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 grow 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 and they are efficient at assimilating proteins (apparent protein digestibility >85%). Furthermore, the protein/energy ratio required for optimum growth (>50 g protein MJ energy‐1) appears to be significantly greater than for other aquatic invertebrates or fishes (20–30 g protein MJ energy‐1). This high protein/energy ratio indicates that protein should not be considered separately from energy in cephalopods. Attempts 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 ≈ 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 protein quality of the diets as well as poor ingestive conditioning of the cuttlefish. Current research focuses on amino acid composition of prepared diets and digestion of proteins and lipids. Finally, the uptake of dissolved organics for nutrition is proposed via the microvillar skin of cephalopods, especially soon after hatching when the surface‐area‐to‐volume ratio is high.