CONCLUSION

Dietary supplementation with GP and GO was safe and well tolerated by goldfish throughout the 10-week feeding trial, with no adverse effects on survival, growth performance, somatic indices, whole-body composition, or liver histology. Although neither GP nor GO significantly enhanced growth, supplementation improved PPV, indicating more efficient protein utilization. More importantly, both GP and GO markedly enhanced body coloration and carotenoid deposition, with GO generally producing greater improvements in carotenoid accumulation in the muscle, liver, and serum than GP. Dietary GO also improved hematological parameters by increasing RBC, WBC, and Hb levels, favorably modulated lipid metabolism through reductions in AST, total cholesterol, and triglycerides together with increased HDL-c, and significantly upregulated the expression of key immunity-related genes, including TNF-α, IL-1β, IL-10, and lysozyme, without altering HSP-70 expression. These findings indicate that GO has greater biological efficacy than GP, likely due to improved bioavailability of lipid-soluble carotenoids and other bioactive compounds.

From a practical perspective, GO represents a promising natural feed additive that could serve as a sustainable alternative to synthetic carotenoid pigments and potentially reduce dependence on chemotherapeutic agents in ornamental aquaculture. The simultaneous improvement in pigmentation, carotenoid bioavailability, hematological status, lipid metabolism, and immune-related gene expression highlights its potential to enhance both the aesthetic quality and overall health of ornamental fish, thereby increasing their commercial value.

A major strength of this study is that it provides the first comprehensive comparison between powder and oil forms of gac arils in an ornamental fish species, integrating evaluations of growth performance, pigmentation, carotenoid deposition, hematological and biochemical responses, liver histology, and immunity-related gene expression within a single experimental framework. This holistic approach provides novel evidence supporting the use of gac-derived products as multifunctional feed additives in aquaculture.

Nevertheless, the study has several limitations. Protective efficacy against infectious diseases was not evaluated through pathogen challenge experiments, antioxidant enzyme activities and oxidative stress biomarkers were not determined, and the molecular mechanisms underlying carotenoid absorption, transport, and metabolism were not investigated. Furthermore, the trial was conducted in a single ornamental fish species under controlled laboratory conditions.

Future studies should evaluate the long-term effects of GP and GO supplementation across ornamental and food fish species, assess their effects under commercial production conditions, investigate the molecular pathways regulating carotenoid metabolism and immune modulation, and validate their protective efficacy through pathogen challenge trials. Additional studies should also assess the economic feasibility of incorporating GO into commercial ornamental fish diets.

Overall, the present study demonstrates that dietary GO, particularly at 10 g/kg, is a highly effective natural functional feed additive that enhances pigmentation, carotenoid deposition, hematological status, lipid metabolism, and immune responses while maintaining normal liver morphology and overall fish health. These findings support the potential of GO as a safe, sustainable, and value-added nutritional strategy to improve the health and market quality of ornamental fish.