From The Collaborative International Dictionary of English v.0.48 [gcide]:
descale \descale\ v. t.
to remove the scales from; -- e.g. of fish, or water boilers.
Syn: scale.
[WordNet 1.5]
From WordNet (r) 3.0 (2006) [wn]:
descale
v 1: remove the scales from; "scale fish" [syn: scale,
descale]