The present invention relates to the use of the pituitary adenylate cyclase‑activating polypeptide (PACAP) for treating viral infections and virus-induced infectious diseases in aquatic organisms. The effectiveness of PACAP used alone or combined with an antiviral molecule and administered orally, by injection or by means of immersion baths has been demonstrated by an increase in the survival of fish or crustaceans infected with a virus. Moreover, it has been observed that, following the use thereof, the body weight of the aforementioned organisms is maintained or increased compared to that of infected organisms that are not treated with these preparations. By means of the reverse transcription-polymerase chain reaction of tissues and organs susceptible to viral infection, it has been shown that PACAP or combinations containing PACAP reduce the viral load in infected organisms.
