Fishing in paddy fields

The main reasons why fish do not swim when the water is turbid are as follows:

1、 Visual limitations

1. Difficulty in finding food

-Fish usually rely on vision to discover food. In clear water, they can easily see food such as plankton and algae. However, when the water becomes turbid, suspended particles block the line of sight, making it difficult for fish to detect food. For example, in a pond where sediment is stirred up and becomes turbid, grass carp, which originally relied on visual predation, have difficulty seeing aquatic plants and other food in the water. Therefore, they will reduce their swimming to save energy instead of blindly swimming to search for food.

2. It's not easy to avoid natural enemies

-Fish also need to detect the approach of predators through visual perception. In murky water, they cannot see the arrival of carnivorous fish such as blackfish in a timely manner. To avoid encountering predators when unable to see their surroundings clearly, fish choose to remain still. For example, in some rivers that have become turbid due to rainstorm, small fish will try to stay in a relatively safe corner and reduce swimming to reduce the risk of being found and attacked by natural enemies.

2、 Respiratory obstruction

1. Risk of gill blockage in fish

-Turbid water often contains a large amount of suspended particles. When fish breathe, water flows through their gills. When there are too many particles such as sediment and organic debris in the water, these particles are easily attached to the gills. For example, after a flood, the water quality in the river becomes turbid, and the sediment in it may clog the gills of fish. Once the gills of a fish are blocked, its respiratory function will be affected and the fish will feel uncomfortable. In order to reduce the amount of water passing through the gills to prevent more particles from entering, the fish will reduce their swimming.

2. Increased difficulty in obtaining oxygen

-The turbidity of water may be due to the presence of a large number of microorganisms or algae in the water. Microorganisms decomposing organic matter or algae respiration at night may consume a large amount of oxygen, leading to a decrease in dissolved oxygen content in water. Meanwhile, these microorganisms and algae themselves also increase the turbidity of water. Fish in this low oxygen and turbid environment will reduce their activity to lower oxygen consumption, as swimming requires more oxygen consumption, while stillness can reduce oxygen demand to some extent.

3、 Inappropriate water quality

1. Effects of chemical substances

-The reason for water turbidity may be the entry of chemicals into the water, such as industrial wastewater discharge or pesticide inflow. These chemicals may alter water quality parameters such as acidity, alkalinity, and hardness. Fish have a certain adaptation range to water quality, and they may feel uncomfortable when the water quality changes. For example, when substances with strong acidity or alkalinity enter the water and make it turbid, fish may be stimulated and experience stress reactions, reducing their swimming to adapt to this poor water quality environment as much as possible.

2. Correlation of water temperature changes

-Sometimes turbidity in water may be accompanied by changes in water temperature. For example, in some small ponds, if a large amount of hot water (possibly from industrial emissions) flows in and causes the water to become turbid, the increase in water temperature will affect the physiological activities of fish. Fish are warm blooded animals, and their body temperature changes with water temperature. When the water temperature is not suitable, the metabolism of fish will be affected, and they will reduce their swimming to adapt to this change.

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