Eggs of most species of shrimps within 12–18 hours after fertilization at temperature and salinity range of 26–30°C and 30–23 ppt, respectively.
The density of nauplii is estimated a day after hatching. Nauplii from three 100 ml water samples taken from the spawning tank are counted and averaged. The total number of nauplii in the tank is then obtained by multiplying the volume by the average density.
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| Fig. 28a. Egg collection | Fig. 28b. Cleaning of eggs by changing water |
Fig. 29. Cleaning of spawning tank
siphoning of water through a filter net
scrub off slides of Tank
remove scum through a scope net
introduce seawater
To determine the hatching rate, the following formula is employed:
Nauplii are then directly transferred to larval rearing tanks.
At the nauplii stage, the larvae hardly feeds and thus depends on its yolk for development. This stage is easy to transport even for long durations. In some cases, where the site of the established hatchery is far from the spawner collecting areas, it is more advantageous to transport the nauplii instead of the spawners which are more prone to stress.
The nauplii are transported to the hatchery in two ways:
plastic containers - Only strong and healthy larvae should be transported. This is done by concentrating the nauplii at the water surface with a light source at night, gather them by scooping with a plastic or glass container. The larvae are then transferred into plastic jars which are half-filled with seawater. The container is then gradually filled up. A 20 liter plastic container can contain a maximum number of 500,000 nauplii. The open end of the container must be properly sealed to prevent leakage. The survival rate after 6–8 hours during transportation is more than 50%.
plastic bags - Each bag containing about 6–8 liters of water can be stocked with 200,000 nauplii. The water in the bags are oxygenated and the open end is closed with rubber bands. The survival rate is about 80–90% if transport takes about 4–6 hours (Fig. 30).
