORVAIA, S.I.; TIMI, J.T.

Simposio; 7th International Symposium on Monogenea; 2013

The distribution of merizocotyline monogeneans, nasal tissues parasites in batoid fishes of thefamily Rajidae was investigated across host species inhabiting the northern Argentine Sea (SouthWest Atlantic). A total of 306 skates belonging to 12 species was sampled, including 52Amblyraja doellojuradoi, 9 Atlantoraja castelnaui, 7 Atlantoraja cyclophora, 6 Bathyrajaalbomaculata, 21 B. brachyurops, 22 B. macloviana, 2 B. scaphiops, 1 Psammobatis bergi, 22 P.normani, 1 Rioraja agassizi, 130 Sympterygia bonapartii and 33 Zearaja chilensis. Two speciesof monogeneans were found, Emprutothrema raiae and a new species of Merizocotyle,representing new records in the South West Atlantic for these genera. Emprutothrema raiae (205specimens) was found on A. castelnaui, P. bergi, P. normani, and S. bonapartii, whereasMerizocotyle sp. (42 specimens) was found on A. doellojuradoi, B. brachyurops, P. normani andZ. chilensis. Only one specimen of P. normani was found parasitized by both species (1specimen of each). Analyses on possible causes of parasite segregation across host species,focusing on those skates species with more than 20 specimens examined, showed that parasitedistribution was independent of host phylogeny. The degree of endemism of host genera was notrelated to parasite distribution since E. raiae, a cosmopolitan parasite of skates, was only foundin endemic genera (unless it were a cryptic species); whereas the new species of Merizocotylewas found in cosmopolitan host genera. Fish samples were from commercial catches and nodata on depth of capture were available. However, due to the known bathymetric distribution ofskates species obtained from literature, it was observed that E. raiae infested those skatesspecies living in shallow waters (depth < 75 m), whereas Merizocotyle sp. parasitized speciesfrom deeper waters (depth > 100 m). Bathymetric distribution of skates arose, therefore, as themain explanatory variable of parasite distribution. As regards haptor abnormalities, at present,there is only one report in the literature of them found in a single specimen of Emputothremastenophallus, being the unique case of malformation in monocotylid monogeneans. In the presentstudy, however, a high proportion of specimens of E. raiae with abnormal haptors was found.These percentages varied according to the host species harboring them (33% of specimensfound in both P. normani and P. bergi, 10% in A. castelnaui and 3% in S. bonapartii). On theother hand, only 2 out of the 42 Merizocotyle sp. showed haptoral abnormalities. Structuralalterations on the attachment organs have been observed in other monogenean taxa, beingwater pollution, environment induced alterations and host immune responses signaled aspossible causes. Further studies of the geographical distribution and host range of theseabnormal individuals could shed light on the possible effect of environmental conditions andspecificity of these parasites, especially for E. raiae, which has been recorded in other 9 speciesof Rajidae throughout the world, and constitutes one exception to the strictly host-specificcondition of the genus Emprutothrema.