For mandarin fish farmers, what they fear most is not bad weather, but the sudden outbreak of a "devastating disease" in the ponds - the infectious splenorenal necrosis virus (ISKNV), which is known as the "number one killer" of mandarin fish. The various secondary bacterial infections it causes can lead to tens of thousands of deaths in a short period of time!
Today, let's thoroughly lift the veil of mystery behind this "killer" and offer the most practical tips on prevention and control.
First, understand: What exactly is ISKNV? Why so fierce?
Infectious spleen and kidney necrosis virus, abbreviated as ISKNV, is a highly pathogenic virus that mainly infects freshwater fish. It belongs to the Iriviridae family. Infectious spleen and kidney necrosis virus is a "tough guy" in the Iriviridae family and can infect mandarin fish, California bass, largemouth bass and other fish, but it is most pathogenic to mandarin fish.
As the name suggests, it mainly attacks the two core organs of mandarin fish: the spleen and the kidneys.
The spleen: It is an essential immune and hematopoietic organ for fish.
Kidneys: Responsible for excreting waste and regulating osmotic pressure.
Once these two organs die, the immune system of the mandarin fish will completely collapse, and its metabolism will be thoroughly disrupted, equivalent to "liver and kidney failure" in the human body. The mortality rate is extremely high, reaching up to 100%. It is not an exaggeration to call it "mandarin fish cancer".
Second, the key! Five typical symptoms of ISKNV onset, early recognition for early loss prevention
Appearance: Diseased mandarin fish usually show symptoms such as floating on the water surface, reduced activity, and accelerated breathing. The body surface shows congestion inside the eyes, bleeding at the base of the fins, and pale gills. The diseased fish swim alone and leave the group, showing the phenomenon of "black head and yellow body". The dying fish has a black body color, swims alone in groups, and the outer edge of the gill cover and the caudal peduncle are congested and ulcerated. The eyeball protrudes with corneal hemorrhage, and ulcers occur at the base of the pectoral fin and the lower jaw.
Anatomy: The liver is ischemic and pale or has many bleeding points, and its texture becomes brittle. The spleen volume has increased to three times the normal size and appears purplish black. Anemia in the medulla of the kidney and congestion of blood vessels in the cortex; Yellow jelly-like secretions accumulate in the intestines. Spotted bleeding foci on the gastric wall.
Disease course: Acute onset. The mortality rate soars from dozens to hundreds of cases per day within 2-3 days, and the pond discharge rate is extremely high within a week.
Iii. Distinguish similar diseases to avoid misdiagnosis
In actual breeding, it is necessary to distinguish it from bacterial sepsis and other viral diseases:
The difference from bacterial sepsis: In viral diseases, the blood does not coagulate, while in bacterial sepsis, the blood coagulates. In viral diseases, the liver loses severe blood and appears as a white liver. In bacterial sepsis, the liver is often characterized by congestion, purple color or uneven coloration. The gill bleeding in viral diseases is pink or white, while bacterial sepsis is generally characterized by congestion and purplish color.
The difference from frog iridovirus disease: Infectious splenorenal necrosis virus disease has a sudden onset and a high mortality rate, while frog iridovirus disease has a longer duration of onset and usually shows a slow and continuous trend of death. Frog iridovirus disease can cause extensive ulcers in the digestive tract.
Four. Scientific Prevention and Control: From "Prevention" to "Emergency Response", One Plan to Safeguard the ponds
There is currently no specific drug for ISKNV (antibiotics are ineffective against the virus!) Therefore, "prevention first, emergency response second" is the core principle.
Pond cleaning and disinfection: Before releasing seedlings, thoroughly remove excessive silt from the pond and evenly sprinkle quicklime (125-150 kg per mu) throughout the pond.
Select specific pathogen-free (SPF) fry: Give priority to choosing mandarin fish fry that have undergone strict testing and been confirmed to be virus-free for breeding.
Strengthen virus detection: Before feeding, virus detection must be conducted on the bait fish. It is recommended to use artificial compound feed to reduce the risk of virus transmission. Regularly conduct random inspections on farmed mandarin fish.
Stable water quality management: Monitor key indicators such as water temperature, dissolved oxygen, ammonia nitrogen, and nitrite every day. Dissolved oxygen should be no less than 5mg/L, ammonia nitrogen no more than 1.5mg/L, and nitrite no more than 0.3mg/L.
Once it is found that mandarin fish are infected with the infectious spleen and kidney necrosis virus, it is strictly forbidden to abuse drugs or frequently change water. The correct medication plan is as follows:
Stop feeding immediately: Reduce the metabolic burden on the fish and prevent further deterioration of water quality.
Oxygenation measures: Increase the operation of oxygenation machines to ensure sufficient dissolved oxygen.
Disinfection treatment: Use compound iodine (0.3ml/m³) for continuous disinfection for 3 days; Or spray the navigator ➕ hailian heavy iodine externally, mainly to prevent bacterial infection.
Oral medication: Oral recommendation: Liver and Intestine Guard ➕ Navigator ➕ florfenicol for 7 consecutive days.
Anti-stress treatment: Sprinkle anti-stress products such as taurine and VC throughout the pond to alleviate the stress response of the fish.
Harmless treatment: Diseased and dead fish are treated harmlessly by methods such as burial.