Three published studies inform on the evolutive history of migrations or the diet of some pelagic fish of the Mediterranean. (Photo: IEO)
Parasites used as natural indicators of fish ecology
Tuesday, June 02, 2015, 03:30 (GMT + 9)
For several years a team of researchers from the Spanish Institute of Oceanography (IEO) has been studying the migration of marine organisms and their trophic relations in the Atlantic Ocean and the Mediterranean Sea.
Scientists believe that the knowledge of these aspects of the species ecology is crucial to the accurate assessment of fishery resources and for responsible exploitation.
Since 2008, parasitologists, veterinarians and ichthyologists of oceanographic centres of Baleares, Malaga, Murcia and Santander of IEO, Cavanilles Institute of Biology and Evolutionary Biology of the University of Valencia and the universities of Cagliari and Sassari (Sardinia, Italy), Istanbul (Turkey) and Malaga have been conducting studies on the use of parasites as natural markers of biology and ecology of fish having commercial interest.
"The conceptual basis of these techniques is that in certain phases of their life cycle, parasites, whose space-time distribution can be known, join the hosts and do not abandon until completing the life cycle, and therefore constitute biological brands that make it possible to deduce information about the ecology of the infected species," explains the IEO.
For example, one implementation of biological markers is the possibility to differentiate host resources with morphological characteristics and similar habits, and then reconstruct their evolutionary history.
In this regard, in 2014 the scientific team published a study on the parasitic fauna of the Scomber colias, a fish inhabiting the Atlantic and the Mediterranean in the journal Acta Parasitologica.
During this investigation, this species was compared with parasitological data of the other three resources belonging to the genus Scomber (S. australasicus and S. japonicus of the Indo-Pacific and S. scombrus of the North Atlantic).
The experts proved the existence of a "strict relation" between the sets of parasites characteristic of each species and its geographical distribution, which, according to the IEO, made it possible to improve the understanding of the evolutionary history of the genus.
The biological brands also provided information for the study of food webs that complement those that can be obtained from the direct analysis of preys found in the stomachs.
The parasites infecting the host through ingestion of certain species of preys will remain long in the host. Therefore, its detection implies that it was fed at some time of the intermediate host although the latter has not been detected in the stomach contents.
The team also studied parasites from the head of the bullet tuna Auxis rochei in the western Mediterranean.
As part of this study, whose results were published in the Journal of Helminthology in 2014, seven parasitic species were indentified, some of which belonged to the family Didymozoidae.
Infection levels of these parasites varied significantly with the size of the host. The scientists discovered that these differences could be attributed to changes in diet and/or habitat changes depending on the size, which contributed to a better understanding of the biology and ecology of this host species.
Finally, the study of biological markers could provide information on the migration of the host.
In 2014 the team published a study of the parasites of the bluefin tuna (Thunnus thynnus) gills of the eastern stock, which is reproduced in the Mediterranean, in the journal Folia Parasitological. There it was explained that the abundance of 11 species of parasites that were found differed depending on the size of the host and its capture area, being this an indication that the different sampling sites are considered discrete units.
By Analia Murias