Effects of dietary supplementation with piscidin 1 on the activity of digestive enzymes in gilthead seabream (Sparus aurata)

The intensification of gilthead seabream (Sparus aurata) aquaculture highlights the need to develop sustainable strategies that reduce reliance on antibiotics. Antimicrobial peptides (AMPs), such as piscidins, represent a promising alternative to antibiotics; however, their effects on digestive physiology remain to be evaluated. This study assessed the effects of dietary supplementation with gilthead seabream synthetic piscidin 1 on the activity of digestive enzymes in this fish species and determined a potential dose-dependent response associated with this antimicrobial peptide. Following a 15-day acclimation period, 36 gilthead seabream juveniles (initial weight: 35.16 ± 1.45 g) were randomly distributed into six 250 L tanks (N = 6 fish/tank). A 17-day in vivo feeding trial was conducted using three experimental diets, including a control (0%), low dose (0.05%), and high dose (0.1%) of piscidin 1, which was protected using carrageenan, pectin, and chitosan microparticles. Following the experimental period, pyloric caeca and intestinal samples were collected to determine specific enzyme activity (mU/mg protein) via spectrophotometric kinetic assays, and soluble protein was quantified using the Bradford assay. In the pyloric caeca, the high dose of piscidin 1 (0.1%) significantly reduced the specific activities of trypsin and chymotrypsin (p < 0.05). In the intestine, trypsin activity remained stable across all treatments, whereas chymotrypsin activity significantly decreased in the group fed the low dose (0.05%). In contrast, aminopeptidase and alpha-amylase activities showed no significant differences among the treatments in any of the analysed tissues (p < 0.05). In conclusion, dietary supplementation with piscidin 1 selectively reduced the levels of certain proteolytic enzymes, especially trypsin and chymotrypsin. The stability of aminopeptidase and α-amylase suggests that piscidin 1 does not cause a generalised alteration of digestive function, nor does it significantly affect the final digestion of peptides and carbohydrates. Overall, piscidin 1 supplementation could lead to a partial reduction in the initial stages of protein digestion, although growth data, feed utilisation, and digestibility are required to determine whether these changes have significant nutritional effects.