Parasites as biological tags for fish stock assessment: limitations and perspectives.

TIMI, J.T.

Viña de Mar

Simposio; VIII International Symposium on Fish Parasites; 2011

Universidad de Antofagasta, Chile

The use of parasites as biological tags for fish stock discrimination has become increasingly popular during last years. This methodology has evolved from using single parasite species as discriminators to comparing entire parasite assemblages by mean of sophisticated multivariate analyses. The growing background of parasite ecology and the increasing number of studies on stock discrimination have evidenced, however that some problems constrain their utility: the disadvantages of using short lived parasites and the lack of replication at short local and temporal scales, both of them providing only snapshots of the actual situation, with no possibilities of inferring about future comparisons. Intrinsic host population traits can also cloud the results; among them host size being one of the most important, especially for long-lived parasites which tend to accumulate with fish size or age and whose influence must be taken into account in case of samples being not homogeneous in terms of host size. Fish size is a source of variability in parasite assemblages, with younger/smaller fish displaying more stochastic communities than older/larger ones, making difficult the interpretation of results. On the other hand, differences between size classes in the relative contribution to within/between samples of both species composition and abundance can be used for making inferences regarding discrimination of stocks by multivariate procedures. These problematic situations are exemplified based in our own results on fish stock assessment in South Western Atlantic waters, a particular region where parasites can be used not only for identifying the boundaries among fish populations, but also among fish assemblages.