Common Spring Disease Prevention and Treatment Techniques for Freshwater Fish
In spring, water temperature begins to rise, and various bacteria and parasites that can cause disease in fish begin to multiply in large numbers. At the same time, after going through the wintering period, fish are weak in constitution and relatively poor in resistance to disease-causing factors, making them prone to infection by various diseases, causing massive deaths of pond fish and bringing relatively large losses to farmers, while also seriously affecting the later growth of surviving individuals. For this reason, effectively carrying out spring fish disease prevention and treatment work is the key to increasing production throughout the year. Based on many years of production practice, the author now briefly describes common spring fish disease prevention and treatment methods as follows, for the reference of farmers.
I. Preventive Measures
1. Improve the aquaculture water environment and carry out water disinfection for prevention.
During the wintering period, because ponds change water less often, metabolic wastes from various aquatic organisms accumulate in the water. After spring water temperature rises, these metabolic wastes begin to decompose, consuming large amounts of dissolved oxygen in the water, and the toxic and harmful substances produced will increase the probability of fish being infected by various diseases. Therefore, after entering spring, in addition to appropriately changing water, applying "Zhongshui Yishuining" or "Yujing Haoshuisu" once every 10 days to 15 days can effectively improve the water environment in which fish live. In addition, in early spring, various biological disease-causing factors such as bacteria, parasite spores, and cysts are still in the early stages of reproduction and development. At this time, using medication to kill insects and sterilize has a better effect and can achieve twice the result with half the effort. Copper sulfate and ferrous sulfate powder Type I at 0.6 ppm to 0.7 ppm, or trichlorfon and phoxim powder at 0.12 ppm to 0.3 ppm, can be regularly splashed over the whole pond to prevent protozoan parasitic fish diseases. Regularly splashing 20 ppm quicklime or 0.02 ppm bromochloro hydantoin over the whole pond once can effectively prevent bacterial diseases.
2. Start feeding early to strengthen the fish's constitution, and attach importance to improving the fish's own resistance.
Fish do not feed for a long time during wintering, consume a great deal of their constitution, and have poor resistance, making them highly susceptible to pathogen invasion. Therefore, after entering spring and as water temperature begins to rise, feeding should begin early, and better compound feed should be given to strengthen nutrition. According to the number of feeding fish, fish body size, and feeding ability, as water temperature continues to rise, the feeding amount should be gradually increased, and feeding should be done in appropriate amounts. At the same time, some nutritional and immunomodulatory agents can be regularly added to the feed, such as sodium vitamin C powder, immunologically active growth promoter, and vitamin E, etc., which can help fish recover their constitution relatively quickly, thereby strengthening the fish's constitution, improving the fish's own immunity and ability to resist disease invasion, and effectively preventing the occurrence and spread of diseases.
II. Characteristics of Spring Fish Diseases and Their Treatment Methods
The epidemiological characteristics of spring fish diseases are as follows: First, bacterial and fungal fish diseases caused by damage to the fish body from frostbite or operations such as pond division and stocking, which are then invaded by harmful pathogenic bacteria. Second, after going through the wintering period, fish are weak in constitution, while at this time various pathogenic organisms or their spores, dormant eggs, larvae, etc. rapidly develop and reproduce in large numbers with the rise in spring water temperature, causing the number of pathogens in the water body to increase rapidly, increasing the chances for fish to come into contact with pathogens and become infected, and making parasitic diseases likely to occur. Common bacterial and fungal fish diseases in spring mainly include saprolegniasis, scale protrusion disease, red skin disease, bacterial gill rot disease, and furunculosis; parasitic diseases mainly include ichthyobodiasis, costiasis, chilodonelliasis, ichthyophthiriasis, Lernaea disease, and Sinergasilus disease, etc.
(1) Bacterial and fungal fish diseases
1. Saprolegniasis. Symptoms of saprolegniasis: This disease is caused by fungal infection. Its main symptom is white cotton-like hyphae growing from wounds. Sick fish have reduced appetite and are restless in the water, often rubbing against other solid objects. Later, the muscles at the affected area rot, the fish swims slowly, and finally dies from exhaustion.
The first treatment method is to soak the fish body in 3% to 5% salt water for 15 minutes to 20 minutes, or splash a mixture of 500 ppm salt and baking soda over the whole pond. The second method is to splash 2 ppm to 3 ppm methylene blue over the whole pond once every 2 days, and after 5 days splash 0.2 ppm to 0.3 ppm hydantoin drugs once more.
2. Scale protrusion disease. This disease is caused by bacterial infection after water quality becomes turbid and the fish body is injured, leading to fluid accumulation in the scale sacs and causing scales to stand upright. It is highly prone to spreading in winter and spring and has an extremely high mortality rate. The main symptom is that the sick fish's scales stand upright, the body surface is rough, and the upright scales open outward. When pressed by hand, liquid spurts out from under the scales, and the scales then fall off.
For this disease, when it occurs, 0.3 ppm to 0.5 ppm chlorine dioxide can be splashed over the whole pond once a day for 2 days to 3 consecutive days. For cage-cultured fish, soak the sick fish in 0.7 ppm to 1 ppm chlorine dioxide for 20 minutes to 30 minutes once a day for 3 consecutive days.
3. Red skin disease. This disease is caused by pathogenic bacteria invading after the fish body is injured. The sick fish shows localized or mostly extensive bleeding on the body surface, scales fall off, fin rays become congested, and the ends of the fin rays rot in a broom-like shape, called "fin rot."
0.04 ppm bromochloro hydantoin or 0.25 ppm super iodine quaternary ammonium drugs can be splashed over the whole pond once a day for 2 days to 3 consecutive days.
4. Bacterial gill rot disease. The pathogen is Flavobacterium columnare, generally caused by direct contact between the fish body and the pathogen. The sick fish's body color turns black, especially on the head; gill filaments swell, mucus increases, and the ends are defective; the skin on the inner surface of the operculum becomes congested and inflamed, and the middle part often erodes into a round or irregular transparent small window, commonly known as "open skylight."
A mixed solution of 0.8 ppm copper sulfate and 1 ppm bleaching powder can be used to soak the sick fish for 15 minutes to 20 minutes; or 0.15 ppm benzalkonium bromide solution can be splashed over the whole pond once every other day for 2 to 3 consecutive times.
(2) Parasitic diseases
1. Ichthyobodiasis. Because this parasite parasitizes the fish body surface, the parasitic site on the sick fish becomes congested, inflamed, and eroded, mucus on the skin and gills increases, gill tissue cells necrose, and the sick fish has difficulty breathing. Microscopic examination shows large numbers of Ichthyobodo parasites.
The treatment method is that before stocking fry, a 0.7 ppm copper sulfate solution and a copper sulfate-ferrous sulfate (5:2) mixture can be used to soak the fish body for 20 minutes to 30 minutes.
2. Chilodonelliasis. The pathogen is Chilodonella cyprini, which parasitizes the gills and skin of freshwater fish. This disease has no special symptoms and is more likely to occur in ponds with poor water quality and small area. It is one of the serious diseases in the late wintering period in northern regions.
A 0.3 ppm to 0.4 ppm mixture of copper sulfate and potassium permanganate (5:2), or 0.7 ppm copper sulfate solution alone, can be splashed over the whole pond.
3. Ichthyophthiriasis. The pathogen is Ichthyophthirius multifiliis. On the skin, fin rays, or fin membranes of sick fish, small dot-like white blisters can be seen with the naked eye. Scales fall off, fin rays split and rot, swimming is sluggish, and the fish float on the water surface. Sometimes they also gather in groups and swim rapidly around the pond, continuously rubbing against the fish body and other objects, or jump out of the water and soon die in batches.
There are two treatment methods: for each mu with a water depth of 1 m, use 500 g chili powder and 100 g dried ginger slices, decoct into 25 kg of medicinal liquid, and splash over the whole pond once a day for 2 consecutive days; or splash 2 ppm methylene blue over the whole pond once every 2 days for 3 consecutive times.
4. Lernaea and Sinergasilus diseases. For disease caused by Sinergasilus parasitism, 0.5 ppm copper sulfate plus 0.2 ppm ferrous sulfate can be splashed over the whole pond.
0.7 ppm crystalline trichlorfon can be splashed over the whole pond once every 2 days for 3 consecutive times. Or for each mu, use 15 kg to 20 kg of pine branches and leaves, tie them into 5 to 6 bundles, insert and hang them around the feeding area, or crush them, soak out the juice, and splash it over the whole pond.
5. Fish louse disease. In low-temperature seasons, fish louse disease is highly prone to spreading, causing fish to become thin and weak, affecting growth, and can also cause concurrent bacterial diseases.
For this type of disease, a 0.3 ppm to 0.5 ppm crystalline trichlorfon solution can be splashed over the whole pond to prevent and treat it.