Why don’t fish keepers appreciate Pimephales promelas? Most commonly known as the fathead minnow, P. promelas is native to the central United States and southern Canada. The species is fairly small— usually not getting any bigger than 2 ½ inches— although the Peterson’s Field Guide says that they can reach 4 inches. Fatheads are bred in ponds throughout the United States, and sold in bait shops. True, the wild type P. promelas isn’t much to look at: dark olive above, dusky horizontal stripe through the middle, transitioning to a dull white on the underside.
An orange color morph, known as the rosy red, is available in the pet trade. The orange morph, too, is under appreciated. The aquarium shops sell them by the dozen, not so much as long time aquarium residents, but for use as feeders. (A while back, there as an article on the NANFA site which held that the rosy red variety was actually a hybrid between P. promelas and other Pimephales species. I was hoping to link to it, but it appears to have been taken down.)
But appearance isn’t what makes P. promelas great aquarium fish. It’s their behavior. The Pimephalesspecies are a select group, unique among cyprinids. Pairs spawn on the underside of rocks or old logs and males guard the eggs until they hatch. All other minnows scatter their eggs among plants or on the bottom, and then swim away.
Like goldfish and many other cyprinids, male P. promelas develop protuberances, called tubercles, on the snout. The common name “fathead” comes from the thick fleshy pad that the breeding male develops from the nape of the neck to the dorsal fin. Wild type males also develop alternating light and dark bands on their sides.
Males stake out a “cave” territory. In the aquarium, they’ll readily make use of an overturned flower pot or a length of pvc pipe, and males compete over spawning locations. Breeding males will periodically herd females into their caves, and then drive the females away after the adhesive eggs have been deposited on the cave roof and fertilized. As dedicated as any cichlid parent, males will aggressively defend the eggs against other fish. When the eggs hatch, however, they seem to lose interest.
Females and other tank mates will greedily consume the tiny fry. To save the fry, I remove the spawning cave place it upright in a separate tank and drop an airstone near the eggs to maintain circulation. Once they start spawning, P. promelas are prolific breeders and probably will lay more eggs than you can successfully raise to adulthood.
In the wild, spawning begins when temperatures climb into the 60s. Mine bred well in the mid 70s. Spawning is also light dependent. The number of eggs per spawn increases with day length, topping off at about 14 hours of light. (If you want to learn more about how day length influences spawning behavior in P. promelas, you might want to check out this masters thesis by a student at Texas Tech.)
P. promelas aren’t hard to care for. They not fussy about water chemistry and will stay healthy if you avoid extremes of pH or hardness and keep up with water changes. Being minnows, they like a reasonable amount of vegetable fair in their diets, and will do well on flakes, cichlid granules, and the occasional spirulina wafer. You probably will need to quarantine—and perhaps even medicate— store bought specimens before introducing them to their regular quarters. Most bait and feeder tanks are overcrowded, and a lot of shop owners don’t bother to keep up with water changes. Such poor conditions can stress the fish and make them susceptible to illness. If you’d like to learn more about them, Robyn Rhudy has a nice page about rosy reds on her site.