The use of S-GnRHa (salmon gonadotropin releasing hormone analogue) in induced breeding and early embryonic development of Gulsha, Mystus cavasius

Abstract

The current study was carried out to optimize the dose of the synthetic hormone for induction, and to observe the embryonic and larval developmental in Gulsha, Mystus cavasius. Induced breeding was conducted by using Ovupin (S-GnRHa) hormone (each 1.5 ml vial contain 0.2 mg of an analogue of S-GnRHa) at four different doses i.e., 0.25, 0.5, 1.0- and 1.50-ml kg-1 body weight (BW) for females, and the half of these doses were applied to males. Among the applied doses, 0.5 ml kg-1 BW for female and 0.25 ml kg-1 BW for male provided the maximum fertilization (83.66%) and hatching (80.0%) rates. The eggs of M. cavasius were strongly adhesive, with covering on egg surface. The average diameter of fertilized eggs just after spawning was 85.58±5.87 µm. After fertilization, the first, second, and third cleavage stages occurred within 20-25, 35-40 and 60-65 min, respectively. The identity of blastomeres was gradually lost and appeared at 64-cell stage to 128-cell stage onwards. The 64-cell stage appeared at 150-160 min and the morula stage 3:00-3:20 h (blastomeres completely lost), respectively. The gastrula stage appeared at 5:0-5:30 h in which the blastoderm spread in both the sides covering about 60-70% area, together with a thread-like germinal ring. Afterward, twisting locomotion was recorded at 23:30 h. The larvae started hatching at 24:00 to 25:00 h. The barbells were partially visible when the larvae were 10-12 h of age. Finally, the yolk sac was fully absorbed in the end of Day 3.