What will happen if the mouth of fish is kept closed?

If a fish's mouth is kept closed, it may struggle to breathe, as fish rely on water passing over their gills to extract oxygen. This can lead to suffocation if the fish is unable to access oxygen-rich water. Additionally, keeping the mouth closed may prevent the fish from feeding, leading to malnutrition over time. Overall, the fish's health would deteriorate rapidly without proper oxygen intake and nutrition.