Investigation on the Incidence of Net Fish in North Harbour of Wanning City, Hainan Province

In mid-July, a large area of ​​dead fish disease occurred in cage fish culture grouper in Xiaohai, Xiaobei, Wanning City. On the 19th, the technicians of the Aquaculture Department of the Hainan Provincial Department of Marine and Fisheries conducted an on-site observation, microscopic examination, and analysis to analyze the incidence.

I. Symptoms of Fish Disease The outbreak of grouper fish disease in the small sea cage of Gangbei, Wanning City was first discovered in early July until the day after the “Cornson” typhoon. A large number of deaths occurred. According to incomplete statistics, 2 million catties of grouper were lost and the economic loss was about 38 million yuan. Technicians observe the fish by naked eyes. The fish body is thin, many small white spots are visible on the surface of the fish body and the sacral region, and a large amount of mucus is formed to form a grayish white film; , sometimes floating on the surface, swimming slowly. The axillary microscopic examination revealed a large number of cryptogenic Cryptocaryon irritans and ringworms, and there was no obvious abnormality in the internal organs during anatomy. The fish disease started from near the fish traps in the small seaport area and spread from one culture area to another. It shows strong regularity and is contagious.

II. Etiological Analysis 1. Comprehensive site investigations, fish disease symptoms, and microscopic examinations were analyzed. It was initially thought that the major outbreaks of this fish disease were mainly caused by the action of two parasites (stimulating Cryptocaryon irritans and ringworms), and they were ill. The tissue of the surimi was severely damaged by the parasite, and a large amount of mucus covered and blocked the respiratory system of the orbital paralysis, causing the appetite of the diseased fish not to eat or eating. The body was thin and the breathing was difficult. The pressure of the typhoon “Conson” was low. The dissolved oxygen is relatively low, eventually causing severe oxygen deprivation and suffocation. In recent years, the water temperature is mostly between 25-30°C, which is the most suitable water temperature for parasite growth and reproduction. It is also the season of protozoal infection in the sea area of ​​our province, which leads to the occurrence of fish diseases.

2. Because the cage fish or the traditional small fish as bait (especially the feeding stage of small and medium-sized fish), small trash itself with a variety of parasites, as a direct input carrier of parasites. After a small amount of parasites are imported, they are parasitized on cage equipment such as cages and floats, as well as parasitized organic matter in the waters. When environmental water quality is appropriate, they can quickly reproduce and grow and damage farmed fish.

3. Farmers' awareness of fish disease prevention is weak, and they are not able to prescribe the right medicines. They have not properly handled dead fish and diseased fish and allowed them to float, causing secondary fish infections and the occurrence of cross-infection in culture areas.

Third, measures and countermeasures 1. Evacuation of fish rafts to reduce stocking densities, and activate conditional farmers to transfer fish rafts to sea areas or ponds with good water flow, good water quality, ease of environmental pressure, and replacement of cages.

2. Organize cultured area farmers to clean up the dead fish and remove them from the dead fish to avoid causing secondary infections and secondary bacterial diseases.

3. Organize the culture owners for emergency treatment. Fresh fish, formalin 200-300ppm solution and oxygenated fish body were soaked for 15-25 minutes (depending on the tolerance of the fish) and treated continuously for 2-3 days. At the same time combined with the use of antibiotic oxytetracycline 10 g / t water immersion once, and feeding antibiotics (such as florfenicol), according to 20mg / kg ratio of fish fed, fed 5-7 days for a course of treatment. Avoid secondary bacterial diseases.

IV. Recommendations 1. Control the number of cages and stocking densities in the sea area to rationalize the layout of cages. The amount of pollutants entering the sea area exceeds the self-purification capacity of the sea area and will cause environmental degradation. Staff should be organized to do in-depth work to reduce the number of cages. Planning cages should be arranged in "goods" to facilitate the exchange of water bodies. The cage capacity is controlled below 7-8 kg/m3.

2. Improve the level of aquaculture technology and strengthen the overall awareness of disease prevention.

(1) Propaganda work is required to require fishermen in the sea area to report fish diseases to relevant departments in a timely manner in order to make predictions, properly handle dead fish and diseased fish, and prevent spread of the disease.

(2) Do a good job of cleaning and replacing cages. It is recommended to replace the cages in about 20 days. Disinfect the fish regularly with fresh water and drugs, once every two weeks.

(3) Guide the fishermen to use formulated feeds to reduce the use of chilled raw baits and prevent eutrophication of the sea area. Guide the development of farmers from the bay culture to offshore development.

3. Strengthen research on fish disease control and establish a fish disease monitoring network.

The editor's posthumous name, Gangbei Xiaohai, has been breeding cage culture since the early 1990s. The breeding species are mainly grouped with green spot and dragonfly grouper. In the past two decades, the benefits of grouper have been relatively good, and the current number of fish row More than a thousand, the breeding density is also growing.

After a large amount of dead fish time occurred in the cage culture in the small sea in the northern part of Hong Kong, the publication found that the entire water area of ​​the pier was covered by cages, leaving only the passage for the ship. The side of the wharf is a living area. According to relevant sources, domestic garbage, sewage discharge, and water phenomena are extremely common. In addition, a large number of fish excrement and residual baits have accumulated at the bottom for many years of cultivation. The storm caused by “Conson” typhoon Disturbance at the bottom of the sediment, coupled with the small amount of rainfall this time caused, the rapid deterioration of the water situation, the proliferation of various types of parasites; On the other hand, due to the narrow port of the north of the harbor, sediment congestion is becoming increasingly serious. The exchange of water bodies inside and outside Hong Kong has caused great obstacles. The water level in the port is relatively shallow, only 2 meters deep at the time of ebb, and only 3 meters deep at high tide.

Prior to the arrival of the "Conson" typhoon, local farmed fish often had symptoms such as hypoxic floating heads. This was exacerbated by the low pressure brought by Conson.

It was also learned that soon after the magazine visited, a large-scale red tide incident occurred in the Lingshui Xincun harbor, which was similar to the Hong Kong environment, and caused great losses to local fish rafts. According to relevant sources, in the future, if the sea area cannot be properly blocked, sediments will be deposited on the bottom of the river, and smooth flow of sediment will be exchanged, disease problems will be difficult to avoid.

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