Low Shrimp Survival or Sudden Mortality: How to Investigate the Cause

Short answer: treat low shrimp survival as an investigation, not a guess. First protect the remaining stock and call your aquatic animal-health professional if animals are dying now. Then rebuild the facts for the affected cohort — species, postlarvae (PL) source, stocking date, count and density, survival by stage, feeding and biomass estimates — and line them up against trends in dissolved oxygen, temperature, salinity, pH, ammonia, nitrite and power or aeration events. Only a qualified professional, usually with laboratory testing, can confirm a disease.

Educational guide, reviewed 13 October 2026. It gives no diagnosis, medicine or chemical advice, and no universal water-quality targets: acceptable ranges depend on species, life stage, system and your local expert protocols.

What should you do first when shrimp start dying?

• Check aeration, power supply and dissolved oxygen in the affected pond or tank immediately, and log the reading with time and location.
• Contact your aquatic animal-health professional or diagnostic laboratory and ask how to collect and preserve samples. Do not improvise sampling for disease testing.
• Check your country's reporting rules. Diseases listed by the World Organisation for Animal Health (WOAH Aquatic Code) are reported through national authorities, and local rules may add others.
• Pause non-essential movement of shrimp, water, nets and equipment between units until advised otherwise.
• Do not start medicines, disinfectants or other chemical treatments without a professional diagnosis and local approval.

How do you define the affected cohort and the size of the loss?

A survival figure is only as reliable as the counts behind it. Write down the cohort before discussing causes:

Estimated survival is usually back-calculated from biomass: estimated biomass divided by average sampled weight gives an estimated count. Small errors in either number move survival a lot, so record how both were measured. The biomass calculator shows the arithmetic, and the shrimp survival and profit calculator shows how different survival assumptions change harvest volume — neither replaces a count.

Which water-quality trends should be pulled for the event?

Look at trends across the days before the event, not a single reading. FAO's shrimp pond manual explains how salinity, temperature, dissolved oxygen, pH and nitrogen compounds affect shrimp growth and survival (FAO water quality management). It is a legacy training manual written for pond culture, so use it for principles and take limits from current species- and system-specific guidance.

• Dissolved oxygen, especially night and dawn readings, with the measurement depth and position.
• Temperature, salinity and pH, including the daily pH swing in ponds.
• Total ammonia nitrogen and nitrite; ammonia toxicity changes with pH and temperature, so record them together.
• Locally relevant parameters your protocol already measures, such as alkalinity, transparency or plankton condition, hydrogen sulphide or rainfall.
• Instrument calibration dates, so a sensor fault is not mistaken for a water event.

Did power, aeration, water exchange or handling change before the losses?

Many investigations turn on timing. Build a timeline that places mortality against operational events:

Comparing affected and unaffected units that share water, feed or PL batches is often more informative than any single reading.

When is farm monitoring enough, and when is a laboratory or veterinary investigation needed?

Urgent or unexplained mortality should go to professionals the same day. Similar signs can come from oxygen depletion, water-quality problems or different infections, so do not treat a pattern of symptoms as a diagnosis. For a wider first-response routine, see the first-response checklist.

How does the investigation lead to a project or equipment decision?

Only once the evidence points to a farm or system cause — for example repeated dawn oxygen deficits, missing backup power or insufficient nursery capacity — does it become a requirements question. Test aeration margins with the shrimp oxygen risk calculator and the oxygen requirement calculator, then write the measured problem, the required outcome and site conditions into a project request. The FishMatch team reviews it and approaches suitable suppliers for written, comparable proposals. See also aeration in tropical shrimp ponds.

Sources: FAO — Shrimp culture: water quality management; FAO — Shrimp culture: grow-out, nursing and acclimation; WOAH Aquatic Animal Health Code. FAO pond material dates from earlier production systems; confirm current practice with local experts.