"as a fiduciary of a trust can i deduct management fees from a brokerage acount"

Yes. The fees, however, are subject to the 2% AGI floor. 

See https://www.irs.gov/instructions/i1041/ch02.html#d0e3466

[Note that this answer is no longer accurate due to the Tax Cuts and Jobs Act - taxpayers cannot claim miscellaneous itemized deductions]

Edited 3/29/2019