Experience sharing on reducing diseases in grouper aquaculture

If animals' healthy living environment cannot be basically guaranteed, excessively high stocking density, restricted movement, and an environment that becomes extremely harsh will all cause a decline in the animals' body resistance, creating conditions for the outbreak and spread of disease.

With breakthroughs in grouper artificial breeding and aquaculture technology, the scale of grouper aquaculture has continued to expand. In particular, industrialized recirculating aquaculture models have become an important support for the development of the grouper aquaculture industry in the north in recent years, but large-scale outbreaks of grouper diseases have also become a major obstacle seriously hindering the development of industrialized grouper aquaculture. At present, the relatively effective measures to reduce outbreaks of diseases in industrialized grouper farming are to comprehensively strengthen the prevention and control of nervous necrosis virus, parasites and bacteria from several aspects, including disinfection of fertilized eggs, cutting off virus transmission routes, monitoring of the aquaculture water environment, aquaculture management, and daily operations. In addition, there are still no effective drugs or other means that can fundamentally cure viral nervous necrosis. The phenomenon of disease outbreaks currently seen in industrialized grouper aquaculture is in fact also common in the livestock and poultry breeding industry, not only causing huge economic losses but even threatening human life safety. The ongoing struggle against livestock and poultry diseases has made people realize that if animals' healthy living environment cannot be basically guaranteed, excessively high stocking density, restricted animal movement, and an environment that becomes extremely harsh will all cause a decline in the animals' body resistance, creating conditions for the outbreak and spread of disease. Therefore, in line with the development of the modern livestock and poultry breeding industry, the concept of animal welfare emerged. Animal welfare is a direct translation of the term “animalwelfare” and arose in the early 1960s. It was proposed in response to problems that appeared in intensive production, such as increased disease, aggravated body damage, rising mortality, and increased abnormal behavior, aiming to call for full attention to the welfare status of livestock and poultry while ensuring their normal production, and to improve the level of welfare in the livestock and poultry production process. In order to define the ideal state of animal welfare, the Farm Animal Welfare Council (FAWC) established the standard framework of the “five freedoms”, namely: freedom from hunger and thirst, freedom from discomfort, freedom from pain, injury and disease, freedom from fear and distress, and freedom to express normal behavior. In recent years, phenomena have appeared in industrialized grouper aquaculture that seriously hinder the healthy development of the industry, such as disease outbreaks, severe cannibalism among fry, high rates of fry deformity, slow fry development, and abnormal body color in market-size fish. Their root causes are closely related to factors affecting the level of grouper animal welfare, such as reduced immunity, abnormal behavior, and stress stimulation caused by excessive stocking density, nutritional deficiency, water quality deterioration, and improper operations. The decline in grouper welfare level caused by changes (deterioration) in conditions such as ammonia nitrogen, pH, dissolved oxygen, temperature, salinity, flow speed, and flow pattern in the aquaculture water environment often manifests as weakened swimming ability, incomplete body surface features, dull body color, slow growth, inactive feeding, and reduced survival rate in grouper. In recent years, a group of enterprises that have succeeded in industrialized grouper aquaculture have begun to recognize the importance of providing a stable aquaculture water environment for grouper, and have successively introduced emerging technologies and facilities such as recirculating water equipment, water quality monitoring equipment, and the Internet of Things into industrialized grouper aquaculture workshops to ensure a suitable growth environment, and have achieved very good application results. Stocking density in aquaculture management is also an important factor related to grouper animal welfare. Too high a stocking density will affect the normal growth of grouper, increase the probability of cannibalism as well as the risks of disease outbreaks and production operations; while too low a stocking density not only reduces resource utilization efficiency but is also unfavorable to the formation of group behavior in grouper. Only an appropriate stocking density can reduce injuries to grouper caused by body contact, lower the probability of mutual interference and competition during feeding, and reduce opportunities for the spread of diseases such as viruses, bacteria, and parasites. In addition, human disturbance stress and operating methods during daily operations such as grading fry, dividing ponds, and feeding will also reduce the welfare level of grouper, leading to decreased immunity of fry, developmental deformities, abnormal body color, and even mass death. To change this situation, it is necessary to improve the skills and quality of practitioners, instill the welfare aquaculture concept of treating farmed subjects well, and formulate and strictly implement reasonable aquaculture protocols. Inappropriate capture, transport and processing operation methods, approaches, and guarantee conditions will also affect animal welfare conditions such as the body surface features, body color, flesh quality, and even survival rate of grouper. In the downstream sector of the grouper aquaculture industry, how to adopt measures and technical means conducive to improving the welfare of farmed fish and product quality according to the consumption habits of domestic consumers, so as to achieve the goal of providing consumers with high-quality, safe protein, will be an important marker of the grouper aquaculture industry moving toward the high end in the future. In summary, at present China's grouper aquaculture is transforming from an extensive small workshop-style aquaculture model to an intensive industrial aquaculture model. Whether in terms of facilities and equipment, or in terms of water quality monitoring, aquaculture management, feed and nutrition, and operating standards, the conditions for implementing welfare aquaculture are already in place. Many problems under extensive and semi-extensive aquaculture conditions that affect the yield and quality of farmed grouper, such as fin rot, bite wounds, abnormal body color, slow growth, developmental deformities, and swim bladder distension caused by reduced animal welfare levels, also now have solutions and pathways through the upgrading of aquaculture models. In the future, many key technical issues still need to be resolved in how to raise the level of welfare aquaculture in industrialized grouper aquaculture, involving many fields such as fish biology, fish aquaculture, environmental ecology, systems engineering, and information technology. It is believed that with the joint efforts of people from industry, academia, and research, a healthy and sustainably developing grouper aquaculture industry that can guarantee animal welfare and product quality will eventually be realized in the near future.