Laserfiche WebLink
<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />3-7 <br /> <br />3.2.3 Culture Techniques <br /> <br />Hatchery culture techniques for humpback chub re based largely on the <br />wet methods developed for warm-water fishes and prev.ously described for the <br />Colorado squawfish. Both artificial spawning (hand stripping) and natural <br />spawning (in gravel-lined raceways) have been em loyed on the species. <br />Females are induced to ovulate egg masses with intra eritoneal injections of <br />carp pituitary (Hamman 1982a). The fish are first nesthetized with 50-100 <br />mg/l tricaine methanesulfonate (MS222) and then inj cted with a preparation <br />of carp pituitary (CP); acetone-dried CP (40 mg) is ixed with a solution of <br />oxytetracycline hydrochloride (10 ml). Th fish are injected <br />intraperitoneally at a rate of 4 mg/kg body weight a 24-hour intervals. <br /> <br />Ripe males exhibit orange to red-orange breedin colors on the pectoral <br />and pelvic fins and the anal fin, as well as the a dominal region. Gravid <br />females are light orange on the sides and at the b se of the pectoral and <br />pelvic fins and the anal fin. Both species exhibi fine tubercles on the <br />head, opercles and paired fins. <br /> <br />In artificial spawning, females are anestheti ed with MS222 and the <br />vent area wiped clean before eggs are stripped in 0 a plastic pan. Milt <br />from males is expelled into the pan with the eggs and a little water is <br />added to acti vate the sperm. To prevent cl umpi ng, eggs are sti rred and <br />washed for about 45 mi nutes unti 1 they are water ardened. The eggs are <br />then poured onto screen trays, covered with hardwa e cloth, and glaced in <br />aluminum recirculating troughs at water temperatu es of 19-22 C. The <br />incubation periods are dependent on water temperatur ; eggs incubated at 21- <br />22 oC, 16-17 oc and 12-13 oc began hatching in 1 2, 167 and 340 hours, <br />respectively, with hatching completed in 146, 266 and 475 hours, <br />respectively. The highest hatching success was se n at 19-20 oC, but the <br />greatest swim-up success occurred at 21-22 oc (Hamma 1982a). <br /> <br />Hand-stripped eggs ranged from 2.6 to 2.8 mm (mean, 2.7) in diameter <br />with 51 to 58 eggs/ml (mean, 55). Average fecu dity of seven females <br />stripped in 1981 (Hamman 1982a) was 2,523 eggs per females or 5,262 per kg <br />of body wei ght. The humpback chub has the lowest ecundity of any of the <br />endangered fishes of the Colorado River. <br /> <br />Humpback chub were observed spawni ng "natura ly" in a gravel-l ined <br />raceway at Willow Beach NFH in May 1981 (Hamman 1982a). Nine females <br />spawned within 24 hours of receiving CP injections, t water temperatures of <br />19-200C. The nine fish deposited a estimated 30,000 eggs, 2.6 to 2.9 mm <br />(mean 2.8) in diameter. The eggs adhered to the gra el substrate. In 1981, <br />natural spawning produced 23,940 swim-up fry and 19,857 fingerlings for an <br />83% survival, while artificial spawning produced 12,381 swim-up fry and <br />9,318 fingerlings for a 75% survival. <br /> <br />The size of newly-hatched larvae was 6.7 to 7.4 mm TL with weights of <br />2.8 to 4.2 mg. Growth rate for the larval fish cultured in the <br />recirculating system at Willow Beach NFH was 29.8 to 40.6 mm TL and 584.6 to <br />883.9 mg in a 56-day period. <br />