Three Major Misconceptions About Fertilizing Water for Shrimp Farming and Their Solutions

Fertilizing water is crucial in the farming of whiteleg shrimp (Litopenaeus vannamei), but certain misconceptions currently exist that cause unnecessary losses and waste.

1. Excessive fertilization before stocking fry

When fertilizing before stocking fry without understanding the specific conditions of the pond's water quality and bottom sediment, blindly using inorganic fertilizers, organic fertilizers, or some microecological preparation fertilizer products - if the water happens to become fertile, fine; if it does not, one assumes the fertilizer amount was insufficient and continues to increase it. This way, not only does the water not become fertile, but it also causes unnecessary waste and leads to deterioration of the bottom sediment and water quality.

1.1 The harms of excessive fertilization

Excessive inorganic fertilizer accelerates alkalization of the pond bottom, making it prone to hardening.

Excessive organic fertilizer: for example, chicken manure has a complex composition. The non-water-soluble nutrients in chicken manure require a long time to decompose and be utilized. Chicken manure particles that sink to the pond bottom easily form a crust-like mud, which floats to the surface at high temperatures and deteriorates water quality, causing ammonia nitrogen and nitrite to exceed standards in the water, creating hidden dangers for farming. Furthermore, the large-particle nutrients in chicken manure can only be utilized by zooplankton, not by algae, thereby shortening the duration of the algae peak period. If poorly fermented, it contains large amounts of ciliates, Escherichia coli, Spirillum, etc., which can easily cause gill and intestinal infections and trigger outbreaks of various diseases.

Biological fertilizers (referring to fertilizers containing microecological preparations): if the dosage is appropriate, the live bacteria can fully decompose organic matter in the water and bottom mud, turning it into available nutrients for algae and achieving the goal of fertilizing water; if used excessively, the live bacteria will over-degrade organic matter, reducing nutrients in the water body, and the water will instead fail to become fertile.

1.2 Solutions

Based on the above situations, clarify the indicators of water quality and bottom sediment, and treat each specific case individually. Generally speaking, for muddy and sandy-muddy ponds that are old ponds, inorganic fertilizer can be used directly in combination with microecological preparations, or microecological preparation fertilizers can be used alone; for sandy ponds, elevated ponds, and new ponds, organic fertilizer can be used in combination with microecological preparations. Organic fertilizer must be fully fermented, and can also be fermented together with microecological preparations. Specific method: for each cubic meter of chicken manure, use 10 kg of microecological preparations and 2 kg of compound fertilizer, mix evenly, choose a sunny place to pile it, and seal with plastic sheeting for 5-10 d. Different water sources require different methods: groundwater has a complex composition - if it is acidic or alkaline, or has high nitrite levels, it should be tested and adjusted before fertilizing, and algae seeds should be introduced when necessary; surface water can be directly fertilized after filtering through an 80-mesh filter; old ponds with thick bottom mud can also use water-fertilizing bacteria alone to fertilize the water.

2. Fertilizing water about 10 days before stocking fry

2.1 The harms of fertilizing water too late

Some shrimp farmers start fertilizing water about 10 d before stocking fry. After 7 d of fertilizing, they see transparency of about 40 cm, scoop up zooplankton in the water with a hand net, then test the fry, and after successful testing, stock the fry. The result is often slow growth of shrimp fry, poor disease resistance, and even disease outbreaks.

2.2 Solutions

Stock fry about 20 d after fertilizing water, because during the water fertilization process, many physical and chemical factors in the pond are undergoing drastic changes, the most obvious being pH changes, showing an "^" pattern: in the early stage, pH keeps increasing, sometimes reaching around 10; after 15 d, it gradually decreases; at around 20 d, pH stabilizes at around 8.5, suitable for shrimp growth. At this time, water color, transparency, and zooplankton are all in optimal condition, most suitable for stocking fry. Therefore, the fertilization time should best be arranged about 20 d before stocking fry.

3. No need to fertilize water in the middle and late stages of farming

3.1 The harms of not fertilizing water in the middle and late stages

In the middle and late stages, pond water transparency is low. Some shrimp farmers believe the water is already fertile enough, that further fertilization is unnecessary or even counterproductive.

Actually, this is not the case. In the middle and late stages of farming, pond water transparency is low, and the water color appears dense on the surface - the possibility of fertile water cannot be ruled out, but another situation also exists: at this time, the water contains plankton and various substances dissolved or suspended in the water such as residual bait, feces, organic debris, dead algae, etc. Through light refraction, this is not the true color of beneficial algae. There are very few algae in the exponential growth phase, and water color transparency is also very low, creating a false appearance of fertile water. Once the algae phase is disrupted, the balance of the water environment is disrupted, water quality gradually deteriorates, harmful substances exceed standards, water quality becomes unstable, and naturally affects shrimp health.

3.2 Solutions

Frequently observe changes in water color. A good pond of water has different colors in the morning, noon, and evening. If the water color shows no change throughout the day, it is best to examine under a microscope to see whether the algae are aging or depleted. If so, based on the characteristics of water quality in the middle and late stages, microecological preparations containing nitrifying bacteria, phosphorus-solubilizing bacteria, potassium bacteria, nitrogen-fixing bacteria, etc. should be added. Through nitrifying bacteria, nitrogen elements are nitrified and converted into available nutrients for algae; phosphorus-solubilizing bacteria decompose long-chain phosphorus in the water, which large amounts of algae cannot directly utilize, into short-chain phosphorus for easy absorption and utilization by algae; potassium bacteria can decompose potassium from silicate minerals and also release phosphorus from apatite; nitrogen-fixing bacteria, through the activity of nitrogenase with special catalytic ability within their bodies, convert molecular nitrogen that plants cannot utilize into ammonia nitrogen that plants can utilize. This not only plays the role of inorganic and organic fertilizers but also avoids their disadvantages, saves energy, and adjusts the microecological balance. Beneficial algae multiply, the algae phase is balanced, and simultaneously harmful algae over-reproduction is inhibited. When algae grow and reproduce, they absorb nitrogen, sulfur, phosphorus and other elements from the water, mediating the balance of substances in the water, avoiding the increase of harmful substances such as ammonia nitrogen, hydrogen sulfide, and nitrite content, making the farming water "fertile, active, tender, refreshing, and stable." When the environment is good, the shrimp fry are naturally healthy. This shows that fertilizing water in the middle and late stages is equally important.