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l‐Type amino acid transporter 2 (LAT2), a key subunit in the y+L system, plays an important role in amino acid transportation in the intestine. In this study, we isolated cDNA of LAT2 from crucian carp and characterized its transcript levels in response to diets of different protein levels, protein sources, Clostridium butyricum, and Lys additive. The full‐length cDNA of LAT2 is 2709 bp long which encodes a protein of 530 amino acids in length. Tissue distribution study showed that LAT2 is abundantly expressed in the foregut and midgut. We found a dose‐dependent effect of dietary protein levels on LAT2 expression. Fish showed high levels of LAT2 after fed with diets of 37 and 42% protein levels. In addition, LAT2 exhibited a higher level of expression after fish meal intake compared with soybean meal intake. C. butyricum intake induced a different effect with different additive levels on LAT2 expression in the foregut of crucian carp. We also demonstrated that in fish fed with Lys additive diet, the LAT2 expression levels increased significantly after 5 h. These results suggest that LAT2 gene expression in the foregut of crucian carp is regulated by dietary proteins and feed additives, providing new strategies for optimizing diet formula for crucian carp.

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