RNA:protein ratios in S. lessoniana did correlate with growth and the amount of food
consumed by the juvenile squid. However, when adjusted for age, the RNA:protein
levels explained only 36% of the variation in body size. This provides a weak ecological
tool to assess growth or to recognise growth as a function of feeding status in wild
individuals. Although age estimates using statolith analysis have been validated and used
to generate growth curves for squid (Jackson, 1994), there is no reliable method to
estimates growth rates for wild cuttlefish. The use of biochemical techniques as an
alternative has been proposed and it was suggested that RNA concentration as a function
of fresh body weight should provide an index (Pierce et al., 1999). However, there was
no evidence in our work to be able to provide a biochemical measure of growth in
cuttlefish S. elliptica. The development of similar indices for use with Sepia officinalis
has been partially successful, in that the correlation of RNA:DNA ratios the growth rate were evident under one temperature regime, but not another (Clarke et al., 1989).
Clearly continued exploration of these indices is needed.