How can diseases in grouper aquaculture be effectively reduced?

With breakthroughs in artificial breeding and aquaculture technology for grouper, the scale of grouper farming has continued to expand. In particular, the industrial recirculating aquaculture model has become an important support for the development of the grouper farming 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 industrial grouper farming. At present, the relatively effective measures to reduce outbreaks of diseases in industrial 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 viral 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 current phenomenon of disease outbreaks in industrial grouper farming is actually also common in the livestock and poultry farming industry, not only causing huge economic losses but even threatening human life and safety. The continuous struggle against livestock and poultry diseases has made people realize that if the basic guarantee for a healthy living environment for animals cannot be provided, excessively high stocking density, restricted animal movement and an extremely harsh environment will all cause a decline in the disease resistance of the animal body and create conditions for the prevalence and spread of epidemics. Therefore, in line with the development of the modern livestock and poultry farming industry, the concept of animal welfare emerged. Animal welfare is a literal translation of the term “animal welfare”, which arose in the early 1960s. It was proposed in response to problems appearing in intensive production such as increased disease, aggravated body damage, rising mortality and increased abnormal behavior, and it aims to call for fully emphasizing 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”, which are: 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. Attention to the welfare status of fishFish are relatively advanced vertebrates among aquatic animals, and studies have proven that they have the ability to perceive, respond to and remember external uncomfortable environments. However, because the scientific community still has some controversy over whether fish and other aquaculture animals are capable of experiencing pain, fear and distress, current welfare evaluations of aquaculture animals still mainly focus on physiological health indicators of farmed animals. As far as farmed fish are concerned, general fish biological characteristics such as appearance traits, growth status, mortality, health status, stress response and behavior can all reflect the welfare status of fish. Related studies have confirmed that when the welfare of farmed fish is affected by environmental, biological and other stressors, the physiological response of the fish body goes through three stages. Stage one: chromaffin tissue releases catecholamines and the hypothalamic-pituitary-interrenal axis (HPI) is activated, stimulating the secretion of corticosteroid hormones and their release into the blood circulation system. Stage two: a series of changes at the physiological and biochemical levels mediated by the various hormones produced in stage one, involving the regulation of almost all physiological functions related to the life activities of fish, such as respiration, metabolism, acid-base and osmotic pressure balance, immune activity and cellular responses. Stage three: on the basis of the physiological and biochemical changes in stage two, farmed fish, because they cannot adapt to the environment or other pressures, experience slow growth, reduced disease resistance, poor reproductive capacity, low mobility and even changes in morphological characteristics. In recent years, scientists in Europe and the United States have carried out exploratory research on the farming welfare of fish such as rainbow trout, sparids and flatfish, and found that different aquaculture conditions such as different water exchange rates, different stocking densities and different ozone concentrations all affect the appearance traits (mainly body surface and fin damage), deformity rate, mortality, behavioral characteristics (mainly swimming, feeding and competition), blood indicators (mainly cortisol and immune factors) and neuroendocrine indicators (mainly growth hormone, neurotransmitters, etc.) of farmed fish. Researchers and the aquaculture industry have therefore gradually used these related indicators to measure the welfare level of fish. Diseased tiger grouperIn the fish farming industry, it is currently generally believed that the links that can affect animal welfare include environmental factors such as facilities and equipment, aquaculture water bodies, and biological factors such as daily operation and management, capture and transport, and feed supply. Therefore, how to avoid the adverse consequences caused by long-term and repeated stress from the environmental and biological sources has become the central goal pursued by fish farming welfare. This is specifically manifested in artificially providing farmed fish with an aquaculture environment that basically conforms to their biological habits and reduces stress, ensuring sufficient nutritional feed, and adopting measures beneficial to the fish's own welfare in the processes of disease prevention and control, aquaculture management, capture, transport and processing, so as to achieve the purpose of providing society with high-quality and safe aquatic products. Improving the level of welfare-based farmingIn recent years, phenomena that seriously hinder the healthy development of the industry have appeared in industrial grouper farming, such as disease outbreaks, severe cannibalism among fry, high deformity rate of fry, slow development of fry and abnormal body color of market-sized fish. Their root causes are closely related to factors affecting the animal welfare level of grouper, 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 velocity 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. Stressed grouper develop bloating and float on the water surfaceIn recent years, a number of enterprises that have succeeded in industrial grouper farming 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 industrial grouper farming 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 the animal welfare of grouper. Too high a stocking density will affect the normal growth of grouper, increase the probability of cannibalism and 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 fry grading, pond splitting 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-based farming concept of treating farmed animals well, and formulate and strictly implement reasonable aquaculture procedures. Inappropriate operation methods and methods as well as safeguard conditions for capture, transport and processing will also affect animal welfare conditions such as body surface features, body color, flesh quality and even survival rate of grouper. In the downstream of the grouper farming 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 and safe protein, will be an important sign of the grouper farming industry moving toward the high end in the future. In summary, at present China's grouper farming is transforming from an extensive small workshop-style farming model to an intensive industrial farming model. Whether in terms of facilities and equipment, or in terms of water quality monitoring, aquaculture management, feed and nutrition, and operating standards, conditions for implementing welfare-based farming are already in place. Many problems under extensive and semi-extensive farming 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 bloating caused by reduced animal welfare levels, also have solutions and pathways through the upgrading of farming models. In the future, there are still many key technical problems to be solved in how to improve the level of welfare-based farming in industrial grouper farming, involving many fields such as fish biology, fish farming, 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 farming industry that can guarantee animal welfare and product quality will eventually be realized in the near future.