Finfish Breeding and Hatchery Management

Unit 3 - Breeding of major carps

3.8. Major carp egg and embryonic developmental stages

• The fertilization of major carp eggs is external.
• The fertilized eggs absorb water and swell considerably in 10-15 minutes and they becomes a little hard and this process is known as water hardening.
• They are bead-like, non-adhesive, semi-buoyant and have a large perivitelline space.
• The size of the eggs varies between 2.5 and 6.5 mm.

Important major carp egg and embryonic stages and time required for each stage are as follows

Sl. no.	Time required at 24-310C (Cumulative)	Stage
1	0 min	Fertilization
2	10-15 min	Water hardening and blastodisc formation
3	30-50 min	First cleavage (2 cells)
4	40-65 min	Second cleavage (4 cells)
5	50-80 min	Third cleavage (8 cells)
6	60-90 min	Fourth cleavage (16 cells)
7	70-120 min	Fifth cleavage (32 cells)
8	2-2½ hrs	Morula stage – less than half of yolk invaded by germ layer
9	2½-3 hrs	Blastula – about half of yolk invaded by germ layer
10	3-3½ hrs	Gastrula – about three-fourth of yolk is invaded by germ layer
11	3-4 hrs	Yolk-plug stage – complete invasion of yolk by germ layer excepting a small pore (blastopore)
12	4-6 hrs	Elongation of yolk mass-embryonic stage starts
13	5-6 hrs	Pea-shaped embryo – somites and myotomes appear
14	8-10 hrs	Comma-shaped embryo- optic vesicles appear, occasional twitching movement starts, gill rudiments and pectoral fin bud appear, heart appear
15	14-15 hrs	Advanced embryo – increase in the number of somites and myotomes, twitching movement quite rapid
16	18-20 hrs	Hatching – it takes place over a period of 2-3 hrs at 24-310C