Multiple biochemical measurements were evaluated as an indirect measure Of juvenile fish growth rate. Juvenile two-spotted gobies, Gobiusculus flavescens (Fabricius), caught in the Kiel Bight, were incubated in a temperature gradient table at 7 different temperatures ranging from 9 to 22.7 degrees C for up to 28 days and sampled weekly. RNA/DNA ratios (RNA/DNA), protein and lipid amounts were measured in whole fish homogenates and compared with calculated weight-based growth rates of the individuals. RNA/DNA values were not significantly correlated with weight-specific growth rates. Lipid- and protein-based growth rates, on the other hand, were highly correlated with weight-specific growth (R(2) of 0.4-0.5) and lipid-based growth rate explained 45.8% variability of weight-based growth in a linear growth model. Weight-based growth rates showed it dome-shaped relationship to temperature with a maximum around 16 degrees C, it trend mirrored in lipid-based growth rates. The results indicate a stage-dependent shift in energy storage and metabolism with it decoupling of RNA/DNA as an index of weight-based growth rate as the juvenile gobies mature and lipids become the main determinant of weight-based growth in these fish.