No fish, nor any organism, dies for no reason. Even if they die from "old age" it is usually due to failure of a vital organ like the heart or kidneys.
Without knowing any recent symptoms, I cannot say what would have killed a fish that died seemingly "from nowhere." If you had owned him for at least two or three years, though, it may have simply been his time.
the plankton population would decrease
yah it would! you would die too if you ate a puffer fish!
a clown fish will die because it is a ocean fish and with out salt water , it will die in fresh water.
all the fish would die
absoulutley not the fish would die soon after you put it in and it might die that day.
Fish have gills and they absorb the water of the sea, ocean or anyplace with water. It's just like air. Without air we would die. Without water fish would die.
If the fish are fresh water fish the kidneys would not work. The fish would die.
Many fish would die off because of changes in the saltwater
No. If all the fish died, there would be no fish. Some fish unlucky enough to be too close, however, may die.
They will die. I did it once and my fish died.
nowhere
nowhere