Dietary Supplementation with R--Limonene Improves Growth, Metabolism, Stress, and Antioxidant Responses of Silver Catfish Uninfected and Infected with IAeromonas hydrophila/I

Increased intensification of the fish farming system requires care in production due to induced stress conditions, which contribute to the occurrence of infectious diseases. In this research, we evaluated how dietary supplementation with R-(+)-limonene, a compound found abundantly in essential oils from plants such as lemon and orange, affects growth, plasma and liver metabolic parameters, and antioxidant and stress responses in silver catfish, Rhamdia quelen, challenged or not with Aeromonas hydrophila. Dietary R-(+)-limonene (L0.5, L1.0, and L2.0 mL/kg of diet) improved the productive performance of fish and increased the expression of insulin growth factor 1 gene, which is related to growth. The metabolic responses indicated that the additive in the feed was not harmful to the health of the animals and increased resistance to A. hydrophila. R-(+)-limonene did not cause damage to the liver and exhibited a hepatoprotective effect against A. hydrophila. The expression of stress-related genes decreased with R-(+)-limonene dietary supplementation. R-(+)-limonene is a monoterpene from plants of the genus Citrus with diverse biological properties. This research evaluated the effects of dietary supplementation with R-(+)-limonene on growth, metabolic parameters in plasma and liver, and the antioxidant and stress responses in silver catfish, Rhamdia quelen, challenged or not with Aeromonas hydrophila. Fish were fed for 67 days with different doses of R-(+)-limonene in the diet (control 0.0, L0.5, L1.0, and L2.0 mL/kg of diet). On the 60th day, a challenge with A. hydrophila was performed. R-(+)-limonene in the diet potentiated the productive performance of the fish. The metabolic and antioxidant responses indicate that R-(+)-limonene did not harm the health of the animals and made them more resistant to the bacterial challenge. Histological findings showed the hepatoprotective effect of dietary R-(+)-limonene against A. hydrophila. Igf1 mRNA levels were upregulated in the liver of fish fed with an L2.0 diet but downregulated with bacterial challenge. The expression levels of crh mRNA were higher in the brains of fish fed with the L2.0 diet. However, the L2.0 diet downregulated crh and hspa12a mRNA expression in the brains of infected fish. In conclusion, the results indicated that R-(+)-limonene can be considered a good dietary supplement for silver catfish.