Hepatic protective effects and oxidative stress modulation via gene expression in zebrafish (Danio rerio) fed with Synechococcus elongatus PCC 7942 as a functional feed additive

Abstract

The inclusion of cyanobacteria in aquafeeds is a sustainable alternative to traditional fishmeal. This study evaluated the effects of Synechococcus elongatus PCC 7942 supplementation on intestinal morphology, liver histopathology, and antioxidant gene expression in zebrafish (Danio rerio). Fish were fed a commercial diet (CF) or the same diet supplemented with S. elongatus (EF) for 35 days. Liver histopathology revealed that 62 % of fish in the CF group exhibited generalized liver alteration, while fish in the EF group showed a lower frequency of generalized alteration (31 %) and a higher frequency of multifocal lesions (46 %), suggesting improved hepatic homeostasis. Intestinal morphometry showed no significant changes in villus length between groups. Gene expression analysis demonstrated a significant downregulation of xenobiotic metabolism genes (cyp1a, gst), antioxidant defense genes (sod1, sod2, cat), and steroid metabolism (cyp19a1a) in fish fed S. elongatus, except for gpx, which remained unchanged. The reduction in antioxidant gene expression, along with improved liver histology, suggests a lower oxidative stress in the EF group, likely due to synergistic effects of S. elongatus in mitigating oxidative damage. These findings indicate that S. elongatus supplementation does not impair intestinal morphology or liver function but supports hepatic homeostasis by reducing oxidative stress and modulating liver histopathology. This highlights its potential as a functional feed additive in aquaculture.