Abstract
It was analyzed in this work the influence of photoperiod on time interval from ovulation induction period to extrusion of ovocits in female bullfrogs (Lithobates catesbeianus). It was used 54 females reared from metamorphosis to 9 months of age under three photoperiods: dark time (DL 0:24), 16 hours of daylight (DL 16:8) and 12 hours of daylight (DL 12:12). Ovulation was induced by intramuscular application of two doses of LHRHa with 12 hours of interval between the injections. After 10, 25, 28, 31, 34 and 37 hours from the first hormone injection, 10-gram samples (3,000 eggs) were extracted from each female at each time interval and fertilized. Egg hatching rate was checked in each sample 72 hours after fertilization. Analysis of variance showed a significant effect of extrusion delay and the interaction between photoperiod and this delay. Extrusion should be carried out 33, 24 and 26 hours after the first hormone dosage in females reared in environments without light, with 12 hours of daylight and with 16 hours of daylight, respectively, to obtain the maximum fertilization rate.
Highlights
Frog raising technology has reached a satisfactory level (Flores Nava, 2000; Teixeira et al, 2001), reproduction is still precarious and natural condition depended in most farms (Costa et al, 1998), which causes interruptions in the production flow (Lima & Agostinho 1988, 1992; Lima et al, 1999)
3 Cuesta Aquicultura, Botucatu, SP, Brasil. It was analyzed in this work the influence of photoperiod on time interval from ovulation induction period to extrusion of ovocits in female bullfrogs (Lithobates catesbeianus)
Extrusion should be carried out 33, 24 and 26 hours after the first hormone dosage in females reared in environments without light, with 12 hours of daylight and with 16 hours of daylight, respectively, to obtain the maximum fertilization rate
Summary
Frog raising technology has reached a satisfactory level (Flores Nava, 2000; Teixeira et al, 2001), reproduction is still precarious and natural condition depended in most farms (Costa et al, 1998), which causes interruptions in the production flow (Lima & Agostinho 1988, 1992; Lima et al, 1999). The use of controlled environment (Agostinho et al, 2002) and of hormones for inducing ovulation (Agostinho et al, 2000) may enable reproduction control of frogs. The first studies supporting bullfrog controlled reproduction were developed by Falcon & Culley (1995), Alonso (1997) and Agostinho et al (2000). These works have contributed to the development of artificial fertilizing techniques, ovulation induction as well as spermiation with gonadotropin-releasing hormone (LHRHa). The fertilization rate, according to Agostinho et al (2000), may vary from 30 to 83%. The causes of such variation are still unknown
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