When deep-sea fishes are brought to the surface of the sea, their bodies burst because of the rapid change in pressure. The correct answer is option 2 - high pressure.

Deep-sea fishes live in an environment where the pressure is much higher than at the surface of the sea. Their bodies are adapted to withstand this high pressure. However, when they are rapidly brought to the surface, the pressure around them decreases significantly.

The decrease in pressure causes a problem because the gases dissolved in their blood, such as oxygen and nitrogen, expand due to the decrease in pressure. This leads to a buildup of gas bubbles in their bloodstream. The gas bubbles cannot be easily expelled from the body, and this can cause the blood vessels and tissues to rupture, leading to their bodies bursting.

It is important to note that it is not the speed of the blood flow that causes their bodies to burst, but rather the change in pressure. The blood flow rate may be affected by the change in pressure, but it is the pressure difference that is the underlying cause of the bursting.