33 set vs fish

PokerStars - $0.50 NL FAST (6 max) - Holdem - 6 players
Hand converted by PokerTracker 4

BTN: 481.14 BB (VPIP: 48.00, PFR: 14.00, 3Bet Preflop: 4.00, Hands: 50)
SB: 31.7 BB (VPIP: 23.40, PFR: 19.15, 3Bet Preflop: 11.59, Hands: 194)
BB: 137.64 BB (VPIP: 17.50, PFR: 13.75, 3Bet Preflop: 0.00, Hands: 83)
UTG: 50 BB (VPIP: 28.10, PFR: 23.33, 3Bet Preflop: 6.17, Hands: 216)
MP: 154.64 BB (VPIP: 68.42, PFR: 42.11, 3Bet Preflop: 14.29, Hands: 19)
Hero (CO): 405.22 BB

SB posts SB 0.5 BB, BB posts BB 1 BB

Pre Flop: (pot: 1.5 BB) Hero has 3♠ 3♥

fold, MP calls 1 BB, Hero raises to 5 BB, fold, fold, fold, MP calls 4 BB

Flop: (11.5 BB, 2 players) 3♣ 6♦ 4♦
MP bets 6 BB, Hero raises to 21 BB, MP calls 15 BB

Turn: (53.5 BB, 2 players) Q♣
MP checks, Hero bets 36 BB, MP calls 36 BB

River: (125.5 BB, 2 players) A♣
MP checks, Hero bets 32 BB, fold

Hero wins 120.5 BB

Is small bet on river ok? I dont think he can call, except with Ax flush draw, but it was more to get called by middle pair, or to induce raise since flush missed and he could represent Ax or bd flush.