To investigate the effects of various starches on the growth, serum biochemical indices, and metabolism of rainbow trout juveniles, cassava starch, wheat starch, pea starch and corn starch were included in diets at the same level of 15% to form four isonitrogenous and isolipidic diets to feed rainbow trout with an initial body weight of (7.7±0.1) g for 56 days. The results showed that the cassava starch group had the highest weight gain (1049.3%) and the lowest feed coefficient ratio (0.83). There were no significant difference in viscera-body ratio, liver-body ratio, and proximate composition of whole body and liver among all the groups (P
>0.05). The liver glycogen content of pea starch group was significantly lower than that of other groups (P
<0.05). There were no significant differences in serum triglycerides, total cholesterol, aspartate aminotransferase and alanine aminotransferase activity among all the groups (P
>0.05). The liver hexokinase activity of cassava starch and wheat starch groups was significantly higher than that of pea starch and corn starch groups (P
<0.05), and the liver phosphofructokinase activity in corn starch group was significantly lower than that in cassava starch and wheat starch groups (P
<0.05). Serum glucose content reached to the highest value at the 7th
hour in all groups, and cassava starch group showed significantly higher serum glucose content than the other three groups from the 1h to 7h (P
<0.05). No significant difference in liver tissue morphology was observed among all the groups. In conclusion, cassava starch is a suitable starch source for rainbow trout juveniles.