Metamorphosis of Macrobrachium rosenbergii

Metamorphosis refers to the set of drastic post-embryonic anatomical and physiological changes that occurring mostly arthropods and amphibians when an immature individual transforms into an adult. It is usually accompanied by a change of habitat and/or behavior.

A large female may produce up to 100 000 eggs and they can reproduce three or four times a year under natural condition. Like other Macrobrachium prawns, M. rosenbergii is a eurohaline species where egg-berried females migrate downstream in rivers to estuaries to reach elevated salinity that is crucial for larvae survival during the extended planktonic larval stage of development.

 The egg of Macrobrachium rosenbergii are slightly elliptical, with a long axis of 0.6-0.7 mm, and are bright orange in color until 2 to 3 days before hatching, when they became grey-black. The larvae hatch as zoeae.

They typically utilize their thoracic appendages to swim, differing from penaeid shrimp which hatch as nauplii. Healthy larvae swarm at the surface of the water especially in the first days. Unhealthy larvae accumulated at the bottom of the tank and are often bluish in color.

Metamorphosis to post larvae is characterized by a radical change in behavior and appearance; for the first time the animals resemble miniature adult prawns and instead of swimming freely in the water, many crawls or cling to the tank surfaces.

 A salinity of 12 ppt seems to be optimum for hatching and early rearing. The time taken for a larval batch to metamorphose varies according to several factors including feeding and environmental conditions particularly temperature.

In a healthy well fed, which is maintained within the optimum temperature range, expect to see the first few post larvae (often referred to as PL) between days 16-20 after stocking. Most of the larvae should have metamorphosed into PL by days 25-32 at the recommended water temperature of 28 – 31 ° C.

It is usually no economic to maintain any batch longer than 32-35 days (90-95% metamorphosis). From hatching to metamorphosis into juveniles the actively swimming larvae undergo 11 moults (11 larval stages) that are morphologically different from one another; the benthic PLs that emerge are basically growing juveniles, capable of osmo-regulation in freshwater.

Mature PLs then migrating up-stream from saline condition in the river to join the older, hierarchical populations.
Metamorphosis of Macrobrachium rosenbergii