Captive Breeding of Endangered Yaqui Topminnow and Yaqui Chub for Recovery Purposes

—Yaqui topminnow Poeciliopsis occidentalis sonoriensis and Yaqui chub Gila purpurea, two federally endangered fishes from the Rio Yaqui basin (Arizona, USA, and Sonora, Mexico), were propagated by various methods. Propagation of Yaqui topminnow was attempted in aquaria and wading pools; the greatest number of offspring was produced in 556-L, plastic wading pools. We added substrate, artificial plants, and a vertical mesh barrier to create refuge for offspring. Fish were stocked when water was 198C; after 1 month, when water temperatures exceeded 218C, Yaqui topminnow started to produce young continuously. On average, 7.4 offspring/d were captured from four pools collectively. Yaqui chub were propagated in 189-L, glass aquaria. We manipulated photoperiod, diet, and substrate to induce spawning of Yaqui chub, but success was only achieved after the water was chilled to 178C for 30 d and then adjusted to 218C over 14 d. After the water was maintained at 218C for 3 d, we covered the bottom of each aquarium with glazed ceramic tiles and a raised plastic grid to protect eggs from predation. Broadcast spawning of Yaqui chub occurred at night; the next morning, we retrieved the tiles and the attached eggs and placed them in incubation tanks. Yaqui chub eggs hatched over the next 5 d, and the hatching success rate averaged 83%. After this initial spawn, manipulation of water temperature was not required to induce spawning, as Yaqui chub spawned each time tiles were placed in the tanks. These methods worked well, and we recommend them for propagation of Yaqui topminnow and Yaqui chub. Less is known about the culture of threatened and endangered fishes than about that of fishes raised for bait and sport. As of 1999, spawning modes were known for only 13 of 43 imperiled minnow species in North America (Johnston 1999). Almost nothing is known about the spawning of the Yaqui chub Gila purpurea and the Yaqui topminnow Poeciliopsis occidentalis sonoriensis, two federally endangered fish species that are endemic to the northern Rio Yaqui basin in Arizona, USA, and Sonora, Mexico. The Yaqui topminnow is a small poeciliid; males rarely grow larger than 25.0 mm total length (TL), and females rarely grow larger than 50.0 mm TL (Minckley 1973). The Yaqui topminnow is found in the Rio Yaqui basin only within the San Bernardino National Wildlife Refuge (SBNWR) in Arizona (AZGFD 2001a). The federal government listed this species as endangered in 1967, and the state of Arizona listed it as endangered in 1988 (USFWS 1967; AZGFD 2001a). Males are distinguished from females by the gonopodium and dark coloration exhibited in breeding season. The Yaqui chub is a cyprinid that grows to 13.0 cm TL (Rinne and Minckley 1991). Its range in Arizona is restricted primarily to artesian ponds in the SBNWR, Leslie Canyon National Wildlife Refuge, and El Coronado Ranch (Turkey Creek and ponds) in the extreme southeastern part of the state (AZGFD 2001b). Federal endangered species listing of the Yaqui chub occurred in 1984, and state of Arizona endangered species listing occurred in 1988 (USFWS 1984; AZGFD 2001b). Researchers have reported that artificial propagation may be required for survival of this species (DeMarais and Minckley 1993). Both species are threatened by loss of habitat through groundwater pumping, land use changes, and introductions of nonnative fishes, frogs, and parasites (DeMarais and Minckley 1993). Our objective was to develop laboratory methods for propagating these two endangered fishes to aid in conservation efforts.