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 MANUEL MARCIAL; CANTATORE DELFINA; INCORVAIA INÉS SILVIA; TIMI JUAN TOMÁS

Rio de Janeiro

Simposio; 7th International Symposium on Monogenea; 2013

Universidad Nacional

The distribution of merizocotyline monogeneans, nasal tissues parasites in batoid fishes of the family Rajidae, was investigated across host species inhabiting the northern Argentine Sea (South West Atlantic). A total of 306 skates belonging to 12 species was sampled, including 52 Amblyraja doellojuradoi, 9 Atlantoraja castelnaui, 7 Atlantoraja cyclophora, 6 Bathyraja albomaculata, 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 species of monogeneans were found, Emprutothrema raiae and a new species of Merizocotyle, representing new records in the South West Atlantic for these genera. Emprutothrema raiae (205 specimens) was found on A. castelnaui, P. bergi, P. normani, and S. bonapartii, whereas Merizocotyle sp. (42 specimens) was found on A. doellojuradoi, B. brachyurops, P. normani and Z. chilensis. Only one specimen of P. normani was found parasitized by both species (1 specimen 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 parasite distribution was independent of host phylogeny. The degree of endemism of host genera was not related to parasite distribution since E. raiae, a cosmopolitan parasite of skates, was only found in endemic genera (unless it were a cryptic species); whereas the new species of Merizocotyle was found in cosmopolitan host genera. Fish samples were from commercial catches and no data on depth of capture were available. However, due to the known bathymetric distribution of skates species obtained from literature, it was observed that E. raiae infested those skates species living in shallow waters (depth < 75 m), whereas Merizocotyle sp. parasitized species from deeper waters (depth > 100 m). Bathymetric distribution of skates arose, therefore, as the main 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 Emputothrema stenophallus, being the unique case of malformations in monocotylid monogeneans. In the present study, 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 specimens found in both P. normani and P. bergi, 10% in A. castelnaui and 3% in S. bonapartii). On the other hand, only 2 out of the 42 Merizocotyle sp. showed haptoral abnormalities. Structural alterations on the attachment organs have been observed in other monogenean taxa, being water pollution, environment induced alterations and host immune responses signaled as possible causes. Further studies of the geographical distribution and host range of these abnormal individuals could shed light on the possible effect of environmental conditions and specificity of these parasites, especially for E. raiae, which has been recorded in other 9 species of Rajidae throughout the world, and constitutes one exception to the strictly host-specific condition of the genus Emprutothrema.