Broodstock fish in this instance refers not just to fish used for egg/sperm take, but a more recent trend in hatchery practices where wild fish are captured from the parent stream (usually by hook and line) the eggs are collected and fertilized, raised in the hatchery, and then released back to the parnt stream. That way, the hatchery fish (or "broodstock fish" as everyone likes to call them) that come back are never more than one generation away from wild lineage.