Could fish’s own defence peptides become functional feed ingredients?

Fish naturally produce small molecules that form part of their first line of defence against pathogens. Known as hot defence peptides (HDP), they have traditionally been referred to as antimicrobial peptides.

Besides acting against microorganisms, these peptides can also play a role in regulating immune responses. Among them are piscidins, a family characteristic of teleost fish that is attracting interest for its potential applications in aquaculture health and nutrition.

In gilthead seabream (Sparus aurata), the Immunobiology for Aquaculture group at the University of Murcia, together with researchers from IMIDA and other institutions, has been studying these compounds for several years.

Studies published in 2025 showed that different piscidins and hepcidins can modulate in vitro processes associated with the immune response. Piscidin 1, in particular, displayed antioxidant and immunomodulatory properties as well as potent antimicrobial activity, opening the possibility of exploring its use beyond cell-based assays.

The next step has been to determine what happens when piscidin 1 is administered to live fish through their feed. One of the main obstacles is that peptides can be degraded during digestion before they have a chance to exert their effects.

To protect the peptide, the researchers encapsulated synthetic piscidin 1 in carrageenan and pectin microparticles coated with chitosan.

The microparticles were incorporated into a commercial feed and given to juvenile gilthead seabream, comparing a control group with two piscidin 1 inclusion level, 0.05% and 0.1%.

The results showed that the peptide retained biological activity following oral administration and produced changes in several immune parameters and in gene expression in the gut, skin and brain, with responses varying according to dose and duration of administration.

The signification of the study lies in the fact that the response was not simply a general activation of the fish’s defences, but rather a modulation of different immune mechanisms.

Supplementation also produced some changes in fish pigmentation and flesh texture without significantly altering the protein, lipid or moisture composition of the muscle.

The researchers therefore consider that piscidin 1 warrants further investigation as a potential multifunctional feed ingredient.

The research is, however, still at an experimental stage. The trial involved 36 healthy juveniles over 17 days and did not include an experimental infection, meaning that it cannot yet establish whether dietary piscidin 1 increases gilthead seabream resistance to disease.

Questions also remain over tis behaviour during digestion, production at large scale and cost. Nevertheless, successfully delivering the peptide through feed while retaining its biological activity represents an important step towards a potential nutritional application.

The next challenge will be to determine whether these results can be reproduced in longer trials and under pathogen challenge, bringing fish’s natural defence peptides closer to their potential use as a new generation of functional ingredients for aquaculture feeds.

Reference: Marín-Parra, C. et al. (2026). Exploring the multifaceted effects of dietary encapsulated piscidin 1 on gilthead seabream (Sparus aurata): From immunomodulation to muscle quality. Fish & Shellfish Immunology, 111717. DOI: 10.1016/j.fsi.2026.111717