Abstract
Crustaceans exhibit a remarkable variation in their feeding habits and food type, but most knowledge on carbohydrate digestion and utilization in this group has come from research on few species. The aim of this study was to make an integrative analysis of dietary carbohydrate utilization in the spiny lobster Panulirus argus. We used complementary methodologies such as different assessments of digestibility, activity measurements of digestive and metabolic enzymes, and post-feeding flux of nutrients and metabolites. Several carbohydrates were well digested by the lobster, but maize starch was less digestible than all other starches studied, and its inclusion in diet affected protein digestibility. Most intense hydrolysis of carbohydrates in the gastric chamber of lobster occurred between 2–6 h after ingestion and afterwards free glucose increased in hemolymph. The inclusion of wheat in diet produced a slow clearance of glucose from the gastric fluid and a gradual increase in hemolymph glucose. More intense hydrolysis of protein in the gastric chamber occurred 6–12 h after ingestion and then amino acids tended to increase in hemolymph. Triglyceride concentration in hemolymph rose earlier in wheat-fed lobsters than in lobsters fed other carbohydrates, but it decreased the most 24 h later. Analyses of metabolite levels and activities of different metabolic enzymes revealed that intermolt lobsters had a low capacity to store and use glycogen, although it was slightly higher in wheat-fed lobsters. Lobsters fed maize and rice diets increased amino acid catabolism, while wheat-fed lobsters exhibited higher utilization of fatty acids. Multivariate analysis confirmed that the type of carbohydrate ingested had a profound effect on overall metabolism. Although we found no evidence of a protein-sparing effect of dietary carbohydrate, differences in the kinetics of their digestion and absorption impacted lobster metabolism determining the fate of other nutrients.
Highlights
Decapod crustaceans live in virtually all marine and freshwater habitats on Earth, and exhibit a remarkable variation in their feeding behaviors, from filter feeding, scavenging, grazing to hunting, and in the composition of their diet
In vitro digestion of all the carbohydrates sources tested by digestive gland extracts of the spiny lobster P. argus resulted in the liberation of glucose (Fig. 1)
The lowest hydrolysis rate (HR) were found for carboxymethyl cellulose (12.361.61), alginate (3.360.70), agarose (3.260.98), and agar (7.460.83) (Fig. 1)
Summary
Decapod crustaceans live in virtually all marine and freshwater habitats on Earth ( a few species are largely terrestrial), and exhibit a remarkable variation in their feeding behaviors, from filter feeding, scavenging, grazing to hunting, and in the composition of their diet. Starch digestibility in shrimp varies from 60% to 96% [1] and in spiny lobsters from 59% (maize) to 91% (wheat) [3]. Those variations depend on several features of the starch itself [7,8,9,10], and on the level of inclusion in diet [11], the throughput rate of the digesta [11], and the activity of digestive carbohydrases [12,13,14,15,16,17,18,19,20,21,22]
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