A major challenge to the commercial culture of the slipper lobster, Thenus australiensis, is to develop a formulated feed that meets the lobster’s nutritional requirements, is highly digestible, and thus can be readily utilised and assimilated. In feed formulation, identifying suitable protein sources is of primary importance. Hence, the present study used novel approaches to evaluate five commercially available protein sources for their potential inclusion in the feed formulation for juvenile slipper lobster T. australiensis.
In a 12-week experiment, bioavailability and assimilation proportion of five protein sources (fishmeal, krill meal, lupin meal, soybean meal and squid by-product meal) were determined using a combined approach of apparent digestibility, gastrointestinal evacuation rate, and carbon and nitrogen stable isotope analysis. Apparent crude protein digestibility varied (79.6% to 95.3%), fishmeal protein was significantly less digestible than lupin meal, squid by-product meal and soybean meal. Gastrointestinal evacuation was completed (≥ 95%) between 4 and 6 hours with no significant differences among protein sources. Overall, squid by-product meal had the best growth performance. Protein source assimilation proportion ranged from 7% for soybean meal to 32% for squid by-product meal, whereas squid by-product meal and fishmeal (29%) were the only protein sources assimilated at approximately their dietary inclusion level (30%). The present study is the first in crustaceans to examine the relationship between apparent digestibility and gastrointestinal evacuation, showing that more digestible protein sources had slower evacuation rates. The combined approaches provide a deeper insight into ingredient utilisation and help understand the lobster’s ability to digest, utilise and assimilate specific ingredients.