The Collaborative International Dictionary of English v.0.48:

Bloater \Bloat"er\ (-[~e]r), n. [See Bloat, Blote.]
   The common herring, esp. when of large size, smoked, and half
   dried; -- called also bloat herring.
   [1913 Webster]

WordNet (r) 3.0 (2006):

bloater
    n 1: large fatty herring lightly salted and briefly smoked