Both monogamous and promiscuous mice species have been used in these types of experiments, for more information studies can expand on this topic. More complex models that have systems that are as close as possible to humans are being looked at. Looking back at more common rodent models for instance the common ASD mouse are helpful but do not fully encompass what a model of the human social behaviors needs to. But these rodents will always just be models and this is important to keep in mind. Zebrafish The endocrine systems between mammals and fish are similar; because of this, zebrafish (Danio rerio) are a popular lab choice. Zebrafish work well as a model organism, part of which can be attributed to the fact that researchers are able to study them starting from the embryo, as the embryo is nearly transparent. Additionally, zebrafish have DNA sex markers, this allows the biologists to individually assign sex to fish, this is particularly important when studying endocrine disruptors as the disruptors can affect how, among other things, the sex organs work, so if by chance there is sperm in the ovaries later on through the testing it can then be pinned to the chemical without the chance of it being a genetic abnormality since the sex was determined by the researcher. Besides zebrafish being readily available, and easy to study through their different life stages, they have hugely similar genes to humans—70% of human genes have a zebrafish counterpart and even more fascinatingly 84% of disease genes in humans have a zebrafish counterpart. Most importantly perhaps is the fact that the vast majority of endocrine disruptors end up in water ways, and so it is important to know how these disruptors affect fish, which arguably have intrinsic value and just happen to be model organisms as well. The zebrafish embryos are transparent, relatively small fish (larvae are less than a few millimeters in size). This allows scientists to view the larvae (in vivo) without killing them to study how their organs develop in particular, neuro development and transport of presumed endocrine disrupting chemicals (EDC). Meaning how their development is impacted by certain chemicals. As a model, they have simple modes of endocrine disruption. Along with homologous physiological, sensory, anatomical and signal-transduction mechanism similar to mammals. Another helpful tool available to scientists is their recorded genome along with multiple transgenic lines accessible for breeding.