Shellfish Breeding and Hatchery Management (2+1)

4.1.5 Identification of larval stages of shrimps

Nauplius stage (N) :

•  Pear shaped with 3 pairs of appendages.
• Moults every 3-5 hours and passes 6 substages (N1-N6).
• Swims actively towards weak source of light.
• No feeding due to absence of mouth and alimentary canal.
• After 2 days, the nauplius converts to protozoea by metamorphosis.

Protozoa stages (PZ) :

 It has 3 sub stages:

PZ I - Broad head and narrow tail with forked end. Eyes sessile.

PZ II - Eyes stalked. Rostrum developed.

PZ III - Abdominal segments develop dorsomedian spines. Uropod bud

appears near forked end of tail.

The stages lasts for 3-4 days and is succeeded by mysis stage.

Mysis stage (M) :

 It also has 3 sub stages:

M I - No pleopod bud

M II - Pleopod bud appears

M III - Pleopod bud with 2 segments

This stage lasts for 3-4 days and then pass to I post larval stage.

First post larval stage (PL1) :

· Superficially resembles 3^rd mysis except for the development of setae on the pleopods.

· First 3 walking legs lose the swimming setae and their claws become functional.

Metamorphosis:

XII POST-LARVAE:

• Teeth on upper and lower margin of rostrum.
• Behavioral changes in swimming.
• Body transparent with slightly brown coloured.
•  Chromatophores on the head.