Good Golly Miss Amazon Molly!

The Amazon molly (Poecilia formosa) is a species of fish found only in the Tuxpan River, the Rio Grande, and the Nueces River in northern Mexico and the southern United States. Within these rivers, P. formosa typically prefers slower moving streams and ditches with plenty of vegetation, and are usually found in freshwater systems.

Amazon mollies are rather small and plain. The body is teardrop-shaped, and adults only grow up to 10 cm (3 in) long. They are mainly silver in color, although they may have rows of small, light brown spots running down their sides. In addition, some individuals may have black spots along their dorsal and tail fins.

Like most other mollies, the Amazon molly is an omnivore. They may feed on algae, seaweed, insects, and mosquito larvae. In turn, they themselves can be prey for larger aquatic insects like giant water bugs, other fishes, alligators, frogs, egrets and herons, and racoons. To avoid predators, P. formosa tends to stay in groups where it is less easy to be singled out.

Perhaps the most interesting feature of the Amazon molly are its reproductive habits. This species is entirely female, and reproduces via a process called gynogenesis. First, females are courted by males from other molly species such as P. latipinna, P. mexicana, P. latipunctata, or P. sphenops. Mating triggers the release of eggs, but the male's sperm is destroyed before it can fertilize them. Instead, the male gets the advantage of increased attractiveness to females of their own species, as these females are more likely to mate with males that have already mated with P. formosa.

After mating, the female broods her eggs for 30-40 days. She then gives live birth to anywhere from 60 to 100 fry, which are all clones of their mother. These young recieve no further parental care, but are fairly independent and are fully capable of reproduction after about 1-6 months, depending on the temperature of the water; warmer waters increase the rate of maturity. Individuals can live anywhere from 1-3 years in the wild.

Conservation status: the IUCN considers the Amazon molly to be Least Concern. However, one of the species that are used to trigger reproduction, the broadspotted molly (Poecilia latipunctata) is Critically Endangered. Primary threats to the Amazon molly include habitat degradation or loss due to construction and damming.

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Photos

Dr. Manfred Schartl

Daily fish fact #578

Devils Hole pupfish!

The most well-known species of pupfish, these fish have their entire population confined to a single 130 meter deep hole, and more specifically a single partially submerged rock shelf in the hole. The conditions in the Devils Hole are very extreme, but the Devils Hole pupfish has many adaptations that help it survive: the pupfish can, for example, stop using oxygen for up to two hours!

The Beautiful Blue Catfish

Blue catfish (Ictalurus furcatus) are members of the bullhead catfish family, native to the drainages of the Mississippi, Missouri, and Ohio river basins and the Gulf of Mexico. Because of their popularity as game fish, this species has also been introduced to freshwater systems throughout North and South America, and is considered invasive in these areas.

Like many catfish, I. furcatus is a bottom dweller. They can often be found near complex structures such as rocky outcroppings, fallen trees, or sunken structures that provide both food and shelter. The blue catfish is an opportunistic predator, consuming any fish or aquatic invertebrates it can find, as well as eggs, small amphibians, and injured or recently deceased animals. Adult I. furcatus are seldom prey for other species due to their size, but hatchlings and juveniles are often food for cormorants, willets, osprey, pelicans, and bald eagles. To deter predators, this species has serrated barbs along their dorsal and pectoral fins, each laced with a particularly painful toxin.

Though they can be difficult prey for other animals, the blue catfish is a popular target for fishermen, and for good reason; they're the largest species of catfish in North America. Adults can easily reach a length of 65 in (170 cm) and a weight of 165 lb (75 kg). As indicated by their name, most individuals are grey or blue, with a lighter underbelly. This species also lacks scales, a common characteristic of catfish, and the face is framed by long whisker-like barbels that help it detect nearby food.

While generally solitary, blue catfish aren't territorial, and tend to ignore each other until the mating season. Reproduction begins in April and continues until June, during which time males attract a female by building a nest and releasing attractive pheromones. Once a female has selected a male, she lays between 4,000-8,000 eggs per kilogram of bodyweight in his nest (i.e. if the female weighs 2 kg, she may lay between 8,000-16,000 eggs). The male then disperses sperm over the eggs. Following fertilization, the male chases away the female and guards the nest for about a week, at which time the eggs hatch. The hatchlings, also known as fry, stay close together in schools for several weeks before growing large enough to disperse. It will take them a further 5 years for them to reach maturity; on average individuals live about 10 years, but can live as long as 25.

Conservation status: The blue catfish is considered Least Concern by the IUCN. Within its native range, populations face minor threats from dams and droughts. Where it has been introduced, the species is considered invasive due to its voracious appetite.

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Photos

Missouri Department of Conservation

NOAA

Earl Nottingham