Prawn farming is a lucrative agribusiness with high demand in both local and international markets. However, profitability depends significantly on the timing of harvest. Harvesting prawns at the right time ensures optimal size, weight, and market price while minimizing production costs. This article explores the best time to harvest prawns for maximum profit, considering biological, environmental, and economic factors.
Table of Contents
Factors Influencing the Optimal Harvest Time
Several key factors determine the best time to harvest prawns:
- Growth Rate and Size
- Water Temperature and Seasonality
- Feed Conversion Ratio (FCR) and Feed Costs
- Market Demand and Prices
- Mortality Rates and Disease Risks
- Harvesting Methods and Labor Costs
Each of these factors plays a crucial role in determining the most profitable harvest window.
1. Growth Rate and Size: When Do Prawns Reach Optimal Market Size?
Prawns grow in stages, and their market value increases with size. The ideal harvest time depends on the species:
- Giant Tiger Prawns (Penaeus monodon) – Typically reach market size (25-30g) in 4-6 months.
- Whiteleg Shrimp (Litopenaeus vannamei) – Faster growing, reaching 15-20g in 3-4 months.
- Freshwater Prawns (Macrobrachium rosenbergii) – Take 5-7 months to reach 30-50g.
Key Considerations:
- Economic Threshold: Harvesting too early results in smaller, lower-value prawns.
- Diminishing Returns: After a certain size, growth slows, increasing feed costs without proportional price gains.
- Size Grading: Larger prawns (U/10 or U/15 counts) fetch premium prices in export markets.
Optimal Strategy: Monitor growth weekly and harvest when 70-80% of the stock reaches the target size.
2. Water Temperature and Seasonality: How Climate Affects Harvest Timing
Prawns are ectothermic (cold-blooded), meaning their metabolism depends on water temperature.
Ideal Temperature Ranges:
- 26-32°C (79-90°F) – Optimal for growth.
- Below 20°C (68°F) – Growth slows significantly.
- Above 34°C (93°F) – Stress and mortality increase.
Seasonal Harvesting Strategies:
- Tropical Regions: Year-round farming with multiple harvests.
- Subtropical/Temperate Regions: Single harvest before winter to avoid cold-induced slowdowns.
- Monsoon Impact: Heavy rains dilute salinity and increase disease risk; harvest before monsoon peaks.
Best Practice: In seasonal climates, stock early (spring) and harvest in late summer/early autumn.
3. Feed Conversion Ratio (FCR) and Feed Costs: Balancing Growth and Expenses
Feed accounts for 50-70% of production costs. The Feed Conversion Ratio (FCR) measures efficiency:FCR=Total Feed GivenTotal Weight GainedFCR=Total Weight GainedTotal Feed Given​
- Early Growth Phase (1-2 months): Low FCR (1.2-1.5) – Efficient growth.
- Late Growth Phase (3+ months): FCR increases (1.8-2.5+) – Slower growth, higher costs.
When to Harvest for Best FCR?
- Economic Optimum: Before FCR exceeds 1.8 for vannamei or 2.0 for monodon.
- Partial Harvesting: Remove larger prawns first to reduce competition and improve FCR for remaining stock.
Profit Tip: Use feeding curves to predict when growth plateaus and plan harvests accordingly.
4. Market Demand and Prices: Timing for Peak Profit
Prawn prices fluctuate based on:
- Festival Demand (Chinese New Year, Christmas, Ramadan) – Prices spike.
- Global Supply (Disease outbreaks in major producers like Ecuador, India, Vietnam) – Export opportunities arise.
- Local Competition (Harvest surges in region) – Prices may drop.
Strategies to Maximize Profit:
- Pre-Festival Harvest: Supply markets before major holidays.
- Avoid Oversupply Periods: Check competitor harvest cycles.
- Export Market Alignment: Harvest when international buyers (US, EU, Japan) have shortages.
Example: Harvesting vannamei in November-December catches high Western holiday demand.
5. Mortality Rates and Disease Risks: Avoiding Losses
Prawn farming faces disease threats like:
- White Spot Syndrome Virus (WSSV)
- Early Mortality Syndrome (EMS)
- Bacterial Infections (Vibrio spp.)
When to Harvest to Minimize Losses?
- Before Disease Outbreaks: Common in monsoon season or temperature fluctuations.
- At First Signs of Stress: Reduced feeding, surface swimming, or discoloration.
- Before Overcrowding: High stocking density increases disease transmission.
Preventive Approach:
- Regular water quality checks (ammonia, nitrites, oxygen).
- Harvest in batches to reduce stress.
6. Harvesting Methods and Labor Costs: Efficiency Matters
Harvesting can be partial (selective) or total (complete drain).
Best Practices for Cost-Effective Harvesting:
- Partial Harvesting: Remove larger prawns first, allowing smaller ones to grow further.
- Night Harvesting: Prawns are more active, reducing stress and improving survival.
- Mechanical Harvesting (Pump Systems): Reduces labor costs in large farms.
Optimal Timing:
- Early morning or late evening to avoid heat stress.
- During low tide (for coastal farms) to ease water drainage.
Here are ten frequently asked questions (FAQs) about prawns:
1. What is the difference between prawns and shrimp?
Prawns and shrimp are different crustaceans. Prawns have three pairs of claw-like legs, while shrimp have two. Prawns also have branching gills and a straighter body compared to shrimp.
2. Are prawns healthy to eat?
Yes, prawns are a good source of protein, low in fat, and rich in omega-3 fatty acids, vitamins (B12, E), and minerals (selenium, zinc). However, they contain cholesterol, so moderation is advised for some diets.
3. How can I tell if prawns are fresh?
Fresh prawns should have a firm texture, a mild ocean-like smell (not fishy), and a translucent appearance. Avoid prawns with black spots, a slimy texture, or a strong ammonia odor.
4. How should I store fresh prawns?
Keep fresh prawns in the coldest part of the fridge (0–4°C) and use them within 1–2 days. For longer storage, freeze them in an airtight container for up to 3 months.
5. Can you eat prawns raw?
Raw prawns can carry parasites or bacteria, so it’s safer to cook them thoroughly. If consuming raw (e.g., in sushi), ensure they are sashimi-grade and properly frozen to kill pathogens.
6. How do you peel and devein prawns?
- Remove the head (if attached).
- Peel off the shell, leaving the tail if desired.
- Make a shallow cut along the back and remove the dark digestive tract (vein) with a knife or toothpick.
7. What’s the best way to cook prawns?
Prawns cook quickly (2–3 minutes per side) and can be grilled, boiled, fried, or sautéed. Overcooking makes them rubbery—they’re done when they turn opaque and pink.
8. Why do prawns turn pink when cooked?
The color change is due to a protein called astaxanthin, which is naturally present in prawns but bound to other molecules. Heat releases astaxanthin, turning the prawns pink.
9. Are prawns safe for people with shellfish allergies?
No. Prawns are shellfish, and people with shellfish allergies should avoid them as they can trigger severe allergic reactions.
10. Are farmed or wild-caught prawns better?
- Wild prawns are often considered tastier but may have sustainability concerns.
- Farmed prawns can be more eco-friendly if responsibly sourced (look for certifications like ASC or MSC), but some farms use antibiotics or harm mangroves.