# Functional Potential of Red Dragon Fruit (Hylocereus polyrhizus) Juice By-Products as a Natural Feed Additive for Juvenile Red Seabream (Pagrus major): Implications for Antibiotic-Free Aquaculture

## TL;DR

This study shows that red dragon fruit juice by-products can safely improve fish immunity and may replace antibiotics in aquaculture.

## Contribution

The study demonstrates the functional potential of red dragon fruit by-products as a natural feed additive in aquaculture.

## Key findings

- RJB contains high levels of phenolic and flavonoid compounds with strong antioxidant activity.
- Fish fed 1% RJB showed improved antioxidant enzymes and lysozyme activity.
- RJB inclusion did not harm growth but enhanced survival after bacterial infection.

## Abstract

Background: The extensive use of antibiotics in aquaculture has raised serious concerns, emphasizing the need for sustainable and natural alternatives. This study evaluated the potential of red dragon fruit (Hylocereus polyrhizus) juice by-products (RJB) as a functional feed additive for juvenile red seabream (Pagrus major). Materials and Methods: The bioactive composition and antioxidant capacity of RJB were analyzed, and five experimental diets containing 0, 0.2, 0.4, 0.8, and 1% RJB were fed to fish for 56 days. Results: Growth performance, feed utilization, body composition, antioxidant enzyme activities, and lysozyme activity were evaluated. RJB contained substantial levels of phenolic and flavonoid compounds and exhibited strong radical-scavenging activity. Dietary inclusion of up to 1% RJB did not significantly affect growth, feed efficiency, or plasma biochemistry. However, fish fed the 1% RJB diet showed increased catalase and glutathione levels, significantly enhanced lysozyme activity, and improved survival following Edwardsiella tarda infection. Conclusion: These results demonstrate that RJB can be safely incorporated into marine fish diets to enhance antioxidant capacity and innate immune defense. The valorization of fruit-processing by-products such as RJB offers a promising strategy for developing antibiotic-free and sustainable aquaculture practices.