Growth rate and nucleic acid ratio in cultured cuttlefish Sepia officinalis (Mollusca: Cephalopoda)

Juvenile cuttlefish Sepia offcinalis were hatched and reared in the laboratory at six ration levels and two temperatures. At 12.5 °C there was little growth whereas at 17.5 °C growth rate responded strongly to ration level. Nucleic acids were extracted into buffer containing 0.01% SDS and assayed by fluorescence using ethidium bromide and bis-benzimide and by absorbance at 260 nm. The sensitivity of nucleic acid assay using ethidium bromide was increased by shortening the excitation wavelength to 305 nm. RNA:DNA ratio was strongly correlated with growth rate in cuttlefish held at 17.5 °C; at 12.5 °C, the relationship was similar but not statistically significant. At low growth rates, RNA:DNA ratios were similar to those reported for larval fish; nucleic acid ratios at higher growth rates were higher than reported so far. This may be related to the very high growth rates achieved by many