Fresh water are all inland water bodies which are salt-free or contain no significant amount of salt.
Types of salt
- Lentic habitat – are standing or stagnant water bodies such as the ponds, lakes, pools and standing swamps.
- Lotic habitat – are free running or flowing water bodies such as rivers, springs and streams.
Characteristics of fresh habitat
- It has low concentration of dissolved salts
- It has varying oxygen level and light intensity that depends on water depth
- It has a fluctuating temperature
- It has extremely low salinity
- The animal may be affected by the relent of the water
- Current of the water may be high.
Zones of freshwater habitat (lake)
A lake consists as example of freshwater habitat has three main zones.
- LITTORAL ZONE: This is the shallow water region in which sunlight penetrates to the bottoms. The producers in the zone are of two types: rooted species that are mostly plants examples water lettuce, duke weeds, water lily, water hyacinth.
The other category of producers are phytoplankton must of which are algae. Such plants are used for food and shelter by amphibious animals and aquatic insects which spend part of their live in the pond or lake.
- LIMNETIC ZONE: This is the open water zone extending to the depth of effective sunlight penetration. The zone consists largely of phytoplankton producers and algae like green flagellates e.g. Euglena. The most abundant vertebrates in the lake are fishes which spend must of their time in the littoral zone though they move freely between the littoral and limnetic zone. Certain birds visit the lakes to feed on worms, small fishes and mollusks’. Example of such birds are herons, storks, flamingos. The most important animal of this zone is the fish.
- PROFUNDAL ZONE: This consists of the bottom and deep water area beyond the depth of effective sunlight penetration. The profound zone is not often found in ponds because they are not usually as deep as the lakes. Since light penetration is pour in this zone, the organisms depend on the limnetic and littoral zones for basic food substance. The animals that are found here have adaptation to withstand periods of low oxygen concentration. Oxygen and light are therefore factors that limit existence of organisms.
Adaptive features of freshwater animals
- Possession of elongated bodies with airs or flattered appendages to enhance buoyancy in water
- Possession of streamlined bodies by mobile organisms to reduce resistance in water e.g. fishes
- Possession of adhesives features like hook, sticky under surfaces, suckers by stationary organisms to enhance attachment.
- Possession of adaptive features like hacmoglobin in the blood of the hookworms extensive breathing tubes and other that enable them to survive in oxygen poor environment
Adaptive features of freshwater plants
- Possession of porous tissues (e.g. water lettuce) or reduced bodies e.g. (Azolla) to enhance
- The leaves of submerged plant are thin and divided to allow more surface area for light absorption in the depth of water and reduce resistance to water flow.
- Possession of hairy roof that are shorter and less branched because they are needed for absorption only and not for anchorage
- Possession of long and flexible submerged items that allows swaying with water current.
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