In recent years, GTM is rife on pangasius that causes huge damage for farmers, even in some cases, commercial pangasius lost up to 50%.
The main cause of this is by reseeding with high density, the environment is polluted, the pathogen is not thoroughly treated before discharge into the river and canal. To limit loss caused by GTM, the farmers need to follow and check strictly the pathogens.
Prevent GTM on pangasius
In the past, GTM usually occurs at beginning of rainning season, peak time is in August – October annually, and often occurs on mature pangasius. However, it appears almost year-round and on alevin as well in recent years. In all stages of infection, the alevin has the biggest mortality up to 90%.
For catfish rearing, close monitoring can help to recognize early signs of GTM to take timely measures, avoid a mass death. After infecting, fish often have unusual signs as below:
The fish’s behavior changes, they float and gather in the flowing area, eat less or stop eating, jump over the water surface. However, pangasius is only defined to be infected by GTM when it has white spots on its liver, kidneys, and spleen.
The high density of fish in the intensive farming system makes fish shock and causes changes in the living environment, this facilitates the outbreak of GTM. The farmers should monitor fish’s behavior in the temperature that GTM can outbreaks easily (from 28 – 30 oC). In bad conditions, its is necessary to adjust measures like change or add more water into the pond.
An inappropriate diet can increase the sensitivity of pangasius to E.Ictaluri bacteria which is the cause of GTM. Overfeeding pollutes the pond by excess food, thereby fish are susceptible to the pathogen.
Feed small fish (50 – 80 gr) maximum 5% of its weight, and 2% for big fish. Shout not feed them when the water level is low or at noon when the sun reaches the highest position in the sky.
Waste accumulation from excess food will produce toxins that affect fish directly and facilitates the development of microorganisms. Therefore, the reseeding density should not be over 60 fish/ m2, check frequently the environmental factors like Oxygen, pH, temperature, salinity, etc. at least once a week at specific times in a day.
In case the fish have unusual behaviors, stop feeding and decrease food amount is a good measure to limit mortality.
Limit the spread of disease
Choose the reputable alevin manufacturing facilities that have checked for dangerous diseases by quarantine unit; should not buy the alevin infected by GTM. The alevin should be monitored carefully, every unusual behavior or symptom of diseases must be timely treated. After arriving at the farming pond, remove the fish which have many scratches; bath them for 5 – 10 minutes in saltwater 0.5% before restocking.
The fish that died by disease (especial is GTM) were thrown into rivers, sold to the farmers who raise pampus argenteus, or buried improperly, these facilitate the spread of disease from one farming area to the others.
To limit the spread of pathogens, the farmers should fertilize farming tools with Chlorine with a concentration at 10 – 15 within 30 minutes, dead fish must be taken out of the pond and buried with CaO for fertilization, wastewater from diseased pond shall be fertilized before discharge into rivers and canals.
The fish infected by GTM is easy to be infected by other pathogens such as parasites, hemorrhagic disease, white liver, or white gill diseases that make the mortality worse. Therefore, the farmers should observe strictly the fish’s health to recognize diseases as soon as possible and take measures timely. Antibiotic is necessary to treat GTM on pangasius, but be careful in choosing antibiotics, do not use antibiotics in drug tolerance and should follow the results of therapy.
GTM on pangasius (Pangasianodon hypophthalmus) in Mekong Delta caused by the bacteria Edwardsiella ictaluri. This bacteria was first isolated on American channel cat (Ictalurus furcatus) that causes septicemia on white catfish (Clarias batrachus) in Thailand and some other catfish.
In 1998, GTM appears in large intensive farming areas in Mekong Delta like An Giang, Dong Thap, Can Tho; then spread to neighboring pangasius farming areas and present in the whole intensive farming area of pangasius.