Diagnosis and treatment of California sea bass fry rotundifolia
_Guo Shaozhong
On February 1, 2021, an aquatic factory farm in the Pearl River Estuary purchased 3 million California perch fry (with a total length of about 0.5 cm) from an aquatic fry breeding farm in Shunde and put them into the fish tank for coarse labeling, and after 12 days of breeding, it was found that the fry swimming slowed down, the feeding was slow, and the dead fish began to die, and the number of dead fish from dozens to tens of thousands of fish every day exceeded 90%, and the loss was heavy. Microscopic examination showed that a large number of wheelworms were parasitic on the surface and fins of the fry.
First, the fry standard coarse situation
California sea bass fry are marked in indoor factory circulating fish tanks, which are round, 3 meters in diameter and 1.0 meters in depth, and each tank is stocked with 300,000 fish tanks, sharing 10 fish tanks (Figures 1 and 2). The standard water is aerated tap water and is oxygenated by pure oxygen. Dissolved oxygen in water 11~13 mg/L, pH 7.2~7.3, nitrite 0.05~0.13 mg/L, temperature 24~25 °C, micro-flowing water aquaculture. On the second day after seedling feeding, the harvest insects that have been bred for 24 hours are fed about 40 grams per 300,000 seedlings, and then fed with micro-granular compound feed, and the amount of feeding per fish tank per day is 50 to 100 grams.
Figure 1 Factory insulation greenhouse Figure 1 Factory insulation greenhouse
Fig. 2 Thick fish tank Figure 2 Thick fish tank
Second, the occurrence of diseases
When the California perch fry first began to coarse, its activity, feeding, and growth went smoothly, and when the standard thickness reached the 12th day, the fry grew to 1.0 to 2.0 cm and found to be slow and unresponsive. What started out as hundreds of dead fish a day gradually increased, killing thousands of them and taking heavy losses (Figure 3). At first, it was also considered to be a viral disease, and the sick fish was sent to the laboratory of Dongguan Animal Disease Prevention and Control Center for related virus screening and testing, and the test result was negative; microscopic examination was carried out on the 20th day, and a large number of wheelworms were found to parasitize the fry.
Figure 3 Death and swimming status of California perch fry in fish tanks Figure 3 Death and swimming status of California sea bass fry in fish tanks
3. Diagnosis and treatment
1. Symptoms Some of the onset fry are swirling in the upper layer of the water body, some swim alone, loose and unfocused; some fry feed slowly, do not grab food, or even do not eat. When the fry are picked up, more mucus is observed on the surface of the fry, and when the fry is shaken in the water for a period of time, it sinks to the bottom and dies (Figure 4), with no other obvious symptoms.
Fig. 4 California perch larvae secrete a large amount of mucus on the surface Of Fig. 4 California perch larvae secrete a large amount of mucus on the surface
2. Diagnosis Because the fry are small and secrete a large amount of mucus on the surface of the body, the fry are placed on a slide, dripped with 1 drop of distilled water, placed in a microscope, and examined at 10 times× 10 times and 40 times × 10 times. The body surface, fin, ventral fin, dorsal fin, and caudal fin parasitize a large number of wheelworms (Fig. 5, Fig. 6), especially the fin and ventral fin, and more than 5 wheel worms can be seen in each field of view (10 times × 10 times), and more than 20 are more than 20. Diseased fry were collected for fluorescence PCR testing of infectious spleen and kidney necrosis virus and largemouth bass iridescent virus, and the results were negative. Through the above tests, the disease was diagnosed as wheelworm disease.
Figure 5 Wheelworm at 10x × 10x Figure 5 Wheelworm at 10x × 10x
3. Treatment Considering that California perch fry are small and weak, the commonly used combination of copper sulfate and ferrous sulfate may cause certain damage to the fry, so the use of "wheel kill" (the main ingredient is a ethylene dipethiocarbamate ammonium) 120 ml / m 3 medicated bath, 1/3 of the water after 1 day. During the medication period, do not feed the feed, keep filling the water with oxygen, and the water body flows. On 48-hour post-microscopy, the surface rotifers of the fry are basically shed, the fin, pectoral fin, and ventral fin have a small amount of parasitism, and there are fewer than two wheelworms per field of view (10 times × 10 times) under the microscope. After the use of the drug, the death of the fry is sharply reduced and gradually returns to normal feeding and growth, and the treatment effect is obvious.
Figure 6 Wheelworm at 40x × 10x
Discussion
Factory nursery using aerated tap water to mark coarse California perch fry can suffer from wheelworm disease and cause mass death of fry, often finding it in a timely manner and delaying treatment. The field is due to the lack of timely discovery, until the later stage of drug treatment, each fish tank only left about 10,000 fry, the loss is heavy. Therefore, it is necessary to strengthen disease prevention and frequent microscopic examination to avoid unnecessary losses.
California sea bass fry are relatively weak, can not withstand the stimulation and poisoning of drugs, the choice of small irritation, high safety of drugs is the treatment of wheelworm disease is the first consideration of the problem, the choice of safe and effective caribial insecticide drugs is the key. Although it is not difficult to control wheelworms, it is not easy to choose drugs and grasp the concentration of drugs, and the low concentration cannot play a therapeutic effect, and it is easy to cause the stress response of fry and cause dead fish. When using insecticides, it is best to use the drug in more than two doses without mastering the dosage of the drug, with a period of time in between.