AP BIOLOGY

Detailed explanation-1: -In case of salmons, it has been theorized by Wisby and Hasler that they imprint on the unique odour of the natal water and as adults follow the same odour cues to their birth homes for spawning. Hence the correct answer is ‘Imprinting’.

Detailed explanation-2: -Salmon change color to attract a spawning mate. Pacific salmon use all their energy for returning to their home stream, for making eggs, and digging the nest. Most of them stop eating when they return to freshwater and have no energy left for a return trip to the ocean after spawning.

Detailed explanation-3: -Salmon and steelhead can return from the ocean to their freshwater habitats to spawn at any time of the year. Migration times and distance can fluctuate greatly within species. The fish “runs” may differ by species, seasons, and locations (though most of these fish return to the streams where they were born).

Detailed explanation-4: -Salmon lay their eggs in many streams and rivers. Depending on the species, a female salmon will lay anywhere from 1, 500 to 7, 000 eggs in a nest or redd she has created by making a shallow depression in the stream bottom. The male fertilizes the eggs and then both fish push gravel over them to protect them.

Detailed explanation-5: -Once their eggs are laid, salmon stop eating and no longer have the stamina to return to the ocean. They continue to breathe and swim, as their internal organs begin to deteriorate, and their skin begins to rot and fester.