Parasite diversity as an indicator of environmental change? An example from tropical grouper (Epinephelus fuscoguttatus) mariculture in Indonesia

SUMMARYFish parasites are used to monitor long-term change in finfish grouper mariculture in Indonesia. A total of 210Epinephelus fuscoguttatuswere sampled in six consecutive years between 2003/04 and 2008/09 and examined for parasites. The fish were obtained from floating net cages of a commercially run mariculture facility that opened in 2001. The fauna was species rich, consisting of ten ecto- and 18 endoparasite species. The ectoparasite diversity and composition was relatively stable, with the monogeneansPseudorhabdosynochusspp. (83–100% prevalence, Berger-Parker Index of 0·82–0·97) being the predominant taxon. Tetraphyllidean larvaeScolex pleuronectisand the nematodesTerranovasp. andRaphidascarissp. 1 were highly abundant in 2003/04–2005/06 (max. prevalenceS. pleuronectis40%,Terranovasp. 57%,Raphidascarissp. 1 100%), and drastically reduced until 2008/09. These parasites together with the prevalence ofTrichodinaspp., ecto-/endoparasite ratio and endoparasite diversity illustrate a significant change in holding conditions over the years. This can be either referred to a definite change in management methods such as feed use and fish treatment, or a possible transition of a relatively undisturbed marine environment into a more affected habitat. By visualizing all parameters within a single diagram, we demonstrate that fish parasites are useful bioindicators to monitor long-term change in Indonesian grouper mariculture. This also indicates that groupers can be used to monitor environmental change in the wild. Further taxonomic and systematic efforts in less sampled regions significantly contributes to this new application, supporting fish culture and environmental impact monitoring also in other tropical marine habitats.