**1. Introduction**

[78] Washburn, P. C. ; Di Giulio, R. T. (1989) Biochemical responses in aquatic animals: A review of determinants of oxidative stress. ToxicolChem, 8(12) 1103-1123.

[79] Watson, D. E., Menard, L., Stegeman, J. J., Di Giulio, R. T. (1995) Aminoanthracene is a mechanism-based inactivator of CYP1A in channel catfish hepatic tissue. Toxico‐

[80] WHO International Programme on Chemical Safety (IPCS), 1993. Biomarkers and risk assessment: concepts and principles. Environmental Health Criteria 155, World

[81] Wilson, C., Tisdell, C. (2001) Why farmers continue to use pesticides despite environ‐

[82] Wisk, J. D. ; Cooper, K. R. (1990) The stage specific toxicity of 2,3,7,8-tetrachlorodi‐ benzo-*p*-dioxin in embryos of the japanese medaka (*Oryzias latipes*). Environ Toxicol‐

[83] Witeck, L. ; Bombardelli, R. A. ; Sanches, E. A. ; Oliveira, J. D. S. ; Baggio, D. M. ; Sou‐ za, B. E. (2011) Motilidade espermática, fertilização dos ovócitos e eclosão de ovos de jundiá em água contaminada por cádmo. R. Bras. Zootec. v. 40, n. 3, p. 477-481.

[84] Yang, C. S., Yoo, J. -S. H., Ishizaki, H., Hong, J. (1990). Cytochrome P450IIE1: Roles in nitrosamine metabolism and mechanisms of regulation. Drug Metabol. Rev. 22, 147–

[85] Yilmaz, M. ; Gul, A. ; Erbasli, K. (2004) Acute toxicity of alpha-cypermethrin to gup‐

py (*Poecilia reticulate,* Pallas, 1859). Chemosphere, v. 56, p. 381-385.

mental, health and sustainability costs. Ecolog Econom.,39:449-462.

logical Apply Pharmacological. 135, 208-215.

Health Organization, Geneva.

220 New Advances and Contributions to Fish Biology

Chem, 9 (9), 1159-1169.

159.

Across vertebrates, the fish heart is structurally relatively simple. The heart of teleosts is unique in structure, composed of four chambers in series: venous sinus, atrium, ventricle and bulbus arteriosus. The two chambers acting as pumps are the atrium and ventricle, a simplified ver‐ sion of that seen in tetrapods. These chambers develop from a simple linear tube [1] and differ not only morphologically but also physiologically with different characteristic rates of contrac‐ tility [2]. Fish heart design is reflective of the needs for oxygen delivery to working skeletal muscle in an often oxygen poor environment. The heart is the first definitive organ to develop and become functional, as embryological survival depends on its proper function. The verte‐ brate-specific development of multiple chambers with enough muscle to generate higher sys‐ temic pressures allowed for perfusion of larger and more complex tissues.

Fish show great variability in the development of the heart and modification of heart per‐ formance capacities to meet tissue perfusion demands imposed by differences in life history. Research has tended to focus on inotropic or chronotropic responses of the heart to stress such as temperature in larger fish such as trout, or on development through the use of ze‐ brafish mutants. Between these sources much has been revealed about the contractile prop‐ erties of the two chambers. This research will be reviewed in the context of roles of the atrium and ventricle in fish in achieving variability in myocardial contractility.
