White Muscle in Shrimp: How to Read the Signs
By Dr. Wiphada Mitbumrung, Ph.D. Applied Marine Biosciences — Fri Sep 25 2026
Thinking Like a Doctor at the Pond
When a person feels sick and visits a doctor, the doctor does not start with a blood test. First, the doctor looks at the patient and asks questions: What symptoms do you have and When did it start? Has anyone else at home been sick? This is called taking a medical history. From these answers and a quick physical check, the doctor forms an idea of what might be wrong, and only then decides which tests to order. A good history saves time, saves money, and points the treatment in the right direction.
Visual inspection, empty gutPhoto credit: Indonesia shrimpDiagnosing shrimp disease works the same way. Our medical history is composed of three parts.
(1) Gross signs are the changes we can see with our own eyes: the color of the muscle, the shell, the gills, the hepatopancreas and whether the gut is full or empty.
Photo credit: AAN(2) Behavior is how the shrimp are eating, whether feed is left in the trays, and how they swim. Are they swimming at the edge, floating at the surface, or hiding at the bottom?
Shrimp gathering at the pond surface.Photo credit: Doctor Shrimp, Bhimavaram, India(3) Mortality pattern is how many die, how fast, at what age, and where the dead shrimp are found.
After we collect this information, we choose representative samples. That means shrimp that truly show the problem, not only the dead ones and not only the healthy ones. Then we send them to a laboratory for PCR, histopathology, or bacterial culture to confirm the real cause.
There is one big difference between shrimp and human patients, though. Many shrimp diseases move very fast. A pond can go from normal to heavy mortality in only a few days, sometimes before the lab result arrives. This is why the farmer's eye is so important. Reading the gross signs correctly will not always give the final answer, but it gives the direction: Should we harvest now? Add more aerators? Add minerals? Use probiotics and clean up the water? Making the right decision early can save the crop.
Photo credit: Copyright © 2026 Doctor Shrimp, Bhimavaram, IndiaWhite Muscle Is a Sign, Not a Disease
Healthy shrimp muscle is clear and see-through. White muscle simply means the muscle has lost this transparency and turned cloudy or white. It is similar to a fever in humans: fever tells you the body has a problem, but it does not tell you whether the cause is flu, infection, or heat stroke. Muscle turns white for three main reasons. The first is physical damage, where the muscle fibers are broken or torn. The second is cell destruction and protein change: when muscle cells are stressed, for example from lack of oxygen or mineral imbalance, acid builds up inside the cells. This acid makes the muscle proteins twist and lose their shape, a process scientists call protein denaturation. It is the same thing that happens when you cook an egg white and it changes from clear to solid white. Once the proteins are denatured, light cannot pass through, so the muscle looks opaque. The third reason is parasite replacement, where parasites grow inside the muscle and slowly replace the normal tissue with their own mass, which looks white and chalky.
Because many different causes lead to the same white color, we must look closely at the pattern of whiteness, the timing in the crop cycle, the other signs, and the water quality. Below are the six most common causes and how to tell them apart.
1. Mineral Deficiency
Photo credit: AANWhen: Mid-to-late cycle, usually after about one month of culture, when shrimp grow fast and need a lot of minerals. Minerals are depleted by phytoplankton, bacteria and benthic organisms as well.
Why: Seawater is naturally rich in magnesium (Mg) and potassium (K). Ponds using low-salinity or fresh water start with low magnesium. When we stock shrimp at high density, they use up these minerals quickly, and their muscles cannot work properly.
What you see: The whiteness is diffuse and cloudy, spreading along the middle of the back and the tail, with no sharp edges. In the first seven days, you may find shrimp in the feed trays that are stiff, bent, and not moving, with pale tail tips. After about ten days, dead shrimp appear in the trays or along the pond edge, and the whole body becomes cloudy. Shrimp are thin with a narrow belly, the shell is soft, thin, and papery, growth is slow, and FCR goes up. Many shrimp cramp and curl right after you catch them in a cast net.
Check: Calcium, magnesium, and potassium levels in the water. If they are low, adding minerals often brings fast improvement.
2. Lack of Oxygen and Temperature Stress
Other environmental stress (Sudden DO, temperature, salinity or handling stress) : Muscle may become diffusely cloudy or opaquePhoto credit: Cischem Agricultural, 2025When: Any stage of culture.
What you see: The whiteness starts at the tail tip and moves forward toward the head. There are scattered deaths with no clear cause.
Check: Dissolved oxygen (especially early morning, before sunrise) and temperature changes. The fix is usually more aeration, reducing feed during stress, and careful handling.
3. IMNV – Infectious Myonecrosis Virus
Muscle necrosis and whitening typically begins in the last abdominal segment; affected muscle may later become orangePhoto credit: Zhang et al, 2014When: Mid-to-late cycle.
What you see: The white areas are separate spots on the tail segments rather than a smooth cloud. The key sign is that these patches later turn orange or reddish, like cooked shrimp. Mortality is chronic and continuous, a steady number every day. Dead shrimp are often seen floating at the surface, and interestingly, sick shrimp often still have full guts just before they die.
Triggers: Sudden salinity changes, heavy rain, and physical disturbance such as netting or sampling.
4. CMNV – Covert Mortality Nodavirus
Cloudy-white muscle distributed throughout the bodyPhoto credit: Nunes et al 2010When: Early-to-mid cycle.
What you see: The tail muscle turns white, but it stays dull white and never turns red or orange. This is the main way to separate it from IMNV. The word covert means hidden: dying shrimp sink and hide in the bottom sludge, so the farmer may not see the dead and only notices that the survival at harvest is much lower than expected. The hepatopancreas is shrunken and pale or yellow-brown, the gut is empty, and the shell is soft.
Triggers: Temperature changes and high total suspended solids (dirty, heavy water).
5. Bacterial Infection (Vibriosis and Photobacterium)
Focal or localized opaque/necrotic muscle. May occur with wounds, redness, melanization, shell lesionsPhoto credit: Limsuwan & Chuchird, 2007When: Any stage, and often after an algae crash, when the water suddenly clears and bacteria bloom.
What you see: The white areas are lumpy or patchy, often with black spots (melanization, the shrimp's immune reaction) or red streaks in some places. The hepatopancreas is shrunken and pale, the gut is empty or white, and you may see tail rot.
Check: Total Vibrio count and ORP. Actions include improving the bottom, stabilizing algae, and using probiotics.
6. Microsporidian Infection
Photo credit: AANWhen: Mid-to-late cycle.
What you see: The muscle becomes solid, chalky, matte white, with large lumps that look like cotton under the shell. This is the parasite replacing the muscle tissue. The outer shell often has a purple-mauve or blue-black tint. Unlike viral diseases, daily mortality is low, but affected shrimp have no market value.
Final Advice
Photo credit: Doctor Shrimp, Bhimavaram, IndiaAlways look at the whole picture, not just the white muscle. Check water quality at the same time you look at the shrimp, because environmental and nutritional problems (minerals, oxygen, temperature) can often be fixed quickly, while viral problems may require emergency harvest to save value. When a virus or parasite is suspected, send representative samples to a lab for PCR, microbial or histopathology to confirm, and keep good records of timing, mortality, and water data. Like a good doctor, a good farmer who reads the signs carefully can act early, even before the final diagnosis arrives.
Digital PCR machinePhoto credit: Doctor Shrimp, Bhimavaram, India
PL samplePhoto credit: Doctor Shrimp, Bhimavaram, IndiaReferences:
Alolod, G. A. L., Guzman, J. P. M. D., Bermeo-Capunong, M. R. A., Konishi, K., Koiwai, K., Kondo, H., & Hirono, I. (2026). Metagenomic insights on the progression of white muscle disease in kuruma shrimp (Penaeus japonicus) caused by Photobacterium damselae subsp. damselae. Journal of Fish Diseases. Advance online publication.
Global Seafood Alliance / Lightner, D. V. (2012). White tail disease in shrimp mimics infectious myonecrosis. Global Seafood Advocate.
Limsuwan, C., & Chuchird, N. (2007). Histopathological study of necrotizing hepatopancreatitis (NHP) infection in Litopenaeus vannamei in Thailand. Proceedings of the 45th Kasetsart University Annual Conference: Fisheries (pp. 574–581).
Nunes, A. J. P., Sabry-Neto, H., & Sá, M. V. C. (2010). Brazil study: Beta-glucans improve survival of IMNV-infected white shrimp. Responsible Seafood Advocate.
Zhang, Q., Liu, Q., Liu, S., Yang, H., Liu, S., Zhu, L., Yang, B., Jin, J., Ding, L., Wang, X., Liang, Y., Wang, Q., & Huang, J. (2014). A new nodavirus is associated with covert mortality disease of shrimp. Journal of General Virology, 95(12), 2700–2709.