Effects of temperature and dietary protein on the growth performance andIGF-ImRNA expression of juvenile mirror carp (Cyprinus carpio)

Abstract

Juvenile mirror carp were fed with five different diets containing 303, 322, 341, 361 and 379 g kg−1 protein and reared at three different water temperatures (18, 23 and 28 °C) for 60 days. We investigated the insulin-like growth factor I (IGF-I) mRNA expression, growth performance and the relationship between IGF-I mRNA expression and the growth performance. The results indicated that the IGF-I mRNA expression, final body weight, specific growth rate (SGR) and feed efficiency (FE) were enhanced significantly with increasing dietary protein levels (P < 0.05), whereas the protein efficiency ratio, hepatosomatic index (HSI) and viscerosomatic index (VSI) were decreased. Moreover, the IGF-I mRNA expression, final body weight and SGR were increased significantly with temperature, whereas the HSI and VSI indices were decreased significantly with temperature. Correlation analysis showed that the IGF-I mRNA expression levels in the brain and liver were positively related to the SGR and FE growth indices (P < 0.01). Finally, the optimal protein requirements for fish growth in different seasons were determined based on the values of SGR and FE, that is 343–348 g kg−1 protein at 18 °C, 354–352 g kg−1 at 23 °C and 371–362 g kg−1 at 28 °C. In this way, we can adjust the dietary protein levels according to culture temperature to reduce any negative impacts on dietary costs and environmental pollution.