Dieta, metabolic and parasitological aspects of Oreochromis niloticus cultivated and wild, in the reservoir of Ilha Solteira, from Grande river, SP

Author(s)

Cibele Diogo Pagliarini

• Document type: Master's Dissertation
• Press: Botucatu. 2019-04-22.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Biociências. Botucatu
• Defense date: 2019-02-22
• Advisor: Igor Paiva Ramos; Cristiéle da Silva Ribeiro

Abstract

Oreochomis niloticus is a non-native invasive fish in Brazil, and currently the most produced and consumed fish in the country. However, the environmental effects/influences of this production system are poorly elucidated. In addition, accidental releases are recurring problems in fish farms. Thus, the aims of this study were to characterize the composition of the diet, muscle metabolic factors and parasitological aspects of wild (from accidental release) and cultivated O. niloticus, besides evaluating the overlap of trophic niche of this species with the wild icthyofauna that inhabits the environment close to the cage fish farm in the Ilha Solteira reservoir, rio Grande, SP. Two samples of O. niloticus and 17 other wild species were taken, during the rainy period (in December 2016) and the dry period (in July 2017). The specimens were euthanized, measured (cm) and weighed (g). In the field, specimens of O. niloticus were submitted to skin scraping to collect the mucus on slides to evaluate the presence of ectoparasites. All fish were necropsied to remove the organs (stomach, intestine, liver, mesentery, kidney, eyes and heart) to parasitological procedures. The stomachs were fixed and the parasitological and diet analysis were performd concomitante.The muscles tissues of O. niloticus specimens were removed, and samples were used in the metabolic analysis, and a part of the material was filleted and submmited to a macroscopic inspection in the candling table, to looking for encisted endoparasites. . For all statistical analyzes we considered the space/time variation [space (local) = specimens from the cage fish farm and natural environment (wild); temporal (season) = dry and rainy]. The diet composition presented significant differences in relation to the local and season of the samples. Oreochromis niloticus presented a wide, varied diet with high dissimilarity considering the local, being the ration, the item with greater contribution to such differences. High trophic overlaps between wild O. niloticus and other species of fish, including native, were observed, demonstrating possible competition for food resources. Differences were also found for some metabolic variables, however, most concentrations were similar between wild and cultivated specimens, demonstrating the influence of fish farming in the trophic structure of the icthyofauna, especially for opportunistic and generalist species. In addition, the analyzed fish presented 11 taxa of parasites, and Enterogyrus spp., larval stages of digeneans and hirudineans (Glossiphoniidae) occurred exclusively in wild specimens of O. niloticus. There was a statistical difference regarding the composition of the parasite community, and the parasite community of wild O. niloticus was more diverse. The epibiotic association between Dolops carvalhoi and Epistylis sp. was observed, being this the first report of epibiosis among these species, which were found parasitizing cultivated and wild O. niloticus in the present study. Wild Oreochromis niloticus tend to remain close to the cages, utilizing leftover of ration coming from the fish farming, facilitating the share and transmissions of parasites. Also, the similarity of metabolic substrate concentration of the muscle tissues (fillets) of the evaluated specimens evidences the great loss of ration to the environment, which in excess, can cause environmental problems, as well as favor the proliferation of some parasites. Thus, the present study has information about the trophic ecology of several species, data on muscle metabolism of the most cultivated and consumed species in the country, host-parasite-environment relationship, dispersion of etiological agents and epidemiology in aquaculture, which may contribute to a better national aquaculture activity. (AU)

• FAPESP's process: 16/23468-6 - Diet, helmintofauna and metabolic aspects of Oreochromis niloticus from cage fish farms escapes
• Grantee: Cibele Diogo Pagliarini
• Support Opportunities: Scholarships in Brazil - Master