The Optimum Lipid Level for the Juvenile Redclaw Crayfish Cherax quadricarinatus: Practical Diets with Soybean Oil as the Lipid Source

Abstract

As a new species in aquaculture, the lipid nutrition requirement for the juvenile redclaw crayfish Cherax quadricarinatus on a dietary basis on a practical formula needs to be evaluated accurately. In this study, the optimum dietary lipid level was explained by analyzing the growth performance, antioxidant state, lipid metabolism, and gut microbiota of C. quadricarinatus after an eight-week cultivation trial. Six diets with different soybean oil levels (named L0, L2, L4, L6, L8, and L10) were fed to C. quadricarinatus (11.39 ± 0.28 g). The results indicated that the specific growth rate and weight gain of crayfish fed the L4 and L6 diets were significantly higher than those of the other groups (P < 0.05). By the analysis of a second-order polynomial regression model according to growth performance (weight gain rate), the optimum lipid level in a practical diet for juvenile C. quadricarinatus was 9.67%. The survival, condition factor, and hepatosomatic index of crayfish were not significantly affected by dietary oil levels (P > 0.05). As the level of dietary lipids increased, the total antioxidant capacity and glutathione peroxidase activity in serum showed a tendency to rise and then fall and the enzyme activity was highest in crayfish fed the L6 diet. Gut lipase and pepsin activities showed the highest value in crayfish fed the L6 diet. There was no significant difference in acetyl-CoA carboxylase and carnitine palmitoyltransferase-1 contents in crayfish among all the groups (P > 0.05). The relative abundance of Proteobacteria in the phylum and Citrobacter in the genus showed a significant decrease in crayfish of the L10 diet, while the relative abundance of Firmicutes in the phylum markedly increased compared to that of the other groups (P < 0.05). In summary, the results indicated that the 10.39% (L6 diet) dietary lipid level could induce better growth performance, antioxidant ability, and digestive enzyme activity. Most of the fatty acid composition of muscle is not closely related to the fatty acid composition of the diet. Moreover, the composition and diversity of the gut microbiota of C. quadricarinatus were changed by high dietary lipid levels.

Figure 1

The relationship between weight gain (WG) (%) and the different dietary lipid levels. Xopt represents the optimal dietary lipid level for the maximum WG of juvenile C. quadricarinatus. Each point in the picture represents the mean value of four replicates.

Figure 2

The correlation between the fatty acid compositions in tail muscle and diets by Pearson correlation matrix analysis. The color scale indicates the correlation value from −1 to 1. The red color indicates a positive correlation. The blue color indicates a negative correlation. ^∗Significant difference (P < 0.05).

Figure 3

The activities of T-AOC (a), SOD (b), GSH-PX (c), and MDA (d) in the serum of C. quadricarinatus fed diets with different lipid levels. All data are expressed as the mean ± SE (n = 6). Different letters indicate significant differences among experimental groups (P < 0.05).

Figure 4

The activities of lipase (a), pepsin (b), and amylase (c) in the gut of C. quadricarinatus fed diets with different lipid levels. All data are expressed as the mean ± SE (n = 6). Different letters indicate significant differences among experimental groups (P < 0.05).

Figure 5

The contents of ACC (a), CPT-1 (b), TG (c), TC (d), and TP (e) in the hepatopancreas of C. quadricarinatus fed diets with different lipid levels. All data are expressed as the mean ± SE (n = 6). Different letters indicate significant differences among experimental groups (P < 0.05).

Figure 6

Differences in bacterial community composition in C. quadricarinatus fed diets with different lipid levels. (a) The numbers of shared and unique OTUs. (b) The relative abundance of gut microbiota in C. quadricarinatus by phylum. (c) Comparisons of the relative abundance of the major bacteria in C. quadricarinatus at the phylum level. (d) The relative abundance ratio at the genus level. The middle shows the difference between proportions of relative abundance in the 95% confidence interval, and P < 0.05 represents a significant difference. (e) Bacterial taxa differentially displayed in the gut of C. quadricarinatus raised were identified by LEfSe using an LDA score threshold of >3.5. Data are expressed as the mean ± SE (n = 4). Different letters indicate significant differences among experimental groups (P < 0.05).

Figure 7

Diversity of the bacterial community in C. quadricarinatus fed diets with different lipid levels. (a) Alpha diversity. (b) Beta diversity. All data are expressed as the mean ± SE (n = 4), and P < 0.05 was considered significantly different.

Figure 8

Correlation-based network analysis of the bacterial community in C. quadricarinatus fed diets with different lipid levels. (a) Each node represents one genus, its colors represent the different phylum levels of bacteria, and its size was proportional to the number of connections (degree). The green edge indicates a negative interaction between two individual nodes. The red edge indicates a positive interaction between two individual nodes. (b) Interspecies interaction types and the ratio of negative interactions in the ecological network.