Effects of feeding Haematococcus pluvialis powder on astaxanthin accumulation, biochemical compositions, antioxidant activity, and gut microbial community in juvenile crucian carp (Carassius auratus L.)

Abstract

The effect of Heamatoccus pluvialis on astaxanthin accumulation, nutrition, antioxidant activity, and gut health in juvenile crucian carp was investigated based on two ratios of alga powder in the feed (1:1 and 2:1). After 93 days of feeding, various organs and tissues of crucian carp, e.g., serum, scale, skin, muscle, kidney, and gut liver, were isolated and tested for astaxanthin content, fatty acids, amino acids, intestinal microbiota, and physiological and biochemical indicators. The results showed that among the various types of tissues, the scales and guts were revealed with the highest contents of astaxanthin (higher than 45.00 μg/g), and 2.35 μg/g in muscles in the fish. Although the compositions of astaxanthin in the fish tissues were mainly dependent on the contents of astaxanthin in the feed, the different tissues in the fish were selective in their uptake of astaxanthin isomers. The astaxanthin isomerization occurred in the fish, as suggested by the presence of two astaxanthin isomers (i.e., 13-Z astaxanthin and 9-Z astaxanthin) which were not available in the feed. The nutritional value of crucian carp muscles was increased by the elevated contents of essential amino acids and polyunsaturated fatty acids. Compared to the control group, the fish fed with H. pluvialis was revealed with significant changes in biochemical parameters and gut microbial compositions. Both the levels of antioxidant activity, as indicated by the blood total antioxidant capacity and the contents of catalase, malondialdehyde, glutathione peroxidase, and superoxide dismutase, and the antimicrobial activity, as indicated by the content of lysozyme, were significantly increased. In the gut, the beneficial bacteria (e.g., Lactobacillus and Lactococcus) became the dominant species, while the abundance of pathogenic bacteria (e.g., Xanthobacter, Legionella, and Gordonella) was significantly decreased. This study provided strong experimental evidence to support the application of H. pluvialis in the feed for crucian carp as an effective way to improve the nutritional value and immune activity of crucian carp, greatly promoting the healthy farming and food safety of crucian carp.

Keywords

• Heamatoccus pluvialis
• Carassius auratus
• Astaxanthin
• Essential amino acids
• Polyunsaturated fatty acids
• Gut microbial composition