10/20 disgusting river spot

[giverofbadbeats]

i have only been at the table for 15 minutes, don't have a read on opponent. he has been very aggressive, but none of his hands have gone to showdown so i can't say whether he is maniacal.

EDIT: I HAVE [Kc Ah]

PokerStars No-Limit Hold'em, $20 BB (6 handed) Poker Stars Converter Tool from FlopTurnRiver.com (Format: 2+2 Forums)

<font color="#C00000">MP (Villain) ($2117)</font>
CO ($2072)
Button ($2000)
<font color="#C00000">SB (Hero) ($2207)</font>
BB ($5464)
UTG ($1717)

Preflop:
<font color="#666666">1 fold</font>, MP (Villain) calls $20, <font color="#666666">1 fold</font>, Button calls $20, <font color="#CC3333">SB raises to $100</font>, <font color="#666666">1 fold</font>, <font color="#CC3333">MP (Villain) raises to $258</font>, Button folds, SB calls $158.

Flop: ($556) 8[img]/images/graemlins/spade.gif[/img], 9[img]/images/graemlins/club.gif[/img], Q[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, Villain checks.

Turn: ($556) A[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, <font color="#CC3333">Villain bets $325</font>, SB calls $325.

River: ($1206) A[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, <font color="#CC3333">Villain bets $1534 (All-In)</font>, Hero?????

feel free to criticize my line here. i realize river check put me in this spot. i figure at this point he either has a boat or nothing. is this an instacall, or is it a fold? i will post results after hearing your thoughts.