Sailfin Mollies are commonly found in estuaries, stagnant drains, shoreline pools and other harsh, brackish habitats throughout the intensely irrigated Imperial valley. With their ability to survive in salinities as high as 87 ppt they can also be found in the Salton Sea itself. While they may be able to stand intense salinities their habitat selection is more restricted by temperature as anything lower than 24°C stops growth and reproduction. Detritus is their main food source followed by algae, and they will only feed on invertebrates when they are incredibly abundant.
Females mature when they reach 25-40 mm in length, and males mature at 20-30 mm. This usually happens within 110-150 days of birth but environmental conditions including temperature and salinity can influence their growth and development. Once they mature, courtship and copulation happens rapidly. Females can store various batches of eggs at one time allowing for a single copulation to fertilize all of them. Embryos feed from both yolk sac and from the mother in utero, leading to bigger and more independent young. The number of offspring each female can produce varies with her size, the local water temperature, and salinity. Sailfin Mollies from ditches usually hold between 20 and 60 eggs but numbers as high as 141 have been found.
Sailfin Mollies can grow to as much as 15 cm in one year but few exceed 8 cm. For males, size is partially determined by the density of predators in the area. Dangerous areas will see males with smaller bodies and less colorful markings making them less conspicuous to predators. Larger and more bold looking fish are found in areas where avoiding predators is less of a concern than attracting females.
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