Finfish Breeding and Hatchery Management

Egg and embryonic development

● The fertilization of  major carp eggs is external.
● The fertilized eggs  absorb water and swell considerably in 10-15 minutes and they become harder and this process is known as water hardening.
● They are round, bead-like, crystalline transparent, non-adhesive and have a large perivitelline space; unfertilized eggs are opaque wihte
● The size of the water-hardened eggs varies between 2.5 and 6.5 mm
● The colour of  eggs may be reddish, yellowish, bluish or copper-red, depending  upon species
● Important major carp egg and embryonic stages and time required for each stage are as follows :

 

Sl. no.	Time required at 24-310C	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 will be completed over a period of 2-3 hrs at 24-310C, newly hatched spawn measures 4-6 mm, has bulbous yolk-sac