What to Do When Fish Gasp at the Surface? Several Situations and Countermeasures

Fish gasping at the surface is a temporary physiological adaptation to oxygen deficiency and other adverse factors in the water environment. If effective measures are not taken promptly, it will gradually worsen or even cause a total pond die-off, resulting in major economic losses. The causes of fish gasping at the surface are diverse, and first-aid measures should be adapted to the situation to be effective. Generally speaking, turning on aerators and flushing with fresh water are effective for most cases of surface gasping, but in some situations these methods only provide temporary relief and treat the symptoms rather than the root cause. The fundamental approach is to identify the cause (of the gasping or floating) and treat it accordingly.

Surface Gasping Caused by Lean Water

In intensive high-yield ponds that have accumulated silt over many years, the bottom mud is generally quite thick, hiding large quantities of plankton and protozoan eggs. After the water temperature warms up in early spring and the pond is disinfected with quicklime and fertilized, these eggs are quickly activated and multiply in large numbers, greatly increasing the oxygen consumption from respiration in the pond. Meanwhile, phytoplankton, which produces oxygen, becomes increasingly scarce, and the pond water quickly becomes lean, appearing grayish-white or light brown. This situation often occurs in April to May and in the early stages of fry rearing. Because the water temperature is not very high at this time and the symptoms of surface gasping are not very obvious, it is often overlooked and accidents occur. Countermeasures:

1. Use insecticides to kill excessive zooplankton and immediately fertilize the water with chemical fertilizer.

2. In conjunction with pond clearing, remove excess sludge, apply organic base fertilizer early in shallow areas, and repeatedly drag with an iron rake to accelerate fermentation and decomposition. Avoid piling up too much.

Surface Gasping Caused by Overly Fertile Water

When large amounts of unfermented manure are applied in the early stage, combined with thick silt and accumulated feed grass residues, the pond water is generally very fertile. After water temperatures rise substantially in summer and autumn, the fermentation and decomposition of fertilizer and organic deposits consume large amounts of oxygen. In this situation, dissolved oxygen in the water is heavily depleted, and oxygen-deficiency surface gasping is unavoidable. Countermeasures:

1. Remove silt once every 2 to 3 years. During feeding management, promptly remove feed grass residues. Organic fertilizers should be fully fermented and applied in small amounts frequently. In high-temperature seasons, chemical fertilizers should be the main type; manure should be fermented and the liquid applied on sunny days at noon.

2. Regularly flush with fresh water and operate aerators reasonably to keep the water quality “fertile, lively, tender and refreshing.”

Surface Gasping Caused by Water Turnover

In the middle to late stages of aquaculture, pond water often breeds large amounts of blue-green algae due to excessive fertility, turning the water blue-green or dark green. A layer of organic floating film often drifts on the downwind side, and large amounts of toxic gases such as hydrogen sulfide, methane and ammonia nitrogen accumulate at the bottom, poisoning the water body. If weather changes suddenly or for other reasons, the blue-green algae age, die and sink. The pond water becomes stratified: the bottom layer is dark as if very fertile, while the upper layer has high transparency. Dissolved oxygen throughout the pond is very low, while toxic substances increase significantly. A fishy, foul odor can be smelled on the downwind side, and water quality rapidly deteriorates - this is what is called water quality deterioration or “water turnover.” If not rescued promptly, severe surface gasping, total pond die-off or even complete loss of production will occur. Countermeasures:

1. Patrol the pond frequently. When the pond water is found to be dark and aging, immediately flush with fresh water or adjust water quality with quicklime.

2. Once water turnover occurs, drain the bottom water and fill with fresh water, replacing 1/3 to 1/2 of the water volume, and simultaneously apply quick-acting chemical fertilizer to make the water fertile as quickly as possible and increase dissolved oxygen.

3. Extend aerator operating time to expel harmful gases.

Surface Gasping Caused by Weather Changes

Thunderstorms on clear evenings, cold winds or turning on aerators can all cause premature convection between the upper and lower layers of pond water. The surface water rich in dissolved oxygen sinks, repaying the oxygen debt; the bottom water, mixed with various harmful gases and even sediment, rises up, causing oxygen deficiency throughout the pond and triggering surface gasping. In addition, during continuous rainy weather, insufficient light weakens phytoplankton photosynthesis, and dissolved oxygen in the water cannot be adequately replenished. Meanwhile, fish and other aquatic organisms continue to respire as normal, thus causing surface gasping.

Countermeasures: Pay attention to weather forecasts. During rainy, humid and stuffy weather, feed less or not at all in the afternoon. Patrol the pond at night, and turn on aerators or flush with water the next morning.

Surface Gasping Caused by Overcrowding of Fish and Other Aquatic Organisms

Some inexperienced fish farmers stock fry without clearing and disinfecting the pond, and do not install filter screens when filling with water. Various wild fish and eggs enter the pond together, causing overcrowding of organisms in the pond and oxygen-deficiency surface gasping in fish. Especially in high-temperature seasons, the solubility of oxygen in water decreases as water temperature rises, while the respiratory intensity of fish increases accordingly. When oxygen consumption exceeds oxygen supply, surface gasping is only natural. Countermeasures:

1. Reasonably arrange stocking density according to specific conditions.

2. Carry out pond clearing and disinfection. When filling with water, install a sieve-cloth filter bag at the water inlet to prevent wild fish and eggs from entering the pond.

3. When necessary, use insecticides to kill excessive zooplankton.

Surface Gasping Caused by Ammonia Nitrogen Poisoning

In ponds where many dead fish from the previous crop were not removed in time, or where chemical fertilizer was accidentally applied in excess, ammonia nitrogen and other harmful substances often exceed limits, causing surface gasping. However, this type of gasping mostly occurs at noon. Fish move sluggishly and will eventually die if the condition persists. Countermeasures:

1. Immediately flush with fresh water and turn on aerators to oxygenate and expel toxins.

2. Apply photosynthetic bacteria or products such as Tangdujing to improve the substrate, but never use alkaline substances such as quicklime.

Surface Gasping Caused by Accidentally Introducing Polluted Water or Overdosing Medications

In addition to floating at the surface, fish will also dart about erratically, jump or swim frantically.

Countermeasures: Quickly introduce fresh water to dilute the concentration of harmful substances.

Surface Gasping Caused by Diseases and Pests

When large numbers of parasites or protozoa parasitize fish gills, they often affect the fish's breathing, causing them to float at the surface, clearly visible, swimming in clusters, occasionally showing spinning symptoms, with grass carp being the most obvious.

Countermeasures: Use insecticides continuously 2 to 3 times.

Surface Gasping Caused by Starvation

When the water is clear and lean and natural food is lacking, silver carp and bighead carp will gather in groups at the surface to search for food, competing for feed powder and swallowing the organic floating film on the downwind side. However, their movements are agile and they swim freely - this is not caused by oxygen deficiency.

Countermeasures: Apply supplementary fertilizer promptly to accelerate plankton reproduction, or feed powdered concentrated feed.

Surface Gasping Caused by Hepatobiliary Syndrome

Grass carp and common carp suffering from hepatobiliary syndrome also show surface-floating symptoms, with disorganized activity, spinning or darting up and down. No obvious symptoms are seen on the body surface, but after dissection the liver appears white-yellow and mottled, the gallbladder is enlarged and dark black, and the fish die one after another. Countermeasures:

1. Symptoms are relieved after switching to lower-protein feed.

2. It is recommended to feed liver-supporting medicated bait or add an appropriate amount of choline chloride to the feed to prevent and treat this disease.

Preventing Fish Surface Gasping by Watching for Early Signs

Fish always show certain signs before gasping at the surface. Understanding these patterns helps with prevention work and achieving the goal of reducing economic losses.

1. Predict based on weather forecasts and the day's weather conditions: In summer, when there is continuous rain, low air pressure, weak wind, heavy fog or other adverse weather, or when the weather turns cloudy in the evening, a thunderstorm occurs, or the water is overly fertile and the weather changes suddenly, surface gasping may occur the next morning.

2. Predict based on seasonal characteristics: Generally, in spring and summer, water temperature gradually rises, fish feeding increases gradually, water quality gradually becomes fertile, and pond fish stocks are high. If weather changes suddenly, surface gasping is also likely to occur. During continuous rainy weather in summer, light intensity is weak, phytoplankton photosynthesis is poor, and surface gasping is most likely to occur. In autumn, adult fish have all reached market size, pond fish stocks are high, and water is fertile. Although air temperature gradually declines, oxygen consumption in the pond water body is increasing, and surface gasping is very likely to occur with even slight weather changes.

3. Predict based on water quality conditions: In summer, plankton concentration in the water body is high. If weather changes suddenly, especially if temperature drops sharply, plankton can easily die in large numbers and the water suddenly becomes clear. At this time, oxygen-consuming factors in the water increase rapidly, and severe surface gasping or even total pond die-off often occurs.

4. Predict based on fish feeding conditions: If few fish come to feed and feeding is not vigorous when bait is applied, and no fish disease is found, it can be concluded that the pond water quality is poor and dissolved oxygen in the water body is low. This phenomenon is usually most obvious at the first feeding in the morning; if the last feeding in the afternoon is also like this, the possibility of early surface gasping at night is very high, and attention should be paid.

This can be judged by observing the feeding behavior of grass carp. Under normal conditions, grass carp generally feed within the feeding area, and you can only see the grass pile moving or grass being dragged below the water surface. If grass carp feed at the edge of the grass pile, or even swim around the pond with grass in their mouths, this is also a sign of low dissolved oxygen in the pond, and surface gasping is likely to occur under such conditions.