Introduction to Common Fish Medications, Part 3

II. Nitrofurans

Nitrofurans are a class of synthetic broad-spectrum antibacterial drugs with many varieties, but only 3 to 4 are used for aquatic disease prevention and treatment. The basic structure of nitrofuran drugs is a furan ring with a nitro group attached at the fifth carbon atom. They have strong antibacterial effects; at low concentrations, they can inhibit the reproduction of many Gram-positive and Gram-negative bacteria; at high concentrations, they have bactericidal effects. Generally, bacteria do not easily develop resistance to nitrofuran drugs. Even bacteria resistant to sulfonamides and antibiotics remain relatively sensitive to nitrofuran drugs. However, nitrofuran drugs are poorly absorbed in the body and are easily and rapidly destroyed after absorption, often failing to reach effective blood antibacterial concentrations in the blood. Only in the intestinal tract can they maintain effective action, so they have a good effect in preventing and treating bacterial intestinal infections in fish. In addition, according to recent reports, nitrofuran drugs have carcinogenic effects, so their use has been restricted. At the same time, long-term use of these drugs can cause liver and kidney damage in fish.

1. Furazolidone (Furazolidone)

[Properties] Furazolidone, also known as furazolidone, is a yellow powder or crystalline powder; odorless, bitter taste; almost insoluble in water and ethanol, and slightly soluble in chloroform; decomposes when exposed to alkali, and gradually darkens in color under strong light. It should be stored protected from light and sealed.

[Action] This product has low toxicity. It has a broad antibacterial spectrum and is effective against many Gram-positive and Gram-negative bacteria. At 5 to 10 micrograms/mL it has a bacteriostatic effect, and at 20 to 50 micrograms/mL it has a bactericidal effect. The drug also has an antiprotozoal effect. Bacteria do not easily develop resistance to this product, and there is no cross-resistance with sulfonamides and antibiotics. After oral administration, it is poorly absorbed from the gastrointestinal tract, blood drug concentration is relatively low, and the concentration in the intestinal tract is relatively high.

[Uses] This product is mostly used to prevent and treat bacterial enteritis, and it also has relatively good efficacy against gill rot, red skin disease, furunculosis, white head and white mouth disease, scale protrusion disease, tail rot, ulcers, vibriosis, eel columnaris disease, and Edwardsiella disease, etc.

[Usage and Dosage] When the feeding rate is 4%, the usual dosage is 2.5 grams of this product added per kilogram of feed, and it should not exceed 5 grams at most. According to a report by Tanaka Jiro of Japan. To prevent and treat gill rot, red skin disease, furunculosis, white head and white mouth disease, scale protrusion disease, ulcers, vibriosis, etc., it can be mixed into feed at a ratio of 0.1% to 0.2% to make medicated bait and fed once a day for 3 to 5 consecutive days. For whole-pond splashing, use 0.3 to 0.5 ppm; splashing should be carried out when sunlight is weak.

2. Nitrofurantoin (Furan