How shrimp farmers can move beyond the misunderstanding of dissolved oxygen management in shrimp ponds

    Pond dissolved oxygen is the lifeline of aquaculture. Feeding and growth of fish and shrimp, regulation of water quality, and maintenance of the bottom substrate are all closely tied to dissolved oxygen management. The level of dissolved oxygen management directly affects the feed conversion ratio, the stability of water quality and bottom substrate, and the approach and execution plan for disease prevention and control.

    There are several sources of dissolved oxygen in a pond: first, photosynthesis by algae; second, oxygen brought in by aerator agitation of the air; third, pure oxygen dissolved in through microporous tubes. Different pond conditions, different farming models and different stocking densities call for different methods and different emphases. This article focuses on dissolved oxygen management in shrimp ponds.

    Shrimp ponds fall into two categories: high-level ponds and earthen ponds; others are omitted here. The original definition of a high-level pond was a hard-bottomed pond above the coastline. Given how things have evolved, the author believes it should be given a more appropriate definition: a flow-through aquaculture pond that facilitates waste collection and discharge and isolates viral vectors. The aeration setup for high-level ponds is above 1.5KW, so the power is completely sufficient; the problem is the current use and management, which is worth discussing. As for earthen ponds, as the name suggests, they are ponds with mud bottoms. The aeration setup for this type of pond ranges between 0.5-1.5KW, which the author believes is far from enough given today's shrimp farming requirements. If the power is insufficient, then good management is even more out of the question. Suitable aeration for earthen ponds should be the same as for high-level ponds, or even higher (since there is no waste collection and discharge), that is, 1.5-3KW/mu.

    The Pacific white shrimp (Litopenaeus vannamei) we farm today is mostly fast-growth fry. Shrimp that grow fast naturally need more nutrients (feed, oxygen, minerals, vitamins, etc.) and a cleaner environment. So when it comes to meeting dissolved oxygen needs, we cannot limit ourselves to meeting the needs of the shrimp alone, nor be satisfied merely with keeping the shrimp from becoming oxygen-deprived; we should do more to meet the needs of the entire pond's algae and bacteria, especially the bacteria in the pond bottom. This is just like what we used to say about aeration in fish ponds: a fish pond aerator should not be positioned as a "life-saving machine" but as a "yield-increasing machine."

    At this point, many people will bristle. Everyone on Earth knows that more oxygen is better; the problem is: money, money, money? Cost is the tiger blocking everyone's path, like a hurdle that cannot be avoided. Let us calm down and think: what is the biggest problem in shrimp farming today? Disease! That's right, disease is the biggest cost. And what about the costs derived from disease, such as medication, water exchange and high feed conversion ratios? We have not even calculated those yet.

    At present, the aeration cost for shrimp is generally around 1 yuan per jin of shrimp. If I raise this cost to 2 yuan, or even 3 yuan, how much impact does that have on our total cost? Calculated at current shrimp prices, it is still negligible. It is understood that many high-level farms in Southeast Asia spend more than 2 yuan on aeration costs.

    As for our medication costs, they are now rarely below 1 yuan, and can even reach 2 yuan (high-density high-level ponds). Feed costs running 1 yuan higher is normal, and selling shrimp early because of disease outbreaks can cost 10-20 yuan. If we invest an extra 1-2 yuan in aeration, can we reduce a lot of other cost expenditures? This math problem is not hard.

    At this point, do you feel less averse to investing in aeration? Let's continue...

    The current state of aerator management in shrimp ponds

    1. During the shrimp farming process, in the early stage the shrimp are small, feeding is low, organic matter is low, and oxygen-consuming substances are low. In the middle and late stages, the shrimp grow bigger and bigger, feeding increases day by day, and oxygen-consuming organic matter such as feces and leftover feed gradually increases. Most people prefer not to turn aerators on in the early stage, then gradually add them one by one in the middle and late stages. This both meets the shrimp's needs and saves on electricity.

    2. Many shrimp farmers like to shut down the aerators when feeding, afraid that the shrimp cannot find the feed, or that the feed will be buried by sludge, or that it will be swept by the current into the waste collection area.

    These two points may seem to make some sense. But the author believes they are both wrong. Let us analyze them together:

    1. Water stratifies.As soon as the aerator stops, the water quickly stratifies. The deeper the water, the lower the dissolved oxygen, and at the pond bottom there is almost zero dissolved oxygen. Frequent shutdowns mean the pond bottom is frequently oxygen-deprived, and frequent oxygen deprivation causes the pond bottom to age. Toxic substances such as ammonia nitrogen, nitrite nitrogen, hydrogen sulfide, indole, aldehydes and phenols are then produced in large quantities. This is why shrimp diseases tend to break out when strong winds and heavy rain occur (bottom turnover) - this is the reason.

    2. High dissolved oxygen is harmful.After the aerator stops, the water stratifies, and algae concentrate in the upper layer of water. Photosynthesis in the upper layer produces high dissolved oxygen, and a short-term sharp rise in dissolved oxygen will inevitably lead to gas bubble disease. This is why, on the first clear day after wind and rain, there is another peak period for disease outbreaks in fish and shrimp (especially fry).

    3. Shrimp are benthic.In the middle and late stages, the pond bottom already has a lot of organic matter. Shutting down the aerators before feeding causes the bottom to become anaerobic, and as the shrimp search for feed they constantly crawl over and disturb the pond bottom (causing bottom turnover), releasing toxic substances. If shrimp keep eating in a low-oxygen, toxic environment, then even if they find the feed, they will have no appetite to eat it, and even if they eat it, they will not grow big quickly.

    At this point, do you feel a bit more fond of investing in aeration?