* Q3 EPS $0.09 vs est $0.08

* Brokerage commission fees down 15 pct

* Sees Q4 EPS below Street view

Oct 22 (Reuters) - Online brokerage TradeStation Group Inc (TRAD.O: Quote, Profile, Research) posted a 57 percent fall in quarterly profit on Thursday hurt by lower brokerage commissions and fees, and forecast weak fourth-quarter earnings.

Net income for third quarter was $3.7 million, or 9 cents a share, compared with $8.7 million, or 20 cents a share, in the year-ago period.

Analysts expected the company to post earnings of 8 cents a ahare, according to Thomson Reuters I/B/E/S.

Net revenue fell 22 percent to $32.4 million. Analysts were expecting revenue of $31.0 million.

Brokerage commissions and fees -- the largest contributor to net revenue -- fell 15 percent to $28.6 million.

During the quarter, TradeStations' daily average revenue trades (DARTs), a key measure of trading activity for retail brokerage firms, fell 27 percent to 79,577.