NUTRITION OF CEPHALOPODS - FUELING THE SYSTEM

Cephalopods offer a unique model for studying animal nutrition due to the predominance of their amino acid metabolism. Since cephalopods gro w at rapid rates for most of their life cycle (3-10% body weight d(-1) ), the demands on protein synthesis are high. As a result, cephalopod body composition ranges between 75-85% protein on a dry weight basis a nd they are efficient at assimilating proteins (apparent protein diges tibility > 85%). Furthermore, the protein/energy ratio required for op timum growth (> 50 g protein MJ energy(-1)) appears to be significantl y greater than for other aquatic invertebrates or fishes (20-30 g prot ein MJ energy(-1)). This high protein/energy ratio indicates that prot ein should not be considered separately from energy in cephalopods. At tempts to supply high levels of protein (> 35% of diet on a wet weight basis) to cuttlefishes with moist prepared diets (pellets and surimi) have been successful in terms of palatability (feeding rates approxim ate to 8% body weight d(-1)) but growth rates (0.7-1.0% body weight d( -1)) have been 25-33% of normal growth rates (3.2-4.0% body weight d(- 1)). The identified limiting factors have been nutrient density and pr otein quality of the diets as well as poor ingestive conditioning of t he cuttlefish. Current research focuses on amino acid composition of p repared diets and digestion of proteins and lipids. Finally, the uptak e of dissolved organics for nutrition is proposed via the microvillar skin of cephalopods, especially soon after hatching when the surface-a rea-to-volume ratio is high.