Falls, W.W., Dennis, C.W., Grier, H.J., Hindle, P.A., Young, J.C.
Abstract:
Induced maturation of common snook, Centropomus undecimalis, was accomplished in three separate regimes at the Stock Enhancement Research Facility: 1) in ponds in ambient conditions, 2) in environmentally controlled tanks, and 3) in an outdoor tank in ambient conditions.
Ninety-eight snook were stocked into three 0.93-acre, plastic-lined ponds during spring-summer 1995. After an average of 116.3 days, 72.2% of the females (n=36) and 50.0% of the males (n=60) were mature. No snook eggs or larvae were recovered from ichthyoplankton samples (n=7) in one pond during May or June.
From 1989 to 1996, five 100-day photothermal-conditioning trials were conducted in tanks. Trials 1-3 were conducted in 1989-91 and evaluated long (16 h) and short (control - 12 h) photoperiods with quasi-domesticated (Trials 1-2) and wild snook (Trial 3) at a constant 30 C. Salinity varied in one treatment of Trial 1 but was constant (32 ppt) in the other treatments. All males and 50.0% of the female held at 16 h light had mature gonads at the end of Trial 1. Fifty percent of both the males and females in Trial 2 matured (16 h light). Mature females from Trials 1 and 2 were injected with HCG (1000 IU/kg) and successfully spawned viable eggs which were fertilized with milt from mature males. These was no gonadal maturation in the wild snook (Trial 3 - 16 h).
Trials 4-5 were conducted in 1995-96 and evaluated the photothermal conditioning of wild-collected snook. Environmental conditions were the same as in Trials 2-3. In Trial 4, no gonadal maturation occurred. Male snook GSI's were 0.139 (n=6) in the long photoperiod (16 h) and 0.145 (n=11) in the short photoperiod. In Trial 5 there was no significant difference in the gonadal maturity between the females held at 16 h light (30.0%; n=10) and those held at 12 h light (22.2%; n=11). GSI's of male snook held at 16 h light (0.414; n=10) were significantly different (t<0.05) than those held at 12 h light (0.127; n=11). Five females from Trial 5 were injected with HCG and strip spawned.
Regressed females (n=24) from Trial 4 were moved into a 117,335 liter outdoor circular tank. Twenty-one female snook (87.5%) matured in ambient conditions after 173 days during spring-summer 1996. Six of the twenty-one females injected with GnRHa spawned with uninjected males and produced viable eggs in the tank of three successive days after injection.
(Florida Department of Environmental Protection, Stock Enhancement Research Facility, 14495 Harllee Road, Port Manatee, Florida 34221-9620, USA)
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