EHP Eradication in Shrimp Ponds: Benthic Remediation Strategy

II. The Three-Step Benthic Eradication Protocol: From Mechanical Removal to Chemical Disinfection, Constructing an Absolute Biosecurity Barrier

EHP spores possess extreme biochemical resistance, rendering conventional high-pressure water-gun rinsing and standard agricultural lime applications completely ineffective. Cultivators must rigorously execute a standardized three-step protocol: Mechanical Desilting Thermal Liming $\rightarrow$ Solar Desiccation. This integrated regime creates a triple-action eradication system combining physical extraction, chemical denaturation, and natural ultraviolet radiation.

Step 1: Mechanical Desilting—Physical Removal of 10–20 cm of Anoxic Black Sludge (Mandatory FAO Standard)

High-pressure water hoses only clean the superficial layer of the pond bottom, leaving EHP spores hidden deep within the soil matrix and interstitial crevices untouched. Operations must strictly conform to the biosecurity specifications of the Food and Agriculture Organization (FAO) by executing thorough physical desilting based on pond morphology:

1. Earthen Ponds:
   Deploy excavators or bulldozers to mechanically dredge and completely remove the 10–20 cm thick layer of black organic sludge. This specific zone represents the primary accumulation reservoir for EHP spores, organic matter, and subterranean toxins. The excavated sludge must be transported completely outside the aquaculture facility for isolated treatment; discharging it into public water systems is strictly prohibited to prevent cross-contamination.
2. HDPE-Lined / Tarpaulin Ponds:
   Focus intensity on overlooked critical biological dead zones, including pond corners, tarpaulin liner welding seams, and sub-surface aeration pipelines. Scrape away all adhered organic bio-fouling and trapped spore matrices to clear any physical obstructions prior to chemical disinfection.

Core Efficacy: This step physically eliminates over 90% of the ambient pathogen load and organic burden at the source, allowing subsequent thermal liming to achieve maximum chemical efficacy.

Step 2: Thermal Liming (Quicklime, CaO) Treatment—Hyper-Alkalinity and Exothermic Synergy for Dual-Action Spore Inactivation

Standard agricultural lime or hydrated lime lacks sufficient alkalinity to destroy EHP spores and merely acts as a pH regulator. Only quicklime (burnt lime, CaO) can induce complete spore inactivation through the simultaneous generation of hyper-alkaline conditions and intense exothermic hydrolysis.

Dr. Tran Huu Loc from the ShrimpVet Research Center in Vietnam has verified the following clinical baseline:

• The Critical Threshold for EHP Spore Inactivation: Environmental Quicklime application is the only practical method capable of establishing and maintaining this hyper-alkaline standard in open ponds.

Precision Operational Specifications:

1. Dosage Optimization:
   For ponds with a confirmed historical baseline of EHP infection, apply a strict dosage of 6 metric tons per hectare (600 kg per 1,000 m²). High volumetric dosing is required to ensure complete chemical penetration.
2. Critical Execution Technique (Dry-Bed Application Mandate):
   Completely drain the pond. Maintain the benthic soil in a moist, humid state (20% to 30% soil moisture; loose texture with zero standing water blocks) before uniformly broadcasting the quicklime across the entire basin.
3. Exothermic Reaction:
   The chemical reaction between CaO and residual soil moisture triggers rapid hydrolysis, driving localized soil temperatures up to 70–80°C while generating a hyper-alkaline matrix of $\text{pH} \approx 12$. This dual-action stress denatures the spore structure.
4. Biological “Suicide Lure” Mechanism:
   The hyper-alkaline environment triggers a false physiological cue, forcing the EHP spores to prematurely extrude their polar filaments. Deprived of a live shrimp host to parasitize, the exposed microsporidians die rapidly. This represents the most efficient biological inactivation mechanism currently available.
5. Mandatory Soil Tilling:
   Immediately following the quicklime application, deep-till or plow the soil to incorporate the chemical into the deep sub-surface layers. This prevents superficial-only disinfection and ensures spores sequestered deep within the soil profile are neutralized.

Step 3: Intense Solar Desiccation—Ultraviolet and Residual High-pH Synergy for Final Reservoir Elimination

Driven by tight commercial crop turnarounds, farmers frequently bypass the drying phase. However, solar UV radiation remains the most cost-effective and biologically powerful natural disinfectant available, as certified by the Central Institute of Brackishwater Aquaculture (CIBA) in India.

1. Desiccation Standards:
   Following the quicklime treatment, expose the pond bottom to direct, unobstructed sunlight for 20 to 30 days continuously, until the soil surface displays desiccation cracks measuring 1–2 cm in width and 5–10 cm in depth.
2. Multidimensional Biosecurity Values:
    

   • Direct Irradiation: Solar ultraviolet rays directly destroy residual EHP spores, opportunistic pathogenic bacteria, and harmful macro-biological or parasitic egg reservoirs.
   • Synergistic Eradication: The interaction between residual high-pH soil matrices and extreme dryness completely deactivates any remaining latent pathogens.
   • Substrate Remediation: This phase restores soil porosity, accelerating the oxidation and degradation of hazardous gaseous compounds like hydrogen sulfide and ammonia nitrogen , which drastically mitigates environmental stress risks for the subsequent stocking cycle.