Whiteleg Shrimp Water Quality Ranges — The Only Numbers You Need to Memorize

In whiteleg shrimp (Litopenaeus vannamei) farming, most mortality starts with water quality rather than with a pathogen. When water quality collapses, immunity drops first — and disease walks in through that gap. Knowing your daily parameters and their target ranges is the foundation of everything else. ■ Temperature — target 28–32°C Shrimp are ectothermic, so water temperature directly sets their metabolic rate. 28–32°C gives the best growth and feed conversion. Below 24°C they barely feed. Above 34°C oxygen demand rises sharply while the water's capacity to hold oxygen falls — a double risk. Keep the daily swing under 3°C. ■ pH — target 7.5–8.5 pH matters less on its own than through what it does to everything else, especially ammonia toxicity. At the same total ammonia concentration, the toxic un-ionized form (NH₃) is about 1.2% at pH 7.5 but roughly 11% at pH 8.5 — nearly a tenfold difference. A daily swing greater than 0.5 also signals a phytoplankton bloom that needs attention. ■ Dissolved oxygen (DO) — keep above 5 mg/L This is the parameter that kills fastest. Growth stops below 4 mg/L, and a few hours below 2 mg/L leads directly to mass mortality. Always measure between 04:00 and 06:00, the daily minimum. Plenty of ponds read 8 mg/L at midday and 2 mg/L before dawn. ■ Salinity — culturable at 5–35 ppt The great advantage of vannamei is its wide salinity tolerance. Culture is possible from 5 to 35 ppt, with best growth around 15–25 ppt. What matters is not the absolute value but the rate of change: a shift of more than 5 ppt in one day will kill animals that have just molted. Always re-measure after water exchange or heavy rain. ■ Ammonia (NH₃) — below 0.1 mg/L Produced as uneaten feed and waste break down. Above 0.1 mg/L you see gill damage and failed molts. As noted above, the higher the pH the more dangerous the same concentration becomes — so ammonia must always be read together with pH. ■ Nitrite (NO₂⁻) — below 1 mg/L Formed at the intermediate step of ammonia breakdown. It blocks oxygen transport in shrimp blood, so with high nitrite the animals suffocate even when dissolved oxygen looks fine. It spikes most easily in new ponds or right after disinfection, before nitrifying bacteria are established. ■ Records matter more than reference ranges Knowing your own pond's normal values beats memorizing textbook numbers. If DO was 6.2 yesterday and 5.1 today, you are still inside the range — but the trend is unmistakable. Accidents are announced when the trend begins, not when the threshold is crossed. Measure at the same time, at the same spot, every day, and write it down. Shrimp365 records these six parameters per tank and alerts you the moment a value leaves its range. Free to use.