Chapter 38 Histopathological Indicators in Fish for Assessing Environmental Stress Ricardo Arturo Ruiz-Picos, Jacinto Elı ´as Seden ˜ o-Dı ´az, and Eugenia L opez-L opez Abstract We present the usefulness of histological and histopathological techniques as tools for evaluation of fish health. Stress at the individual level is frequently presented in the form of tissue damage and we are interested in the study of this level as a health indicator, since it is intermediate between the biochemical and reproductive levels. In addition, we analyzed two case studies conducted using the viviparous fish Goodea atripinnis, the first about the health status by size class of the fish species in the Yuriria Lake, which is affected by a complex mixture of xenobi- otics from agriculture, industry, and wastewater, and the second about chronic exposure to a herbicide based on glyphosate. In both cases, various anomalies were found in the liver (fibrosis, cellular disorganization, hemorrhages and vacuoles, pyknosis, and cell lysis), and gills (lamellar fusion, sloughing, hypertrophy, hyper- plasia, and leukocyte infiltration). Both studies demonstrated the utility of fish as sentinel organisms and histopathological analysis as a useful tool in environmental biomonitoring to detect early warning signals in aquatic environments. Keywords Tissue damage • Histopathological analyses • Gill and liver damages • Target tissues • Chronic exposure 38.1 Introduction Water bodies are systems that are constantly altered by a variety of pollutants from various sources. The increase in the synthesis of chemicals for domestic, industrial, and agricultural use has generated a continuous discharge of these chemicals, which R.A. Ruiz-Picos • E. L opez-L opez (*) Laboratorio de Bioconservaci on y Manejo, Escuela Nacional de Ciencias Biol ogicas, Instituto Polite ´cnico Nacional, Prolongaci on de Carpio y Plan de Ayala, Col. Sto. Toma ´s, 11340 Ciudad de Me ´xico, Mexico e-mail: eulopez@ipn.mx J.E. Seden ˜o-Dı ´az Coordinaci on Polite ´cnica para la Sustentabilidad, Instituto Polite ´cnico Nacional, Av. Instituto Polite ´cnico Nacional y Wilfrido Massieu, Edificio de la Biblioteca Nacional, Col. Zacatenco, Ciudad de Me ´xico, DF, Mexico e-mail: jsedeno@ipn.mx © Springer Science+Business Media Dordrecht 2015 R.H. Armon, O. Ha ¨nninen (eds.), Environmental Indicators, DOI 10.1007/978-94-017-9499-2_38 663