Pangasius (Pangasianodon hypophthalmus) is a potential aquaculture species with high economic in tropical regions, as well as a major aquaculture product on world markets. Pangasius is cultured in some Asian countries like Vietnam, Thailand, Laos, Cambodia, Myanmar, Indonesia, Malaysia, Bangladesh, India and the Philippines... They grow fast, have a good quality of meat and are highly adaptable to harsh environmental conditions. For this reason, the farming area has been constantly expanded and the stocking density is also increased to boost production. Therefore, Pangasianodon hypophthalmus farmings are facing serious disease outbreaks due to environmental degradation and the spread of pathogens.
Parasitic is one of the main disease effects on fish health. They infect fish through the water environment, when infected in large numbers the fish will grow slowly, even cause high mortality. Especially, parasitic infection creates the opportunity for bacteria and virus diseases. Parasitic disease is considered as one of the serious disease effects on fish health and farmers' s economy as well.
This article does not only provide the necessary information about each characteristic of parasites and point out the clinical signs that appear on the fish to identifies them but also recommends some efficient products to treat and prevent parasitic diseases.
Parasitic diseases on Pangasianodon hypophthalmus
I. External parasites
1. Monogenea group
The Monogenea group includes several gill and skin parasites that belong to Thaparocleidus. Most monogeneans move freely on the fish's body surface feeding on mucus and epithelial cells of the skin and gills, with heavy infections in both pond and cage cultured systems. Monogeneans are external parasites with specialized posterior attachment organs characteristic to each species and require a single host. There are two common kinds of Monogenea group parasitics commonly on Pangasius: Dactylogyrus spp. and Gryrodactylus spp.
No. | Dactylogyrus spp | Gyrodactylus spp |
1 | Predominantly affects the gills | Commonly found on the skin. |
2. | Oviparous (egg-layers) release eggs into the water, which hatch into a free-swimming stage (oncomiracidium) that seeks out a fish host. | Viviparous (livebearers) release live larvae that are immediately parasitic. |
3. | Four of eyespots | Do not have eyespots.
|
4. | One conspicuous pair of large hooks and up to 12 smaller hooklets | A pair of large hooks and 16 marginal hooklets. |
- Causes:
+ Environmental degradation caused by high stocking density, low water quality management.
+ Parasitic diseases often occur in the rainy season or low temperature, suitable environmental conditions for them to grow about 22 – 28oC.
- Clinical signs:
+ Unusual behavior (ability to catch feed decreases, loss of appetite, swim slowly…)
+ Pruritus may be exhibited by fish as flashing- fish often rub against submerged objects.
+ The parasite may destroy the gill by excessing mucus present, affecting the respiratory system of the fish and creating the opportunity for secondary infection.
+ Appear ulcerates on fish’s skin, create the second infection by bacteria, virus, fungi….
2. Trichodina spp., Apinosoma spp. and Chilodonella spp.
They are parasitic mainly on the external organs such as gills, skin, fins stimulate excessive mucus production on gills and body surface with frayed fins. The gill fibers are destroyed, affecting the respiration, growth of fish and creating conditions for fungi, bacteria to infiltrate to cause disease. Infections can be observed year-round but are heaviest when climate conditions are unstable.
They are parasitic on external organs such as gills, skin, and fins make the parasitic areas excited to release more mucus, destroyed gill fibers affecting respiration, fish growth, and conditions for fungi, bacteria invade and cause disease
- Cause: The parasites appear most in ponds with high stocking densities and poor water quality. The disease causes damage mainly in the fry and fingerling stages. The disease occurs all year round but mainly in the rainy season.
- Clinical signs: Fish feels itchy when are infected by these parasites. The diseased fish is pale, viscous, and the fins are torn. When exposed to high intensity can cause the mass death of fish.
3/ Ichthyophthyrius multifiliis
It causes Icthyophthiriasis, also known as ‘Itch’ or ‘white spot disease’ which affects the early stages of Pangasius. They are up to 1 mm in size characterized by white spots shaped. Incidences of large-scale mortality are common in nursery and rearing ponds with numerous white spots on skin, fins, and gills.
Clinical signs:
- Fish infected appear white spots (less than 1 mm) on the skin, fin, and gill.
- Destroying the gill epithelium leading to respiratory loss of their function. Therefore, diseased fish floats head on the water surface and swimming slowly and weakly.
- The skin, gills increase mucus production, they are vicious and pale in color.
II/ Internal parasites
1. Myxobolus spp.
Myxobolus species belong to the Myxozoa and are commonly found on Pangasius. Which created milky white fluid cysts (0.5-3 mm diameter) containing spores that can be seen on internal or external organs with notable infections in the kidneys and gills. The Myxobolus spp. infections in fishes occur when the water environment is poor quality, high stocking density.
Clinical signs:
- Fish swimming slowly at the water surface, excess the mucus present
- Fish have reduced appetite and as a consequence become weak and vulnerable to bacterial infection.
- Pale skin; hemorrhage on the abdomen area, gill cover, fins; Swollen eyes and anus
- White cysts containing spores appear on internal and external organs, particularly in the kidneys and gills.
2/ Balantidium spp.
Members of Balantidium are unicellular and endocommensal parasites in the intestine of their hosts. The larger the fish, the higher the susceptibility rate and the intensity of the infection. However, high intensity but still does not affect fish much, but fish with enteritis or bacterial infection will get worse.
3/ Spectatus spp. và Spinitectus spp.
They belong to the roundworm group, a common parasitize in the gut and intestinal of the fish. Resulting in damage intestinal wall by sucking out the nutritional leading to digestive disorders. Affecting fish growth and pave the way for microorganism to penetrate.
PREVENTION FROM PARASITIC DISEASE
- Pond Improvement: Use CaO lime (10-15 kg / 100m2) to spread on the pond bottom and dry under the sunshine for 3-7 days to kill the spores of the pond bottom. Able to use with Fresh Water, dissolve 1kg /1.500-2.000 m3, before 2-3 days stocking to disinfect water pond aim at eliminating pathogens keeping a clean water environment for fish growth
- Water quality management:
+ Measure the water quality factors (Ph, NH3, NH4, H2S…) regularly to maintain a stable water environment for fish to live in.
+ Using Bitech- Yucca to destroy the organic matter, reduce the toxic gas in culture ponds, minimize the parasite development in ponds.
+ During the farming process, it is necessary to check the daily amount of food, avoid overeating. The excess makes the dirty water environment create conditions for the parasite to grow. Using Zeolite – Yucca to improve water quality decomposes organic matter and excess food.
- Observe the fish behavior daily to monitor their health status. Add support product as Vitamin C Antistress, Lactozyme, Vimelec concentrated, Sorpherol, Vemevit No 9.100 or Prozyme for fish to enhance their immunity system regularly.
TREATMENT FOR PARASITIC DISEASE
+ Prazi fish: Mixing to the feed 1kg/10 tons of fish
+ Vime- Clean: 1 kg/ 2 tons of fish
+ Fenben 20%: 1 kg/4 tons of fish (internal parasite); 1kg/8 tons of fish
+ Mectin Fort: 1 L/ 75 tons of fish
+ Anti- Parasite: 1kg/1000m3
REFERENCES
K.P. Jithendra. Parasites and Parasitic Diseases in Fish Culture System
Nguyen Thi Thu Hang and Dang Thi Hoang Oanh. Identification of parasitic groups creating cysts in catfish (Pangasianodon hypophthalmus)
Tu Thanh Dung, 2017. Striped catfish diseases (Pangasianodon hypophthalmus) and diseases management in pond.
