A method for reducing parasites in aquatic animals is provided. The method includes administering to the aquatic animal a compound comprising propyl propane thiosulfonate (PTSO) having the formula R—SOa-S—R, where R represents n-propyl group (—CH2—CH2—CH3) and a is 2 and also propyl propane thiosulfinate (PTS) having the formula R—SOa-S—R, where R represents n-propyl group (—CH2—CH2—CH3) and a is 1, so that a combination of PTS and PTSO is administered to the aquatic animal resulting in the reduction of a plurality of crustaceans infecting the aquatic animal in response to administering the combination of PTS and PTSO to the aquatic animal.
