The cells then migrate down the sides of the yolk (8 h panel) and begin forming a head and tail (16 h panel). The tail then grows and separates from the body (24 h panel). The yolk shrinks over time because the fish uses it for food as it matures during the first few days (72 h panel). After a few months, the adult fish reaches reproductive maturity (bottom panel). To encourage the fish to spawn, some researchers use a fish tank with a sliding bottom insert, which reduces the depth of the pool to simulate the shore of a river. Zebrafish spawn best in the morning due to their Circadian rhythms. Researchers have been able to collect 10,000 embryos in 10 minutes using this method. Male zebrafish are furthermore known to respond to more pronounced markings on females, i.e., "good stripes", but in a group, males will mate with whichever females they can find. What attracts females is not currently understood. The presence of plants, even plastic plants, also apparently encourages spawning. Exposure to environmentally relevant concentrations of diisononyl phthalate (DINP), commonly used in a large variety of plastic items, disrupt the endocannabinoid system and thereby affect reproduction in a gender specific manner. Zebrafish are omnivorous, primarily eating zooplankton, phytoplankton, insects and insect larvae, although they can eat a variety of other foods, such as worms and small crustaceans, if their preferred food sources are not readily available. In research, adult zebrafish are often fed with brine shrimp, or paramecia. Zebrafish are hardy fish and considered good for beginner aquarists. Their enduring popularity can be attributed to their playful disposition, as well as their rapid breeding, aesthetics, cheap price and broad availability. They also do well in schools or shoals of six or more, and interact well with other fish species in the aquarium. However, they are susceptible to "Oodinium" or velvet disease, microsporidia ("Pseudoloma neurophilia"), and "Mycobacterium" species. Given the opportunity, adults eat hatchlings, which may be protected by separating the two groups with a net, breeding box or separate tank. In captivity, zebrafish live approximately forty-two months. Some captive zebrafish can develop a curved spine. The zebra danio was also used to make genetically modified fish and were the first species to be sold as GloFish (fluorescent colored fish).