Development of New Green Feed for Large Water Surface Ecological Fishery

Zhenyan YANG, Yichun LOU, Lixia MENG, Juntian HAO, Weiguo CHEN, Aimei WANG

1. Jinan Academy of Agricultural Sciences, Jinan 250316, China; 2. Aquatic Technology Extension Department of Jinan Agricultural Technology Service Center, Jinan 250300, China

Abstract In view of the fact that cages and bait are not allowed in large water surface aquiculture, 1-2 kinds of new green feeds "plankton+microecologics" were developed to solve the problems of yield reduction, slow growth and difficulty in fishing of aquatic organisms caused by extensive mode. The new green feed is ecological, environmentally friendly and residue-free, which not only supplements nutrition but also meets the requirements of environmental protection.

Key words Large water surface, Ecological fishery, Green feed, Development

1 Introduction

In 2023, the No.1 Document of the Central Committee of the CPC proposed scientifically demarcating restricted areas to develop ecological fisheries on large water surface. Shandong Provincial Department of Agriculture and Rural Affairs, Shandong Provincial Department of Natural Resources, Shandong Provincial Department of Eco-environmental Protection and Shandong Provincial Department of Water Resources jointly compiled theDevelopmentPlanoftheLargeWaterSurfaceEcologicalFisheryinShandongProvince(2021-2025). ThePlanclearly stated that "it is necessary to give full play to the ecological function of large water surface fishery, protect the ecological environment of water areas, ensure the supply of high-quality aquatic products, promote the high-quality development of large water surface ecological fishery, give full play to the platform role of universities, research institutes and modern agricultural industrial system in Shandong Province, highlight the main role of enterprises in scientific and technological innovation, carry out technology research and development around the fields of green feed development and precise feeding, and promote collaborative innovation of production, education, research and application."

In recent years, with the implementation of continuous large-scale propagation and artificial releasing, the quantity of species resources released on large water surface has recovered, but the traditional fishery resources continue to decline, especially the traditional fish resources. Taking Xueye Reservoir in Laiwu District, Jinan City, Shandong Province as an example, the output of silver carp and bighead carp decreased from 1 000 000 kg to 300 000-350 000 kg per year now. The problems of miniaturization, younger age and lower value of fishery resources group structure are outstanding. Therefore, while protecting the environment of large water surface, improving the output of large water surface fishery and providing more high-quality aquatic products for the society are urgent problems to be solved at present.

2 Necessity of green feed development

Through experiments, green ecological plankton and beneficial bacteria were selected to combine and match instead of traditional feed, and artificial feeding (spraying) was adopted to artificially lure and domesticate the cultured varieties in the lake area, so as to solve the problem that no bait can be put in restricted waters such as reservoirs. It is extremely urgent to change the extensive mode of "culture at the mercy of the elements", which leads to the decline of fish resources. The new green feeding mode can increase the number of fish resources in water, improve the growth speed of fish in water to achieve the goal of increasing output and economic benefits without polluting water. The research of green feed accords with the development plan of large water surface ecological fishery in Shandong Province, and can solve the conflict between the development of large water surface fishery and environmental protection needs, and play a demonstration role for the ecological fishery culture in the large and medium-sized reservoirs in the whole city and even the whole province.

3 Present situation and development trend at home and abroad

China’s feed industry is developing rapidly. With the development of biotechnology, a variety of biotechnology products have been developed as feed additives——the core technology of feed industry. Microecologics have attracted worldwide attention because they are natural, non-toxic, safe, reliable, have no side effects, no residue, and cause no environmental pollution. The research and application of microecologics has a broad application prospect for developing green feed, and has solved many problems caused by long-term use of antibiotics in aquaculture. It has been listed as a key technical project promoted by the Ministry of Agriculture in the 21stcentury. The research, promotion and utilization of microecologics are in line with the overall requirements of sustainable development in China.

Since the 1970s, the feed microecologics have been used in the United States of America, and new antibiotic substitutes have been developed in Japan and some developed countries in Western Europe, and microecologics have been rapidly popularized. In the United States of America, more than 50 000 t of microbial feed additives are used annually, and the annual sales have exceeded 200 million US dollars; more than 5 000 t of microecological additives are used every year in Japan, with a value of more than 20 million US dollars. Every year, the total sales of microbial feed additives in the world have exceeded 2.5 billion US dollars.

With the deepening of scientific research and the continuous improvement of science and technology, feed microecologics have achieved great breakthroughs in strains, production technology and dosage forms, and the stability and processing resistance of products have been gradually improved. The research on feed microecologics in China began in the 1980s, and related products appeared one after another in the 1990s. At present, hundreds of feed microecologics have been registered.

The development and wide application of microecologics have played a positive role in the development of aquaculture in China. Microecologics are a kind of green environment-friendly products, and can not only have health care function, but also avoid the residue of antibacterial drugs. With the development of "white agriculture", microecologics will play a more important role in aquaculture.

At present, scholars at home and abroad have made some explorations on the application of microecologics in aquaculture, and achieved ideal results. However, compared with the research and application in medicine and animal husbandry, there is still a big gap and it is still at a low level. In view of the special environment of aquaculture and the in-depth development of biological science, it is a general trend to develop green feed with the development of high-quality, safe, environmentally friendly and efficient aquaculture as the guide, in order to improve production performance, reduce bait coefficient, reduce waste discharge and ensure product safety. At present, there is no research and development achievement of "algae+microecologics" green aquatic feed in China, and this study will greatly promote the development of ecological and healthy aquaculture on large water surface.

4 Research content

4.1SelectionofgreenfeedrawmaterialsChlorella,Scene-desmusand aquatic compound EM bacteria can be selected as raw materials of green feed.ChlorellaandScenedesmusshow very strong photosynthesis, and have rich nutrients and super reproductive ability. In aquaculture, chlorella and scenedesmus can not only be primary producers to provide oxygen for aquaculture water, but also be a very important part of bait resources. They are natural initial feed for various kinds of fish and direct bait for filtering-feeding fish.ChlorellaandScenedesmuscan effectively utilize organic matter such as ammonia nitrogen and nitrite, thus improving the ecological environment of water body, and can also inhibit harmful algae such as cyanobacteria, Euglena and dinoflagellate.ChlorellaandScenedesmusmultiply rapidly after being implanted into water and become dominant populations. Easy propagation and benefits determine the necessity of extensive culture and directional culture. They are two kinds of algae that are very easy to obtain and can be widely used on a large scale[1-2].

EM bacteria are a new type of compound microecologics, which are composed of photosynthetic bacteria, lactic acid bacteria, yeast, actinomycetes,Bacillusaceticusand other microorganisms. EM bacteria are a natural bait for filtering-feeding fish[3]. EM bacteria have the functions of promoting growth, improving feed utilization rate, enhancing disease resistance, deodorizing and improving ecological environment. The fermented EM bacteria emit a sweet and sour mellow taste, which can attract the fish.

4.2Cultureofgreenfeed

4.2.1Culture of chlorella and scenedesmus. (i) Treatment of water for culture. The water for culture of chlorella and scenedesmus can be directly selected, but it can only be used after full disinfection. Generally, it was sterilized with 50 mg/L bleach for 12 h, then neutralized with the same amount of sodium thiosulfate, and then inoculation could be carried out with starch potassium iodide as an indicator to detect that there was no residual chlorine. (ii) Culture vessel. In the experiment, a wide-mouth plastic bucket of 100 L was selected for propagation. (iii) Selection of algae species. Generally, bright green algae species without peculiar smell should be selected, and microscopic examination showed that the algae cells had no adhesion and were uniform, and they were in the exponential growth period. It is best to use a 350-mesh sieve when inoculating. (iv) Inoculation time and density. As long as the conditions are suitable, 8:00-10:00 is the best inoculation time, and we should pay attention to light and keep a good ventilated environment. The inoculation density was 4 000 000-4 500 000 million/mL. (v) Nutrient salts. 30 g of urea, 30 g of ammonium nitrate, 6 g of potassium dihydrogen phosphate, 0.5 g of ferric citrate, a dose of vitamin B1and a dose of vitamin B12were applied per ton of water body, and after 3-4 d, 1/3 of top dressing was applied. (vi) Light. Under suitable temperature conditions, the optimum illumination was about 10 000 lx. In summer, sunshade nets should be provided for cultivation, and special attention should be paid to avoiding direct sunlight; in cloudy days in spring and autumn, 1 kW iodine tungsten lamp can be used to increase illumination time and intensity. (vii) Timely feeding. After 3-5 d of culture, the density of algae cells reached 8 000 000-10 000 000/mL, and it can be put into use. Attention should be paid to feeding in exponential growth period.

4.2.2Culture of EM bacteria. (i) Culture tools. The tools include plastic bucket (50 L) with a lid that can be sealed for culture, mixer (it can be replaced by disinfectant stick), air pump, plastic bucket with an open mouth. Plastic bucket, mixer and all containers and tools used in the culture process should be cleaned, disinfected by bleaching powder and exposed to the sun to ensure dryness for later use. (ii) Culture water. After 1 d of precipitation, the culture water was disinfected with 50 mL/L bleaching powder. After 3 d, the upper water was taken and put in a plastic bucket with an open mouth, and fully aerated with an air pump. After residual chlorine was eliminated, it can be used. Aerated tap water or natural well water can also be used. (iii) The required culture medium and medicine. EM bacteria stock solution, brown sugar or molasses (desulphurized), yeast extract powder, trace elements, bleaching powder. (iv) Operation method. Taking 50 L of bacteria solution as an example, a 50 L plastic bucket that can be sealed contained 20 L of culture water, then 1.25 kg of brown sugar or molasses, 100 g of yeast extract powder and 50 g of trace elements were added in turn, 2.5 L of EM bacteria stock solution was added after stirring evenly, then water was added to make the volume up to 50 L. After stirring evenly again, it was closed for fermentation. The propagation kit can be bought in the market and propagation can be completed according to the matching requirements in the manual. Exposure to the sunlight was avoided during culture, the optimum temperature of culture was 25-35 ℃, and the fermentation period was 4-5 d. If the temperature was lower than 20 ℃, the sealing time can be extended for 2-3 d before use. A large amount of gas will be produced in the fermentation process. When it was cultured for about 2 d, the cap was opened and it was stirred before sealing. (v) Quality control. (a) See the color: The fermented bacterial liquid was brown, and there was white bacterial film on the upper layer, which was a normal phenomenon, because aerobic bacteria grew and multiplied rapidly after contacting oxygen on the surface to form bacterial film on the liquid surface. (b) Smell: It was sour and sweet. (c) Measure pH: Generally, the pH of fermented EM bacteria was 3.1-3.5. The lower the pH, the higher the lactic acid production in the surface fermentation process and the better the fermentation effect. (d) Microscopic observation: Morphological observation and counting can be carried out by microscope, and the total quantity of viable bacteria in good quality bacteria solution can reach more than 3×109cfu/mL.

4.3Studyonthefoodcallingeffectofgreenfeed

4.3.1Pre-test preparation. It was carried out in a 5 m×15 m net cage. The net cage is made of polyethylene with a mesh size of 2 cm. Before releasing fish species, the cage should be strictly inspected, and there should be no holes. The net cage was put into the water one month in advance, so that algae such as aquatic plants can be attached to the mesh to avoid causing injury to fish species. Silver carp and bighead carp (about 15 cm) were selected, and 200 fish were put into each cage, and the ratio of silver carp to bighead carp was 3：1. Vigorous and regular fish species with no diseases should be selected. Before releasing fish species, 2% salt water was used to sterilize and disinfect them.

4.3.2Test methods. There are 3 experimental groups and 1 control group in this experiment. The fish in the control group were not fed and allowed to grow naturally; the fish in the experimental group were fed with the mixture of chlorella,chlorella and scenedesmus, and the mixture of chlorella, scenedesmus and EM bacteria, respectively. When feeding, we should adhere to the principle of "fixed time, fixed point, fixed quantity and fixed person". The feeding amount should not be too large or too small. Too large amount will easily lead to the diffusion and waste of bait in water, and too small amount will not achieve the artificial feed calling and domestication effect. Silver carp and bighead carp were domesticated and cultured artificially by spraying liquid bait and simulating artificial feeding[4]. When feeding, the bucket or metal can be knocked to make a sound, so that the experimental fish can form conditioned reflex to gradually achieve the feed calling effect.

4.4StudyontheeffectofgreenfeedonfishgrowthThe growth data of four groups of silver carp and bighead carp were measured every month. The main measurement indexes were body lengthL(cm) and body weightW(g), and the fatness coefficient was calculated and analyzed by the formulaK= (W/L3)×100.

4.5Studyontheformulaofseveraldifferentgreenfeeds

The domesticated fish species were randomly divided into three experimental groups. Before feeding, chlorella, scenedesmus and EM bacteria were mixed according to the ratio of 1：1：1, 1：2：1 and 2：2：1, respectively[5]. The body lengthL(cm) and body weightW(g) of the three groups of fish were measured regularly, and the fatness was calculated, in order to explore the best biological bait formula suitable for the growth of silver carp and bighead carp in this study.

5 Conclusion

This experiment proves that the research and development of "algae+microecologics" green aquatic feed can effectively improve the growth rate of fish, improve the utilization rate of feed, enhance the disease resistance of fish, improve the water quality, and make it easy to domesticate and catch fish on large water surface. The new green feed is ecological, environmentally friendly and residue-free, which not only supplements nutrition but also meets the requirements of environmental protection, so it is suitable for wide popularization and application.