Y

Year Class
All of the fish/offspring of a given fish species in a given year

Yearling
A one year old fish.

Yield-per-recruit
The expected lifetime yield-per-fish of a specific age (e.g., per age 2 individual). For a given exploitation pattern, rate of growth, and natural mortality, an expected equilibrium value of Y/R can be calculated for each level of F.

Yolk
The food part of an egg.