The Collaborative International Dictionary of English v.0.48:

Birt \Birt\ (b[~e]rt), n. [OE. byrte; cf. F. bertonneau. Cf.
   Bret, Burt.] (Zool.)
   A fish of the turbot kind; the brill. [Written also burt,
   bret, or brut.] [Prov. Eng.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Brill \Brill\, n. [Cf. Corn. brilli mackerel, fr. brith
   streaked, speckled.] (Zool.)
   A fish allied to the turbot (Rhombus levis), much esteemed
   in England for food; -- called also bret, pearl, prill.
   See Bret.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Bret \Bret\, n. (Zool.)
   See Birt.
   [1913 Webster]