The Role of Kidneys in Fish
220.127.116.11.3 identify the role of the kidney in the excretory system of fish and mammals
- Saltwater fish are hypotonic, meaning that their environment has a higher concentration of solutes than inside the fish.
- To reduce the amount of water lost from the body, saltwater fish continuously drink the salt water.The salt is absorbed in the kidneys and excreted but the water is retained. This means that the fish only produces a small amount of urine.
- This is the case for bony salt water fish, not for cartilaginous fish that have their tissues isotonic to the sea water.
- Freshwater fish are hypertonic, meaning that there is a higher concentration of solutes inside their body compared to their environment.
- Water constantly diffuses into freshwater fish and so the kidneys have to circulate the water rapidly, resulting in a dilute steam of urine constantly being excreted by the fish.
- The kidneys also actively reabsorb salts as the fresh water has a low concentration of salt.