Immunostimulant effects of Pituitary Adenylate Cyclase-Activating Polypeptide and double-stranded (ds)RNA in Orconectes propinquus.

Disease outbreaks in crustacean aquaculture caused by opportunistic and obligate pathogens cause severe economic losses to the industry. Antibiotics are frequently used as prophylactic treatments worldwide, although its overuse and misuse has led to microbial resistance, which has driven the search for novel molecules with immunostimulant and antibacterial activities. Antimicrobial peptides (AMP) and double-stranded (ds)RNAs constitute promising immunostimulants in the fight against infectious diseases in aquaculture. Scientists have made significant progress in testing these molecules in aquatic organisms as potential candidates for replacing conventional antibiotics. However, most studies have been conducted in teleost fish, thus little is known about the immunostimulatory effects in crustaceans, especially in freshwater crayfishes. Consequently, in the present work, we evaluate the immunomodulatory effects of the AMP Pituitary Adenylate Cyclase Activating Polypeptide (PACAP) and high molecular weight (HMW) Poly (I:C) in the northern clearwater crayfish Orconectes propinquus. Two bioassays were conducted to evaluate the effects of different doses of PACAP and Poly (I:C) HMW, different administration routes, as well as the effects of the combined treatment on the crayfish immune system. Results showed the immunostimulatory role of PACAP and Poly (I:C) HMW with effects depending on the dose, the site of injection and the treatment assessed. These findings offer new insights into the crayfish immune system and contribute to the development of effective broad-spectrum immune therapies in aquaculture.