TOPIC 3 - LIFE CYCLE AND SYSTEM OF TIGER SHRIMP

Figure 1: Giant Tiger Prawn, Penaeus monodon

P. Monodon Taxonomy

Kingdom: Animalia

Phylum: Arthropoda

Subphylum: Crustacea

Class: Malacostracea

Order: Decapoda

Suborder: Dendrobranchiata

Family: Penaeidae

Genus: Penaeus

Species: P. Monodon

The giant tiger prawn, Penaeus monodon, is found in the Indian Ocean and western Pacific (Indo-West Pacific). The prawns are distributed from east and southeast Africa to northern and eastern Australia, Japan, Pakistan and the Malay Archipelago. It is cultured commercially in much of its range. Western Indian Ocean and western Pacific populations have separate evolutionary histories. The largest of all the cultivated shrimp, it can grow to a length of 36 cm and is farmed in Asia.

Figure 2: Life Cycle of Tiger Shrimp

The eggs are demersal and tend to sink while larvae are Planktonic. Prawn larva thrives mainly offshore and undergoes three main stages: nauplius, protozoea, and mysis. At the postlarval and juvenile stages, the prawn migrates toward the estuary. As it grows, it starts moving to the shallow coastal waters. The adult prawn inhabits the open sea.

Sexes are separate and can be easily distinguished through the external genitalia located at the ventral side. The thelycum in females and petasma in males. During mating, the male deposits the spermatophore inside the thelycum of the female. Mating can only occur between newly molted females and hard-shelled males. Spawning tanks place throughout the year. The eggs are fertilized in the water after the female simultaneously extrudes the eggs and the spermatophore. The number of eggs released by a single spawner varies from 248,00 to 811,000.

Eggs

The eggs are small, spherical, and vary from 0.25 to 0.27 mm in diameter. The developing Nauplius almost fills up the entire space inside the egg. At 28-30°C, the eggs hatch 12-17 h after spawning.

Nauplius Stage

Stage after eggs have hatched. The prawn Nauplius is very tiny, measuring from 0.30 to 0.58 mm in total length. It swims intermittently upward using its appendages in a “bat-like” manner. It is attracted to light and in aerated tanks, it will concentrate in the most lighted areas if aeration is stopped. The Nauplius molts through each of six sub stages for a total of about 1.5-2 days. The substrates differ from each other mainly on the furcal spine formula. The latter indicates the number of spines at each side of the furca.

Protozoea Stage

Its body is more elongated and measures from 0.96 to 3.30 mm in total length. It consists of the carapace, thorax and abdomen. It can also be distinguished by its movements, it swims vertically and diagonally forward towards the water surface.

The protozoea undergoes three sub-stages. The paired eyes of protozoea can be obscured as two dark spots in the upper portion of the carapace. These eyes become stalked at protozoea II. At protozoea III, the dorsal medain spine at the sixth abdominal segment first appears.

Figure 3: Eyestlak Ablation

Eyestalk ablation 

The removal of one (unilateral) or both (bilateral) eyestalks from a crustacean. It is routinely practiced on female shrimps (or prawns) in almost every marine shrimp maturation or reproduction facility in the world, both research and commercial. Two ways of eyestalk ablation is by incision and pressing the eye. The most commonly accepted theory is that a gonad inhibitory hormone (GIH) is produced in the neurosecretory complexes in the eyestalk. This hormone apparently occurs in nature in the non-breeding season and is absent or present only in low levels during the breeding season. By inference, then, the reluctance of most penaeids to routinely develop mature ovaries in captivity is a function of elevated levels of GIH, and eyestalk ablation lowers the high hemolymph titer of GIH. The effect of eyestalk removal is not on a single hormone such as GIH, but rather effects numerous physiological processes

Mysis Stage

Shrimp-like with the head pointing downward. Its body measures from 3.28 to 4.87 mm in total length. The telson and uropods are developed. The mysis swims in quick darts accomplished by bending the abdomen backwards. For mysis sub-stages, the most prominent change is the development of pleopods. The pleopods appear as buds at Mysis I, which protrude at Mysis II and finally become segmented at Mysis III.

Post larval Stage

The post larval resembles an adult prawn. At post larvaI the rostrum is straight and exceeds the tip of the eye.  Plumose hairs are present on the swimming legs.

THE HATCHERY FACILITIES

Larval and Post larval Tanks

Rubberized canvas, marine plywood, fiberglass, or concrete. These can either be circular, oval or rectangular, depending on the operator’s preference or financial capability. The capacity of each tank may be from 1-20 t but 10-12 t tanks are more economical and practical. Depth should only be about 1m because tanks which are too deep are difficult to manage.

Figure 4:Larval Tanks

Algal tanks

Minute plants (phytoplankton) are needed as food for the early life stages of prawn. Algal tanks must be shallow (ideally 0.5 m deep) to allow sufficient light prevention.

Spawning Tanks

It is advantageous to have smaller tanks with volumes ranging from 0.25 to 1 to where egg washing is done.

Artemia Hatching Tanks

Artemia or brine shrimp is a protein-rich live food organism given to prawn larvae starting at the Mysis stage. Artemia is available in cyst form which has to be hydrated and incubated in tanks for at least 18-24 h.

Reservoir

Storage tank is necessary for chlorination and holding of filtered and treated water for daily use. This must have a total capacity of at least 50% total larval tank volume.

Aeration System

Aeration is necessary in hatchery operations to keep food particles and algal cells in suspension and to maintain sufficient dissolved oxygen levels. Continuous aeration is essential during operations. A standby generator will be very useful during power interruptions.

Figure 5:Paddle Wheel Aerator

Preparation of Spawning, Larval, and Nursery Tanks

To prevent disease outbreak, the hatchery should be totally dried after several production runs. Tanks and facilities in the hatchery must also be cleaned well prior to a hatchery run. New tanks need to be filled with fresh or seawater for at least a week to avoid mortalities due to toxic effects of chemicals used during construction of the tanks.

Selection and Stocking of Spawners

Nauplius to be reared to the fry stage can come from broodstock wild or pond-reared immature females induced to mature by unilateral eyestalk ablation. Wild spawners female prawns caught from the sea with developed ovaries. The number of spawners needed for a hatchery runs is dependent of the nauplii requirement. For every million nauplii about 4-5 wild spawners or 7-8 m female broodstock are needed. Spawner procured as nauplii source must be carefully selected to obtain high fertilization and hatching rates of eggs. Stage of maturity should not be used as the basis for selection. Spawners must also be disease free. To ensure development of the eggs, females should be mated to ensure release of sperm cells necessary for fertilization.

Stocking of Nauplii

During stocking and throughout the culture period, prawn must not be exposed to abrupt changes in environmental conditions. The prawn must be given time to gradually adapt to new conditions to avoid stress and mortalities.

Feeding

Nauplii subsits on the yolk stored in their bodies. Larvae start to feed at the first protozoeal sub stage ( diatoms like Skeletonema or Chaetoceros) Larvae at the second protozoeal sub stage may be fed Tetraselmis. At the Mysis Stage, some fish protein must be present in the diet. Newly hatched artemia nauplii and microparticulate diets, most commonly used protein source which contain about 45-50% protein. When they reach the postlarval stage, egg custard, trash fish, mussel meat or ground dried acetes (small shrimp or alamang) can be given to supplement the Artemia nauplii diet.

Figure 6: Feeding the Prawns' Babies

Seawater Quality and Quantity

Seawater with minimum seasonal fluctuation in quality is most desirable. It should not be affected by inland discharges containing agricultural runoff or industrial wastes. Turbidity should be as low as possible. Adequate volume of seawater should be available when needed. The best method to determine the suitability of seawater for larval rearing is to conduct preliminary larval rearing experiments using pails or small tanks on the site. The production of post larvae with reasonable survival rate from eggs in a series of at least three runs would indicate the likelihood of success.