Captive Care Notes: Pikeminnows (Ptychocheilus, Family Cyprinidae)
Juvenile Northern Pikeminnow (Ptychocheilus oregonensis) are often collected in shallow waters where they school with Speckled Dace (Rhinichthys osculus) and Redside Shiner (Richardsonius balteatus). Use as large a seine as possible, as they're nimble fish that easily evade dipnets and smaller two-person seines. Unfortunately, their hardiness in the wild is not matched in captivity, where they tend to be skittish and otherwise not very happy that they're contained in a glass box. For this reason don't keep them in anything smaller than a 55-gallon aquarium. Simulating river currents with powerheads is a good idea, but be sure to provide areas of cover where the fish can hang out and relax. Considering their carnivorous nature, a high-protein diet is recommended. Aquarists who are successful in keeping this fish will have to contend with where to keep them once they outgrow their tanks. But every home aquarist I've talked to who have attempted to maintain Northern Pikeminnow has not been able to keep them alive for longer than five months.
Because of their endangered status, Colorado Pikeminnow (P. lucius) cannot be kept by the average home aquarist. However, aquarists can keep this fish vicariously by viewing them at the Ocean Journey aquarium in Denver. The biggest trick in keeping them is making sure they don't eat the other endangered Colorado River fishes -- Humpback Chub, Bonytail, and Razorback Sucker -- that share their exhibit. For this reason, only pikeminnows that are smaller than their tankmates are kept. As they grow, they are exchanged for smaller ones from the U.S. Fish and Wildlife Service, which propagates them at various national fish hatcheries.
At hatcheries, Colorado Pikeminnow are kept in large concrete raceways around 30 m (100 ft long), 2.4 m (8 ft) wide, 1.2 m (4 ft) deep. Boulders and cobble are placed at the top 10 m (32 ft) of the raceways to simulate spawning habitat. Water circulates from the bottom of the raceway to the top, where it flows over the artificial gravel beds. When water temperatures reach 15C (59F), males begin acquiring breeding tubercles. As the temperature climbs to 18C (64F), males begin producing sperm. Females become gravid when temperatures reach 20C (68F). Although most cultured pikeminnows are induced to spawn with hormone injections, they will spawn naturally under these conditions. According to hatchery observations, two to three males pursue each female, as if guiding her to the spawning site. She settles on the bottom while the males, one on each side, nudge her genital papillae. With a quick shudder or vibration, she releases her eggs. After the males fertilize the eggs, the adults leave the spawning area, but return 3-4 minutes later and spawn again. Females lay 8,000-11,000 eggs, which begin hatching around four days later. Fry are raised in acre-size, 3-feet deep earthen ponds, which are treated with organic and inorganic fertilizers to stimulate algae and zooplankton growth. The fry are also fed a commercial trout starter diet. Although salmon managers may cringe to hear it, adult pikeminnow are fed hatchery raised trout!