Shellfish Breeding and Hatchery Management (2+1)

Identification of larval stages of shrimps

Objective : To familiarize with the identification characters of Penaeid shrimps

Procedure

Follow the points given below to identify the 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.

Protozoea 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.

Significance:

Identification of different larval stages is of much importance in successful operation of a hatchery. As the different larval stages need different types of food and water quality environment, it becomes necessary to identify and segregate them from other groups .