From Nookipedia, the Animal Crossing wiki
The cherry salmon (ヤマメ, Yamame) is a common fish and a member of the salmon family. It can be found in the river between 4 am to 9 am and 4 pm to 9 pm from March to June, as well as 4 am to 9 pm from September to November. Its shadow size is between small and medium, about the same size as the crucian carp. Its selling price is unusually high for a common fish.
Donating to the Museum
In Animal Crossing
When the player is donating it to the museum in Animal Crossing, Blathers will say the following:
"This is one of those fish that seem to mysteriously dissappear from time to time. Drives fishermen batty, wot!"
In Wild World
When the player is donating it to the museum in Wild World, Blathers will say the following:
"Cherry salmon are known for their flavor and beauty, eh wot? Indeed, that is likely why they are called the queens of mountain-stream fishing. Hoo hoo! Of course, the males of the species might object to that moniker!"
In City Folk
When the player is donating it to the museum in City Folk, Blathers will say the following:
"The first thing you notice when looking at a cherry salmon is undoubtedly its green, polka-dot body, wot? All those different sized dots overlapping each other... How very chic!"
The cherry salmon appears in the center left tank.
In New Leaf
"The spotted pattern on cherry salmon serves as a camouflage and is rather common in all salmon. Most cherry salmon spend their lives in rivers, but some do migrate to the ocean to fully mature. They are popular with anglers because of their well-balanced physique and beautiful patterns. Plus, their nervous nature makes them a good challenge to catch, which just adds to the fun."
Once the player has caught a particular fish or bug, they can find information about it in the bug or fish menu. Once the cherry salmon has been caught, the following information can be found in the fish menu:
The Oncorhynchus masou or cherry salmon (also called seema) is a type of salmon. It can be found in the western areas of the Pacific Ocean, namely Japan and Korea. It has a landlocked sub-species called the Taiwanese salmon, found in Taiwan. It gets the name cherry salmon from the color it goes when it hits maturity, where the stripes on its sides develop a crimson tinge. It feeds mainly on insects, but also feeds on small fish and crustaceans. It is an endangered, harmless fish.
Names in other languages