AU2021232694A1

AU2021232694A1 - Method for hatching and culturing grouper using chlorella

Info

Publication number: AU2021232694A1
Application number: AU2021232694A
Authority: AU
Inventors: Chengtan HUANG; Min Huang; Jun Pan; Lei Ye
Original assignee: Hainan Green Algae World Biotechnology Co Ltd
Current assignee: Hainan Green Algae World Biotechnology Co Ltd
Priority date: 2021-06-17
Filing date: 2021-06-17
Publication date: 2023-01-19
Anticipated expiration: 2041-06-17
Also published as: WO2022261886A1; AU2021232694B2

Abstract

The present disclosure relates to the field of grouper cultivation, in particular to a method for hatching and culturing grouper using chlorella. The present disclosure applies the self-produced natural green microalgae product to the indoor industrialized culturing of grouper, breaking through the problems of extremely low hatching survival rate of grouper and serious pollution, and opening up the whole process of indoor industrialized culturing, which provides a boost for the transformation to indoor industrialized culturing of grouper. - 23 -

Description

METHOD FOR HATCHING AND CULTURING GROUPER USING CHLORELLA FIELD

[0001] The present disclosure relates to the field of grouper cultivation, specifically to a method for hatching and culturing grouper using chlorella.

BACKGROUND

[0002] Groupers belong to Perciformes and live in temperate and tropical waters. They mostly live in the coral reefs and crevices between seabed gravel, and do not migrate long distances. Groupers have variable body color, often brown or red, with stripes and spots, and are a large or medium-sized marine fish of warm water. Grouper is rich in nutrients, tender and white, similar to chicken, and known as "sea chicken". Grouper on the market is regarded as precious seafood. In addition, it is also a low fat, high-protein, high-quality edible fish, and it has been promoted as one of the four famous fish by Hong Kong and Macau in China. Grouper fish are often found in high-end hotels and restaurants, with high prices and short supply. Driven by economic interests, grouper aquaculture has developed rapidly.

[0003] Grouper cultivation is currently the fourth largest culturing species in China. In recent years, due to the continuous increase in market demand for grouper, the production of grouper in China has increased year by year. The annual increase of grouper cultivation exceeds 21%, and its growth rate far exceeds that of the top ranked bass and flounder. Grouper has become the only species other than large yellow croaker that has sustained and rapid growth.

[0004] At present, the open-air hatching of groupers in the outer pond (from the eggs to 3cm larvae) is affected by factors such as weather, water quality, bait and the like, and the hatching success rate is extremely low. Even if the fry are hatched, their survival rate is basically less than 5%, and the fry quality is not high. Currently, in the indoor factory circulating water hatching, the Guangdong Marine Fishery Experiment Center has achieved the most successful survival rate of 12.5%, but there are also various problems that lead to a low success rate.

[0005] The process of grouper culturing from 3 cm larvae to 15 cm fries is called "marked thick". During this process, the stage of growing from 3cm larva to 4-5 cm fry is extremely easy to fail. There are two main reasons:

[0006] 1. Since the 3cm larvae are hatched from outside ponds, they are potentially at risk of virus infection, or their physique immunity is low, so they are very easy to die

[0007] 2. At this stage, the larvae have weak resistance and are more susceptible to infection by harmful pathogen in the external water. And the more the infection, the more the farmers use drugs, which leads to the increase of the resistance of the pathogens. Besides, after the polluted water is discharged to the coast, the number of pathogens carried by the external water also increases sharply, forming a vicious circle.

[0008] Since the 1970s, Southeast Asian countries, Kuwait, Chinese mainland, Hong Kong, and Taiwan, etc. have successively carried out research on artificial culturing of grouper. From the perspective of industrialized production, Taiwan was the first to achieve success.

[0009] In Chinese mainland, the research on artificial culturing technology of grouper began in the 1980s. The first success of the artificial culturing of the blue grouper was achieved by the Zhejiang Marine Fisheries Research Institute. Since then, the Institute of Oceanology of Chinese Academy of Sciences has achieved the success of the artificial culturing of the red grouper and the giant grouper. The marine fish culturing research team (Guohua Chen team) of Hainan University started research on promotable artificial culturing of grouper in Hainan, which was supported by One Hundred New Agricultural Technology Projects in Hainan Province in 1998.

[0010] The research and development of foreign varieties is currently showing the development trend of both high yield and high quality. The international seed industry system presents the development characteristics of "enterprise as the main body, integration of culturing, reproduction and promotion", and the international breeding industry market structure is showing a monopolistic development trend. In contrast, the development of China's aquatic seed industry presents that the construction of the genetic culturing and the original seed system are gradually improving, and the innovation of culturing technology and the cultivation of new varieties have made great progress. However, at present, China's aquatic seed industry still has a large number of problems, such as requiring a great deal of imported foreign seedlings; not high level of improved varieties, and low rate of genetic improvement. Compared with the large international seed companies, most aquatic seed companies are relatively small, and their core competitiveness and industry advantages have not yet been formed.

[0011] The traditional hatching and culturing mode of grouper is based on outdoor hatching in outside ponds. Due to factors such as weather, water quality, and bait, the hatching success rate is extremely low. Even if the larvae are hatched, their survival rate is basically less than 5%, and the fry quality is not high. Currently, in the indoor factory circulating water hatching, the Guangdong Marine Fishery Experiment Center has achieved the most successful survival rate of 12.5%, but there are also various problems that lead to a low hatching success rate. In addition, problems such as extensive culturing, frequent pests and diseases, and extremely low survival rate of fry have caused farmers to abuse illegal drugs such as antibiotics in order to preserve the quantity of goods, resulting in a decline in the quality of fish because of containing medicinal products, as well as serious water pollution.

[0012] The success rate of grouper hatching is a difficulty in the industry. The hatching success rate is low and very unstable, about 0 . 1 -10%. The three stages of high mortality in the hatching process are the mouth opening and feeding stage, the fin spine growing out stage and the fin spine retracting stage (Table 1).

Table 1 Three major stages of grouper hatching and culturing

Three major Opening and feeding Fin spine growing out Fin spine retracting stages of stage stage stage grouper hatching 1. Lack of suitable baits, 1. Deaths from insufficient 1. Viral nervous necrosis difficult to open mouth, nutrient or unbalanced (symptoms: floating, and starved to death; nutrition, and not smooth spinning, black body, 2. Poor physique and metamorphosis etc.); weak anti-stress ability development; 2. Deaths from of the larvae; 2. Direct stress deaths from insufficient baits due to Reasons 3. Unstable water body sudden changes in weather high larvae density, and (high pH), high and instability of the water incomplete nutrition incidence of gas bubble body, or deaths from other lacking EPA and DHA; disease; diseases; 3. Water quality and 4. Stress deaths from 3. Deaths from high bottom quality pollution drastic changes of incidence of gas bubble that exceed the environment before and disease, or deaths from viral self-purification capacity after unpacking, sudden diseases; of the water body; changes in weather, etc., 4. Mass mortalities of fry if 4. Poor biological quality or deaths from viral there is too much moss in of the bait carrying diseases. the pond after the wing bacteria and viruses that developed. cause the disease of the fry; 5. Too much stress due to sudden changes in weather; 6. Hypoxia and high incidence of gas bubble disease.

[0013] Chlorella is rich in essential fatty acids for fry growth such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Internationally, extensive and in-depth research on the application of chlorella to the bait food industry has been done, and many countries and regions have carried out commercial production of chlorella. The United States, Japan, Israel and Chinese Taiwan have used chlorella powder as a health food and excellent feed additive for more than 30 years. Microalgae cultivation is an important link in aquaculture and industrialized production, and is an important aspect of fish, shrimp, and shellfish culturing, especially the bait for the cultivation stage, the success of which is directly related to the success or failure of artificial seedlings.

[0014] Seawater fish cultivation is inseparable from microalgae, but because most farmers and enterprises cannot guarantee a stable supply of fresh microalgae during the incubation and process, they have to choose algae powder in order to improve the survival rate of seedlings. This is also a major factor leading to a high rate of hatching failure, because in the high temperature milling process of microalgae, amino acids and active substances lose their activity due to high temperature, which greatly reduces the nutritional content of algae powder, and ultimately fails to achieve the expected effect.

[0015] Microalgae, as excellent and suitable bait for larva and fry growth, is mostly used in the larva and fry stage of fish, shrimp, crab and shellfish growth. The addition of microalgae can improve the growth performance of the cultured objects, supply the insufficient nutrients in the composite feed, reduce the feed cost, increase the survival rate, enhance the disease resistance, increase the body color, improve the quality of aquatic products, etc.. For example, the key to the success or failure of green clam culturing is whether a large number of high-quality algae that meet the needs of larva and fry can be cultivated. The survival of shrimp companies is mainly determined by the result of shrimp larva rearing. Shrimp seed fed with unicellular algae has better metamorphosis time, vitality, size, and water quality than those unfed with unicellular algae, while the survival rate of shrimp seed directly affects the ups and downs of the industrial chain. Using unicellular algae as the most suitable bait for grouper larva and fry in the early stage, if the cultivation is carried out properly, it can not only save costs and reduce the environmental load of the rearing water body, but more importantly, it can increase the survival rate and lay a solid foundation for the development of fry.

SUMMARY

[0016] In view of this, the present disclosure provides a method for hatching and culturing grouper larva and fry. This method solves the problems of extremely low hatching survival rate of grouper and serious pollution.

[0017] In order to achieve the above-mentioned purpose of the invention, the present disclosure provides the following technical solutions.

[0018] The present disclosure provides a method for hatching and culturing grouper fry, comprising the following steps:

preparing worms: starting to prepare ss rotifers temporarily 3-4 days before placing fish eggs, and using a microbicide (JunKe) to remove bacteria, viruses, organic impurities and dead worms;

placing egg: selecting eggs which have less than 40 dead eggs (bottom-sinking eggs) per hectogram; and placing the eggs in purified seawater, and the density of the fish eggs in the final water body is greater than 7000 eggs/ton;

the day of egg placement is counted as Day 1; from Day 2 of egg placement, adding 50-100 g of photosynthetic bacteria (with a viable amount of 1.0~2.x101° cfu/g) and 50-100 g of bacillus (with a viable amount of 1.0-2.Ox101 cfu/g), to make the concentration of each bacterium in the water body reach 1000 cfu/ml; from Day 3 of egg placement, adding chlorella algae every morning as 1.2~1.5 L of chlorella algae liquid per ton of water body, and the density of the chlorella algae liquid is calculated as 14-20 million cells/mL; after the addition, waiting for 1 hour before taking samples to detect the density of algae in the water body, to make the density of algae in the water body reach 50,000~100,000 cells/ml; from Day 3 of egg placement, adding rotifers every day, and measuring the algae content in the morning and afternoon to ensure that the algae content in the aquaculture water is greater than 150,000-300,000 cells/mL; from Day 3 of egg placement, adding 10-30 g of EM bacteria (with a viable amount of 1.0~2.x10 cfu/g); from Day 10 of egg placement, reducing the daily adding amount of chlorella by 20~30% based on the previous day until the amount of chlorella added reaches 1-2 L of chlorella algae liquid per ton of water body, and the density of the chlorella algae liquid is calculated as 14-20 million cells/ml; according to the size of fry, gradually changing worms; changing the water daily; and on Day 21 of egg placement, the fries are ready.

[0019] In some specific embodiments of the present disclosure, from Day 3-5 of egg placement, adding 30-50 g/ton of water body of rotifers (rotifer content not less than 1000/g) every day, feeding with the worms once every 2-3 hours, monitoring the worm content in the water body once every 3 hours and adding extra if there are less than 20 rotifers/mL; the whole process is under light;

the rotifers are screened by double-bag filtration, with an outer bag of 350 mesh and an inner bag of 250 mesh, and the rotifers sandwiched between the outer bag and the inner bag are used.

[0020] In some specific embodiments of the present disclosure, from Day 6-7 of egg placement, adding 30-50 g/ton of water body of rotifers (rotifer content not less than 1000/g) and adding 100 g/ton of water body of copepods (copepod content not less than 200/g) every day, feeding with the worms once every 2-3 hours, monitoring the worm content in the water body every 3 hours and adding extra if there are less than 20 rotifers/mL water body or less than 2 fleas/ml water body; light is on from 8:00 am to 7:00 pm; the rotifers are screened by double-bag filtration, with an outer bag of 350 mesh and an inner bag of 250 mesh, and the rotifers sandwiched between the outer bag and the inner bag are used; the copepods are screened by single-bag filtration with a 200 mesh filter.

[0021] In some specific embodiments of the present disclosure, from Day 8-9 of egg placement, adding 30-50 g/ton of water body of rotifers (rotifer content not less than 1000/g) and adding 200 g/ton of water body of copepods (copepod content not less than 200/g) every day, feeding with the worms once every 2-3 hours, monitoring the worm content in the water body every 3 hours and adding extra if there are less than 20 rotifers/mL water body or less than 2 copepods/ml water body; no light;

the rotifers are screened by double-bag filtration, with an outer bag of 350 mesh and an inner bag of 200 mesh, and the rotifers sandwiched between the outer bag and the inner bag are used; the copepods are screened by single-bag filtration with a 200 mesh filter.

[0022] In some specific embodiments of the present disclosure, from Day 10-13 of egg placement, adding 15-30 g/ton of water body of rotifers (rotifer content not less than 1000/g) and adding 200-300 g/ton of water body of copepods (copepod content not less than 200 copepods /g) every day, feeding with the worms once every 2-3 hours, monitoring the worm content in the water body every 3 hours and adding extra if there are less than 2 copepods/ml water body; no light;

[0023] In some specific embodiments of the present disclosure, from Day 13-20 of egg placement, adding 300-800 g/ton of water body of copepods (copepod content not less than 200 copepods /g) every day, feeding with the worms once every 2-3 hours, monitoring the worm content in the water body every 3 hours and adding extra if there are less than 2 copepods/ml water body; no light;

the copepods are screened by single-bag filtration with a 150 mesh filter.

[0024] In some specific embodiments of the present disclosure, from Day 21 of egg placement, adding 800-1500 g/ton of water body of copepods (copepod content not less than 200 copepods /g) every day, feeding with the worms once every 2-3 hours, monitoring the worm content in the water body every 3 hours and adding extra if there are less than 2 copepods/ml water body; no light;

the copepods are screened by single-bag filtration with a 100 mesh filter.

[0025] In some specific embodiments of the present disclosure, the pH range is 8.2-7.8, and the daily drop are not greater than 0.15; the DO range is 4.5-6 mg/L; and the ORP range is 100-300.

[0026] In some specific embodiments of the present disclosure, the range of ammonia nitrogen is <0.15 mg/L; and the range of nitrite is <0.1 mg/L.

[0027] In some specific embodiments of the present disclosure,

early stage (before fin spine retraction): the upper limit of ammonia nitrogen alarm is <0.12 mg/L, the upper limit of control is <0.15 mg/L; the upper limit of nitrite alarm is <0.06 mg/L, the upper limit of control is <0.1 mg/L;

later stage (after fin spine retraction): the upper limit of ammonia nitrogen alarm is <0.15 mg/L, the upper limit of control is <0.2 mg/L; the upper limit of nitrite alarm is <0.06 mg/L, the upper limit of control is <0.1 mg/L.

[0028] The present disclosure applies the self-produced natural green microalgae to the indoor industrialized culturing of grouper, breaking through the problems of extremely low hatching survival rate of grouper and serious pollution, and opening up the whole process of indoor industrialized culturing, which provides a boost for the transformation to indoor industrialized culturing of grouper.

BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the examples of the present disclosure or in the prior art, the drawings used in the examples or the prior art will be briefly introduced below.

[0030] FIG. 1 shows the changes of dissolved oxygen in the water during the culturing process;

[0031] FIG. 2 shows the pH change in the water during the culturing process;

[0032] FIG. 3 shows the changes in the survival rate of grouper using chlorella during the culturing process.

DETAILED DESCRIPTION

[0033] The present disclosure discloses a method for hatching and culturing grouper by using chlorella. Those skilled in the art can learn from the disclosure and appropriately improve the process parameters. It is to be understood that all such alternatives and modifications are obvious to those skilled in the art and are considered to be included in the present disclosure. The method and the application of the present disclosure have been described according to the preferred embodiments, and it is obvious that the method and application described herein may be changed or appropriately modified and combined without departing from the content, spirit and scope of the present disclosure.

[0034] The present disclosure applies the self-produced natural green microalgae product to the indoor industrialized culturing of grouper, breaking through the problems of extremely low hatching survival rate of grouper and serious pollution, and opening up the whole process of indoor industrialized culturing, which provides a boost for the transformation to indoor industrialized culturing of grouper.

[0035] The following is the difference between products used in the present invention and commercial products:

Table 2

Fresh algae Shandong Algae powder Products used in algaemud Algr Similarproducts thepresent in themarket invention

Full cold high temperature All are small Large-scale Cost chain baking, high workshop-type production, while transportation, energy production, and the relying on Hainan's high freight consumption, and cost is high. geographical high cost advantages with abundant sea water and sunlight, and a strong logistics network, which greatly reduces the production costs. Local algae species, No continuous multiple rounds of Nmovontinous t domestication. The Low algae High-temperature improvement ofthe algae have high Vitality vitality, easy drying, with lack rapid decline in vitality, are more to decay and of nutrients and rductd vitality suitable for high-heat smell. algae vitality lost. and poo' environment, and have a good sustainability. water-cultivating effect. Cultivation in No sound the open-air Mixed with other standardized track pool, substances; the production process; Factory culture, less Quality pollutants and purity and quality the quality of impurities and high heavy metals are greatly products varies degree of sterility. exceedigths reduced. greatly from batch exceeding the to batch. standard.

[0036] The present disclosure will be further explained below in conjunction with examples.

Example 1 Preparation before cultivation

[0037] 1) Before eggs were placed into a pool, the hatching bucket was cleaned, and the air stone and air cake, light pipes and water pipes were connected.

[0038] 2) The hatching bucket was disinfected with bleach, soaked for one night, and drained cleanly.

[0039] 3) The hatching bucket was cleaned again to ensure that the bleach remaining on the inner wall of the hatching bucket was cleaned.

[0040] 4) The electric wires, water pipes, air pumps and other equipment were checked for whether they functioned well.

Example 2 Preparing worms as feed

[0041] Preparing ss rotifers temporarily 3-4 days before placing eggs. The rotifers introduced from the outer pond were washed and prepared temporarily, and they were screened and washed every day. Microbicide (JunKe) was added to remove bacteria, viruses, organic impurities and dead worms.

Example 3 Placing eggs at Day 1

[0042] 1) The day before egg placement, the seawater was purified and added to the hatching tank.

[0043] 2) On the day of egg placement, suitable eggs were chosen and the eggs were detected. Detection method: few dead eggs (dead eggs: sinking or whitish); for live eggs, high permeability and good suspension, full oocysts under microscopic examination, no empty cells or dead embryos. Ensuring that there are less than 40 dead eggs (bottom-sinking eggs) in each bag of eggs (a hectogram).

[0044] 3) The amount of eggs used per unit of water was calculated. All the eggs were mixed well and added to the hatching tank based on the calculated amount to ensure that the density of the eggs in the final water body is greater than 7000 eggs/ton. Calculation method: After the fish eggs were added to the water body, they were mixed thoroughly for half an hour. Then 500 ml of the water body was scooped with a beaker to count the number of fish eggs, which was multiplied by 2000 to get the number of fish eggs in one ton of water.

[0045] 4) An online sensor was set to ensure real-time remote data transmission and alarm. The lower limit of alarm was DO: 4.8 and pH: 8.0.

Example 4 Adding bacteria and algae at Day 2-3

[0046] 1) From Day 2, 100 g of photosynthetic bacteria (with a viable amount of1.x1010 cfu/g) and 100 g of bacillus (with a viable amount of1.Ox10 cfu/g) were added every day to make the concentration of each bacterium in the water body reach 1000 cfu/ml.

[0047] 2) From Day 3, chlorella products were added every morning as 1.2-1.5 L of fresh chlorella algae liquid per ton of water body (the density of fresh chlorella algae liquid was calculated as 14-20 million cells/ml). If it cannot be reached, the volume was recalculated for the addition. After the addition, waiting for 1 hour before taking samples to detect the density of algae in the water body, to make the density of algae in the water body reach 50,000-100,000 cells/ml.

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Example 6 Enhancing rotifers: with chlorella. Enhancing copepods (water flea): with chlorella, eel meal, shrimp flakes, and yeast powder

[0048] 1) From Day 3, worms were added according to the feeding process shown in Table 3.

[0049] 2) Starting from the addition of worms, the amount of algae added was doubled, and the algae content was measured once in the morning and afternoon. It is necessary to ensure that the algae content in the aquaculture water was greater than 150,000-300,000/ml. The algae were added extra if the algae content was lower than this value, or the algae content dropped rapidly in the afternoon.

[0050] 3) 1-5 ppm of EM bacteria (g/ton of water) was added daily.

[0051] 4) Changing the water,

After the material was passed, water was changed using the micro-flow water exchange method: 1-2 400-liter columns were used to store water, and the water in the columns was sucked into the aquaculture pond in a siphon manner. The water inlet rate was adjusted to reduce the stress on the fry. The process of each water change should not be rushed, and it should be more than 3h.

[0052] 5) At this stage, it is necessary to pay attention to the changes of pH, DO and ORP at all times to ensure that the pH and DO were stable. If the pH showed a downward trend, additional algae liquid needed to be added. If DO showed a downward trend, whether the air pump functioned well was check, and the air output of the air stone was adjusted to maintain a stable DO value.

pH range: 7.8-8.5, the daily drop cannot be greater than 0.15;

DO range: 4.5-6 mg/L;

ORP range: 100-300;

[0053] 6) The ammonia nitrogen and nitrite of the water quality were checked once a day. If there was an abnormality, checking again and reporting in time.

Ammonia nitrogen range: <0.15 mg/L;

Nitrite range: <0.1 mg/L;

If ammonia nitrogen and nitrite continued to rise, emergency measures should be taken: increasing the amount of water change (30-50% of the water change rate) to restore the water quality index to the process set standard.

Example 7 Adding worms, bacteria and algae, and changing water at Day 10-20

[0054] 1) Continuous changing the water.

[0055] 2) The daily adding amount of fresh chlorella was reduced by 20-30% (based on the previous day) until the amount of fresh chlorella added reached 1-2L of fresh chlorella algae liquid per ton of water body (The density of the chlorella algae liquid was calculated as 14-20 million cells/ml). Abruptly stopping adding algae or reducing the amount rapidly should be avoided.

[0056] 3) According to the size of the fry, gradually changing the worms, and the feeding process is shown in Table 3.

Example 8 Fry are ready at Day 21

[0057] 1) Continuous changing the water.

Ammonia nitrogen range: <0.2 mg/L, nitrite range: <0.1 mg/L

[0058] 2) According to the size of the fry, gradually changing to larger water fleas, and the time of feeding with worms was changed to 3-5 times a day. The feeding process is according to the worms feeding process.

Example 9 Control of ammonia nitrogen and nitrite

[0059] 1) The amount of one-time water change should not exceed 30%.

[0060] 2) When the fry was weak in the early stage, the water should be changed slowly and steadily. When the vigor of the fry was strong in the later stage, the water should be changed quickly (within half an hour) to exchange the water with high concentration of ammonia nitrogen and nitrite at the bottom.

[0061] 3) After the water change was completed, checking the ammonia nitrogen and nitrite again. If there was a significant drop, the control goal was achieved. If there was no drop or there was a continuous rise, the bottom suction operation should be carried out (full communication with the person in charge on site was required before bottom suction).

Effect Factor Example 1 Dissolved oxygen

[0062] 1) The air blower for the culturing pond was adjusted to maintain the air pressure at 0.2-0.4 mpa.

[0063] 2) The air inlet valve of the culturing pond was adjusted to make the air bubbles evenly dispersed in the culturing pond.

[0064] 3) The algae addition operation was carried out according to Examples 3-7 every day.

[0065] The result is shown in FIG. 1.

[0066] During the hatching process of grouper, the dissolved oxygen in the water body should be maintained above 4 mg/L. According to FIG. 1, it can be seen that the dissolved oxygen was maintained above the normal value, and the addition of chlorella can ensure the dissolved oxygen level in the water. In addition, it can be seen that in the first three days of culturing, the dissolved oxygen had an upward trend. This stage was the hatching process of the fish eggs to the fish fry, and the oxygen consumption was low. After the addition of chlorella, the dissolved oxygen was at a higher level. There was a downward trend in the next few days, as the oxygen consumption increased after the fry hatched, and the worms and EM bacteria added were all aerobic organisms, resulting in a continuous decline in dissolved oxygen. This also suggests that the amount of algae should be increased on Day 5 of culture to increase the level of dissolved oxygen in the water body and reduce the ammonia nitrogen value of the water body at the same time.

Effect Factor Example 2 pH value

[0067] The algae addition and water exchange operations were carried out according to Examples 4-7.

[0068] The result is shown in FIG. 2.

[0069] The optimum pH range for grouper hatching is 7.9-8.3. It can be seen from FIG. 2 that the pH was in the appropriate range, but in the middle and late stages of aquaculture, the pH dropped significantly and was lower than the optimal range. It also can also be seen that the pH curve was highly consistent with the changes in the dissolved oxygen curve, with high dissolved oxygen corresponding to high pH, and low dissolved oxygen corresponding to low pH, showing an obvious positive correlation. This is because during photosynthesis of chlorella, they absorbed acid radical ions such as carbon dioxide and nitrite to generate oxygen and increase the pH of the water. The results are shown in FIG. 2. The process described in the disclosure can maintain the pH of the aquaculture water in the optimum pH range for fry growth.

Effect Factor Example 3

[0070] Related experiments were performed according to the processes described in Examples 1-9. The result is shown in FIG. 3.

[0071] Through the culturing method provided by the present disclosure, the survival rate of grouper hatching and culturing can be increased from 3% to more than 20%.

[0072] The method for hatching and culturing grouper fry by using chlorella provided by the present disclosure has been described in detail above. The principles and embodiments of the present disclosure have been described with reference to specific examples, and the description of the above embodiments is only to assist in understanding the method of the present disclosure and the core idea thereof. It should be noted that, several improvements and modifications may be made by those skilled in the art to the present disclosure without departing from the principle of the present disclosure, which improvements and modifications also fall within the protection scope of the claims thereof.

Claims

1. A method for hatching and culturing grouper fry, comprising the following steps:

preparing worms: starting to prepare ss rotifers temporarily 3-4 days before placing fish eggs, and using a microbicide to remove bacteria, viruses, organic impurities and dead worms;

placing egg: selecting eggs which have less than 40 dead eggs per hectogram; and placing the eggs in purified seawater, and the density of the fish eggs in the final water body is greater than 7000 eggs/ton;

the day of egg placement is counted as Day 1; from Day 2 of egg placement, adding 50~100g of photosynthetic bacteria with a viable amount of 1.0~2.0x1010cfu/g and 50~100 g of Bacillus with a viable amount of 1.0-2.0x1010 cfu/g every day, to make the concentration of each bacterium in the water body reach 1000 cfu/ml;

from Day 3 of egg placement, adding chlorella algae every morning as 1.2~1.5 L of chlorella algae liquid per ton of water body, and the density of the chlorella algae liquid is calculated as 14-20 million cells/mL; after the addition, waiting for 1 hour before taking samples to detect the density of algae in the water body, to make the density of algae in the water body reach 50,000~100,000 cells/ml;

from Day 3 of egg placement, adding rotifers every day, and measuring the algae content in the morning and afternoon to ensure that the algae content in the aquaculture water is greater than 150,000-300,000 cells/mL;

from Day 3 of egg placement, adding 10-30 g of EM bacteria with a viable amount of 1.0~2.0x1010cfu/g every day;

from Day 10 of egg placement, reducing the daily adding amount of chlorella by 20~30% based on the previous day until the amount of chlorella added reaches 1-2 L of chlorella algae liquid per ton of water body, and the density of the chlorella algae liquid is calculated as 14-20 million cells/ml;

according to the size of fry, gradually changing worms;

changing the water daily; and on Day 21 of egg placement, the fry are ready.

2. The method according to claim 1, wherein, from Day 3-5 of egg placement, adding 30-50 g/ton of water body of rotifers that are no less than 1000 rotifers/g every day, feeding with the worms once every 2-3 hours, monitoring the worm content in the water body once every 3 hours and adding extra if there are less than 20 rotifers/mL; the whole process is under light;

3. The method according to claim 1 or 2, wherein, from Day 6-7 of egg placement, adding 30-50 g/ton of water body of rotifers that are no less than 1000 rotifers/g and adding 100 g/ton of water body of copepods that are no less than 200 copepods/g every day, feeding with the worms once every 2-3 hours, monitoring the worm content in the water body every 3 hours and adding extra if there are less than 20 rotifers/mL water body or less than 2 fleas/ml water body; light is on from 8 am to 7 pm;

the rotifers are screened by double-bag filtration, with an outer bag of 350 mesh and an inner bag of 250 mesh, and the rotifers sandwiched between the outer bag and the inner bag are used; the copepods are screened by single-bag filtration with a 200 mesh filter.

4. The method according to any one of claims 1 to 3, wherein, from Day 8-9 of egg placement, adding 30-50 g/ton of water body of rotifers that are no less than 1000 rotifers/g and adding 200 g/ton of water body of copepods that are no less than 200 copepods/g every day, feeding with the worms once every 2-3 hours, monitoring the worm content in the water body every 3 hours and adding extra if there are less than 20 rotifers/mL water body or less than 2 copepods/ml water body; no light;

5. The method according to any one of claims 1 to 4, wherein, from Day 10-13 of egg placement, adding 15-30 g/ton of water body of rotifers that are no less than 1000 rotifers/g and adding 200-300 g/ton of water body of copepods that are no less than 200 copepods/g every day, feeding with the worms once every 2-3 hours, monitoring the worm content in the water body every 3 hours and adding extra if there are less than 2 copepods/ml water body; no light;

6. The method according to any one of claims 1 to 5, wherein, from Day 13-20 of egg placement, adding 300-800 g/ton of water body of copepods that are no less than 200 copepods/g every day, feeding with the worms once every 2-3 hours, monitoring the worm content in the water body every 3 hours and adding extra if there are less than 2 copepods/ml water body; no light;

the copepods are screened by single-bag filtration with a 150 mesh filter.

7. The method according to any one of claims 1 to 6, wherein, from Day 21 of egg placement, adding 8001500 g/ton of water body of copepods that are no less than 200 copepods/g every day, feeding with the worms once every 2-3 hours, monitoring the worm content in the water body every 3 hours and adding extra if there are less than 2 copepods/ml water body; no light;

the copepods are screened by single-bag filtration with a 100 mesh filter.

8. The method according to any one of claims 1 to 7, wherein the pH range is 8.2-7.8, and the daily drop are not greater than 0.15; the DO range is 4.5-6 mg/L; and the ORP range is 100-300.

9. The method according to any one of claims 1 to 8, wherein the range of ammonia nitrogen is <0.15 mg/L; and the range of nitrite is <0.1 mg/L.

10. The method according to any one of claims I to 8, wherein,

early stage (before fin spine retracting): the upper limit of ammonia nitrogen alarm is <0.12 mg/L, the upper limit of control is <0.15 mg/L; the upper limit of nitrite alarm is <0.06 mg/L, the upper limit of control is <0.1 mg/L;

later stage (after fin spine retracting): the upper limit of ammonia nitrogen alarm is <0.15 mg/L, the upper limit of control is <0.2 mg/L; the upper limit of nitrite alarm is <0.06 mg/L, the upper limit of control is <0.1 mg/L.

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