1) Newly hatched salmon 2) Young salmon 3) Young salmon or trout 
A recently hatched salmon or trout (also see Grilse, Parr and Smolt)
• (n.) Young fish; fry.
<marine biology> A larval salmonid that has hatched but has not fully absorbed its yolk sac, and generally has not yet emerged from the spawning gravel. ... Absorption of the yolk sac, the alevin's initial energy source, occurs as the larva develops its mouth, digestive tract and excretory organs and otherwise prepares to feed on natural prey...
The developmental life stage of young salmonids and trout that are between the egg and fry stage. The alevin has not absorbed its yolk sac and has not emerged from the spawning gravels.
Al'e·vin noun [ French alevin , Old French alever to rear, from Latin ad + levare to raise.] Young fish; fry. 
the developmental life stage of young salmonids and trout that are between the egg and fry stage. The alevin has not absorbed its yolk sac and has not emerged from the spawning gravels
The developmental life stage of young salmonids and trout that are between the egg and fry stage. The alevin has not absorbed its yolk sac and has not emerged from the spawning gravels. 
a fry, esp. a salmon, whose yolk is depleted.