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SPAWNING AND HATCHING OF THE RAZORBACK SUCKER (Xyrauchen texanus) Theophilus D. Inslee Hatchery Biologist, U.S. Fish and Wildlife Service, P. 0. Box 217, Dexter, New Mexico 88230 Abstract Razorback sucker (Xyrauchen texanus) broodstock was obtained from Lake Mohave in January, 1981 and 1982. Fish that survived spawning in 1981 were held in a culture pond and spawned again in 1982. Spawning techniques tested in 1981 were: induced spawning with HCG and carp pituitary in circular or rectangular tanks, stripping, and pond spawning. Egg incubation was tested in McDonald hatching jars, Heath incubators, on gravel in circular ` tanks, and on nets suspended in culture tanks. Other facets studied were fungus control on incubating eggs, size of eggs, and techniques to hold larvae until swim-up. In 1982 studies were oriented to determine the most efficient hormone rate, the best site of injection, improved hatching techniques, egg enumeration, fry enumeration, fry holding techniques, fungus control, and to develop hatchery constants to enhance the culture of razorback suckers. One of the major ob3ectives was to compare spawning success of brood fish Procured from the wild versus brood fish held in culture ponds for one year. The spawning method that showed the most promise in 1981 was hormone injections of HCG daily and stripping of eggs. -The Heath incubator was the superior method for egg incubation. Formality dip at 1:75 to 1:200 for ten minutes controlled fungus and did not kill developing embryos. In 1982 daily injec- tions of HCG in the muscle at 100 IUflb. of female weight was found to be the most effective hormone dosage. Egg viability at 96 hours was increased from 27.7% to 61.1! by stripping at 12 hour intervals after the start of egg ovulation, then enumerating eggs and moving to incubator trays as soon as eggs had water hardened (from 45 to 60 minutes after fertilization). As compared to a water hardening period from 1.5 to 6 hours. Fungus was con- trolled on incubating eggs with. a ten minute dip of 1:100 formality in the Heath. tray. Flow-through treatment of a stack of eight trays was not success- ful due to the dilution of the chemical when it reached the lower trays. The gravimetric method of egg enumeration was believed to be more accurate than either water displacement or the von Bayer method. Sample counts and weights from I00 trays resulted in a mean of 130 eggs per gram. Fry enumera- tion after hatching utilizing the water displacement method on 67 samples was found to be 233 fry/ml. The brood fish maintained far a year in a culture pond spawned as well or better than those obtained directly from T..ake Mohave. They ripened about one month later which greatly enhanced overall production. They were more predictable than wild fish although the 431