Effects of dietary red pepper extracts on growth, hematology, pigmentation, disease resistance, and growth- and immune-related gene expressions of goldfish (Carassius auratus)

Abstract

The market value of ornamental fish largely depends on the presence of carotenoids, which improve body coloration as well as growth and immunity. However, not many natural carotenoid sources have been tested as a dietary supplement for ornamental fish. The present study investigated the effect of dietary red pepper extracts (RPEs) supplementation on growth, feed utilization, coloration, total carotenoid content, hematology and blood stress biomarkers, genes related to growth and immunity, and disease resistance in goldfish. Four experimental groups included goldfish with no dietary RPE supplementation (control) and those with one of the three RPEs in diets: red bell pepper, chili spur pepper, and Jinda pepper (referred as to RBPE, CSPE, and JPE, respectively). Twenty goldfish (initial body weight: 8.02 ± 0.01 g/fish) per aquarium with triplicate tanks were fed one of these diets until apparent satiation thrice a day for 10 weeks. Goldfish in the JPE group had the highest growth performance and the lowest feed conversion ratio with significant differences from the control group. The L* , a* , and b* values were mostly higher in the RPE-supplemented groups compared to the control group, and the increases in the a* value at the head, abdominal region, and tail positions were particularly noticeable. The highest total carotenoids were found in the RBPE group for fin and skin, and in the JPE group for serum. Dietary supplementation of JPE resulted in the highest level of white blood count, albumin, and high-density lipoprotein cholesterol, and the lowest low-density lipoprotein cholesterol level (P < 0.05). In addition, fish in the JPE group showed significantly lower blood glucose and serum cortisol levels than the control group. The hepatic expression of genes related to immunity, TNF-α, IL-10, and lysozyme, was significantly up-regulated in the JPE group. In addition, supplementation with RPEs increased the cumulative survival rate of goldfish after infection with Aeromonas hydrophila. The expression of IGF-1 and IGF-2 was significantly up-regulated in the CSPE and JPE groups. Taken together, these results suggest that all RPEs have the potential as supplementation to improve pigmentation for goldfish diets, while JPE can further increase growth, feed utilization, hematology, disease resistance, and genes related to growth and immunity responses.