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<br />Table 1. Summary of data for six spawning female bony tail
<br />chub of unknown age, May 1981, at Willow Beach (Arizona)
<br />National Fish Hatchery.
<br />
<br />Fish
<br />Total length
<br />(mm)
<br />
<br />533a
<br />487
<br />492
<br />564
<br />518
<br />511
<br />
<br />Eggs
<br />
<br />Weight
<br />(g)
<br />1,280
<br />1,160
<br />1,065
<br />1,500
<br />1,150
<br />956
<br />
<br />Fecundity
<br />(No. of eggs)
<br />
<br />o
<br />27,300
<br />22,100
<br />32,500
<br />37.700
<br />5,8~0
<br />
<br />Fertilization
<br />("70)
<br />
<br />o
<br />97
<br />94
<br />95
<br />91
<br />98
<br />
<br />aFish received three injections.
<br />
<br />May 1981, water temperature 20 "C). Breeding males also had
<br />a light orange coloration at the base of the pectoral and pelvic
<br />fins; breeding colors were not present on the females. All
<br />males were producing seminal plasma with active, sperm;
<br />however, no sex products could be expressed from any female
<br />until after hormonal injections.
<br />Five females ovulated 18 to 20 h after the first injection;
<br />one female failed to ovulate after receiving three injections.
<br />Egg diameters ranged from 2.0 to 2.3 mm (mean, 2.2 mm);
<br />volumetric measurements varied from 103 to 151 eggs/mL
<br />(mean, 130 eggs/mL). Total fecundity was 125,450 (mean,
<br />25,09O/female) or 21,514 eggs/kg of body weight (fable 1).
<br />
<br />Incubation and Hatching
<br />
<br />Eggs placed in the 20-21 "C water began hatching at 99 h
<br />and were completely hatched by 174 h; total length of newly
<br />hatched fry averaged 6.8 mm (Thble 2). During the incuba-
<br />tion period at 20-21 "C, dissolved oxygen ranged from 9.25 to
<br />9.5 mg/L, ammonia nitrogen from 0.03 to 0.04 mg/L,
<br />carbon dioxide from 2.77 to 2.95 mg/L, pH from 8.0 to 8.05
<br />units, and water hardness from 325 to 355 mg/L. Eggs placed
<br />in the cool water (16-17"C) began hatching at 170 h and
<br />hatching was completed by 269 h; newly hatched fry averaged
<br />6.8 mm in total length (Thble 2). Eggs placed in the cold water
<br />(12-13"C) began hatching at 334 h and were finished by 498 h;
<br />total length of these newly hatched fry also averaged 6.8 mm
<br />(Thble 2). -
<br />
<br />Culture
<br />
<br />When fry began swimming to the surface, 48 to 120 h after
<br />hatching, 26,438 were placed in raceways Bl and B2; the
<br />remaining 80,000 fry were transferred to Dexter National
<br />F'lsh Hatchery in New Mexico.
<br />During the flJ'St 14 days the fry were very active and fed
<br />near the surface. These fish (mean, 9.7 nun TL) swam in
<br />schools, but by day 21 the fry (mean, 11.5 mm TL) were
<br />scattered throughout the culture system. This behavior was
<br />believed to be due to the decline in zooplankton, which also
<br />occurred by the third - week.
<br />
<br />202
<br />
<br />Table 2. Summary of data from incubating eggs of bony tail
<br />chub at three different water temperatures.
<br />
<br /> Water temperature (oC)
<br />Incubation data 20-21 20-21 16-17 12-13
<br />Number of eggs 80,600 37,700 5,85oa 1,300
<br />First cleavage (h) 3 3 4 5
<br />Embryo forming (h) 22 24 29 52
<br />Embryo developed (h) 68 69 101 162
<br />Pigmented eyes (h) 76 79 133 222
<br />Hatching began (h) 99 107 170 334
<br />Hatching ended (h) 165 174 269 498
<br />Percent hatch (0]'0) 91 88 55 4
<br />Number hatched 73,346 33,176 1,787 52
<br />Age of swim-up fry (h) 48 48 72 120
<br />Percent swim-up 98 99 96 25
<br />Number of fry 71,879 32,844 1,715 13
<br />
<br />· A total of 2.600 eggs were transferred to Utah State University at Logan.
<br />
<br />Fry were fed a' supplemental diet of commercial trout
<br />starter beginning on day 21. They were fed 4 to 5 times daily
<br />(0.25 to 0.50 kg of feed per day). By day 28, most fISh (mean
<br />18.1 nun TL) readily accepted the prepared diet. Schooling
<br />behavior was observed again on day 28 and continued
<br />through day 70.
<br />Throughout the present study, continuous water tempera-
<br />ture recordings were made and carbon dioxide, ammonia
<br />nitrogen, dissolved oxygen, and pH were analyzed each week
<br />. to monitor water quality during culture. Water temperature
<br />varied from 12.8 to 24.4 "C, carbon dioxide from 1.8 to
<br />4.4 mglL, ammonia nitrogen from 0.01 to 0.81 mg/L,
<br />dissolved oxygen from 7.6 to 10.0 mglL, and pH from 7.8 to
<br />9.0 units.
<br />On day 42 (when mean fry total length was 31.1 nun),
<br />Icthophthirus multifilis was microscopically identified on twc
<br />dead fISh. To prevent further losses, multiple treatment:
<br />(three treatments on alternate days) of formalin at 15 mg/I
<br />(Allison 1957) were used. By day 49, the parasite was believe<
<br />to be eliminated; however, weekly prophylactic treatment
<br />were continued to prevent further outbreakS.
<br />Samples of fISh were collected each week to determin
<br />growth (Thble 3). On day 70, a total of 18,775 fmger1in8
<br />(mean 49.S mm and 974.6 mg) were removed from racewa)
<br />Bl and B2; survival rate was 71070. The fISh had increase
<br />7-fold in total length and 348-fold in weight during 70 day:
<br />
<br />I
<br />
<br />Discussion
<br />
<br />Based on the collection of gravid females, ripe males, ar,
<br />the appearance of juvenile fISh in - the upper Green RiV(
<br />Vanicek and Kramer (1969) concluded that bonytail chul
<br />apparently spawn: in June and July when the water temper
<br />_ ture reaches 18 "C; however, natural spawning of this sped
<br />has been observed-in Lake Mohave during May (Jonez 81
<br />Sumner 1954). During the present study, spawning occurr' I
<br />in May at water temperatures of 20-21 "C. Based on the thr I'
<br />different egg incubation temperatures used in this stu
<br />
<br />/'mg. F<Sh-Odt. (- October 19 I
<br />
<br />,J
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