Changes in growth performance, gene expressions related to protein absorption and hepatic metabolism of triploid crucian carp (Carassius carassius triploid) caused by dietary protein level

The aim of this study was to investigate the effects of dietary protein inclusion level on growth, protein absorption pathway and liver metabolism-related pathway in triploid crucian carp (Carassius carassius triploid). Six experimental diets with different protein levels (26%, 29%, 32%, 35%, 38%, 41%) were formulated. A total of 540 fish with an initial weight of 11.79 ± 0.09 g were randomly assigned to 18 cages and six treatments with three replicates of 30 fish each for 8 weeks feeding. The results showed that the specific growth rate (SGR) and feed efficiency (FE) of triploid crucian carp were highly positively correlated with protein content (p < 0.05). The broken-line regression analysis showed that the optimal dietary inclusion level was determined to be 39% considering SGR of triploid crucian carp. In addition, genes related to protein absorption were influenced by the protein inclusion level of dietary. The mRNA expressions of pept1, lat2, cdx2, jak2 and sp1 exhibited similar change tendency and promoted to highest expression at 41% groups, 32% followed. Furthermore, the expressions of hepatic metabolism genes tor, s6k1, igf1, ampd1 and adsl reached peak at 38% dietary protein inclusion level, while 4e-bp2 gene showed the highest expression levels at 41% dietary protein inclusion level. Finally, igf1 expression in liver and cdx2 in intestine showed high pearson coefficients with dietary protein level suggesting their expressions were significant positively regulated by dietary protein level. In conclusion, this study evidenced the influence of dietary protein level on growth, protein absorption pathway, TOR and IGF pathways of hepatic metabolism related in triploid crucian carp. 39% dietary protein inclusion level would be optimum level of triploid crucian carp dietary, which will lead to a better growth and high feed efficiency of triploid crucian carp.