Freshwater habitats include in-land lakes, streams and rivers that do not include estuaries. Freshwater fish and plants are adapted to the particular low levels of salinity available in their environment. As in saltwater, freshwater fish and plants have an interdependent relationship within their ecosystem. Fish rely on plants to feed, grow and reproduce. Plants feed on the biological waste of fish to grow and reproduce.
High concentrations of vegetation in freshwater areas promote higher levels of oxygen in the water for fish. Plants submerged in freshwater improve oxygen levels in lakes and streams more so than plants floating on the surface of the water. By absorbing the excretory waste produced by fish, submerged plants also purify the water. Toxic ammonia from the urea of fish is used by plants for fertilizer. The plants, thus, provide a cleaner and healthier environment for the fish.
Lakes and streams with high levels of vegetation are home to a greater diversity of fish than areas without vegetation. Many freshwater fish must spawn on or around plants. Such fish lay their eggs along the plants or around them in nests. The plants provide a great place to hide eggs from predators and serve as food for the fry once hatched.
Many species of fresh water fish feed on plants. Plants serve as immediate sustenance for fry hatching from eggs lain in the area. Also, plants can provide a banquet for fish and animals that prey on fish who seek the cover of plants for safety, food and reproduction. The excretory waste of fish living amongst plants provides nutrient enrichment of the soil that encourages continued growth of the plants.
Plant densities correlate to the level of diversity of fish in a freshwater environment. However, vegetation can become too dense to allow ample movement for fish to swim and reproduce. The inability to swim may reduce the environmental conditions necessary for fish to properly reproduce or seek shelter from predators.
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