Aquaculture is the fastest-growing food production sector globally and is essential for meeting the protein demands of a growing population. However, disease outbreaks remain one of the biggest threats to farmed fish, often leading to heavy economic losses and increased use of antibiotics and chemotherapeutics. To build a more sustainable and resilient aquaculture industry, there is growing interest in functional feeds, particularly natural immunostimulants, which can enhance innate immune defences without compromising fish growth.
This study investigated the effects of a phytobiotic diet enriched with the natural immunostimulant Natcontrol on Chinook salmon (Oncorhynchus tshawytscha), a high-value species central to New Zealand’s aquaculture industry, which generates over NZ$400 million annually in export revenue. Over a six-month feeding trial, fish health was assessed through the expression of key antimicrobial peptide genes: hepcidin (HAMP) and liver-expressed antimicrobial peptide 2 (LEAP2). Three isoforms of each gene were identified and characterised, accounting for the salmonid-specific whole genome duplication.
Results showed that the Natcontrol diet induced upregulation of all HAMP isoforms across tissues, particularly in the liver. LEAP2 expression responded in an isoform- and tissue-specific manner: LEAP2.1 and LEAP2.2 were upregulated in the liver, anterior kidney, spleen, and skin, while LEAP2.3 responded in the gills and skin. Crucially, the Natcontrol diet did not negatively affect weight gain or feed conversion ratio (FCR), indicating that immune stimulation occurred without compromising growth performance.
This research demonstrates that dietary immunostimulants like Natcontrol can trigger beneficial immune responses in Chinook salmon while maintaining production efficiency. These findings offer a promising avenue for reducing reliance on antibiotics and improving fish health in both New Zealand and global aquaculture, aligning with long-term sustainability and biosecurity goals for the industry.