What will happen in your shrimp pond during raining
By Dr.Wiphada Mitbumrung, Ph.D. Applied Marine Biosciences — Wed Jul 01 2026
Heavy rainfall, especially during the monsoon season, can significantly impact water quality and bottom conditions in outdoor shrimp grow-out ponds, making it essential for farmers to understand these processes and be prepared to manage the associated risks. The monsoon brings prolonged periods of rain, fluctuating salinity, and increased organic load, all of which can stress shrimp and elevate disease risks. Rainfall intensity can be classified into three categories: light rainfall (brief showers lasting less than 1 hour or drizzle for 1–3 hours), moderate rainfall (continuous showers lasting 1–3 hours), and heavy rainfall (prolonged showers exceeding 3 hours). Each level of rainfall requires specific management responses, including appropriate treatment dosages, to maintain stable pond conditions, prevent bottom deterioration, and safeguard shrimp health throughout the rainy season.
Mineral
Mineral dilution is a common consequence of increased freshwater input from rainfall, which lowers both the mineral concentration and salinity in shrimp ponds. This shift can elevate the proportion of toxic un-ionized ammonia (NH₃), making ammonia more harmful to aquatic organisms. As mineral levels drop, shrimp struggle to regulate mineral uptake, increasing the risk of deficiencies that may lead to soft shells, incomplete molting, and overall stress.
pH
Rainwater typically has a low pH of around 6.2–6.4 due to the dissolution of atmospheric CO₂, which forms carbonic acid. When this acidic rain enters shrimp ponds, it can lower the overall pH of the water, triggering molting in shrimp. This sudden molting increases vulnerability to cannibalism and stress. Additionally, the sudden drop in pH often leads to mass die-offs of phytoplankton, whose cellular contents (rich in simple sugars) are released into the water through autolysis. These sugars drive a rapid bloom of heterotrophic bacteria, which consume large amounts of dissolved oxygen through aerobic respiration. This process produces more CO₂, which further leads to a critical situation where pH continues to decline until phytoplankton populations recover and re-stabilize the pond ecosystem.
Turbidity
Rain increases suspended solids in shrimp ponds due to the erosion of soil from pond levees. Strong winds can stir up bottom sludge, releasing toxic hydrogen sulfide (H₂S) under anaerobic and low pH conditions. The oxidation-reduction potential (ORP) of the sludge becomes negative, promoting the reduction of compounds such as sulfates into H₂S, which is highly toxic to shrimp as it disrupts the oxidation step in aerobic respiration. As a result, the pond bottom becomes an unfavorable environment during rainfall. However, shrimp often gather at the pond bottom during rain to escape the stress caused by the noise of raindrops hitting the water surface. This behavior coincides with reduced dissolved oxygen levels near the pond bottom, leading to increased competition for oxygen and a heightened risk of H₂S toxicity.
Temperature
Rain typically has a temperature 5–6°C lower than the surrounding environment, which can cause pond water temperatures to drop by 3–5°C. In response to thermal stratification, shrimp tend to migrate toward deeper pond areas where temperatures and salinity are more stable. Additionally, due to the lower density of rainwater, a cold freshwater layer can form above warmer, saltier water, creating a halocline that slows solar heating and prolongs stratification. As cold-blooded animals, shrimp have body temperatures that are directly affected by environmental conditions; thus, lower temperatures from rainfall reduce their appetite and metabolic activity. A 1°C decrease in water temperature can reduce shrimp feed consumption by 5–10%. If normal feed rations are maintained during these conditions, uneaten feed accumulates and undergoes bacterial decomposition, further lowering pH and increasing biological oxygen demand (BOD). Thermal stratification and competition for oxygen not only stress shrimp but also reduce the activity of decomposing bacteria, leading to the accumulation of organic matter.
Dynamic of phytoplankton and bacteria
After heavy rainfall, high levels of suspended solids in the pond reduce sunlight penetration, often leading to sudden crashes in phytoplankton populations. When temperatures rise again, a massive bloom of heterotrophic bacteria typically follows, driven by the abundance of organic material from dead algae settling on the pond bottom. These bacteria, responsible for decomposing organic matter, proliferate rapidly due to the increased availability of nutrients. As decomposition intensifies, oxygen consumption rises sharply in an already low-oxygen environment. This results in a continuous decline in dissolved oxygen levels, regardless of the time of day. The high BOD from heterotrophic bacteria, combined with the absence of oxygen production from now-dead autotrophic organisms, worsen the situation. Under these stressed conditions, pathogenic bacteria may outcompete beneficial microbes, increasing the risk of disease outbreaks. If shrimp are already weakened by sudden environmental changes, their susceptibility to infections rises significantly.
Recommendation for monsoon season:
1. If during production there are precipitations, mineral applications are required to reduce the impact of water dilution from rainfall. Dosage should be adjusted according to the rainfall intensity.
2. Probiotic application should be stopped during the rainy day.
3. Feeding rate will be reduced 20% after light and moderate rainfall, while after heavy rainfall feeding will be postponed until the conditions in the pond stabilize.
4. Turning on additional aerators is strongly recommended during moderate and heavy rainfall.
Blue Aqua product application:
How Rainfall Disrupts Shrimp Pond Balance
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