Question

Give reasons: “There is a mass mortality of fish in a pond”.

Answer 1

“There is a mass mortality of fish in a pond” is a true statement.

The following reasons might be responsible for the decline in the number of fish in the pond:

1. Release of pesticides into the pond: Pesticides are chemicals that kill the pests in the field. These chemicals, if released into the pond or river, might cause a decline in the number of fish as they are toxic to the metabolic and respiratory systems of the fish.
2. Release of toxic waste from industries: Industries are the major cause of water pollution as they release toxic chemicals into the rivers which ultimately affect the life of aquatic organisms.
3. Release of heavy metals such as lead and mercury: Heavy metals have harmful effects on humans as well as aquatic animals such as fishes if they are released into the river, and may affect the number of fishes in the pond. Mercury leads to neurological disorders and the eventual death of the fish. Also, mercuric poisoning of the water leads to bioaccumulation of mercury in the fishes leading to Minamata disease in humans that consume these contaminated fishes.
4. Eutrophication: The nitrogen and phosphorus surface run-offs lead to excessive nutrition in water bodies. This leads to increased growth of algae that thrive on the nutrition-rich water. The rapidly growing algae utilize all the dissolved oxygen. As a result, aquatic organisms including fishes are deprived of oxygen and die.