Thomas Labs Fish Pen (Penicillin) exerts a bactericidal action on gram-positive and some gram-negative bacteria. Penicillin is a broad spectrum antibiotic effective against a number of pathogenic bacteria associated with fish.

Fish Pen (Penicillin) exerts a bactericidal action on gram-positive and some gram-negative bacteria. Penicillin is a broad spectrum antibiotic effective against a number of pathogenic bacteria associated with fish diseases.