Task 1 Cambridge 10 - Life Cycle of Salmon

Question Task:

You should spend about 20 minutes on this task.

The diagrams below show the life cycle of a species of large fish called the salmon.

Summarise the information by selecting and reporting the main features, and make comparison where relevant.

Write at least 150 words.

MODEL ESSAY:

The chart describes the stages the salmon fish goes through until it becomes an adult. Overall, there are three stages in its life process. The small fish is found in lower rivers, then it migrates into the sea after it is fully developed.

Firstly, the salmon lays eggs among minute pebbles which change into reeds after approximately five to six months, and are mostly found in very slow –paced rivers. These are usually found at the upper parts of the river. In a period of four years, the reeds are called fry and measure from 3-8cms long, and as a result get to the lower river section.

The salmon again increases in length and width to between 12 and 15cms and are referred to as ‘smolt’ at the second stage when is it ready to migrate into the sea.

Finally, the adult salmon emerges in approximately five years, would have grown to be 70-76cms long,  and with mature gills and fins to help it  survive the harsh conditions the ocean brings. Opposite genders of the mature fish meet and mate following which the female lays eggs among small pebbles and life process commences again.

Fun Facts!

• Sac fry or alevin – The life cycle of salmon begins and usually ends in the backwaters of streams and rivers. These are the salmon spawning grounds, where salmon eggs are deposited for safety in the gravel. The salmon spawning grounds are also the salmon nurseries, providing a more protected environment than the ocean usually offers. After 2 to 6 months the eggs hatch into tiny larvae called sac fry or alevin. The alevin have a sac containing the remainder of the yolk, and they stay hidden in the gravel for a few days while they feed on the yolk.

• Fry – When the sac or yolk has almost gone the baby fish must find food for themselves, so they leave the protection of the gravel and start feeding on plankton. At this point the baby salmon are called fry.

• Parr – At the end of the summer the fry develop into juvenile fish called parr. Parr feed on small invertebrates and are camouflaged with a pattern of spots and vertical bars. They remain in this stage for up to three years.

• Smolt – As they approach the time when they are ready to migrate out to the sea, the parr lose their camouflage bars and undergo a process of physiological changes that allows them to survive a shift from freshwater to saltwater. At this point the salmon are called smolt. Smolt spend time in the brackish waters of the river estuary while their body chemistry adjusts (osmoregulation) to the higher salt levels they will encounter in the ocean. Smolt also grow the silvery scales which visually confuse ocean predators.

• Post-smolt – When they have matured sufficiently in late spring and are about 15 to 20 centimetres long, the smolt swim out of the rivers and into the sea. There they spend their first year as post-smolt. Post-smolt form schools with other post-smolt and set off to find deep-sea feeding grounds. They then spend up to four more years as adult ocean salmon while their full swimming and reproductive capacity develops.

Fry and fingerling are terms that can be applied to juvenile fish of most species. But some groups of fishes have juvenile development stages particular to the group. This section details the stages and the particular names used for juvenile salmon.

SOURCE: https://en.wikipedia.org/wiki/Juvenile_fish