Transcriptome analysis reveals the effects of dietary protein level on growth performance and metabolism in adult Procambarus clarkii farming in rice field

To assess the optimal dietary protein requirement of adult red swamp crayfish (Procambarus clarkii) farming in the rice field, six isoenergetic and isolipid diets were formulated to contain graded levels of 28%, 31%, 34%, 37%, 40% and 43% crude protein (called Diet 28–43 group). Each diet was assigned to a triplicate of 20 experimental crayfish with the average initial body weight of (15.17 ± 0.23) g for 42 days. Our results showed that the final body weight, weight gain rate and specific growth rate of red swamp crayfish adult in the Diet 34, Diet 37, Diet 40 and Diet 43 groups were significantly higher than those of other groups (P < 0.05), but no significant difference was found in meat yield, hepatosomatic index and survival rate among all groups. The highest crude protein content of muscle was found in crayfish fed the diet containing 37% protein (P < 0.05). Hemolymph total protein, globulin and total bilirubin concentration showed a positive correlation with dietary protein level, but alanine transaminase activity was negatively correlated with dietary protein level (P < 0.05). Different dietary protein level had no significant effect on the aspartate transaminase activity of crayfish (P > 0.05). Activities of trypsin and lipase in the intestine were significantly affected by dietary protein levels (P < 0.05), while amylase activity showed no significant difference (P > 0.05). Moreover, higher dietary protein significantly increased the antioxidant and non-specific immunity enzyme activity. Broken-line regression analysis based on weight gain rate and specific growth rate showed that the optimal dietary protein level for maximum growth performance of crayfish was 32.68%. According to the present study on the growth performance, the muscle of Diet 28 group (SM) and Diet 34 group (LM) individuals were selected for transcriptome sequencing. The results showed that there were 444 differential genes in SM and LM, of which 282 genes were up-regulated and 162 genes were down-regulated. DEGs of SM and LM groups differential genes were mainly enriched in citrate cycle, pyruvate cycle, glycolysis/gluconeogenesis, etc. Beyond that, transcriptomic results also hinted that glycolysis/gluconeogenesis and citrate cycle signaling pathways might be its growth change mechanisms. In addition, the aldo, eno, pk, pdhb, adh, sdha, fh, mdh2, cs were also identified as the key factors involved in glycolysis/gluconeogenesis and citrate cycle pathways. In conclusion, combining growth performance and transcriptome data, we recommended that diets with 32.68%− 34.00% protein were optimal for red swamp crayfish in the rice-shrimp farming pattern.