The fish family includes sharks, whales, hagfish, and lungfish among others. Fish are water vertebrates and can exist in both fresh water and salt water depending on their adaptability. All fish are aquatic, and they survive by breathing oxygen that is dissolved in water. The two primary groups of fish include bony fish and cartilaginous fish. The aquatic habitat and environment are what determine the ecological structure of the fish. The entire system in which the fish lives is what is referred to as the fish ecology. Fish thrive well on sea nutrients, which are found at the bottom of water systems commonly known as phytoplankton. Various places that offer habitat to the fish are the oceans, lakes, seas and rivers, where their type of food thrives. For adaptability, fish have various organs that enable them to survive in water.
The kind of environment in which fish live varies depending on amounts of oxygen, the amount of salt, water temperatures, types and amounts of food, breeding areas and types of hiding areas. Salinity is one of the factors. Some fish can thrive in salty water while others cannot. Anadromous fish are those that can survive in both. Most fish species can survive in colder water as it has the capability of holding more oxygen than warm water. However, the range of temperature within which different fish can survive varies with some surviving in both warm and cold water. Although it is impossible for fish to select accurately the temperature that is adequate to them, they are found in the water close to that temperature. Water quality and water cover, availability of food and the amount of competition among the different fish influences a fish’s environment too (“Where Do Fish Live?,” n.d).
Fish have various roles in the environment. To start with, the organism is a source of food for many people. It, therefore, forms an important part of the food chain. In addition, fish provide important nutrients required by another organism therefore aids in regulating the food web. It is important to note that fish forms an important part of the marine biotic community by excreting nutrients that are necessary for the growth of algae and sea grass. Other ecological importances of fish include using the scales to make artificial pearls, using the isinglass from the fish air bladders to produce glue, creating fish silage from the fish heads, which are considered to have high levels of nutrition, making nitrogenous fertilizers and processing vitamin D and blubber oil from fish liver and whales respectively (Cantoria, 2013).
External and Internal Features of a Fish
External features
The nostrils of a fish are not used for breathing like for other vertebrates. They form the route towards the central organs of smell, which help detect the food location. Fish also have large round pupils that never vary in size. This shape of the eyes is necessary because of the refractive index of water, which can only be achieved through the movement of the lens in and out, as the fish is unable to reshape its lens like the mammals. Their eyes have spherical lenses with their retinas having both cone cells and rod cells. Most species also have color vision. The mouth of a fish defines the type of prey it takes in. the larger the mouth, the larger the prey. The organism also has a sense of taste as it filters out through the gill rakers what is not prey before swallowing its food (Mackean, 2004). Depending on the species, some fish have teeth while others do not. At this point, it is important to mention that fish can be carnivorous, omnivorous or herbivorous.
Source: “Fish Anatomy”, n.d
The operculum is a bone-like structure that covers and protecting the gills. There are some types of fish that lack the operculum, but instead have separate gill stilts for every gill. The lateral line is a canal or tube that is filled with jelly and is located just below the skin. It has a series of tiny pores that open to the water outside. The canal has nerve endings that make the jelly vibrate sending impulses to the brain In the case of any water disturbance. It, therefore, aids the fish in sensing water pressure and currents. This system enables even the blind fish to escape in case of any danger.
The fins of a fish are responsible for giving the fish direction of movement as they swim and balance. The anal fin contributes to the forward thrust of the movement of a fish. The dorsal, ventral and anal fins which are sometimes referred to as the median fins control the yawing and rolling movement of a fish during swimming. These fins increase the surface area of the fish presented to water. The pectoral and pelvic fins commonly referred to as paired fins, causes the fish to swim either downwards or upwards depending on the angle at which the muscles are held by the water, by controlling the pitch. The pectoral fins are highly mobile and lie in front of the center of the gravity. The paired fins also control the speed of the fish and determine when to slow down or stop (Mackean, 2004).
Scales can be classified as either cycloid and ctenoid. Cycloid scales have smooth rounded edges while ctenoid is characterized by jagged edges. Most fish have a mucus layer covering their bodies, which is responsible for preventing infections. The vent is an external opening that is found immediately in front of the anal fin. It forms to the opening of the reproductive and urinary tracts (“Fish Anatomy”, n.d).
Internal organs
The spine is the framework upon which the body of a fish is made. It connects the tail of the fish to the skull. It is hollow and protects the spinal cord. The spine is flexible having the ability to contract in a series, which causes a wave-like movement that enables the fish to move. The spinal cord relays sensory information and instructions.
Source: “Fish Anatomy”, n.d
The swim bladder is a hollow organ that is filled with gas and enables fish to maintain buoyancy. Fish such as the shark and the dogfish lack the swim bladder and, therefore, sink whenever they stop swimming. Whenever the fish moves to regions with varying depths, it is required to regulate the pressure. In certain fish, the bladder opens into the gut of the organism and at this point, the air pressure is controlled by either releasing air through the mouth or gulping. There are, however fish that lack the opening and in such cases, the blood vessels around the bladder absorb or secret the air, therefore, controlling the pressure.
Gills form the respiratory system in a fish. If a fish is to remain alive, these organs should not be tampered with, as they are very delicate. The kidneys are responsible for filtering waste materials from the blood. The kidney too regulates the levels of water and salt concentration in the blood. It is this regulation that enables some fish to survive either in fresh or salty water. The kind of intestines a fish has is determined by the type of food it feeds on. Piscivorous, which are fish that feed on other fish, have shorter digestive systems while the herbivorous tend to have longer systems since plants are fibrous and tough and could be hard to break them down in a shorter digestive system. The pyloric caeca is an organ with fingerlike projections located near the stomach and is responsible for secreting enzymes that are required for digestion. The vent as mentioned earlier is a genital tract on which sperms and eggs are released and also the site for waste elimination.
The liver in fish secrets enzymes that is necessary for breaking down fats. It is also the storage site for carbohydrates and fats. Other functions of the liver include waste excretion, destruction of old blood cells and maintaining a desirable blood composition. The heart as expected is one of the most vital organs as it transports blood throughout the body. It is through it that nutrients get to cells, and other organs and waste products are carried to the liver and kidneys for elimination. The gonads consist of the female bass that releases eggs and the male organs that produce milt that is necessary for fertilizing the eggs. The male gonads are smaller as compared to those of females. Lastly, muscles provide locomotion and movement in fish (“Fish Anatomy”, n.d).
Fish have evolved over the years to become the masters of the water. They are diverse, complicated and have a long evolutionary history. Fish are considered to be the first true chordate, having being on the continent for about five hundred million years. The first fossil to prove their long existence is known as the Upper Cambrian fossil Anaspis and is said to have been a jawless fish. Fish evolved in the Silurian and Devonian period. In the middle of the Silurian period, the diversification of the jawless fish was experienced with the true variety of fish flourishing towards the end of the Devonian period (Kagle, 2008).
In case a fish is moved to an entirely different environment that is not similar to its usual, it will not survive. Say, for example, a freshwater fish is taken to saline conditions. Since the organ system of this fish is conditioned to survive in fresh water, it will die. This means that the organ system will not be efficient enough to enable the fish to survive. The oxygen level in this water is certainly low, and it would require an increase in the level of hemoglobin to ensure that the respiratory system functions effectively. This, however, cannot happen overnight and, therefore, the fish will die due to lack of enough oxygen. If the fish was alternatively moved to land, it will without a doubt die, as the respiratory system is not compatible with that of the organisms that live on land. A significant change of the fish’s environment would cause fish to become extinct in the long run.
In conclusion, fish is one of the best-adapted animals in the water. It has various organs, including fins, gills and the lateral line that enables them to survive in water. Depending on the size and structure, a fish can be either prey or predator. Fish are believed to be one of the oldest chordates with the mammals and amphibians evolving from them. They have various roles in the environment, which range from ecological to economic roles. The fish is best adapted to aquatic life, and a significant change in its environment would lead to the malfunctioning of the organ system and the ultimate death of the organism.
References
Cantoria, C. S. (2013, January 1). The Ecological Importance of Fish. Retrieved March 16, 2016, from Bright Hub: http://www.brighthub.com/environment/science-environmental/articles/84726.aspx
Fish Anatomy. (n.d.). Retrieved March 16, 2016, from Florida Fish and Wildlife Conservation Commission: http://myfwc.com/fishing/freshwater/fishing-tips/anatomy/
Kagle, R. (2008, January 1). The evolutionary Steps of Fish. Retrieved March 16, 2016, from Serendip Studio: http://serendip.brynmawr.edu/exchange/node/1904
Mackean, D. G. (2004). Fish - Structure and Function. Retrieved March 16, 2016, from Biology Resources: http://www.biology-resources.com/fish-01.html
Where Do Fish Live? (n.d.). Retrieved March 16, 2016, from Discover Boating: http://www.discoverboating.com/resources/article.aspx?id=113
