Estudio de las poblaciones de peces en los ríos Champotón y Amacuzac (México)aplicación de biomarcadores, bioindicadores e índices biológicos para evaluar su estado de salud

Abstract

For the development of the thesis, two river systems were selected, River Amacuzac and River Champotón, that belong to the Priority Hydrological Regions proposed by the National Commission for Knowledge and Use of Biodiversity (CONABIO), which were selected because they involve several aspects, including: their diversity, their use and finally because them are areas poorly known, also they are in the Mesoamerica hotspot, defined as areas that present high endemism and also a considerable loss of habitat, which means that there are potential risks for these areas. Field collections were conducted over an annual cycle in the rivers Amacuzac and Champotó. River Amacuzac is one of the most important rivers of the state of Morelos, highly impacted by its tributaries such as River Cuautla and River Apatlalco which are heavily polluted by discharges of urban sewage, hospitals, industries, and a sugar mill, furthermore since 1980 exotic fish species have been introduced from governmental politics for purposes of aquaculture and the aquarium fish producers. On the other hand, River Champotón was studied, which is impacted by urban and farming areas and is considered by CONABIO as a poorly known area. In each of the ecosystems under study nine sites were elected from the upper to the lower portion of it. Water samples were collected in each study sites, using different methods and equipment for water quality assessment (water temperature, dissolved oxygen, pH, conductivity and salinity), to evaluate the water quality of River Champotón (hardness, orthophosphate, ammonium, nitrate and nitrite, alkalinity, BOD and total coliforms and faecal), samples were taken in duplicate. Fish were collected with different fishing methods along a stretch of 100 m (River Champotón) to 500 m (River Amacuzac) for an average of one hour at each study site. The samples were fixed in 10% formalin and transported to the laboratory for their taxonomic identification. Adult specimens of Astyanax aenues fish species at each study site of River Champotón were dissected immediately to extract the liver for biomarker evaluation. Materials were transported to the laboratory in liquid nitrogen. Spatial and temporal distributions of fish fauna from both ecosystems were determined at community level. Responses at population-level were assessed with Astyanax aeneus with somatic index (gonadosomatic, hepatosomatic and condition factor) in order to characterize the patterns of the life history and population structure and to evaluate the various responses of the fish under stress by the exposure to mixtures of pollutants into the ecosystem, considering the use of a battery of biomarkers (lipid peroxidation, glutathione S-transferase, -O-dietilasa etoxiresorufina (EROD) and lactate dehydrogenase). The integration of the global variations of the biomarkers battery was carried out with the Integrated Biomarker Response (IBR), which is a multivariate method. Our results indicate that these aquatic ecosystems are compromised at several levels of organization and also they are important because they have several attributes associated with ecosystems susceptible for conservation: (a) high specific richness; (b) the presence of several endemic species; (c) the limited distribution of some species; (d) species included in the protection criteria set by Mexican legislation (NOM 2010); (e) the rivers are located in regions sustaining the impact of natural events (River Champotón, primarily) and may therefore be considered as fragile ecological systems; (f) presence of several species of commercial importance; g) dominance of exotic species, particularly in River Amacuzac.