Is he bluffing?

Villain is unknown, do you call or not and why?

***** Hand History for Game 2853233268 *****
$100 NL Texas Hold'em - Friday, October 14, 16:33:35 EDT 2005
Table Table 54847 (6 max) (No DP) (Real Money)
Seat 5 is the button
Total number of players : 6
Seat 1: stene666 ( $201.05 )
Seat 2: BalsamFred ( $80.45 )
Seat 4: mkang02 ( $174.05 )
Seat 6: packstar ( $129.25 )
Seat 5: Kingfish__ ( $112.65 )
Seat 3: DMoney41 ( $97.50 )
packstar posts small blind [$0.50].
stene666 posts big blind [$1].
** Dealing down cards **
Dealt to Kingfish__ [ Ac Ad ]
BalsamFred calls [$1].
DMoney41 folds.
mkang02 folds.
Kingfish__ raises [$3.50].
packstar folds.
stene666 folds.
BalsamFred calls [$2.50].
** Dealing Flop ** [ 9s, Js, 6c ]
BalsamFred checks.
Kingfish__ bets [$6].
BalsamFred calls [$6].
** Dealing Turn ** [ Tc ]
BalsamFred checks.
Kingfish__ bets [$15].
BalsamFred calls [$15].
** Dealing River ** [ 6d ]
BalsamFred is all-In [$55.95]
Kingfish__ ???