Prawn farming, also known as shrimp aquaculture, is a lucrative industry that contributes significantly to global seafood production. However, disease outbreaks remain a major challenge, leading to massive economic losses for farmers. Preventing diseases is crucial for maintaining healthy prawn stocks, ensuring high survival rates, and maximizing profitability.
This comprehensive guide explores the most common prawn diseases, their causes, symptoms, and—most importantly—effective prevention and control strategies to help farmers boost productivity and profits.
Table of Contents
1. Common Prawn Diseases and Their Symptoms
1.1 White Spot Syndrome Virus (WSSV)
Cause: A highly contagious viral infection caused by the White Spot Syndrome Virus.
Symptoms:
- White spots on the shell
- Lethargy and reduced feeding
- Reddish discoloration
- High mortality rates (up to 100% within days)
Impact: WSSV is one of the most devastating diseases, causing rapid die-offs and severe financial losses.
1.2 Early Mortality Syndrome (EMS) / Acute Hepatopancreatic Necrosis Disease (AHPND)
Cause: Bacteria (Vibrio parahaemolyticus and other Vibrio species) producing toxins.
Symptoms:
- Empty gut and pale hepatopancreas
- Slow growth
- Sudden mass mortality within 35 days of stocking
Impact: EMS can wipe out entire ponds, severely affecting production.
1.3 Taura Syndrome Virus (TSV)
Cause: Taura Syndrome Virus (Picornaviridae family).
Symptoms:
- Reddish tail and body
- Soft shells
- Lethargy and erratic swimming
- High mortality in juvenile prawns
Impact: TSV affects mostly Pacific white shrimp (Litopenaeus vannamei), reducing survival rates.
1.4 Yellowhead Disease (YHD)
Cause: Yellowhead Virus (YHV).
Symptoms:
- Yellowish head and gills
- Swollen, pale hepatopancreas
- Rapid death within 2-4 days
Impact: High mortality in post-larvae and juvenile stages.
1.5 Vibriosis
Cause: Vibrio bacteria (V. harveyi, V. alginolyticus, V. vulnificus).
Symptoms:
- Lethargy and loss of appetite
- Darkened body color
- Necrosis (tissue death) in muscles and gills
Impact: Vibriosis causes slow growth and secondary infections.
1.6 Black Gill Disease
Cause: Fungal (Fusarium spp.) or parasitic (protozoans like Zoothamnium).
Symptoms:
- Blackened gills
- Labored breathing
- Reduced growth and survival
Impact: Affects oxygen uptake, leading to stress and mortality.
1.7 Enterocytozoon Hepatopenaei (EHP) – Microsporidian Infection
Cause: Microsporidian parasite (Enterocytozoon hepatopenaei).
Symptoms:
- Slow growth (stunted)
- White fecal strings
- Loose shells
Impact: Reduces feed conversion efficiency, increasing production costs.
2. Causes of Prawn Diseases
Several factors contribute to disease outbreaks in prawn farming:
- Poor Water Quality (low oxygen, high ammonia, nitrites)
- Stress (overcrowding, sudden temperature changes)
- Contaminated Feed (carrying pathogens)
- Introduction of Infected Stock (untested post-larvae)
- Lack of Biosecurity (poor pond management)
3. Prevention and Control Strategies
3.1 Proper Pond Management
- Regular Water Quality Monitoring (pH 7.5-8.5, dissolved oxygen >4 mg/L, ammonia <0.1 mg/L).
- Adequate Aeration to prevent low oxygen stress.
- Regular Water Exchange to reduce waste buildup.
3.2 Biosecurity Measures
- Disinfect Equipment & Ponds (chlorine, iodine, or lime treatment between cycles).
- Use SPF (Specific Pathogen-Free) Post-Larvae from certified hatcheries.
- Avoid Overstocking (follow recommended stocking densities).
3.3 Feed Management
- Use High-Quality Feed (avoid moldy or contaminated feed).
- Probiotics & Immunostimulants (boost immunity, e.g., Bacillus spp.).
- Avoid Overfeeding (excess feed degrades water quality).
3.4 Disease Monitoring & Early Detection
- Regular Health Checks (look for abnormal behavior, discoloration).
- PCR Testing for viruses (WSSV, YHV, EHP).
- Isolate Infected Ponds to prevent spread.
3.5 Natural & Chemical Treatments
- Probiotics (reduce harmful bacteria like Vibrio).
- Herbal Extracts (neem, garlic – natural antimicrobials).
- Approved Antibiotics (only under veterinary guidance to avoid resistance).
3.6 Selective Breeding for Disease Resistance
- Use Genetically Improved Strains (e.g., WSSV-resistant shrimp).
4. Economic Benefits of Disease Prevention
Preventing diseases leads to:
✔ Higher Survival Rates (more prawns for harvest)
✔ Better Growth Performance (faster time to market)
✔ Reduced Medication Costs (lower expenses on treatments)
✔ Improved Feed Efficiency (lower FCR = more profit)
✔ Higher Market Prices (healthy prawns fetch premium prices)
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.