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It has been documented that Colorado squawfish (Toney 1974) and northern squawfish, Ptychocheilus oregonensis (Jeppson 1957; Patten and Rodman 1969) wi11 spawn on gravel, rubble, and rock substrate. Two layers of spawning substrate were therefore placed in the uppermost 10 m of raceways A3 and A9. The bottom layer consisted of boulders (30-40 cm) and the top layer of cobble (4-10 cm in diameter). Water introduced at the upper end flowed through the substrate, creating an artificial spawning environment. Water depth over the substrate ranged from 10 to 76 cm. The wild adults were held in raceways A3 or A9. Raceway A2 was used as a holding and spawning facility for the hatchery-reared adults. A fresh-flo pump (~ hp) was stationed at the center of this raceway and water was pumped towards the upper and lower ends at 0.0 I m3/ s to create a single recirculating system. In late April, as water temperature reached 150C, males began acquiring small tubercles on the head, operculars, and pectoral and pelvic fins. In May, when the water temperature approached 180C, males began producing seminal plasma with active sperm. By June, when the water temperature reached 200C, tubercles had spread over the entire surface of the males, except for the abdominal area and caudal fin. Females showed no spawning characteristics until June (200C water temperature). A few females acquired small tubercles on the head, operculars, pectoral and pelvic fins, but most had none. Females were normally larger than males (Table I). The abdominal region started to soften and distend as females became gravid. Genital papillae became swollen and inflamed just before spawning. Spontaneous Spawning Eight wild females and 19 wild males were placed in raceway A9 in an attempt to observe natural spawning. The spawning act of Colorado squawfish had never ?een observed, and special care was taken to try to fill In some of the data gaps. When spawning observations Induced Spawning were completed,S females and 12 males were tra ferred to raceway A3. ganic (ammonium p ial trout starter) ferl lankton bloom. Z ocerans, were obser' easurements . of eg ae, and fingerlings WI ages were to the ne bers of eggs spawn ble substrate were ] servations, and the nu ced on the fertility ra merated before they lities. Spawning was induced by injections of carp pitui~~: (Ball and ~acon 19~4;. Clemens and Sneed 1962). Acetone-dned carp pltUltary (40 mg) was mixed wit a solution of oxytetracycline hydrochloride (10 mt)' Before the intraperitoneal injection of 4 or 8 mg/k~. body weight, each female was anesthetized with tricain~ m~th~nesulfonate at 50-100 mg/ L (Le.itritz 1960)' !n~ect.lOns were repeated after 24 h (a maXImum oft\VO' InjectIOns per female). . Five wild females were injected at 4 mg/ kg body~ weight and allowed to spawn naturally on the cobble' substrate in raceway A3. Hatchery-reared females were injected at 4 mg/kg (39 fish) or 8 mg/kg (39 fish) of body weight. When. eggs could be expelled with slight pressure, the female was anesthetized and wiped dry before the eggs were stripped into a plastic pan. Milt from four males was~ added to the eggs and water was added to activate the - sperm. Eggs were stirred and washed for 45 min to prevent clumping. When the eggs had water hardened, (about 50 min) they were poured on screen trays (53 X 53 cm) which were covered with lA-mm mesli hardware cloth, and then placed in three aluminum. troughs (3.5 X 0.55 X 0.3 m) and slanted into the: incoming water at a 300 angle. Heated weater (20-: 210 C) entered two troughs and cold water (12-l30 entered the third trough, all at 8 L/ min. e wild squawfish i rved. Three females June. The spawning a ter depth of 25-45 c 210e. Two to three earing to guide her t female slowly settll les, one on each side, 'is caused the female vement, followed by a release of eggs. The all fish would swim ales and presumabl~ ear and repeat the beh t a 48-h period. Patten ilar spawning behavi( n estimated 25,000 el jected females. Egg mm. Since all eggs , were allowed to hat I an at 96 h and was hed fry ranged from extended incubatio extended spawning p imated 7,500 fry were Rearing Facilities The rearing facilities consisted of three recirculating systems or six concrete raceways (30.5 X 204 X 1.2 rnf and were designated as A9 and A 10, B I and B2, an.: Cl and C2. Water was recirculated by a Y4-hp fresh-ill? pump at the rate of 0.01 m3/s. These raceways we . filled 2 weeks before spawning (except A9 and A 10)( obtain warmer water temperatures; small amounts. . Tab~e 1. Co.mparison of total lengths and weights of Colorado squawfish being held at Willow Beach (ArizoA: Natzonal Fish Hatchery as of 1 July 1980. ''t' ild fish transferred Age Length (mm) observed daily. One Fish (years) No. Average Range Average eceiving the first ca Hatchery-reared les spawned within Females 6 78 429 390-441 681 tion, and a fifth fern Males 6 52 402 381-425 590 nd injection. No diffe Wild een the first or last Females unknown 8 681 619-756 2,824 red 1.2 X 1.2. 1.2 X Males unknown 19 578 hsoflO,20-55,and 174 ., , Fish-Cult. 43 (4),