Parasites as biological tags for stock discrimination of the Brazilian flathead, Percophis brasiliensis Quoy et Gaimard, 1824, in the South Western Atlantic

BRAICOVICH, P.E.; TIMI, J.T.; ETCHEGOIN, J.A.

Viterbo, Italia

Simposio; 7th Internationsl Symposium on Fish Parasites; 2007

Universitá degli studi della Tuscia y Societá Italiana di Parassitologia.

The aim of this study is to identify different stocks of the Brazilian flathead Percophis brasiliensis Quoy et Gaimard (Percophidae, Perciformes) in the Argentinean and Uruguayan seas, by using parasites as biological tags. A total of 117 fish were examined for parasites between September 2005 and March 2006. Only specimens of comparable length were included in the analysis. Fish were caught in four zones: North of the Argentine-Uruguayan Common Fishing Zone (34º 30´-36º 30´S; 53º 30´-56º W; n = 35), South of the Argentine-Uruguayan Common Fishing Zone, near Mar del Plata city (38º 08’S–57º 32’W; n = 59), El Rincón zone (39º- 49º S; 60º - 62º W; n = 51) and San Matías Gulf (41º 40´- 42º 10´S; 63º 50´- 65º W; n = 32). A multivariate discriminant analysis was implemented to discriminate stocks and these results were corroborated by comparing parasite prevalence and abundance among zones. The 100% of the fishes were parasitized. A total the 117,361 parasites, belonging to 23 species, were found in the overall sample. A discriminant analysis allowed the identification of three discrete stocks in the four zones (percentage of correctly classified samples = 86.44), with flatheads from both north and south of the Argentine-Uruguayan Common Fishing Zone clumping together, as a single unit of stock. The principal differences were observed between the samples of the Argentine-Uruguayan Common Fishing Zone and those from both southern zones (El Rincón and San Matías Gulf). The importance of each parasite species for discriminating between groups, evaluated as the contribution of each variable to the total sum of Mahalanobis distances, showed that Anisakis simplex was related to southern areas, while Grillotia sp., Corynosoma australe and Hysterothylacium sp. were important in determining the position of fish from the Argentine-Uruguayan Common Fishing Zone. Comparisons of both prevalence and abundance confirmed these results, with fish from the Argentine-Uruguayan Common Fishing Zone being characterised by higher values for Grillotia sp., C. australe, Corynosoma cetaceum, Nybelinia sp., Scolex polymorphus, Moravecia argentinensis and Hysterothylacium sp., while the samples from El Rincón and San Matías Gulf showed higher values of A. simplex. On the other hand, samples from San Matías Gulf were characterized by lower values of parasitism for all other species considered. Differences in environmental factors and their influence on the distribution of zooplankton and other host involved in the food web should be shaping differentially the community structure in each zone resulting in identifiable stocks of the Brazilian flathead. Financial support by grant from ANPCYT (PICT 15192).