Zebrafish and mammalian genomes when compared have prominent similarities with about 80% of human genes expressed in the fish. Additionally, this fish is also fairly inexpensive to breed and house in a lab partly due to their shorter life span and being able to house more of them, compared to mammalian models. Directions of research Research on endocrine disruptors is challenged by five complexities requiring special trial designs and sophisticated study protocols: The dissociation of space means that, although disruptors may act by a common pathway via hormone receptors, their impact may also be mediated by effects at the levels of transport proteins, deiodinases, degradation of hormones or modified setpoints of feedback loops (i.e. allostatic load). The dissociation of time may ensue from the fact that unwanted effects may be triggered in a small time window in the embryonal or fetal period, but consequences may ensue decades later or even in the generation of grandchildren. The dissociation of substance results from additive, multiplicative or more complex interactions of disruptors in combination that yield fundamentally different effects from that of the respective substances alone. The dissociation of dose implies that dose-effect relationships use to be nonlinear and sometimes even U-shaped, so that low or medium doses may have stronger effects than high doses. The dissociation of sex reflects the fact that effects may be different depending on whether embryos or fetuses are female or male. Legal approach United States The multitude of possible endocrine disruptors are technically regulated in the United States by many laws, including: the Toxic Substances Control Act, the Food Quality Protection Act, the Food, Drug and Cosmetic Act, the Clean Water Act, the Safe Drinking Water Act, and the Clean Air Act. The Congress of the United States has improved the evaluation and regulation process of drugs and other chemicals. The Food Quality Protection Act of 1996 and the Safe Drinking Water Act of 1996 simultaneously provided the first legislative direction requiring the EPA to address endocrine disruption through establishment of a program for screening and testing of chemical substances. In 1998, the EPA announced the Endocrine Disruptor Screening Program by establishment of a framework for priority setting, screening and testing more than 85,000 chemicals in commerce. While the Food Quality Protection Act only required the EPA to screen pesticides for potential to produce effects similar to estrogens in humans, it also gave the EPA the authority