01 · AquaGrow
What it is
IMNV can damage muscle and produce white, opaque abdominal or tail areas. Similar whitening also follows noninfectious injury. Do not assume that mineral addition, a water change or a photograph can settle the diagnosis.
Signs to watch for
- Opaque white areas in abdominal muscle or tail, sometimes with red or damaged tail tissue.
- Weakness or abnormal behaviour during or after stressful events.
- Increasing deaths or continuing low daily mortality; some sick shrimp may still have a full gut.
Common causes
- Infectious myonecrosis is caused by an RNA virus. Vannamei is susceptible, and losses may appear suddenly or continue at a lower level after an acute episode.
- Similar signs can have other causes: Handling-related muscle cramp or noninfectious muscle damage. Other infections, oxygen stress or nutritional problems affecting muscle.
How to confirm the cause
- Ask for validated IMNV-specific RT-PCR (a laboratory test for RNA genetic material) testing and histology (microscope examination of tissue) when indicated; an ordinary visual inspection is insufficient.
- Give the laboratory the timing of handling, water changes and mortality so infectious and noninfectious causes are considered together.
What to do immediately
- 1
Check oxygen, aeration and recent stress events promptly.
- 2
Contact a qualified professional and arrange suitable samples while affected shrimp are available.
- 3
Track whether whitening and deaths persist after water conditions improve; retain photographic and feed records.
- 4
Keep affected stock, equipment and water separate. Agree on safe disposal and any harvest or discharge with your professional.
Prevention: your practical checklist
- Use traceable seed from a documented health programme with relevant screening.
- Handle shrimp gently and avoid unnecessary capture, overheating or abrupt salinity changes.
- Maintain stable water quality and prevent transfer of sick shrimp or raw crustacean material between units.
- Assign nets, trays and boots to each pond; clean and disinfect equipment under the farm’s biosecurity plan.
- Keep seed-batch, feeding, water-quality and mortality records so a change is noticed early.
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
It appeared after cast-netting. Is it only cramp?
Not necessarily. Handling can reveal a stress response in infected shrimp too. Continued opacity or deaths requires professional assessment and testing.
Can mineral products confirm or cure IMNV?
No. Water chemistry may need correction if measurements show a problem, but product response is not an IMNV test or proof of viral clearance.
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.
- Infection with IMNV — clinical signs and diagnostic criteria ↗World Organisation for Animal Health — Aquatic Manual (2023)
- Infectious myonecrosis — field guide ↗NACA / Australian Government — historical Asia–Pacific identification field guide; not current surveillance