To pursue his newly demarcated research program, Trinkaus chose to work on Fundulus heteroclitus, a species of teleost fish commonly called the mummichog or the killifish. He remembered observing the process of epiboly in these fish embryos as a student at the embryology course at the MBL and remarked how beautiful and intriguing it was to see the phenomenon unfold in the transparent eggs (Trinkaus 2003, 92).
In addition to the transparency and the relatively large size (~2 mm) of their eggs, Fundulus have other attributes that make them a good choice organism to carry out experimental embryological research. For Trinkaus, Fundulus were readily available and easy to acquire during the early summer in Woods Hole, as these fish are very common along the Atlantic coast, especially in brackish waters, like estuaries, which, in turn, makes them easy to access and to collect. Once in captivity, Fundulus are easy to fertilize in the lab. Researchers can identify the gravid females by their white, swollen bellies, and gently squeeze the eggs out of the females into a petri dish. A similar procedure is conducted on males, identifiable by the yellowish hue of their bellies, to extract the milt, or the fish’s seminal fluid, which is then added to the eggs. In addition to being easy to manipulate and fertilize, Fundulus eggs and embryos provide a good experimental model because they are permeable and resilient to a range of environmental conditions, such as a variety of salinities and osmotic pressures (Atz 1986, 113).