Sufficient oxygen, suitable temperature, adequate food, current and turbid water and enemy-free environment are required for good reproduction of roe fish. Cotton fish do not lay eggs without suitable environment. In the absence of a suitable environment, mature eggs are absorbed by the body. This phenomenon is called atresia. Atresia occurs year after year in closed ponds. Therefore, roe fish does not breed in closed reservoirs. Only physical aging occurs. Closed ponds contain more organic waste. Such water has high BOD (Biological Oxygen Demand) value and low O2 content. Regeneration does not occur in stagnant water. When O2 is low, sexually mature fish cannot stimulate the gonads to induce sexual reproduction. Eggs and larvae do not easily fall prey to enemies in the clear water of closed reservoirs. Excretion is uncertain as the water in closed reservoirs fluctuates. So roe are not interested in spawning in stocked ponds.