Propagation of Endangered Moapa Dace
We report successful captive spawning and rearing of the highly endangered Moapa Dace, Moapa coriacea (approximately 650 individual fish in existence at time of this study). We simulated conditions under which this stream-dwelling southern Nevada cyprinid and similar species spawned and reared in the wild by varying temperature, photoperiod, flow, and substrate in 14 different spawning and rearing treatments in a propagation facility. Successful spawning occurred in artificial streams with the following characteristics: water flow directed both across the bottom gravel substrate into a cobble bed and across the upper water column; 12–14 fish/stream (0.016–0.026 fish/L depending on water level); static water temperature of 30–32°C; photoperiod of 12 h light and 12 h dark; gradual replacement of water from their natal stream with on-site well water; a combination of pelleted, frozen and live food; and minimal disturbance of fish. Nevada Department of Wildlife now uses these techniques successfully to produce fish in a culture setting. Identification of the effective combination of factors to trigger spawning in exceptionally rare fishes can be difficult and time consuming, and limiting factors can be subtle. Sufficient numbers of available test fish, close study and replication of wild spawning conditions, careful documentation, and patience to identify subtle limiting factors are often required to effectively rear and spawn fishes not previously propagated.
The Warm Springs area of the Muddy River system in southeastern Nevada, where Moapa Dace occur in the wild.
Diagram of aquarium system used, unsuccessfully, to quarantine Moapa Dace. A 240 L acrylic aquarium (top) was used to hold the fish. Pottery and plastic plants were provided as cover. A 60 L glass aquarium (bottom right) was used as a sump. The sump provided biological filtration and a submersible pump placed in the sump was used to circulate water through the ultraviolet sterilizer and back into the holding aquarium. Water overflowed into piping on right back into the sump. Plumbing signified by solid black lines was flexible vinyl tubing; open pipe was made of rigid polyvinyl chloride. Arrows show direction of water flow.
Diagram of system used successfully to rear and propagate Moapa Dace. Fish were located in an 800 L fiberglass artificial stream (left). Silt and sand (not depicted), gravel, cobble, boulders, pottery, and plastic plants were provided as substrate and cover. A 1,200 L cylindrical fiberglass tank was provided as a sump (right). For biological filtration, two 18.95 L plastic buckets were suspended above the water level in the sump. Submersible pumps forced water into the buckets and then it trickled through filter pads and bio-balls back into the sump. Another submersible pump in the sump circulated water through an ultraviolet sterilizer and back into the artificial stream. For the water velocity treatment, which ultimately led to successful spawning of Moapa Dace, a submersible pump was placed on the bottom of the artificial stream directing flow along the substrate. At the left end of the artificial stream, water would enter the pipes and overflow. Then the force of gravity would cause it to upwell through the bottom of the sump. Plumbing signified by solid black lines was flexible vinyl tubing; open pipe was made of rigid polyvinyl chloride. Arrows show direction of water flow.
Detailed view of submersible pump providing additional flow along substrate and upwelling into cobble bed. This photograph shows the characteristics of the artificial stream where most of the successful spawning took place.
Number of Moapa Dace larvae captured over time in the two artificial stream environments subjected to the modified water flow treatment. Solid lines represent numbers of Moapa Dace captured in streams immediately following spawning events. Treatment in stream 1 stopped after 392 days (no fish were produced after day 291) and stopped in stream 2 after 204 days. Some fish escaped to the sumps and were not enumerated in this figure.
Relationship between Moapa Dace young total length and time, fit by a von Bertalanffy growth curve and 95% confidence envelope. All fish fed ad libitum.
Contributor Notes
Associate Editor: D. Buth.