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<br />
<br />(about 0.5 kg of feed per system per day). By day 35,
<br />most fish were readily accepting the prepared diet. On
<br />several occasions, river water (l2-130C) was slowly
<br />introduced to the systems to compensate for evapora-
<br />tion, to improve water quality, and to adjust water
<br />temperature. Addition of cold river water usually lowered
<br />the temperature from 23-240C to l7-1SoC in about.
<br />30 min, but on one occasion the temperature dropped
<br />to 10 Celsius degrees in 10 min. The feeding behavior
<br />of the fish at this cooler temperature was benthic, but
<br />as the water temperature increased they began feeding
<br />near the surface again.
<br />Weekly samples of fry were collected to determine
<br />growth rates (Table 2). On day 63 (average, 30 mm
<br />TL) cannibalism was observed in raceways A9 and
<br />AIO, probably resulting from overcrowding. A small
<br />number of swimming fingerlings were seen with caudal
<br />fins protruding from their mouths.
<br />
<br />Table 2. Growth rate for larval Colorado squawfish
<br />reared in three recirculating systems at Willow Beach
<br />(Arizona) National Fish Hatchery.
<br />
<br />Age Averagea total length. (mm)
<br />( days) A9 and AIO Bl and B2 Cl and C2
<br />I b 7 7 7
<br />7 8 8 8
<br />14 9 9 10
<br />21 14 14 15
<br />28 19 19 20
<br />35 21 23 24
<br />42 25 25 25
<br />49 27 27 28
<br />56 28 30 3l
<br />63 30 33 32
<br />70 34 35 35
<br />77 37 36 37
<br />84 42 38 44
<br />91 44 39 46
<br />98< 47 4] 48
<br />105 49 42 50
<br />107 49 42 50
<br />
<br />a Average length of 10 fish per system; actual measurements were to
<br />the nearest 0.5 mm and averages were to the nearest whole
<br />millimeter.
<br />b Age of newly hatched lanaI fish.
<br />C Age of fingerlings when removed from the three recirculating
<br />systems.
<br />
<br />On day 9S, all fingerlings were removed from the
<br />three systems and the survival rates determined (Table
<br />3). A total of 34,S43 Colorado squawfish fingerlings
<br />(42 to 50 mm TL) were then transferred to other
<br />facilities for culture and experimental bioassay studies.
<br />Water quality was a problem during the last 2 weeks
<br />of this study. Water temperature was controlled
<br />
<br />176
<br />
<br />Table 3. Survival rate for Colorado squawfish;'~art
<br />in three recirculating raceway culture systems
<br />Willow Beach (A1:izona) National Fish Hatchery.'
<br />
<br />b~trate produced 25
<br />iching success); inje(
<br />rally on cobble substl
<br />000 fry (67% hatd
<br />'~t were hand stripp
<br />000 fry (3% hatching
<br />Survival of squawfi!
<br />odified raceways. 1
<br />;Culture conditions ine
<br />l.5 mgj L), high amm
<br />-earbon dioxide (15.0
<br />overcrowding, and s
<br />temperatures (lOoC i
<br />ulture might not be th
<br />squawfish progeny, L
<br />attempted and proven,
<br />dequate.
<br />If spawning and re,
<br />ow, the Colorado sq
<br />waters of the upper an
<br />Hatchery propagation
<br />the restoration of this
<br />
<br />Recirculating
<br />system
<br />A9 and AIO
<br />Bl and B2
<br />Cl and C2
<br />Total
<br />
<br />Number of fish.
<br />
<br />Stocked Harvested
<br />
<br />19,000 16,156
<br />10,000 7,612
<br />14,000 11,075
<br />43,000 34,843
<br />
<br />~<)
<br />Surviva
<br />(%)
<br />85
<br />76
<br />79
<br />80
<br />
<br />between 21 and 260C; however, at the end temperatureS
<br />dropped to 12-130C. Ammonia nitrogen (NH3-N)
<br />varied from 0.03 to 2.0 mgJL, carbon dioxide (CO~
<br />from 2.5 to 15.0 mgj L, pH from 7.5 to 9.0 units, and
<br />dissolved oxygen (02) from 1.5 to 9.9 mgj L. On day.;
<br />93, an oxygen depletion (1.5 mgj L) occurred in"
<br />raceways CI and C2, resulting in 60 mortalities. Anz
<br />immediate flushing of the system prevented further::.
<br />losses.
<br />
<br />Discussion
<br />
<br />Vanicek and Kramer (\ 969) found that nearly aU
<br />squawfish age VII and older were sexually mature.
<br />Seethaler (1978) found sexual maturity occurred after
<br />squawfish exceeded a total length of 400 mm and an
<br />age of VI years. In the present study the age at which
<br />Colorado squawfish first become sexually mature was
<br />documented. Hatchery-reared squawfish at Willow
<br />Beach began becoming sexually mature at age V
<br />(males) and age, VI (females). Total lengths and,
<br />weights of the mature squa wfish were 317 to 376 mm;,
<br />and 220 to 340 g (males; data obtained I July 1979);
<br />and 425 to 441 mm and 675 to 830 g (females; data ~
<br />obtained I July 1980). ....
<br />Vanicek and Kramer (\ 969) determined that Colo-
<br />rado squawfish spawning occurred after the wa.ter
<br />temperature reached 21.I0C; this was based on npe
<br />fish, spawned fish, and the appearance of juvenile ~sh
<br />in the Green River. Toney (1974) reported captIve
<br />squawfish spawned when the water temperature was
<br />22.20C. During the present study, uninjected females
<br />spawned at water temperatures of 20-210C, and
<br />injected females spawned at temperatures of IS-24~C.
<br />Although the optimum temperature for reproduct~on
<br />is probably between 20 and 220C, induced spawnmg
<br />may occur at a lower water temperature (lSoC). 'J
<br />Several techniques were used to spawn Colorado~,
<br />squawfish: (l) uninjected, natural spawning on cobble
<br />substrate; (2) injected, natural spawning on cobbl.e
<br />substrate; and (3) injecting, hand stripping, and aru.,
<br />ficial fertilization. Of these, injecting and naturaL
<br />spawning on cobble substrate proved far superior.~:
<br />Uninjected females that spawned naturally on cobble
<br />
<br />Prof!. Fish-Cult. 43 (4), October 1981/
<br />t
<br />
<br />1 thank Lyle Miller,
<br />he staff at Willow Be,
<br />ssistance during this I
<br />eviewing the manuscr
<br />
<br />all, R. c., and E. H. Bac
<br />in the propagaton of min
<br />lemens, H. P.. and K. f
<br />pituitary materials to
<br />Wild/. Servo Res. Rep.
<br />
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