Dietary pyrroloquinoline quinone alleviated intestinal damage of juvenile yellow catfish (Pelteobagrus fulvidraco) induced by oxidized fish oil: insight from intestinal digestive enzyme, antioxidant status, morphology, inflammation, and microbiota.

Feeding oxidized fish oil to cultured fish harms their intestine, but whether pyrroloquinoline quinone (PQQ) can counteract this damage had not been explored. This 56-day study investigated the protective effects of dietary PQQ against oxidized fish oil-induced intestinal injury in juvenile yellow catfish (Pelteobagrus fulvidraco). Four hundred and eighty yellow catfish (initial weight approximately 12 g) were randomly assigned to four groups in triplicate: control (fresh fish oil), PQQ (fresh oil + 5 mg/kg PQQ), OFO (oxidized oil), and PFO (oxidized oil + 5 mg/kg PQQ). Fish fed OFO diet showed significantly reduced intestinal lipase and trypsin activities, lower antioxidant capacity (total antioxidant capacity, superoxide dismutase, catalase), higher malondialdehyde content, shorter and fewer mucosal folds, upregulated pro-inflammatory cytokines (interleukin-1β, interleukin-8, and tumor necrosis factor-α), downregulated transforming growth factor-β, and a disrupted gut microbiota. Dietary PQQ supplementation in the OFO diet largely reversed these adverse effects, restoring most parameters to levels comparable to the control group. PQQ also reversed the OFO-induced increase in Firmicutes and decrease in Proteobacteria and restored the relative abundances of Pseudomonas, Variovorax, Enterobacter, and Candidatus Arthromitus to levels comparable to the control group. Taken together, PQQ effectively protected the juvenile yellow catfish intestine from oxidized fish oil-induced damage by improving digestion, boosting antioxidant defenses, reducing inflammation, and rebalancing the gut microbiota. PQQ is therefore a promising functional feed additive to mitigate lipid oxidation-related problems in aquafeeds.