Parasites are one of the disease-causing agents in fish. They appear in all farming models, especially in high-density pond farming, where the infection rate is very high. Parasitic diseases severely impact fish health, leading to slow growth, low productivity, food safety concerns, and even mortality, primarily during the fingerling stage. At the same time, they pave the way for pathogenic viruses, bacteria, and fungi. Parasites do not appear in isolation but are often found alongside other diseases such as hemorrhage, ulcers, white spots on the body…. (referred to as co-infection of parasites and bacteria).

LIFE CYCLE OF FLUKES

Monogenean flukes have a direct life cycle on the fish host. *Dactylogyrus* flukes lay eggs, which can sink to the pond bottom or attach to aquatic plants in the water. On the 4th day, the eggs hatch into free-living larvae that quickly seek a host to continue their parasitic life. By the 10th day, they develop into adult flukes and participate in reproduction. Warmer weather accelerates the egg-laying rate. *Gyrodactylus* flukes are viviparous, meaning they give birth to live young. The fluke's body can contain 2-3 embryos, each containing a fluke resembling the adult, also known as "embryo within embryo" or "three generations in one". When the young fluke emerges from the mother fluke's body, it continues to parasitize the fish and causes damage similar to the adult fluke. The life cycle of *Dactylogyrus* is 19 days, and *Gyrodactylus* is 13 days.

In reality, with high-density fish farming, contaminated water sources, and unstable weather conditions, various internal and external parasites proliferate significantly, affecting fish by causing poor appetite, slow growth, reduced immunity, making them susceptible to diseases, and poor feed absorption, leading to a high FCR.

To address this issue, a safe, periodic internal and external deworming schedule is needed for each fish development stage, as follows:

• Fish < 300g stage: Check for parasites every 25–30 days and deworm when you find them, using AQUA PRAZI as labelled: mix 100 g into 20–30 kg of feed (equal to 100 g for 200–300 kg of fish) for 3–5 days in a row; stop feeding 1 day before deworming. At this stage fish are still small, with poor resistance and tolerance, and are growing fast, so AQUA PRAZI keeps them safe during deworming and avoids weakened fish afterwards, which could affect nutrient absorption and growth.
• Fish > 300g stage: Use AQUA PRAZI as labelled, as above, dosed by fish weight. If fish have 'rice disease' (myxosporean cysts), call Than Vuong technical support at +84 867 957 568 before using any drug.
• After deworming, mix in BIOMAX 1 g/1.5 kg feed and AQUAMOS 1 kg/1,500–1,800 kg feed for 3–5 days. Disinfect the water with POWER GLUTA 1 bottle/5,000 m³ of water; 24–48 hours later re-seed probiotics with MAX 4000 1 pack (250 g)/6,000–7,500 m³ of water, or NIAZYME 1 kg/8,000 m³ of water in ponds that are hard to exchange or have a lot of bottom organic matter. For fingerlings, see Pangasius nursery protocol with Than Vuong products.

**Note: To increase the effectiveness of internal and external deworming, it is recommended to stop feeding 1 day before deworming. After deworming, it is necessary to supplement with nutrients, vitamins, and liver detoxifiers to help fish quickly recover from parasite-induced damage, as well as to boost their immunity and promote optimal development.**

The purpose of safe, periodic internal deworming according to each fish development stage is to help fish grow well, absorb feed effectively, eliminate parasites that attach and absorb nutrients inside and outside the fish's body, enhance antibodies to improve disease resistance, promote rapid growth, and reduce FCR during the farming cycle.

Applying the products according to the above procedure will achieve the most optimal results in safe internal and external deworming for each fish development stage, helping farmers succeed in their fish farming season.

Author Fish Technical Staff – NGUYỄN MINH ĐỨC