01 · AquaGrow
What it is
A stiff bent body or opaque muscle can follow handling, low oxygen or abrupt environmental changes. Similar white muscle also occurs in infectious conditions, including IMNV. Persistent whitening or deaths require investigation.
Signs to watch for
- The body bends stiffly or cannot straighten normally during or after handling.
- Abdominal or tail muscle becomes white or opaque rather than translucent.
- Poor swimming, weakness or deaths may accompany severe or persistent muscle damage.
Common causes
- “Muscle cramp” describes contraction; “white muscle” describes appearance. They are not identical diagnoses. Muscle injury can have environmental, nutritional or infectious causes.
- Similar signs can have other causes: IMNV and other infectious causes of muscle damage. Handling injury, oxygen shortage, temperature or salinity shock and nutritional problems.
How to confirm the cause
- Measure oxygen and review temperature, salinity and handling events promptly; record whether the problem started before or after capture.
- Arrange professional examination and targeted tests such as IMNV RT-PCR (a laboratory test for RNA genetic material) and histology (microscope examination of tissue) when signs persist, recur or accompany mortality. Ask the laboratory which causes its panel covers.
What to do immediately
- 1
Stop unnecessary handling and check oxygen and aeration immediately.
- 2
Review measured water changes and correct identified problems gradually with professional guidance.
- 3
Photograph the appearance, record timing and watch whether unaffected shrimp develop signs.
- 4
Contact a qualified professional and arrange suitable samples if whitening persists or deaths occur; do not delay because the event followed netting.
Prevention: your practical checklist
- Sample gently, avoid prolonged air exposure and minimise unnecessary handling.
- Avoid the hottest or oxygen-poor periods for routine sampling when practical.
- Maintain stable water conditions, reliable aeration and an appropriate acclimation plan.
- Use complete, well-stored feed rather than guessing individual nutrient deficiencies.
- Keep pond-specific equipment and a record of all handling and water changes.
When to call an expert
- Call an aquatic animal health professional urgently if deaths rise, shrimp gather at the surface, or breathing becomes difficult. Check dissolved oxygen while arranging help.
- Arrange an assessment if these signs persist, feeding falls or growth stays behind the crop trend. Send water readings, recent input records and photographs; ask the laboratory how to collect samples.
Farmer questions
The shrimp straightened again. Is the pond safe?
Recovery from a cramp is reassuring but does not establish the cause or rule out other illness. Continue observing feeding, mortality and water measurements.
What makes testing more urgent?
Persistent opacity, repeated events, spread beyond handled animals, falling feeding or any increasing mortality justify prompt professional investigation.
What should I record before asking for help?
Note the pond ID, culture day, recent deaths, feed intake, water test readings and recent changes. Ask the laboratory about suitable samples before adding a treatment. A photograph alone cannot confirm the cause.
Sources & further reading
AI-assisted educational content and translations, source-checked 17 October 2026. Not an individual diagnosis or prescription. Independent aquaculture-health and native-language specialist approvals have not been supplied. Sources do not endorse AquaGrow.
- Training manual — section 5.4, White muscle syndrome and differential causes ↗ICAR-CIBA, December 2022; historical technical reference
- Infection with infectious myonecrosis virus — signs and diagnostic criteria ↗WOAH Aquatic Manual
- Disease prevention and health management — muscle cramp and external signs ↗FAO; historical training guidance