Describe the different species suitable for prawn culture with emphasis on the methods of prawn cultivation.

Species Suitable for Prawn Culture

Prawns are broadly classified into freshwater prawns and marine/brackish water prawns (often referred to as shrimp in commercial contexts). The choice of species depends on factors like growth rate, disease resistance, market demand, and adaptability to local environmental conditions.

Freshwater Prawn Species:

These species primarily thrive in freshwater environments, though their larval stages often require brackish water.

• Macrobrachium rosenbergii (Giant River Prawn / Malaysian Prawn):
  • The most commonly cultured freshwater prawn globally and in India.
  • Known for its large size, rapid growth, and adaptability to various freshwater conditions, including ponds, lakes, and rivers.
  • Requires brackish water (around 12 ppt salinity) for larval development before juveniles are acclimated to freshwater for grow-out.
  • Can reach 25-32 cm in length.
• Macrobrachium malcolmsonii (Monsoon River Prawn):
  • The second largest fast-growing prawn in India, commonly found in rivers draining into the Bay of Bengal.
  • Cultivated in monoculture and polyculture systems.
• Macrobrachium nipponense (Oriental River Prawn):
  • Primarily farmed in large quantities in China, with some cultivation in other Asian countries.

Marine/Brackish Water Prawn Species (Shrimp):

These species are typically farmed in brackish water environments along coastal areas.

• Penaeus monodon (Giant Tiger Prawn):
  • One of the most significant cultured marine prawn species in Asia, including India.
  • Valued for its large size, high price, and fast growth rate.
  • Suitable for farming in brackish water environments and can tolerate a wide range of salinity.
• Penaeus indicus (Indian White Prawn):
  • Indigenous to the Indian Ocean, widely cultivated in India and Southeast Asia.
  • Tolerant to high temperatures and salinity fluctuations, making it suitable for coastal areas and estuaries.
• Litopenaeus vannamei (Pacific Whiteleg Shrimp):
  • Originally native to the Pacific coast of Latin America, it has gained global popularity due to its fast growth, high survival rates, disease resistance, and amenability to high-density culture.
  • Can tolerate a wide range of salinities (0.5-45 ppt) and thrives particularly well at lower salinities (10-15 ppt).
  • Specific Pathogen Free (SPF) broodstock availability is a key advantage.
• Other potential species in India: Metapenaeus ensis, M. monoceros, M. brevicornis, Penaeus semisulcatus, and P. merguiensis.

Methods of Prawn Cultivation

Prawn cultivation methods involve several stages, from seed production to grow-out and harvesting. These methods vary in intensity, from traditional extensive systems to technologically advanced intensive systems.

1. Seed Production (Hatchery Phase):

The production of healthy post-larvae (PL) is the foundation of successful prawn culture.

• Broodstock Management: Healthy adult prawns (broodstock) are maintained in controlled environments. For M. rosenbergii, berried females are preferred, often with a 4:1 female-male ratio.
• Larval Rearing: Fertilized eggs hatch into zoeae (larval stages). These larvae require specific brackish water conditions (e.g., 12 ppt for M. rosenbergii) and are fed with various items like Artemia nauplii, zooplankton, and egg custard. Water quality parameters (pH, dissolved oxygen, temperature, ammonia levels) are strictly maintained. Larvae undergo multiple molts, typically 11 stages for M. rosenbergii, before metamorphosing into post-larvae (PL). This phase usually lasts 28-35 days.
• Nursery Rearing: Post-larvae are often reared in nursery tanks, ponds, or hapa net cages for 15-60 days to grow into juveniles before stocking into grow-out ponds. This improves survival rates and leads to larger prawns at harvest.

2. Grow-out Culture Systems:

This is the main phase where prawns are grown to marketable size. Pond design, water management, feeding, and stocking density are critical.

a. Extensive Culture System:

• Characteristics: Low stocking densities (e.g., 1-4 PL/m² for freshwater prawns; 1,000-10,000 PL/ha for brackish water prawns). Relies heavily on natural food productivity in the pond.
• Pond Management: Minimal or no supplementary feeding. Water exchange is often tidal-dependent. No active water quality management or aeration.
• Yield: Lower production, typically less than 500 kg/ha/year for freshwater prawns and 100-500 kg/ha/year for brackish water prawns.
• Advantages: Low capital and operational costs, environmentally less impactful if managed correctly.

b. Semi-Intensive Culture System:

• Characteristics: Moderate stocking densities (e.g., 30,000-50,000/ha for freshwater prawns; 10,000-50,000 juveniles/ha for brackish water prawns).
• Pond Management: Combines natural food with supplementary commercial feeds. Water exchange is often controlled using pumps in addition to tidal exchange. Some aeration may be provided. Pond preparation involves filling and fertilizing to stimulate algal bloom.
• Yield: Higher production than extensive systems (e.g., 750-1,500 kg/ha in 8 months for freshwater prawns; 500-4,000 kg/ha for brackish water prawns).
• Advantages: Balanced approach between cost and production, better control over environmental factors.

c. Intensive Culture System:

• Characteristics: High stocking densities (e.g., up to 100,000/ha for freshwater prawns; 60 PL/m² or more for brackish water prawns, even up to 150/m² for L. vannamei).
• Pond Management: Relies entirely on formulated high-protein commercial feeds (50-70% of total cost). Requires strong aeration, continuous water exchange (more than 20% of total pond volume), and meticulous water quality management (pH, dissolved oxygen, ammonia, temperature). Substrates/shelters are often used to increase surface area and reduce aggression.
• Yield: Very high production (e.g., 4-6 tonnes/ha in 4-5 months for brackish water prawns; 10-12 tonnes/ha/crop for L. vannamei).
• Advantages: Maximizes production per unit area, high profitability.
• Challenges: High capital and operational costs, increased risk of disease outbreaks, significant waste generation.

d. Other Cultivation Methods:

• Polyculture with Fish: Prawns (especially freshwater species like M. malcolmsonii and M. rosenbergii) are grown alongside compatible fish species (e.g., Indian Major Carps, Chinese carps, Tilapia). This enhances resource utilization and can lead to synergistic benefits. For instance, M. malcolmsonii at 10,000-20,000/ha with carps at 2,500-3,500/ha can yield 300-400 kg prawn and 2,000-3,000 kg carps/ha/year.
• Cage and Pen Culture: Involves placing cages or pens in open water bodies like rivers, lakes, or coastal waters. Suitable for areas with limited land. Stock management can be by batch or cull-harvesting.
• Biofloc Technology (BFT): An advanced system that promotes the growth of beneficial microbial flocs (aggregates of bacteria, algae, protozoa, and organic particles) in the culture water. These flocs serve as natural food and help maintain water quality by consuming waste products, reducing the need for water exchange.
• Recirculating Aquaculture Systems (RAS): Closed systems where water is continuously treated and reused. This minimizes water usage and allows for strict control over environmental parameters, reducing disease risk and environmental impact. It includes solids filters, biofilters for nitrification, and denitrification units.

3. Pond Preparation and Management for Grow-out:

Regardless of the system, certain practices are common:

• Site Selection: Ponds require good water retention (clay or loam-based soil, pH 6.5-8.5), access to quality water, and protection from flooding.
• Pond Construction: Ponds are typically 0.5-1 ha in size with depths of 1.5-2.0m, designed with a gradual slope for efficient drainage and harvesting. Embankments should be high enough to prevent prawn migration.
• Pond Preparation: This involves drying the pond bottom, liming to adjust pH, filling with water, and fertilizing to promote natural food organisms. Predator and weed fish eradication is crucial.
• Stocking: Healthy, disease-free post-larvae or juveniles (PL 15-20) are procured from reliable hatcheries and stocked at appropriate densities.
• Feeding: Commercial pelleted feeds are provided, with feeding rates adjusted based on prawn size, density, and water quality. Feed conversion ratio (FCR) is an important economic factor.
• Water Quality Monitoring: Regular monitoring of parameters like dissolved oxygen, pH, temperature, salinity, ammonia, and nitrite is essential to prevent stress and disease. Aerators and water exchange are used to maintain optimal conditions.
• Disease Management: Biosecurity measures, use of SPF broodstock, proper pond hygiene, and early detection are crucial.
• Harvesting: Prawns are typically harvested after 4-8 months, depending on the species and desired size. Methods include draining the pond (batch harvesting) or using seine nets for continuous harvesting (cull-harvesting).