The RNA, DNA, and protein content of larval cod Gadus morhua reared in the laboratory at 3 temperatures and 3 densities of prey was measured. The data were used to define a quantitative relationship between RNA/DNA ratio (R/D), water temperature (T ), and protein-specific growth rate (SGR, % d -1 ). The nucleic acid content of each larva was determined with both a 2-dye flow-injection fluorometric assay (FIA) and a 1-dye/1-enzyme fluorometric microplate assay (MFA) in order to calibrate each methodology. The resulting equations were: SGR = 3.65 R/D + 1.02 T -13.05 for FIA, and SGR = 4.03 R/D + 0.88 T -11.16 for MFA. Measured growth rates ranged from negative (-8% d -1 ) to 20% d -1 . Water temperature and larval R/D explained 37 to 39% of the variability in the observed growth rate. The models are applicable over temperatures ranging from 2.5 to 9.5°C and can be used to determine short-term growth rates of cod larvae collected from both the laboratory and field.