Level codes:

 PASSWORD
 PRISONER
 FISHHEAD
 MOREFISH
 FISHFISH
 TINYFISH
 FREDFISH
 BIGFISHY
 EATDEATH
 EATFISHY
 SLOWFISH
 FISHFAST
 PLUNGERS
 MOPHAPPY
 JANITORS
 THROMULI
 PARAKEET
 FUZZYDOG
 SPAMKEET
 BABYHEAD
 FISHNOSE
 FISHTOES
 FOOTFISH
 FISHBONG
 ABCDEFGH