Whiteleg Shrimp Farming Protocol in Lined Ponds – PART 2

by: Nguyễn Thị Thúy Vi 01 Month 12, 2025

III. PRE-STOCKING POND PREPARATION

1. Pond Cleaning

a. Cleaning the Nursing Pond (Ao Vèo)

For newly constructed / first-time-use ponds

Use a high-pressure washer to rinse the entire liner surface to remove dust, soil, organic debris, and algae.
Scrub the liner using a soft brush or cleaning mop, especially at pond corners and around the siphon pit.
After scrubbing, spray a disinfectant solution of Chlorine (10 ppm) or KMnO₄ (2 ppm) over the liner surface, and soak the siphon pit in the solution for 1–2 hours.
Then, either fill the pond with water (if needed immediately) or sun-dry for 1–2 days.

For ponds previously used

Discharge all old water completely.
Collect and remove remaining sludge, shrimp feces, organic debris, and solid waste.
Clean the siphon pit and bottom drain pipes.
Use a high-pressure washer to remove organic slime, algae, and biofilm from the liner.
Scrub thoroughly, paying attention to corners and the siphon area.
After washing, spray Chlorine (10 ppm, or 20 ppm if previous crop had disease) or KMnO₄ (2–5 ppm) on the liner surface.
Soak the siphon pit in disinfectant for 1–2 days.
Inspect the water inlet and outlet system to ensure no blockage or algae buildup.

b. Cleaning the Grow-out Pond (Ao Nuôi)

For newly constructed / first-time-use ponds

Use a high-pressure washer to rinse the entire liner surface, removing dirt, algae, and sediment.
Scrub the liner with a soft brush, especially pond corners and siphon areas.
After scrubbing, apply Chlorine (10 ppm) or KMnO₄ (2 ppm) and soak the siphon pit for 1–2 hours.
Then fill with water or sun-dry for 1–2 days.

For ponds previously used

Discharge all old water completely.
Remove leftover solid waste: shrimp feces, dead shrimp, and accumulated sludge.
Clean the siphon pit and drainage pipes.
Use a high-pressure washer to remove slime, algae, and organic biofilm.
Scrub carefully, especially around the siphon area.
After washing, apply Chlorine (10–20 ppm) or KMnO₄ (2–5 ppm) and soak the siphon pit for 1–2 days.
For ponds previously infected with EHP:
- Spray NaOH (40 ppm) on the liner and soak the siphon pit for 1–2 days, then drain.
- Follow by applying Chlorine (40 ppm) or KMnO₄ and soak again for 1–2 days.
Check all water inlet/outlet systems to avoid blockages and biofouling.

2. Water Filling & Water Treatment

a. Water Treatment in the Raw Water Settling Pond (Ao Lắng Thô)

Function:

Pre-filter water from canals, rivers, or storage reservoirs.
Remove coarse impurities: silt, sediment, dead organics, fish eggs, large organisms.
Initial disinfection before transferring to storage ponds.

Procedure:

Filter water through 2–3 layers of thick cotton cloth or 250–300 micron mesh bags.
Set inlet and outlet at opposite corners for better settling.
Maintain a 2–3 day retention time.

Chemicals used:

KMnO₄: 3–5 ppm – disinfection, algae suppression, organic removal.
CuSO₄: 3–5 ppm – kills algae, fungi, parasites, mollusks.
PAC: 10–15 ppm – coagulates and removes organics.

b. Water Treatment in the Storage Settling Pond (Ao Lắng Chứa)

Function:

Receive water from the raw settling pond.
Disinfect, eliminate pathogens, stabilize water quality.
Reduce turbidity, remove toxic gases, stabilize pH and color.
Store water long-term before moving to the “ready” pond.

Procedure & Chemicals:

Strong disinfection using Chlorine 30–40 ppm, applied evenly.
KMnO₄: 3–5 ppm to disinfect and remove organics.
Run aerators continuously for 48–72 hours to remove chlorine residue and raise DO.
Water retention: at least 5–7 days, monitoring algae density and water clarity.

c. Water Treatment in the Ready-to-Use Settling Pond (Ao Lắng Sẵn Sàng)

Function:

Hold fully treated water before transferring to nursing or grow-out ponds.
Acts as a “buffer” to prevent shock when topping up water in culture ponds.

Procedure & Chemicals:

Disinfect using BKC (1–2 ppm) or H₂O₂ (3–5 ppm), which also helps reduce algae.
Stabilize pH, alkalinity, minerals using lime or bicarbonate.
Aerate continuously for 48–72 hours to maintain DO and reduce toxic gases.

3. Algal Bloom Conditioning (Coloring the Water) - (For systems not using biofloc)

a. In Nursing Ponds (Ao Vèo)

Natural organic method:

Ingredients: Molasses (2–3 kg) + 500 g color-forming probiotics + 50 L clean water.
Mix and ferment for 6–12 hours, then apply evenly across the pond.
Repeat if water color is not yet stable.

Advantages:
Natural, increases beneficial bacteria, limits harmful algae.

Biological coloring method:

Use specialized biological water-coloring products (probiotics + organics + minerals).
Maintain stable diatom or green algae populations; avoid blue-green algae and euglenoids.

Monitoring:

Desired water color: light brown / tea-brown (diatoms: good), or light green (acceptable).
Water clarity: 30–40 cm.
If too clear → add molasses + probiotics.
If too dark → replace 10–20% water and apply probiotics.

b. In Grow-out Ponds (without nursing ponds)

Natural organic method:

Molasses 5–7 kg, probiotics 2 bags (500 g each) + 100 L water.
Ferment 8–12 hours, apply evenly.

Biological coloring method: Same principles as ao vèo.

Monitoring: Same color and clarity standards.

4. Environmental Parameter Checklist Before Stocking

To ensure safe stocking:

pH: 7.8 – 8.2
Alkalinity: 90 – 120 mg/L
Toxic gases (NH₃, NO₂): 0
Mineral balance (Ca, Mg):
- Ca = salinity × 12
- Mg = salinity × 40
Salinity: 5 – 30‰
Water clarity: 30 – 40 cm

IV. SEED SELECTION & STOCKING METHODS

1. Methods for Selecting Postlarvae (PL)

a. Traceability of broodstock and postlarvae

Choose postlarvae with clear, verifiable origin from reputable hatcheries.
Must have:

Full disease-free certificates for broodstock and PL batches.
PCR test results confirming pathogen-free status.

This is the most important criterion in seed selection.

b. Quality inspection by visual observation

Indicators of healthy postlarvae:

Behavior: Active swimming, good mobility, strong rheotaxis (swim against the current), evenly distributed in the tank.
Appearance: Full gut line, clear body color, no deformities, complete appendages.
Reflex response: When tapping the container, PL should react quickly.
Weak, slow-reacting PL indicate poor quality.

Size & uniformity:

Whiteleg shrimp PL commonly stocked at P12–P15, length 9–11 mm, uniform size, correct developmental stage, no deformities.

Color:

Healthy PL: transparent body with brown/dark-brown pigmentation.
Pink/reddish PL: possible stress during nursing or transport.
Clean shell, no unusual discoloration → indicates good growth and molting frequency.

c. Microscopic examination

Collect 20 PL immediately upon arrival to evaluate:

Muscle opacity (tail muscle, swimmerets)
Gut-to-muscle ratio
Muscle color uniformity
Body deformities
Hepatopancreas color & structure

d. Stress test

Conduct stress assays to ensure PL robustness:

Formalin shock: 100 ppm
Salinity stress: Sudden drop to match pond salinity

Strong PL survive and recover quickly.

e. PCR testing

Ensure PL are free from major pathogens, including:

WSSV, MBV, EHP, TSV, IHHNV, HPV
Vibrio spp. (pathogenic strains)

f. Checking PL quality upon arrival

PL bags must be intact, full of oxygen, and PL swimming evenly.
Check pH & salinity in random 3 bags and compare with nursing pond salinity to decide on acclimation duration.

2. Recommended Stocking Density

a. Depending on pond type, farming model, area, salinity, and nursery duration

Nursery in floating tanks / liner ponds (100–300 m² with cover): => 1,000 – 3,000 PL/m²

Nursery in large ponds (500–1,000 m²): => 500 – 1,000 PL/m²

Biofloc nursery (with roof): => 3,000 – 5,000 PL/m²

b. Direct stocking (no nursery stage): => 200 – 300 PL/m²

3. Stocking Methods

a. Acclimation (temperature & salinity)

Steps:

Float PL bags on pond surface (or acclimation tank) for 15–20 minutes to equalize temperature.
Open the bag and add pond water gradually in increments of 10–20% each time for 30–60 minutes.
Check salinity & temperature every 15 minutes, ensure:
- Salinity difference ≤ ±2 ‰
- Temperature difference ≤ ±1°C

When PL swim actively → ready for release.

b. Best time for stocking

Early morning (5–7 AM)
Late afternoon (4–6 PM)
Avoid stocking during midday heat, heavy rain, storms, or when temperature < 26°C.

c. Stocking procedure

Cut/tear the bottom of the PL bag and release near the aeration line or paddlewheel.
If concerned about quality → release 5–10% first as a quick adaptation test.

d. Important notes during stocking

Never stock PL when:

Water environment is unstable (just colored, new algae bloom, toxic algae present).
Right after heavy rain or before storms.
Water temperature < 26°C.
Using disinfectants within 24 hours before stocking.
DO is low or toxic gases are present.

Additional recommendations: