Temperature and salinity effects on plasma insulin-like growth factor-I concentrations and growth in juvenile turbot (Scophthalmus maximus)

The effects of temperature and salinity on plasma IGF-I levels and its interrelationship with growth, daily feed intake and feed conversion of juvenile turbot (initial mean weight 14 g) were investigated by rearing fish at 10, 14, 18 and 22 °C and 15, 25 and 33.5‰ for 3 months.The plasma IGF-I levels increased with increasing temperatures reaching a plateau around 18 °C. Further, both temperature and salinity had a significant effect on growth, daily feed intake and feed conversion efficiency in juvenile turbot. Growth, food consumption, and food conversion efficiency were highest at 18 °C and 15‰, and lowest at 10 °C and 33.5‰. Although there was a high variation between IGF-I values within all groups there was a positive relationship between IGF-I levels and specific growth rates and daily feed intake. The levels of IGF-I were almost three times higher for fish with higher growth rates than for those with lower growth. In addition, the results show evidence for an increased appetite in fish with high plasma IGF-I levels. Interestingly, there was no correlation between environmental salinity and IGF-I levels, although decreased salinity improves growth and feed conversion efficiency.