Several possibilities exist, some of which a biologist could detail better than I. It is really not at all unusual, even in December, for very bright hatchery hens to have at least "loose" eggs.

Hatchery fish undergo "selection" in the same way wild fish have for eons, but the selection is directed toward entirely different characteristics. Hatcheries are generally spawning the fish that come in first. These fish have developed tendencies to run up the river quickly, in a big mass, and to be ripe when they arrive at their destination (the hatchery). The ones you caught, were perhaps a bit late in getting to their destination, so dumped their eggs as it was simply"their time".