by Adler Ma
The full classification of the Atlantic Salmon is Kingdom Animalia, Phylum Chordata, Class Osteichthyes, Order Salmoniformes, Family Salmonidae, Genus/Species Salmo salar. Kingdom Animalia includes all multicellular heterotrophic organisms with no cell walls (animals); Phylum Chordata includes all backboned animals (vertebrates); Class Osteichthyes is the group of fish with jaws and bony skeletons; Order Salmoniformes is consisted of several types of salmon and fish similar to salmon, including trout; Family Salmonidae specifically refers to fish that are generally considered to be “salmon”, and the Genus Salmo pertains to the Atlantic Salmon.
There are generally two types of Atlantic salmon: the best-known migrates from the spawning location to the Atlantic Ocean and returns to the same location to lay its eggs. Another subspecies that never travels to the ocean is commonly referred to as “landlocked” salmon. The Atlantic Salmon are can easily be distinguished from other Osteichthyes by their silvery colour, the characteristic of being spotted and deformed during the spawning season, small scales, a round dorsal fin, and comparatively large size- in fact, the largest salmon ever caught weighed more than a human child. Landlocked salmon exist in a wider variety of colours than seagoing salmon, such as black and green, do not become as deformed, and are generally much smaller. The bodies of salmon are thin and long, allowing them to travel upriver more easily.
During the first few years of their lives, young salmon called “parrs” stay in the inland water bodies where they are born. They later develop into grey smolt. It is at this time when oceanic salmon and landlocked salmon separate their paths- the former travels downriver to the Atlantic ocean whilst the latter makes its way into an inland lake. After spending several more years of their life in the vast expanses of an ocean or lake, salmon become sexually mature. At this time, they undergo several physical changes and force themselves upriver back to their breeding ground. Obviously, this journey is harder for oceanic salmon than inland salmon. Because of this, the seagoing salmon travelling back usually have a low rate of survival and must encounter a series of man-made as well as natural obstacles. This is the primary reason in the decrease of the salmon population in recent years. After spawning, Atlantic salmon usually return to the ocean and repeat the cycle again, this time as fully grown kelts.
The salmon encounters several obstacles as it attempts to make its way inland. A classic example of the mass destruction of a population of salmon caused by man-made hindrances occurred on the Hudson River in New York. Before the Industrial Revolution, it was swarming with salmon travelling between the spawning ground and the Atlantic Ocean. However, dams and water wheels powering mills were soon constructed on the river. Regardless of the obstacles, hordes of salmon charged upriver and were killed by the dams and rapidly spinning wheels wave-by-wave, resulting in complete extinction of all salmon south of Massachusetts. The salmon presently in Maine face other obstacles. According to the 17th November 1999 issue of PR Newswire, these salmon “are facing threats from aquaculture, fish disease, habitat modification, and catch-and-release fishing.” The diseases include swimbladder sarcoma virus, anaemia, and coldwater disease.
Salmon are evolutionarily successful Osteichthyes because of their inborn sense of reproductive duty and their long, sleek body shapes, which enables them to move swiftly to catch prey as well as moving swiftly upriver. Unlike some species, all salmon have the will to reproduce and will try the utmost to achieve that goal even if it results in death. Though this may have a negative impact on salmon populations when humans and their destructive structures intervene, it obviously has a positive impact on the species’ overall ability to pass on its genes to the next generation because, as each generation is guaranteed to have offspring.
This article is included in H2G2's official Edited Guide. The URL of the edited entry is http://www.bbc.co.uk/dna/h2g2/alabaster/A882920