A multiple scale look at parasites as biological tags in marine fish: from host stocks to regional fish assemblages

TIMI, J.T.

Viterbo, Italia

Simposio; 7th International Symposium on Fish Parasites; 2007

At a regional scale, the use of parasites as biological tags in the South-western Atlantic has been a successful tool for the discrimination of stocks of marine fishes in all population studies to which it was applied. From a number of previous studies on stock composition of several fish species, some general patterns have been recorded: 1) a differential latitudinal distribution of parasites is a common feature in fish hosts, and is probably directly related to environmental (oceanographic) conditions, especially water temperature, 2) some parasites, identified as suitable biological tags are common to all host species and widely distributed in the local fauna, 3) many of these species show low specificity, use paratenic hosts and are transmitted via trophic interactions, and, more importantly, 4) independently of variations of parasite burdens among host species due to differential habits, diet, size, etc., of fish, this group of parasites displays similar latitudinal patterns in all host species they parasitize. Therefore, on the basis of existing information it can be predicted that these few species should be enough for discriminating populations of other fish species in further studies. This prediction is confirmed with ongoing studies on stock discreteness of two fish species, previously not investigated for parasites. However it only can become realistic if predictability in parasite burdens can be found. Despite no long-term studies having been carried out on temporal repeatability in population attributes of fish parasites in the South-western Atlantic, the strongest evidence supporting it was the finding that parasite species of 16 component communities from four anchovy populations, sampled in a period of three years, occurred as a nested subset pattern, indicating that there are some general, large scale processes structuring parasite communities at the level of host species. Furthermore, and beyond the limits of host species, parasite species of low specificity, common in the study area, and shared by several fish species (larval anisakid nematodes, larval trypanorhynch cestodes and juvenile polymorphid acanthocephalans) displayed a nested subset pattern across component communities of 12 fish species in the northern region of the Argentine sea. This departure of random assembly within the regional compound community of these larval parasites, is evidently indicative that not only fish populations, but fish assemblages can be identified according to the occurrence of a given group of parasite species suitable as “regional” biological tags. The use of these parasites as biological tags in the region will be a successful tool to be applied in future studies, not only for delineation of host populations, but also for the identification of harvest locations, even when no fish from other regions are available for comparisons. Financial support by grant from CONICET (PIP 5996/06).