basically the fish is the guy that will call you all the way down with marginal holdings. this is easy to identify by paying attention to the action going on at your table. once you identify the fish it is your duty to god to bet like your on a religious crusade. here is an example...

PokerStars No-Limit Hold'em, $0.10 BB (9 handed) Poker-Stars Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

yAAwn ($10.75)
Button ($30)
Hero (LDO REDZILL4) ($9.90)
BB ($13.05)
UTG ($10.95)
UTG+1 ($11.80)
MP1 ($8.55)
MP2 ($11.80)
MP3 ($5.85)

Preflop: Hero (LDO REDZILL4) is SB with K, A.
2 folds, MP1 calls $0.10, 2 folds, yAAwn raises to $0.5, 1 fold, Hero (LDO REDZILL4) raises to $1.8, 1 fold, MP1 folds, yAAwn calls $1.30.

Flop: ($3.80) 7, A, K (2 players)
Hero (LDO REDZILL4) bets $3.65, yAAwn calls $3.65.

Turn: ($11.10) 7 (2 players)
Hero (LDO REDZILL4) bets $4.45 (All-In), yAAwn calls $4.45.

River: ($0) 9 (2 players, 1 all-in)

Final Pot: $20

Hero (LDO REDZILL4) SHOWS ACE HEART KING DIAMOND HOLLA
yAAwn SHOWS ACE SPADE SIX SPADE

So as you can see what i did is i carefully observed all the villains at the table and realized that this particular villain would not fold if he had a hand. so what i did is i 3bet my ace king for value because he will call with a really wide range. THAN once i paired my hand i tried to get all in as fast as i can get. as you saw. and i won. basically this is how you victimize bad players and get money for hookers and cocaine, or whatever your into.