Recent advances in ovulation synchronization and superovulation in ...

Abstracts. II International Symposium on Animal Biology of Reproduction, Nov. 19-22, 2008, São Paulo, SP, Brazil.
Influence of the temperature on the final oocyte maturation induced by hypophysation in
P. argenteus
R.D.V.S. Morais 1 , F.P. Arantes 1 , F.S. Lemos 1 , Y. Sato 2 , E. Rizzo 1 , N. Bazzoli 3
1 Laboratory of Ictiohistology, Morphology Department, ICB/UFMG, CP, 486, Belo Horizonte, MG, Brazil; 2 Hydrobiology and
Hatchery Station of Três Marias, CODEVASF; 3 Graduate Program on Zoology of Vertebrates – PUC Minas,
Belo Horizonte, MG, Brazil.
Introduction
Final oocyte maturation (FOM) and ovulation are critical points for fish cultivation. Temperature acts at different
levels of the reproductive process, interfering in the sequence of events and time of FOM and ovulation (1).
Variations in temperature can cause changes in the dynamics of cytoskeleton elements, leading to microtubules
aggregation, when the temperature is higher and its breakdown when temperature is lower, interfering in the nuclear
migration during FOM (2). The aim of this experiment was to analyze the sexual steroids levels and the cytoskeleton
organization on the FOM; spawning and fertilization of Prochilodus argenteus submitted to spawning induced by
hypophysation in two temperature regimes.
Material and Methods
The experiments were conducted in the Hydrobiology and Hatchery Station of Três Marias, MG –CODEVASF, in
two reproductive seasons. In each experiment were used 30 females in advanced maturation, which were captured in
São Francisco River and acclimated during 2 months in cultivation tank. The fish were transferred to tanks with
continuous flow of water, and separated into two groups of 15 individuals (group A = 22-23 ºC; group B = 25-
26 ºC). Both groups were submitted to spawning induced by hypophysation using two doses of crud carp pituitary
extract (CCPE). To examine the serum profiles of sexual steroids, blood samples were collected in the following
times: 0h, 14h, 23h, 25h and 26h after the first CCPE dose. Fecundity was determined considering the weight of
spawned oocytes and the number of oocytes per gram of spawned oocytes. The males received a single dose of
CCPE. After fertilization, the eggs were placed in incubators for development. The fertilization rates were
determined after the blastopore closure in at least 100 eggs. The larva abnormality rates were obtained in at least 50
recently hatched larvae of each sample.
Results and Discussion
The final oocyte maturation process occurred similarly in both groups, although in Group A (22-23 o C) this process
was slower, with a delay of approximately 2 hours. Moreover, several oocytes of the group A didn’t complete the
FOM. Germinal vesicle migration toward the micropyle started after the first CCPE dose and germinal vesicle
breakdown occurred after the second CCPE, similar to findings of other authors (3). At this stage, the chromosomes
in metaphase were near the micropyle. Spawning occurred in 100% of females of the group B and 67% of the group
A. The fertilization rates were above 80% and the larval abnormalities were below 10%, with no statistical
differences between the groups. Fecundity was higher in the group B (25-26 o C). The profiles of sex hormones
showed similar tendency in the two groups and with others studies (3). An increase in the testosterone levels
occurred after the first dose of CCPE, decreasing before spawning. The 17β-estradiol levels exhibited few variations
during FOM, and the 17α-hydroxyprogesterone (17α-P) levels increased at the time of spawning and declined
afterward. Group A presented a late elevation peak of 17α-P, and thus the spawning was delayed.
Immunohistochemistry reactions showed tubulin associated to the germinal vesicle and an actin ring in the cortex
probably responsible by the ooplasmic segregation and fertilization events. In conclusion, the results indicated that
lower temperatures impair the final oocyte maturation and spawning of P. argenteus under cultivation.
References
(1) Glasser F, Mikolajczyk T, Jalabert B, Baroiller JF, Breton B. 2004. Gen Comp Endocrinol, 136:171-179; (2)
Nogales E, Medrano FJ, Diakun GP, Mant RG, Towns-Andrews E, Bordas J. 1995. J Mol Biol, 254:416-430; (3)
Senthilkumaran B, Yoshikuni M, Nagahama Y. 2004. Mol Cell Endocrinol, 215:11–18.
Support: FAPEMIG, CNPq and CODEVASF
E-mail: rrvidal@pop.com.br
Anim. Reprod., v.6, n.1, p.227, Jan./Mar. 2009 227