Different diets can affect the digestion and immunity of common carp (Cyprinus carpio) according to enzyme activity assay and transcriptome sequencing

The goal of this study was to prove the benefit of mixed diet for common carp (Cyprinus carpio) liver health in rice field. Common carp is a typical omnivorous fish. They can generally prey on both plant and animal diets in rice paddy mode. In this research, the common carp were randomly divided into three groups: animal diet group (group AD), plant diet group (group PD) and mixed diet group (group MD). Growth index, enzyme activity (digestive and immune), and transcriptome profile were performed to evaluate the effect of different diets on carp health. The results showed that the final weight of common carp is lesser than initial weight and the activity of trypsin and lipase were the highest in animal diet group. On the contrary, the body weight loss and α-amylase activity were the highest in the plant diet group. The mixed diet group had the highest the acid phosphatase (ACP) and alkaline phosphatase (AKP) activity in liver. “Protein digestion and absorption”, “bile secretion”, “hematopoietic cell lineage” and “intestinal immune network for IgA production” pathways belonging to the digestive and immune systems had significant enrichment between common carp fed a single type of diet and a mixed diet. These results indicate that rice-fish system is more conducive to common carp health, certainly, it is better for economic benefits if providing additional diet for fish.