Don't know for sure. Another possibility is a recovering kelt. While trapping a couple creeks we routinely got rather chrome bright female kelts who were gorging on Carpenter Ants. They were recovering condition fast. In fact, the one I remember best had a belly that almost felt like a male; it was already tight. We saw kelts in the creeks in August so that becomes another possibility if there was a lot of food around. And they would be aggressively feeding.