What is "lake herring"

Powan \Pow"an\, Powen \Pow"en\, n. (Zo["o]l.) A small British lake whitefish ( Coregonus clupeoides, or Coregonus ferus); -- called also gwyniad and lake herring.

1. n. cold-water fish caught in Lake Superior and northward [syn: cisco]

2. important food fish of cold deep lakes of North America [syn: cisco, Coregonus artedi]