Culture of Giant Fresh Water Prawn

Dharmendra Kumar Meena*., A. K. Sahoo*., Debabrata Panda* and B.K Bahera*.

*Central Inland Fisheries Research Institute, Barrackpore, Kolkata, 700 120

Corresponding author: Dharmendra Kumar Meena

* Email : dkmeenafnb@gmail.com

Macrobrachium rosenbergii, commonly known as giant freshwater prawn and forms a priced commodity among the species from freshwater aquaculture. The species distribute in the major river systems of the country, while many estuaries form a high potential ground for the breeding. Till past few decades the species was being cultured traditionally with the seed collection from the natural river resources. But in the recent years the culture of giant freshwater prawn has expanded significantly both in area under culture i.e 43,395 ha from 12,022 ha and number of hatcheries established, as the onset of white spot diseases in tiger shrimp.

In addition to the disease resistance to white spot, the species has many advantages such as i) high growth rate compared to other freshwater prawn ii) can be cultured under freshwater to saline zone upto 10 ppt iii) can be cultured as monoculture or mixed culture with carp fishes iv) market rate is always higher compared to fishes.

Morphology of Giant Fresh Water Prawn

The general external anatomy of the freshwater prawn M. rosenbergii, and provides some notes on the function of various major parts of the body. Internal morphology (circulatory, respiratory, digestive, excretory, reproductive and nervous systems) is not covered in this manual, which concentrates on farming, but further information is available in the references cited in the introduction to this section.

Freshwater prawn eggs of this species are slightly elliptical, with a long axis of 0.6-0.7 mm, and are bright orange in colour until 2-3 days before hatching when they become grey-black. This colour change occurs as the embryos utilize their food reserves.

Most scientists accept that the larvae go through 11 distinct stages (Uno and Kwon 1969) before metamorphosis, each with several distinguishing features which are described and illustrated in Annex 1. However, from stage VI onwards their size is variable, which has led to some workers, notably Ling (1969) to describe only eight stages. Stage I larvae (zoeae) are just under 2 mm long (from the tip of the rostrum to the tip of the telson). Larvae swim upside down by using their thoracic appendages and are positively attracted to light. By stage XI they are about 7.7 mm long. Newly metamorphosed postlarvae (PL) are also about 7.7 mm long and are characterized by the fact that they move and swim in the same way as adult prawns. They are generally translucent and have a light orange-pink head area.

The body of postlarval and adult prawns consists of the cephalothorax ('head') and the abdomen ('tail'). The bodies of freshwater prawns are divided into twenty segments (known as somites). There are 14 segments in the head, which are fused together and invisible under a large dorsal and lateral shield, known as the carapace. The carapace is hard and smooth, except for two spines on either side; one (the antennal spine) is just below the orbit and the other (the hepatic spine) is lower down and behind the antennal spine. The carapace ends at the front in a long beak or rostrum, which is slender and curved upwards. The rostrum extends further forward than the antennal scale and has 11-14 teeth on the top and 8-10 underneath (Figure 1). The first two of the dorsal (top side) teeth appear behind the eye socket (orbit).

The front portion of the cephalothorax, known as the cephalon, has six segments and includes the eyes and five pairs of appendages. The final three of these six segments can be seen if the animal is turned upside down and the appendages of the thorax (see below) are moved aside. The cephalon segments therefore support, from the front of the animal:

• Stalked eyes;

• The first antennae, which each have three-segment peduncles (stalks) from which three tactile flagella emerge;

• The second antennae, which each have five-segment peduncles and a single, long flagellum;

• Mandibles, which are short and hard and are used to grind food;

• The first maxillae, which are plate-like (lamelliform), hidden below the second maxillae, and used to transfer food into the mouth; and

• Second maxillae, which are similar to the first maxillae but have an additional function. Part of these appendages are constantly beating, thus producing a current of water through the gill chamber to promote the respiratory function of the latter.

The two pairs of antennae are the most important sites of sensory perception; the peduncles of the first antennae contain a statocyst, which is a gravity receptor. The mandibles and first and second maxillae form part of the six sets of mouthparts (see below).

The rear portion of the cephalothorax, known as the thorax, consists of 8 fused segments which have easily visible pairs of appendages. These appendages consist of 3 sets of maxillipeds and 5 pairs of pereiopods, as follows:

• The first and second maxillipeds are similar to the first and second maxillae and function as mouthparts (see above);

• The third maxillipeds, which are also mouthparts but look rather like legs;

• First and second legs (pereiopods), which have pincers (chelae). These pincer-ended legs are also called chelipeds. The first legs are slender but the second pair bear numerous small spines and are much stronger than any other leg. The second chelipeds are used for capturing food, as well as in mating and agonistic (fighting) behaviour; and

• Third, fourth and fifth legs (pereiopods), which are much shorter than the second cheliped, have simple claws (not pincers), and are sometimes called walking legs. Eggs are extruded from oval gonopores in the base of the third pereiopods of females, which are covered with a membrane. In males, sperm is extruded from gonopores which are covered by flaps, situated in the base of the fifth pereiopods.

The pereiopods include chemoreceptor cells, which are sensitive to aqueous extracts of food and to salts (and may therefore be involved in migratory and reproductive processes). The left and right second legs (chelipeds) of M. rosenbergii are equal in size, unlike some other Macrobrachium spp. In adult males they become extremely long and reach well beyond the tip of the rostrum..

The tail (abdomen) is very clearly divided into 6 segments, each bearing a pair of appendages known as pleopods or swimmerets (as this name implies, they are used for swimming, in contrast to the walking legs). The first five pairs of swimmerets are soft. In females they have attachment sites for holding clusters of eggs within the brood chamber (see below). In males, the second pair of swimmerets is modified for use in copulation. This spinous projection is known as the appendix masculina. The sixth pair of swimmerets, known as uropods, are stiff and hard. The telson is a central appendage on the last segment and has a broad point with two small spines which project further behind the point. The telson and the uropods form the tail fan, which can be used to move the prawn suddenly backwards.

Differences between male and female Giant Fresh Water Prawn

1. Mature male prawns are considerably larger than the females

2. Male have Second chelipeds are much larger and thicker than female.

3. The head of the male is also proportionately larger, and the abdomen is narrower. The head of the mature female and its second walking legs are much smaller than the adult male.

4. A ripe or 'ovigerous' female can easily be detected because the ovaries can be seen as large orange-coloured masses occupying a large portion of the dorsal and lateral parts of the cephalothorax.

5. Male have three morphomites whereas incase of female there is no such distinction.

6. Male gonophores are situated at the base of 5^th pereopods incase of female it is at 3^rd pair of pereopds.

7. Male has central lump on fisrt abdominal somite but female does not.

8. Male has appendix masculina but female has brood chamber.

For culture of giant freshwater prawn, more focus should be given on the following points

Site selection and farm construction:

Selection of suitable site is pre-requisite for establishing a prawn farm. Farming site should be connected to approachable road for transportation of seed, fertilizers, feeding materials, farm equipment. Soil and water testing may be carried out before farm construction for assessing the productivity status, water holding capacity of the soil. Sandy-clay or sandy loam soil is suitable. For establishing the prawn farm the pond should be prepared in such a way that entire water may be drained out. The pond size can ideally vary between 0.1 and 1 ha area. Since prawns are migratory in mature, they try to migrate from one pond to other during rainy days and cool weather.

Therefore the bund height of the pond should be at least 0.5 m above the water level. While the depth of pond should not be more than 1.5 m, as it affects the growth of prawn. Layering the bottom of the pond with sand or small pebbles with hide outs helps in movement and shelter to the prawn, leading to the increase in production capacity.

Preparation of pond:

To kill the unwanted fishes Mahua oilcake is applied @ 2,500 kg/ha. Alternatively combination of urea @ 100kg and bleaching powder @ 200 kg/ha can also be used, with urea applied 18 h before the bleaching powder application. In a newly excavated pond 5-7 tonnes cow dung/pig manure and 200-500 kg lime/ha should be applied. To maintain the planktonic population in the pond, organic and inorganic fertilizers like poultry droppings, pig and cow manure may be applied after stocking of juveniles at periodical intervals. In prawn farming Calcium form an important component in moulting process. Therefore after a heavy shower calcium level in the water may decrease which is signaled by lowering of water pH. If the pH decreases below 6.5, the molting process is arrested. For this purpose, 50 kg lime/week should be applied to maintain calcium balance in water.

Prawns are cannibalistic in nature and having territorial behavior. During starvation they attack the weaker members of their own group. To prevent such situations special arrangements may be made by providing hide outs during moulting time. Water hyacinth can be kept in the pond under bamboo frame. Apart from this large palm leaves, plastic pipes, small asbestos sheets can also be used.

Rearing of postlarvae in nursery:

It is observed that releasing the post-larvae directly into the pond results in poor survival, emphasizing raising the PL in nursery pond till 30-50mm.

Concrete tanks are usually used for nursery cycle. Complete drainage of water from such nursery tanks helps for easy harvesting of the juveniles. Earthen ponds are not suitable for nursery rearing as continuous aeration makes the water muddy, beside wastage of feed through mixing with the mud and its further decomposition leading to decrease in dissolve oxygen levels and microbial infection. As soon as the postlarvae becomes juveniles, they should be reared in low saline water of 3-7%0. Before stocking of juveniles in rearing ponds physic-chemical parameters of the water like Dissolve oxygen, temperature, pH, NH₄, Ca⁺² , and Mg⁺² should be analysed and need to be kept within desire limit. Depending upon the water volume 5-10 PL/lt should be stocked for 2-4 weeks. During these period provision of shell strings has to be made so that they can hide while moulting. Groundnut oilcake, small mussel, chicken feed, fish meal with 30-40% protein may be used as feed. Juveniles attain 40-60mm within a rearing period of 2-4 weeks,

which can be transferred to the grow-out ponds. Starting from breeding to larval rearing one complete cycle requires around 2-3 months.

Rearing into grow-out ponds:

On arrival at the pond bank utmost care should be given to acclimatize the juveniles to the temperature by floating the transport bags in the pond for 15 minutes before emptying them into the water (as shown in figure). Severe mortalities can be caused not only by thermal shock but also by sudden changes in pH. If the water pH is more than 0.5 pH units different from the pH in the juvenile holding tank or the nursery ponds, acclimatize the juveniles to this pH level slowly (over a one-day period) in nursery before transporting and stocking them at the grow-out pond. Generally for better growth in semi-intensive, stocking rates vary between 4 and 20 PL/m2 (40 000-200 000/ha). In stagnant water where facility for water exchange is is not available stocking density should be kept between 30,000 to 50,000 juveniles/ha. During these period 30-40% crude protein out of which 50 % should be from animal origin and 50% from plant origin is given as diet. The feed is provided @ 3-10% of the standing biomass/day in two rations during morning and evening.

In addition to feed, suitable water conditions also required for better growth and survival i.e temperature 26-32⁰C, pH 7-8.5, DO > 2.5 ppm, total hardness 100-150 ppm, calcium 30-80 ppm, phosphorus 0.01-0.9 ppm and nitrogen 0.05-0.5 ppm. Any imbalance of these parameters affects the growth as well as production. Prawn being a bottom dwelling animal, the optimum growth and development depends upon the pond soil, which should be alkaline. Therefore to make soil fertile, fused lime should be applied.

The culture practice of M. rosenbergii may be categorized as i) monoculture ii) polyculture iii) integrated culture

Monoculture of M. rosenbergii:

A stocking rate of about 4 juveniles/ m2 (40 000/ha) is recommended for the monoculture of Macrobrachium rosenbergii. There are some advantages in using larger juveniles for stocking. For example, it has been demonstrated that increasing the average stocking weight at 4 animals/m2 from 0.17 g to 0.75 g increases production at harvest by nearly 30%. However, this stocking size advantage does not apply indefinitely; research has shown that stocking 3 g animals did not improve production because the animals matured too rapidly. In addition, grading nursed juvenile prawns before stocking also has significant advantages under monoculture practice. It has been found to increase average harvest size and total pond production. Size grading is a way of separating out the faster growing prawns and lowering the suppression of growth that they cause to other prawns; it can also result in improved feedconversion ratios (FCR). Another means of improving in production freshwater prawn culture is to place artificial substrates in the ponds, which makes it feasible to increase stocking rates above the level recommended earlier for ponds without substrates. PVC fencing. The above points are more effective in increasing the higher production under monoculture.

Polyculture of M. rosenbergii:

Records exist of the polyculture of various Macrobrachium species in combination with single or multiple species of fish, including tilapias, common carp, Chinese carps, Indian carps, ,mullets, ornamental fish. Other combinations may be feasible. The inclusion of freshwater prawns in a poly-culture system almost always has synergistic beneficial effects, which include:

• more stable dissolved oxygen levels

• reduction of predators

• coprophagy (the consumption of fish faeces by prawns), which increases the efficiency of feed

• greater total pond productivity (all species) and the potential to increase the total value of the crop by the inclusion of a high-value species.

Integrated culture with M. rosenbergii:

The wastewater from ponds containing prawns being reared in monoculture or polyculture with fish can be used for the irrigation of crops. Prawns can also be reared in paddy fields, without depressing rice production. This has proved especially valuable in Viet Nam, where it has been shown that the income from prawns in integrated rice-prawn culture can be two or three times as great as that from the cultivation of rice. The introduction of freshwater prawns reduces the area devoted to rice paddy (because deeper areas where prawns can shelter when the rice field is dry have to be provided). It also reduces weeding costs (prawns eat weeds) and fertilization costs.

Prawns being a high value commodity and possessing great potential for export offer greater scope for their larger scale adoption both under monoculture and polyculture. In India, MPEDA is providing incentives and technical assistance for the development of prawn farming, greater R&D interventions and credit support given in recent years is expected to boost the growth of prawn seed production and farming in the country.