Growth and tissue composition as a function of feeding history in juvenile cephalopods

We present the results of a series of experiments that examined the effect of feeding history on the growth and tissue composition of juveniles of two tropical cephalopods; the squid Sepioteuthis lessoniana and the cuttlefish Sepia elliptica. Juveniles were reared in individual containers for between 35 and 42 days at different ration levels, three ration levels for the squid and two levels for the cuttlefish. Although differences in ration were sufficient to cause different growth rates, both in body length and mass, the effects on tissue composition were less definitive. Sepioteuthis juveniles on the highest rations had higher concentrations of water, but no difference in lipid, carbohydrate or protein when compared with their lower ration siblings. In the case of juvenile cuttlefish no difference in tissue composition was detected between the two ration levels. RNA:protein ratios were also determined for the juveniles to provide an estimate of instantaneous growth. A significant correlation was found between body size and RNA:protein ratio in the squid; those juveniles that ate more had higher RNA:protein ratios than lower ration individuals. Significantly, the juvenile cuttlefish showed no relationship between growth rate and RNA:protein ratios, which means that we are unable to use this measure to estimate the growth rates of wild individuals. In conclusion, ration level did affect growth rates and food availability is an important factor in modifying growth rates of wild individuals. However, we could not find, at the individual level, an index or measure that could be used to explain the variability of observed differences in growth rates as a function of nutritional history.