Fish Anadromy In Fish

According to Quinn (2005), there are about one hundred and sixty species of fish that migrate between saltwater and freshwater habitats as part of their life cycle. This is a behaviour that has been called diadromy. Some of these fish spawn at sea and migrate to freshwater for growth, a characteristic which is called catadromy. Others spawn in freshwater and migrate to sea for growth, a characteristic called which is called anadromy. Salmon falls in the third category of anadromous fish. This paper aims to examine the nature of anadromous salmonids which have the ability to exist in two different environments during their life time. Specifically, the paper will focus on the Atlantic salmon, also known as Salmo Salar. Atlantic salmon are fish,

The Atlantic salmon’s life starts as an egg. The eggs are laid in fresh water by mature female salmons in nests called redds usually in the fall. During winter, the eggs develop into very small salmon which are called alevin. Starting their lives as eggs embedded in gravel, the emerging alevins continue to hide in the gravel until their yolk sack is depleted (Quinn, 2005). Within a relatively short period of time however, the alevins start to explore and swim around in the redd looking for food. It is only in the spring that the alevins are able to swim out of the redd. By this time, the alevins have consumed the yolk sack and when this happens, they cease to be called alevins and they now become fry. It is not long before the fry grow into what are called parr. Parr are only two inches long and are usually camouflaged (Palm et al, 2009). For two to three years, the parr grow in the fresh water they were born into, to become smolts which are sexually active and eventually migrate to the ocean in the springtime. Smoltification is a transformation during which the parr develop salt water tolerance and silvery scales which work better for predator avoidance in the sea (Quinn, 2005). Smoltification can also be defined as the sum of all physiological and behavioural changes that are coordinated to prepare the freshwater fish for successful life in salt water after migration. The process of smoltification is

In the sea salmon spend varying amounts of time feeding and growing in an environment rich in food resources (Ackerman, 2017). It has also been noted that salmon undergo their greatest feeding and growth in salt water. Salmon’s therefore may primarily migrate to the ocean in order to maximise their feeding potential so that they may in turn reach optimum growth (Larsen, 2006). Again, since the diet of salmon changes at smoltification from small to larger food, most of the food that the new diet may consist of might not be found in the rivers in the amounts that would be sufficient for the adult salmons (Standen et al, 2004). According to Ackerman (2017)The levels of energy (lipids and proteins) that the fish has amassed during its time out in the open ocean also correlate to the distance that the fish have to migrate back up freshwater to reach their spawning grounds. This means that they need to feed more for this process to successfully happen and the open ocean provides the perfect feeding ground for fish their size. After all as Jonsson and Jonsson (2007) state, age of first sexual maturation is influenced by the growth rate at sea, where a higher growth rate means an earlier return to the river to