Experimental design
Pooled swollen or water-hardened eggs (approximately
600 eggs) were distributed uniformly into a
temperature controlled Thermo Lab (GFL 1070,
Germany) each equipped with four different chambers
containing 3.5l of water (having individual
temperature control at a precision of 0.01 °C) at four
test temperatures (26, 31, 33 and 36°C). A uniform
flow rate of 0.5L min− 1 was maintained in
incubation chamber until hatching. Fertilized eggs
were kept in suspension by using a sieve made of
bolting silk. Continuous aeration was provided in the
chambers to maintain optimum dissolved oxygen
level (N5mg L−1
) and the pressure of air blower was
adjusted as to maintain eggs in suspension. A fixed
photoperiod of 12L: 12D (Light:Dark) was maintained
with light exposure from 6.00 to 18.00 h. Eggs
were taken out from each chamber at various time
intervals and ontogenic stages were observed under a
light microscope (Olympus, Japan) coupled with a
camera. Each temperature treatment was repeated
under similar conditions four times (considered as
replicates) using fertilized eggs from separate brood
stock.