Farming Knowledge

Shrimp are low level animals, do not have a specific immune system, so their resistance to pathogens is poor. Therefore, when growing in captivity, shrimp are very susceptible to diseases from many different agents such as viruses, bacteria, fungi, toxic algae…

Shrimp are low level animals, do not have a specific immune system, so their resistance to pathogens is poor

Unlike in the natural environment, cultured shrimp grown in the artificial stocking environment are very sensitive to pathogens. Because no matter how well it is handled, the pond is essentially a closed environment with waste from shrimp feces, rotting leftovers, decomposing peeled shrimp shells, etc., gradually accumulating during the farming process. This creates the ideal conditions for pathogens to develop, making it easier for shrimp to get disease once they are shocked or have reduced resistance. The following are some of the most common pathogens:

1. Virus

Viruses, also known as super bacteria, are microscopic parasites that cannot reproduce and make their own proteins, so they are completely dependent on their host. In farmed shrimp, it can be said that viruses are the main pathogens with common dangerous diseases such as White Spot Syndrome Virus (WSSV), Infectious Myonecrosis Virus (IMNV), Taura Syndrome Virus (TSV) …

Virus disease has the ability to spread quickly and widely, and in the acute stage can easily cause mass mortality of shrimp. Currently, there is no preventive vaccine as well as specific medicine for virus diseases, so it is still mainly to prevent diseases by thoroughly cleaning and disinfecting ponds and doing good selection of varieties.

2. Bacteria

Bacteria are a group of single-celled organisms that are small and usually have a simple cell structure without a nucleus. Bacteria are agents that are frequently present in ponds, which are both beneficial such as Lactobacillus, Bacillus spp., Nitrosomonas… and harmful and pathogenic for shrimp, especially Vibrio spp.

In shrimp, there are common bacterial diseases such as luminous disease, acute necrosis, black spot disease, white feces disease… To prevent diseases, it is necessary to manage the pond environment carefully and use probiotic products such as TA-Pondpro to promote the growth of beneficial probiotics in ponds. In addition, it is also possible to use T-Food, a probiotic product using fermented Lactobacillus spp, to improve the intestinal biota of shrimp, both to help limit the growth of harmful bacteria and to strengthen the ability to digest food for shrimp to grow quickly.

For severe infections, antibiotics can be used, but be very careful about the dose and duration of use.

3. Protozoa

Protozoa are a simple life form, although the body has only one cell, it is capable of carrying out a full range of life activities as a complete multicellular organism. Poorly cared ponds, excess food, and high organic content will create ideal conditions for protozoa to proliferate, especially strains of Zoothamnium, Epistylis, Vorticella… They will compete for dissolved oxygen. At the same time, it attaches to the shrimp body (along with algae, fungi and other species) causing coagulation disease, black gill disease which, if not treated promptly, will cause shrimp to weaken, molt abnormally and may be superinfected with other pathogens factors.

In addition, these protozoa also cling to the pond bottom, creating a viscous layer on the surface, accumulating waste and becoming the residence of many harmful bacteria. This slime is also the favorite food of shrimp, thereby indirectly causing liver and intestinal diseases. Therefore, it is necessary to periodically treat the pond bottom and water with probiotic products to stabilize the quality of the culture environment. In parallel with maintaining a high dissolved oxygen content, it is necessary to carefully manage the shrimp’s diet, ensuring adequate nutrition but also avoiding excess.

4. Environment

The environment, specifically water quality, is one of the major factors affecting the health and development of shrimp. There are many factors that determine the quality of the environment such as temperature, dissolved oxygen, pH, alkalinity… and also heavy metals, and changes in these factors will indirectly or directly cause disease. for shrimp.

For example, the environment with low pH conditions and many heavy metal ions such as Fe3+, Al3+ will cause black gill disease on shrimp (due to salted heavy metal ions); Or the environment accumulates a lot of organic substances, causing the concentration of toxic gasses NH3, H2S to increase, combined with factors with low dissolved oxygen content and high pH can cause swelling of gills and yellow gills.

To limit pathogens from the environment, the best way is to implement environmental management measures well. Along with regularly checking, monitoring and quickly handling when problems occur.

Besides the factors mentioned above, shrimp can also get sick by many other factors such as fungi, algae, weather… In addition, the resistance of shrimp is also a decisive factor because when shrimp have weak resistance or frequent shock it will easily be penetrated by pathogens.

5. Prevention is better than cure

For farmers, the occurrence of disease in the herd is a risk that no one wants to happen. Because once shrimp are sick, with a high density stocking environment and scavenging habits, the disease will quickly spread to the whole shrimp population. The treatment of the disease, no specific medicine or expensive, is effective because the diseased shrimp often stop eating, causing the medicine mixed in the feed not to get into the shrimp’s body.

Prevention is better than cure

Therefore, in shrimp farming, disease prevention is still the key factor determining the success or failure of the crop. It is necessary to do well in disease prevention right from the breed selection, pond improvement and water treatment, while maintaining favorable environmental factors for shrimp growth by:

• Improve venturis to provide oxygen, create favorable conditions for probiotic to decompose waste and release toxic gasses;
• Cut excess feed to reduce waste pressure polluting the pond environment;
• Limit water change, and only replace it with treated water through settling ponds;
• Periodically every 7-10 days, use TA-Gold probiotic products to decompose detritus, and at the same time add probiotic to help a favorable pond environment for shrimp to grow;
• Improve the resistance of shrimp with vitamins and minerals.

It is necessary to closely monitor the health status as well as the water environmental parameters to have treatment intime. In case of detecting diseased shrimp, it is necessary to identify the pathogens early by accurate testing methods such as histopathology, PCR and conduct the right treatment with the right drug, right dose, right time.

A study from the Global Aquaculture Alliance Publications concluded: “Based on the movement of food through the intestines of whiteleg shrimp, shrimp consume food faster when at 32 degrees Celsius.”

The rate of consumption and digest feed varies with the temperature of the culture environment and other factors. Laboratory studies and actual experiments by researchers show that the eating process of whiteleg shrimp will be affected by different water temperatures.

Experiment in the laboratory

Experiments carried out in a laboratory at Kasetsart University, Thailand showed that several empty gut shrimp weighing 12g were placed in a tank filled with purified seawater to assess the amount of food passing through the shrimp’s gut at temperatures of 24, 26, 28, 30, 32 and 34 degrees Celsius with normal shrimp farming conditions.

And the stages are recorded as follows:

• When food is first observed in the intestine
• About half of the intestine
• When the intestines are full, before the stool is passed
• When the stool begins to be excreted
• When the intestines begin to empty
• When the intestines are completely empty

Feed was applied at 3% of body weight according to the food table developed by Kasetsart University. Therefore, the applied food intake was 1% of body weight per meal in three daily meals. Food such as feces, peas and leftovers are vacuumed before each feeding.

Experiment results

For most treatments, it takes only 5 minutes to see feed in the intestines after eating at first, but a significant difference in the rate of digestion begins to appear after that. For example, it takes up to 55 minutes at 24 degrees Celsius compared to 20 minutes at 34 degrees Celsius for shrimp intestines to fill. Once the stools begin to be passed, the difference increases even more, as this takes up to 105 minutes at 24 degrees Celsius compared to 35 minutes at 34 degrees Celsius.

Real test

Evaluation of feed consumption using feed trays at different temperatures was carried out during the 2010 summer cycle.
The experiments were carried out in 8 pounds with an area of ​​0.25 ha, stocking 150 fish/m2. Evaluation when feed consumption increased sharply (at average weight 6g and fed at 3.5% body weight) and ended at harvest (14g weight and fed at 2.5% body weight).

The feed table was used as a reference for feed dosage, but the number of feed trays was preferred for the daily feed adjustment. Only 4% of the daily intake is put in the tray, the rest is kept.

Feeding at high temperature

Feed was applied at the same dose to the ponds at 6am, 10am, 3pm and 6pm at different temperatures. Temperatures were recorded before each application, and feed trays were checked. 1 to 3 hours after feeding. Feed dosage was increased to a ceiling 30% higher than the corresponding levels in the feed table.

The results in the three temperature ranges in Table 2 show that at 32-34 degrees Celsius, leftovers are never found, while in the 26 to 28 and 29 to 31 ranges, the waste is consumed. Feed intake is considered to calculate the appropriate feed dose.

The time it takes for food to pass through the digestive tract of shrimp at 6 test temperatures under laboratory conditions

Feeding at high temperature

During the summer cycle, it has been observed that feeding at 32°C or higher can produce excessive vegetative growth, perhaps due to the amount of nutrients released from the feed and the accumulation of a lot of organic matter at the bottom. As a result, a mass of dead algae accumulates on the pond surface. This situation becomes dangerous when excess feed causes the presence of harmful compounds such as Nitric and the proliferation of Vibrio and other pathogenic bacteria, which causing shrimp mortality

It is worth mentioning that shrimp in some ponds of the experiments that were fed only 3 times/day had better feed conversion and survival rates than shrimp in ponds that were fed 4 times/day, probably due to the remove of 3pm dose, when the temperature peaks above 32°C. With less feed being used, farming conditions as well as shrimp survival rates are improved.

Consume feeding trays at different temperatures. Feed dosage is calculated from the Data Feed Table using the Information below

Conclude

Nutritionists at Kasetsart University have found that the ideal temperature for shrimp to best digest nutrients is between 29 and 31 degrees Celsius, which coincides with the best feed conversion range observed in this experience. According to the experiments described here, shrimp feed digestion at temperatures between 24 and 28 degrees Celsius can take 3-4 hours, giving the interval between each feed can be as long as 5 -6 hours to allow shrimp to fully digest and consume feed for each amount.

On the other hand, at temperatures higher than 32 degrees Celsius, digestion is much faster and food consumption can be higher. However, there is danger in increasing the feed dosage to the extent that it can lead to higher organic matter concentrations in the pond bottom, increase of plant and disease-causing bacteria populations. Finally, it is important to avoid feeding at temperatures above 32 degrees Celsius, under improved production and pond conditions.

During the culture process, ponds may lose water color or algae loss due to many different reasons. If left untreated, this phenomenon will adversely affect the health of shrimp, especially in the first month of stocking.

Watercolor is a combination of organic and inorganic compounds (soluble or insoluble), including algae growth. In shrimp ponds, algae is the main factor used to color the water because it is both a natural food source for shrimp and increases the dissolved oxygen content in the water through photosynthesis, while helping to reduce the amount of oxygen in the water. Toxic gases from the decomposition of organic matter. When the water is well colored, beneficial algae will quickly grow and make the pond water yellow-brown (silica algae – Bacillariophyta) or light green (green algae – Chlorophyta) are the two most suitable water colors for shrimp culture.

Water color reflects the quality of the shrimp’s habitat

However, during the farming process, the pond water may become discolored, especially in the first month, due to objective reasons (such as prolonged heavy rain, sudden temperature rise and fall) and subjective reasons such as:

• Not making water color good enough before stocking, causing algae to grow slowly or not to develop;
• Poor management of the farming environment causes the pond to lack nutritional salts (N, P, K…), with too many mosses and algae strain that inhibit the growth of algae;
• Overfeeding, causing high levels of suspended organic matter, causing turbidity and hindering algae photosynthesis;
• Improper use of chemicals, resulting in mass death of algae (algae collapse).

If algae collapses due to improper use of chemicals, farmers need to immediately add dissolved oxygen in the pond to prevent and rescue shrimp from floating on the water surface due to lack of oxygen. Then, use TA-Pondpro probiotic to decompose dead algae, absorb toxic gases NH3, H2S, NO2 to clean pond water, avoiding adverse effects on shrimp. With a pond of 1000m3 of water:

• Soak 500g TA-Pondro with 4 liters of clean water, incubate anaerobically for about 12 hours;
• At 1 o’clock at night, splash 03 kg of No79 mineral into the pond, then continue to use the TA-Pondpro mixture.

The pond water is mossy green due to algae blooms

After using probiotic to clean the algae, if the clarity of the water is too high, the water color must be made to the appropriate level of 30-40 cm. While waiting to make water color, artificial colors can be used to reduce the light shining on the bottom (causing toxic algae on the bottom to grow rapidly and difficult for shrimp to catch feed). It is best to cause water color in the settling pond first and then supply it to the culture pond, according to the formula:

• 1kg TA-Gold +10kg rice bran + 5kg soybeans (ground) + 4kg molasses for 500 to 2,000m3 of water;
• Incubate 12-24 hours before pouring into the pond.

In other cases, it is necessary to clearly determine the cause and level of algae loss in order to have appropriate treatment. However, prevention is better than cure, in order to avoid the loss of water color, farmers need to regularly check and maintain water environmental factors at a stable level. Should periodically 5-7 days, add probiotics to the pond to support the development of microbiota and decompose excess organic matter; and every 10 days, use mineral N79 and probiotic TA-Pondpro to supplement trace minerals and stabilize alkalinity and pH of water. Besides, it is necessary to strictly manage the diet to avoid excess organic matter, affecting water quality and environment.

To maintain water color, it is necessary to maintain stable water environmental factors. To do this in the farm, it is necessary to have a pond system with a depth of >1m.

Breed selection is one of the most important stages of the shrimp farming process because the quality of the breed is the main factor determining the survival rate of the shrimp herd, as well as the growth rate, production cost and quality of commercial shrimp.

Whiteleg shrimp Postlarvae stage

The stocked whiteleg shrimp were post larvae 10-12 days old (PL10-12). At market prices, the cost of buying a breed usually accounts for less than 10% of the product price, but it is a decisive factor to 60% of the success of the crop.

Choosing a poor quality breed means risk of problems such as: disease, poor disease resistance, low survival rate, slow growth rate, etc. causing costs to increase, and risk losing everything in the worst case. Therefore, farmers need to be very careful, choose quality and suitable seeds according to the following criteria:

1. Having a clear origin and origin

Shrimp are healthy from the origin, so when choosing shrimp breed for stocking, people need to find out the origin of the broodstock, the rearing process, how’s the feed, etc. and should only buy from reputable breed production/suppliers, especially those with:

Broodstock shrimp of clear origin, are disease-free (SPF) or disease-resistant (SPR) shrimp, have undergone strict quarantine, isolation and disease screening when rearing;

Breeds have a rearing period of 22-25 days (from the date of spawning to the stage of PL12), are raised by a process without antibiotics, chemicals and are fed with fresh algae, live food such as rotifers, artemia , etc.

2. Ensure technical requirements

Whiteleg shrimp seed PL12 must meet at least the following technical requirements:

In addition, people can also evaluate other appearance factors such as: slender, long abdominal segments; full abdominal muscles; shell-filled meat; balanced head and body, etc. at the same time visually check by shocking method:

• Formalin shock 100 ppm
• Shock by suddenly lowering salinity to 0%

Visual inspection of shrimp seed quality

With the above shocking method, if the shrimp is 100% alive after 30 minutes, it is qualified and if it is over 90% after 1 hour, it can be considered a healthy breed.

3. Check for pathogenic bacteria and viruses

To check for pathogenic bacteria and viruses, farmers can rely on experience, observing the morphology and expression of shrimp to recognize the typical manifestations of each disease, for example:

• Shrimp infected with yellow head disease (YHV) are usually pale yellow in the cephalothorax; gills white, light yellow or brown;
• Shrimp infected with white spot disease (WSSV) often appear round white spots under the chitinous shell, especially in the cephalothorax and in the last abdominal segment;
• Shrimp infected with hepatopancreatic necrosis disease (NHP) often have an empty digestive tract; soft crust; black or dark gills; Hepatopancreas necrosis is pale white, soft, easily crushed.

However, this sensory examination is not guaranteed by conducting PC or histopathological examination of diseased shrimp breed samples. Understanding that, Truc Anh Biotech hatchery has invested in a PCR laboratory to test PL12 shrimp before delivering to customers, ensuring that the shrimp are clean of diseases such as white spot, yellow head, Taura syndrome, etc. This will help you feel more secure with your chosen breed.

In addition to the three criteria mentioned above, farmers should also depend on the type of farming, the season of stocking, as well as the environmental and weather conditions, to choose the right breed. Once the breed has been selected, it is also necessary to pay attention to the stages of packaging and transportation from the hatchery to the pond. In addition, in order for the breed to adapt and develop quickly, it is necessary to inform the hatchery of the salinity and pH of the pond 2-3 days before delivery so that the difference between the breeding tank and the rearing pond is not more than 5%.

To ensure a successful shrimp crop, pond preparation is an important technical step that should be paid attention to right from the start because well-prepared ponds can limit pathogens and create a favorable environment for shrimp growth.

At the beginning of the pond, when growing whiteleg shrimp, especially intensive farming, preparing the pond is the first technical step that needs to be done carefully. Because, not to mention the risk of spreading pathogens, it is also difficult for farmed shrimp to grow well if the captive environment is poor in nutrients or affected by toxic gases such as H2S, NH3 and NO2 (due to long-term accumulation). wastes from excess feed, shrimp manure and organic matter during farming). Therefore, to eliminate these harmful agents, people need to prepare the pond well according to the following notes.

Thoroughly clean and disinfect the pond bottom

1. Pond cleaning and disinfection

In order to eliminate all kinds of enemies (crabs, snails, insects, trash fish…) as well as destroy pathogens that may be present in the pond, it is necessary to drain the water, dredge the mud and conduct thorough cleaning and disinfection of the pond bottom. carefully follow these steps:

• Pond bottom pump to clean waste;
• Dig the soil with a depth of 5-10 cm, apply agricultural lime to kill bacteria and stabilize the pH of the pond bottom. Need to adjust the amount of lime to suit the pH of the soil;

Table 1. Amount of lime used by soil pH

• Supply water to the pond at about 1 meter and soak for 3 to 5 days;
• After that, wash all the water with quicklime and dry the bottom for at least 10 days before officially supplying water for stocking.

With old ponds, the time to dry the pond bottom should last from 1 to 2 months to completely interrupt the crop, kill pathogens, mineralize and restore the bottom environment. In addition, it is also necessary to repair and clean the pond banks, water supply and drainage systems, as well as fence nets, canvas, to limit leakage and avoid intermediate host species causing diseases from outside.

2. Prepare water supply to the pond

The water supplied to the pond should be thoroughly filtered and kept pure to minimize the density of pathogenic bacteria and ensure there is enough plankton in the water to make food for shrimp in the first month of culture. Especially with the model of intensive shrimp farming, it is necessary to build a settling pond to treat the water source before supplying it to the pond according to the following steps:

• When the tide level is highest, collect water into the pond through filter bags to limit garbage and enemies;
• Allow to stabilize for 3 to 7 days and then disinfect, disinfect in the morning (about 8 o’clock) or afternoon (about 4 o’clock) with TA-Superdine or Finishnano and other biocides approved for use in aquaculture. products such as Chlorine, Iodine, BKC…;
• Continuously fan water for 10 days to release germicidal residues;
• Stocking tilapia (size 50g/fish) into the settling pond at a density of 3-5 fish/m2 and maintained continuously throughout the process.

Next, the treated water is taken from the settling pond into the rearing pond through a filter bag to reach the water level from 1.4 to 1.5 meters and then proceed to color the pond water with TA-Gold according to the formula: 1kg TA- Gold +10kg rice bran + 5kg soybeans (ground) + 4kg molasses for 500 to 2,000m3 of water, incubated for 12-24 hours before splash into the pond.

Allow 5 to 7 days for the water color to reach standard, then check and adjust the environmental factors of the pond water so that it is within the appropriate threshold when stocking. To increase water quality, essential minerals can be added with TA-Mix 100 or probiotic products such as TA-Pondpro, but absolutely no inorganic fertilizers or chemicals are used during this period.

Table 2. Parameters of water quality supplied to the ponds

Once the water has been supplied to the pond and the color has been grown, the breed must be stocked within 15 to 30 days after that. To save time and costs, farmers can consider using ponds from the previous crop to continue growing the new crop if the amount of sludge at the bottom of the pond is small and the water quality is still good, but it is necessary to treat the water and the bottom with probiotics products with a dosage 2-3 times higher than normal before stocking.

Preparing the pond is an important technical step

In addition, farmers also need to pay attention to install a suitable venturis system to ensure the oxygen demand for farmed shrimp. And the pond preparation should also consider the different characteristics between different farming models such as semi-intensive, 1-stage intensive, 2-stage intensive or 3-stage intensive.