How Fish Have Evolved To Become Suited To Its Environment

Erica Twilley

BIO 101: Principles of Biology

October 30, 2012 Angela Romo, Facilitator
University of Phoenix

Fantasy Literature and Fantastic Language

Fish are aquatic organisms that have several features that allow them to survive in their environment. All fish have fins, which help them keep going in a specific direction by guiding them and providing thrust. Their bodies are streamlined to help reduce friction as they swim through the water. Their skeleton is important for this, too. The skeleton provides the framework for the outer structures and the muscles provide the power that allows the fins to thrust them through the water. The hindbrain is responsible for sending the signals for movement and keeping the fish balanced. The swim bladder is also important for swimming. It is a gas-filled organ found in the abdomen of fish that allows the addition or removal of gas to let the fish move up or down in the water. If fish did not have this organ, they would have to keep swimming so that they would not sink. This organ allows them to expend less energy as they adjust the depth at which they want to float. Some fish can use their swim bladder to send or receive sounds. Their eyes allow them to see their prey and predators. The midbrain of the fish is responsible for vision, motor responses, and learning. Gills allow for gas exchange so that they can breathe in the water. The oxygenated blood will be circulated by the arteries, veins, and capillaries. Some fish have a modified circulatory system that allows them to maintain a higher body temperature, which provides more energy to allow them to swim faster.
The jaws of fish can vary depending upon the type of prey that they consume. If a fish is a bottom feeder, it will have a mouth an inferior mouth, like a catfish. Some of these fish have suction cup shaped mouths, too. If it is a surface feeder, it will have a mouth that is turned up to feed on insects. Fish that feed in mid-water have a terminal mouth and predatory fish, usually, have wide mouths, while fish that eat plants have smaller mouths. The esophagus of fish is short and can expand, which allows them swallow large objects. Once something is consumed, it goes to the stomach from the esophagus where gastric juices digest break down food and prepare it for digestion. Food goes through the pyloric ceca and into the intestine where most of the absorption takes place. Depending on the diet of the fish, their intestines can be different lengths. Digestion ends at the anus where waste is expelled. Fish must also be able to regulate water movement over the surface of their body, osmoregulation. Marine fish have tissues that are less salty than their surrounding environment. They keep water continually moving out through the skin and gills. In order to stay hydrated, these fish will drink large amounts of water and produce small amounts of concentrated urine. Their gills are also adapted to secrete salt. Freshwater fish have tissues that are saltier than their environment. Water is constantly entering their bodies through the skin and gills. These fish do not drink water and produce large amounts of diluted urine. The kidney has a different function in different fish

References
Anatomy and Physiology. (2002). Retrieved from http://www.seaworld.org/infobooks/BonyFish/anatomy.html
Fish. (2012). Retrieved from http://7salemanimalkingdom.wikispaces.com/Fish
Vertibrate Kidneys. (2011). Retrieved from http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/V/VertebrateKidneys.html