How to recognize and effectively treat ulcer disease in grouper fish

In marine fish farming, it is not uncommon for farmers to face the problem of grouper skin ulcers. This disease is caused by bacterial infection and not only affects fish quality, but can also leave serious consequences if treatment is delayed. To help farmers identify it early, understand the cause correctly, and know how to prevent and treat it effectively, Vemedim would like to introduce the following article with practical and scientific solutions. Let’s take a look!

Causes of grouper skin ulcers

Skin ulcer disease in grouper is one of the common problems in aquaculture, especially in coastal cage farming areas. If not detected early and treated promptly, the disease can cause mass mortality, reduce productivity, and lead to significant economic losses. The problem of grouper skin ulcers can arise when many favorable factors combine. Some of the main causes include:

Pathogenic bacteria:
The main pathogenic bacteria are Vibrio spp., Aeromonas hydrophila, and Pseudomonas spp., which enter the fish through scratches or skin injuries.
When fish have reduced resistance, the bacteria multiply rapidly, causing red ulcers, skin erosion, and bleeding.
Polluted farming environment:
Water in cages accumulates organic waste, and toxic gases such as NH₃ and H₂S weaken fish health, creating favorable conditions for bacteria to grow.
Dirty water also reduces the fish’s natural immunity, making disease outbreaks more likely.
High stocking density:
When stocked too densely, fish are more likely to collide and get abrasions, leading to skin wounds that become entry points for bacteria.
Stress from high density also weakens fish and reduces disease resistance.
Stress and poor nutrition:
Fish lacking vitamin C, minerals, or experiencing sudden changes in temperature or salinity will have reduced resistance.
Unbalanced nutrition and poor-quality feed are also factors that can cause the disease to spread quickly.

*Grouper skin ulcers are caused by Vibrio spp., Aeromonas hydrophila, and Pseudomonas spp. entering from the farming environment*

>> See more:

Recognizing grouper skin ulcers

Farmers can detect the disease based on external and internal symptoms in the fish:

External signs

Grouper with skin ulcers will develop many red sores on the body, usually at the base of the fins, the abdomen, or near the mouth.
The ulcers spread, scales peel off, muscle is exposed, and bleeding occurs.
Pale skin, excessive mucus, torn fins.
Grouper with skin ulcers will swim sluggishly, eat less, or stop eating altogether.

Internal signs

The liver, kidneys, and spleen of the grouper become enlarged and pale.
Fish may show signs of internal organ hemorrhage, inflamed intestines, and mucus discharge.

If not treated, the disease can cause 20–60% mortality in the stock, especially under poor environmental conditions. The disease not only affects fish health but also directly impacts the farmer’s economy:

Fish quickly become weak, grow slowly, and feed conversion ratio increases.
High stock losses, increased medication costs, and major economic damage.
Increased risk of other diseases such as fungal and parasitic infections.
Market fish are of poor quality and difficult to sell.

*Grouper skin ulcers are easy to recognize through abnormalities and lesions on the fish’s body*

How to prevent grouper skin ulcers

Farmers should implement comprehensive preventive measures, combining environmental management, seed selection, nutrition, and stocking density control below to limit grouper skin ulcers:

Farming environment management

Regularly change the water and maintain good water flow.
Clean cages regularly to avoid accumulation of waste and leftover feed.
Use probiotics Vemedim Vime-Protex, Vemedim Vime-Iodine to improve water quality and limit pathogenic bacteria.

Choose healthy fish seed

Select fingerlings that are not deformed, not scratched, and swim actively.
Bathe fingerlings in 2–3% dilute saltwater for 5–10 minutes before stocking.
Stock at a reasonable density to reduce stress and competition among fish.

Proper nutrition

Feed quality feed that is free from mold.
Supplement vitamin C, minerals, and digestive enzymes with Vemedim ANTI – SHOCK, Vemedim GLUSOME 115, Vemedim ADE B.complex to increase fish resistance.
Avoid overfeeding, which pollutes the water environment.

*To prevent grouper skin ulcers, regularly clean the fish tank, choose healthy, high-quality seed, and proactively boost fish resistance*

Treatment measures for grouper skin ulcers

When fish are found to be sick, farmers should immediately apply the following measures to minimize losses:

Isolate sick fish: Move them to a separate tank to limit spread.
Bathe fish with chemicals:
2–3% table salt for 10–15 minutes.
KMnO₄ at a concentration of 2–3 g/m³.
Use antibiotics to treat ulcers such as Vemedim Amoxi 700, Vemedim Doxy 20%, Vemedim OTC 5000 by mixing them into feed (according to expert instructions).
Support supplements: high-dose vitamin C and probiotics help increase resistance and shorten recovery time.

*If the grouper stock shows signs of skin ulcers, isolate the sick fish and bathe them with chemicals as directed, while also boosting the stock’s resistance*

Grouper skin ulcers are a common problem but can be completely controlled if farmers properly implement prevention and treatment measures. Managing the farming environment, selecting healthy seed, providing adequate nutrition, and regularly preventing disease with biological products are the keys to minimizing risks. With Vemedim’s professional solutions, farmers can feel confident in improving productivity, protecting their fish stock, and aiming for a successful, sustainable crop. Please contact Vemedim for detailed advice!