Oral salmon acylated ghrelin increases food intake in common carp (Cyprinus carpio) via ghrelin receptors, likely through sensory nerves rather than systemic absorption.

This animal study investigated whether orally administered salmon acylated ghrelin (sAG) could stimulate food intake in common carp (Cyprinus carpio) and sought to identify the local mechanism behind any such effect. Carp were fed experimental diets containing a range of sAG concentrations in single-shot feeding trials, and additional voluntary feed intake was measured afterward. The study found that diets containing sAG at or above a certain threshold produced a significant, dose-dependent increase in feed intake that plateaued at higher concentrations. Notably, plasma ghrelin levels did not rise following oral administration, as confirmed by two separate radioimmunoassay methods, suggesting that sAG was not absorbed into the bloodstream. To probe the mechanism, researchers used a ghrelin receptor antagonist ([D-Lys3]-GHRP-6) and capsaicin — both abolished the orexigenic effect — pointing to a local signaling pathway involving growth hormone secretagogue receptors and peripheral sensory (likely vagal afferent) neurons. The authors propose this represents a non-circulatory gut-brain axis mechanism in fish. Limitations include that results are limited to a single fish species under controlled laboratory conditions, and translation to other vertebrates or aquaculture settings requires further research.

Why this grade: All experiments were conducted exclusively in common carp (Cyprinus carpio) under controlled laboratory conditions, with no human or clinical data presented.