31 International Journal of Zoological Investigations Vol. 6, No. 1, 31-48 (2020) _______________________________________________________________________________________ ISSN: 2454-3055 Histological and Ultrastructural Analysis of Tilapia rendalli Liver as an Environmental Assessment Tool for Cachoeira River, Bahia, Brazil Fábio Flores-Lopes 1* , Milane Alves Correia 2 and Daniela Mariano Lopes da Silva 1 1 Departamento de Ciências Biológicas, Universidade Estadual de Santa Cruz – UESC, Rodovia Ilhéus-Itabuna, Km 16, CEP 45650- 000, Ilhéus, BA, Brasil 2 Programa de Pós-Graduação em Zoologia Aplicada, Universidade Estadual de Santa Cruz – UESC, Rodovia Ilhéus-Itabuna, Km 16, CEP 45650-000, Ilhéus, BA, Brasil *Corresponding Author Received: 17 th December, 2019 Accepted: 4 th February, 2020 Published online: 13 th February, 2020 https://doi.org/10.33745/ijzi.2020.v06i01.003 ______________________________________________________________________________________________________________ Abstract: Due to the degradation of aquatic ecosystems, environmental monitoring studies have been developed with the aid of conventional and biological tools. The objective of this study was to evaluate the environmental quality of the Cachoeira River, Bahia, Brazil by physico-chemical analysis of water and histopathological and ultrastructural analysis of Tilapia rendalli (Boulenger, 1897) liver. Samples were collected at six points in the municipalities of Itapé, Itabuna and Ilhéus, between 2010 and 2012. Water samples were filtered through 0.7 µm GF/F glass-microfiber membranes, and ion analysis (Mg +2 , Ca 2+ , K + , Na + , Cl - , NH4 + , NO3 - , PO4 3- , SO4 2- ) was performed by ion-exchange chromatography. Fish specimens were collected using a seine-type drag net and fixed in 10% formalin. For histological analysis, the samples were embedded in paraffin, sectioned and stained with hematoxylin- eosin. For ultrastructural analysis, the samples were embedded in Epon resin, and sections were prepared and contrasted with 0.5% uranyl acetate. Semi-quantitative histopathological analysis were performed based on the severity of alterations. There were high concentrations of nutrients in water samples, and at all points sampled, the specimens showed histopathological and ultrastructural changes. Points 1, 2, 3 and 4 were characterized as moderate to severe both for histopathological and ultrastructural changes, indicating that these points had greater degradation than the others. Keywords: Histopathology, Environmental monitoring, Tilapia, Ultrastructure, Liver Citation: Fábio Flores-Lopes, Milane Alves Correia and Daniela Mariano Lopes da Silva: Histological and ultrastructural analysis of Tilapia rendalli liver as an environmental assessment tool for Cachoeira River, Bahia, Brazil. Intern. J. Zool. Invest. 6 (1): 31-48, 2020. https://doi.org/10.33745/ijzi.2020.v06i01.003 ______________________________________________________________________________________________________________ Introduction Aquatic environments have been increasingly affected by human activities, resulting in damage to biodiversity (Moraes and Jordan, 2002; Abdel-Moneim and Abdel-Mohsen, International Journal of Zoological Investigations Contents available at Journals Home Page: www.ijzi.net