Causes, Symptoms and Treatment of Saprolegniasis in Fish

The overwintering period for fish is the season when winter fish diseases are prevalent. When pathogenic bacteria are present, diseases such as saprolegniasis are prone to occur at low temperatures, and sometimes it seems very difficult to prevent. So how do you treat fish with saprolegniasis? What are the symptoms?

Pathogen

It is a fungal disease caused by water molds. More than ten kinds of water molds have been found on the body surface and eggs of freshwater aquatic animals in China, among which the most common are Saprolegnia and Achlya. Saprolegnia has a very wide temperature adaptation range and no selectivity for aquatic animal species; any injured body or egg can be infected and develop the disease. It often parasitizes wounds, and after absorbing nutrients from the skin it rapidly germinates, growing outward, with hyphae penetrating inward into the muscle and growing outward as cotton-like filaments, causing tissue necrosis.

Epidemiology

Saprolegniasis, also known as dermatomycosis or white hair disease, occurs throughout the year, but is most prevalent in early spring and late winter when the water temperature is 10-15°C, when outbreaks are severe, as it is suited to low-temperature reproduction. All kinds of aquaculture animals are susceptible to infection, and it often brings serious economic losses.

Symptoms

Most diseased fish swim abnormally, have reduced appetite and become sluggish. Water mold parasitizes the head, snout tip, tail, trunk or fin rays of the diseased fish, and sometimes even the gills, with mud and algae adhering to it, appearing as if covered with cotton wadding, and finally the fish become emaciated and die.

Treatment Methods

1. If the number of diseased fish is small and local treatment is possible, they can be soaked in an iodine-containing disinfectant, such as a 20 mg/L povidone-iodine solution, or 2 mg/L potassium permanganate mixed with 1% saline to soak the diseased fish for 20-30 minutes;

2. Or splash the whole pond with 800 mg/L of a table salt and baking soda mixture (1:1);

3. Or administer oral antibacterial drugs (such as sulfonamides) to prevent and treat secondary bacterial infections;

4. There are other common types of fishery drugs on the market for the prevention and treatment of saprolegniasis.

Prevention and Control Measures

1. Remove excess mud and thoroughly clear the pond with 20-30 kg per mu of quicklime, which can reduce the occurrence of this disease;

2. Handle fish carefully during catching and transportation so as not to injure the fish body; it is best to soak them in a 20 mg/L povidone-iodine solution preparation for 15-20 minutes;

3. When broodfish are injured, apply 1% potassium permanganate aqueous solution, iodine tincture, etc. to the fish body; in severe cases, inject streptomycin sulfate into the abdominal cavity or muscle at 50,000-100,000 units per kg of fish;

4. Splash or soak the whole pond with a 0.04% table salt and baking soda mixture;

5. For saprolegniasis alone, salicylic acid alcohol solution, dithiocyano-methane solution or gallnut powder, etc. can be chosen for splashing or soaking in the whole pond; refer to the product instructions for dosage. If it is a mixed infection, it should be handled flexibly according to the actual situation.

How to treat saprolegniasis in goldfish?

1. Splash a mixture of 250 grams of table salt plus 250 grams of baking soda into a 100 cm × 55 cm × 45 cm fish tank, repeating several times for a marked effect.

2. Dissolve 0.3 grams of malachite green or methylene blue in 100 kg of water and soak the fish body for 10-20 minutes; after a few days the hyphae can be seen to fall off. Soak in 1.2%-3% saline once a day for 5-10 minutes each time.

3. The specific remedy: soak in a malachite green solution at one to two parts per million (1-2 ppm) for 20-30 minutes each day.

4. Mix two parts per million (2 ppm) potassium permanganate with 1% saline and soak the diseased fish for 20-30 minutes.

5. Raise the water temperature to inhibit the growth of water mold. In addition, a 15-watt ultraviolet lamp can be used for several hours of irradiation each day to effectively inhibit and eliminate water mold.

Whether preventing or treating saprolegniasis, the focus is on disinfection, disinfecting the water body and disinfecting the diseased fish. As long as the pathogens are eliminated, saprolegniasis in goldfish will improve.