All in call after hitting Q flush on river

My opponent is somewhat new to the table. The only read I have on him is that he is somewhat loose aggressive, but I haven't seen him make any extremely crazy plays.

PokerStars No-Limit Hold'em, $0.25 BB (6 handed) converter

BB ($57.75)
mikever ($40.30)
MP ($8.75)
CO ($23.75)
Button ($23.35)
SB ($8.85)

Preflop: mikever is UTG with J[img]/images/graemlins/heart.gif[/img], Q[img]/images/graemlins/diamond.gif[/img].
<font color="#CC3333">mikever raises to $0.75</font>, <font color="#666666">1 fold</font>, CO calls $0.75, <font color="#666666">3 folds</font>.

Flop: ($1.85) 6[img]/images/graemlins/diamond.gif[/img], T[img]/images/graemlins/diamond.gif[/img], 8[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(2 players)</font>
mikever checks, CO checks.

Turn: ($1.85) 4[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">mikever bets $0.75</font>, <font color="#CC3333">CO raises to $2.5</font>, mikever calls $1.75.

River: ($6.85) 3[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">mikever bets $5</font>, <font color="#CC3333">CO raises to $20.5</font>, mikever ???