On July 23-26, 2021, at the invitation of Guangdong Hengxing Feed Industry Co., Ltd. and Wuxi Sanzhi Biotechnology Co., Ltd., the field visited and inspected the breeding and disease of deep-water cage golden pomfret (oval pomfret) in Zhanjiang Donghai Island, Xuwen, Beihai Tieshan Port and other sea areas, at present, the breeding of golden pomfret in several areas has generally begun to develop disease, mainly streptococcosis, which has caused certain losses, and some areas such as Qinzhou Port have begun to occur seawater small melon worm disease (stimulating cryptonuclear worm disease), overall, Diseases have gradually become an important obstacle to the cultivation of golden pomfret and are becoming more and more intense.
On-site visits
The main cause of the high incidence of disease
01 There is no continuous parental selection, and seed degradation has become prominent
During the visit, it was found that some large farmers obtained seedlings through self-breeding and self-cultivation, selected some able-bodied individuals from their own breeding adult fish as reserve parents, raised them until the fourth year of sexual maturity for breeding, eliminated after 5 years, and then selected parents from the farmed commercial fish. There is a lack of parental exchange between different groups or regions in this process, and inbreeding occurs. Some nursery enterprises do not strengthen the parents when purchasing sea-caught golden pomfrets as parent breeding, and the feeding bait is mainly chilled sea fish, streptococcus and Nocardia bacteria, etc. are likely to enter the parental pool through this route, and pass it on to the offspring after spawning and hatching.
Golden pomfret seedlings are different from the groups they grow, and the physique is not strengthened at the seedling stage, and some seedlings are weak when purchased, which is prone to disease.
02 Improper handling of sick and dead fish
After the onset of the disease in cage culture, some farmers directly fish out the dying fish and dead fish and discard them around the cage, some of the sick and dead fish are attached to the net until they decay, and a large number of highly pathogenic pathogenic bacteria exist around the cage, forming a regional outbreak and repeated pathogenic conditions.
Rotting dead fish on the side of the cage and sick and dead fish in the marine area
03 The ability to grab food is extremely strong
About 1 minute after feeding the feed, the golden pomfret is caught for dissection, and the stomach of the fish with a size of about 100g has contained 20-30 grains of feed, and the stomach can be seen to be nearly transparent when the abdominal cavity is opened, extremely inflated, and the feed in the stomach can be directly seen. Such a high-intensity feeding method will cause a great burden and pressure on the stomach and foregut in a short period of time, through the dissection of fish in different cages, gastric ulcers and intestinal lesions are more common, forming an important way of pathogen invasion.
Dissecting the abdominal cavity of the fish after feeding for 1 min can be seen with a gastric wall as thin as a piece of paper, the feed removed from the stomach
04 On-site service is not systematic
The grass-roots service force in the concentrated area of golden pomfret breeding has less on-site service, and the frequency of on-site inspection of fish steaks by aquatic technology promotion systems, fish pharmacies and feed factory service personnel is low, and the real situation of aquaculture is not deeply understood, and it is impossible to predict possible diseases in advance, and it is impossible to prevent diseases in advance.
Liver lesions and gastrointestinal lesions are found at a high rate during routine physical examinations
Body surface ulcers, mouth ulcers, etc. are found during daily physical examinations
05The depth of the service is not enough
The basic skills of technical service personnel in the breeding area are not strong, and the routine service work such as fish body inspection, gill silk microscopy, internal organ inspection, etc. is almost not carried out, and the condition of the fish cannot be objectively judged, and there is a lack of scientific understanding of the pathogens, causes, precipitating factors and prevention and control of fish diseases.
06 Lack of common sense of basic drug use
During the visit, it was found that farmers and technicians did not have a clear understanding of the pharmacology and medicinal properties of antibiotics and other drugs, misinterpreted the impact of antibiotics on physique and shortened the feeding time of antibiotics under this cognition, only dared to feed antibiotics for three days, and through three days of feeding may just control the number of dead fish, but did not completely control the disease, after stopping the drug harmful bacteria multiply in large quantities, resulting in recurrence, resulting in repeated attacks of the disease.
If you cannot correctly grasp the feeding dose of the drug, it will be reduced to about half of the normal feeding after the onset of the disease, and the amount of drug added in the unit quality feed will not be correspondingly improved, which will lead to a low dose of drug intake and a poor treatment effect. At low bait rates, the dose of the drug should be calculated according to the body weight of the fish.
Due to the high incidence of disease, there are the following risk points in the whole golden pomfret culture
01 Pathogenic bacteria drug resistance problem
The diseases that are more harmful to the cultivation of golden pomfret are streptococcosis, cryptonucleosis, Benedoniasis and neuronal necrosis virus disease, among which streptococci are widely affected, causing greater harm. In the prevention and control of streptococcal disease, there is a long-term, excessive use of antibiotics, some sea areas have emerged specific antibiotic resistance, if can not form a systematic prevention work, the incidence of disease is further improved, bacterial resistance is further enhanced, the loss caused by streptococcus will be further increased in the future.
02 Risk of further seed degradation
Due to the lack of awareness of good seeds, the long breeding cycle of fry breeding, and the high cost, there are no good seed farms above the municipal level in the nursery enterprises of golden pomfret. Without standardized parental breeding, seed preservation and other work, long-term self-propagation and self-rearing, etc., will further lead to a decline in the quality of seedlings, the incidence of further increase, breeding will be more difficult.
03 Farmers lack basic understanding of feed and disease prevention and control
Some farmers do not know much about the basic common sense of aquaculture, think that the disease is highly related to feed formula, after the onset of the disease, they begin to contact the feed formulator, and even change the feed, the understanding of conventional feed and functional feed is not clear, the functional feed is defined as a drug that can treat the disease, and it is expected to control the disease by feeding functional feed.
In view of the above situation, the main suggestions are as follows
01 Build a professional service system
It is recommended that aquatic technology promotion systems, fishery medicine clinics, feed enterprises and other levels of the construction of service systems, design service processes, service standards, the implementation of services to the front line of aquaculture, through services to improve the awareness and understanding of farmed fish, through standardized fish body inspection in advance to find problems, deal with small problems in advance, to avoid the emergence of larger problems.
02 For problems such as high incidence of streptococcus
After feeding sensitive antibiotics for more than 5 days, start adding antibacterial Chinese herbal medicine or functional feed for the digestive tract on the third day of feeding, and continue to feed antibacterial Chinese herbal medicine or functional feed for 5-7 days after stopping antibiotic feeding to restore intestinal health. It should be noted that factors such as the bait rate should also be taken into account when calculating the dose of the drug, and it is best to calculate the dosage according to the weight to ensure adequate drug intake.
03 High attention to the digestive tract
The way of bacterial invasion is the trauma of the body surface, the trauma of the gills and the trauma of the digestive tract, in view of the fact that the gastrointestinal trauma is more common in the cultivation of golden pomfret, the design of the prevention plan for fish diseases should focus on the health of the digestive tract, and reduce the probability of gastrointestinal problems by optimizing the feeding scheme and feeding functional feed.
04 Strengthen the parents and seedlings
Improve the awareness of good seeds, do a good job of high-quality parent reserves, strengthen the feeding of parents, give sufficient nutrition, promote the development of gonads, improve the quality of fish eggs and fry, do a good job in fry breeding, focus on feeding at the seedling stage, and ensure that the fry have excellent physique.
05 Establish disease prevention and control laboratories or service stations
When conditions permit, establish a fish disease prevention and control laboratory, mainly set up several functional areas such as pathogen detection, microscopic microscopy, water quality testing, and drug susceptibility experiments, and screen high-quality fry through routine fish body examination, pathogen detection and other services, find problems in fish bodies in advance, find small problems in advance, and avoid big problems.
06 Diseased and dead fish harmless treatment
The sick and dead fish after the onset of the disease are collected and harmlessly treated, avoiding random discarding, and cutting off the way for the pathogen to be transmitted by the sick and dead fish.
Aquaculture is a systematic work, involving many factors, fish disease prevention and control should start from the farmed animals themselves, not only to understand the pathogen, but also to understand the causes and precipitating factors, the establishment of a standardized fish disease prevention and control process, in order to better prevent the outbreak of disease.
Source: Scientific Fish Farming Author: Jiangsu Vocational College of Agriculture and Animal Husbandry Science and Technology Yuan Sheng Guangdong Hengxing Feed Industry Co., Ltd. Wei Zhenna Wang Zhuoduo Wuxi Sanzhi Biotechnology Co., Ltd. Jiang Rong Xu Hui