bream, n. — Green’s Dictionary of Slang

bream n.

[the use of fish to denote glasses of varying sizes, as are the fish themselves; note a similar form of ranking used by British Rail freight wagons, which were labelled trout, perch, whale etc]

(US) a half-pint (300ml) of liquor.

1975

G. Underwood ‘Razorback Sl.’ in AS L:1/2 56: bream n Half pint (of liquor).

In phrases

a whole different bucket of bream (n.)

(Aus.) something completely different.

1983		J. Byrell (con. 1959) Up the Cross 23: With Fenmore, though, it was a whole different bucket of bream.
1996		J. Byrell Lairs, Urgers & Coat-Tuggers 52: But this was a whole different bucket of bream. This was the Cup.