Why is it that when it rains, the air pressure is low and fish are easy to suffocate? Can you make me understand?

To be precise, the air pressure drops in summer, which leads to rain.

The relationship between air pressure and rain should be above humidity.

The air contains more water vapor, and the average molecular weight of the air decreases, that is, the air density decreases, which leads to the decrease of air pressure. The cold front (wind) forms a low-pressure area (is it called this). Water vapor passes through the border, and it rains when it is cold.

Secondly, fish will suffocate because of the decrease of air pressure in the air, so the air in the water can easily overflow from the water.

The air in the water decreased, so the fish suffocated.