Why do dead fish face up on their stomachs floating on the water?

If you have ever seen dead fish in a pond, lake or tank, you will definitely see them belly up on the water. Have you ever wondered why dead fish are not lying on their sides and lying on their stomachs, so that their stomachs are not?

In order to find out why the dead fish face up to the abdomen, we need to find out how the fish maintain their buoyancy when alive.

Fish bodies include water, protein, fat, bone, carbohydrates and nucleic acids. Fish often contain a lot of bone and protein, but their fat is lighter than water, which makes fish float in the water.

To swim deeper or find shallow water fish depends on an agency especially bubble to adjust the density.

Why do dead fish face up on their stomachs floating on the water? Picture 1

Water enters the mouth of the fish and passes through the gills, where oxygen is introduced into the bloodstream. In fish, a little oxygen is released in the form of oxygen gas which is fed into the fish bubble. The size of the bubble depends on the pressure on the fish body. When the fish floats to the surface of the water, the surrounding water pressure drops and the oxygen in the bubble is pushed back to the bloodstream and brought. Conversely, when the fish sinks, the water pressure increases, the bubble is filled with oxygen. This mechanism allows fish to change depth and prevent gas bubbles from forming in the blood if the pressure changes too quickly.

However, because fish bubbles are almost entirely at the center of the body, close to the stomach, but still slightly shifted to one side making the fish more prone to tilt. This is why the fish must flutter the finnage even if they do not move or have balance in the water.

Why do dead fish face up on their stomachs floating on the water? Picture 2
Swimming bladder.

When the fish die, the oxygen in the bubble remains, along with the breakdown of the tissues that will produce more gas but they have no way to escape causing the fish's abdomen to expand. At that time, the fish died as a bubble, floating on the surface of the water. Because the backbone and muscles on the back are heavier, this part will sink to the bottom and the abdomen will turn up.

Why do dead fish face up on their stomachs floating on the water? Picture 3

But not every dead fish is floating. In some cases, the fish dies when there is no air in its bubble, the fish will sink and decompose as usual in the water. In the process of decomposing an amount of gas is created inside the fish, and when there is enough gas, the body of the fish will float to the surface of the water again.

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