Absorption of biochemical components and feeding behavior with natural and carbohydrate-rich diets in Ruditapes decussatus and Venerupis pullastra clams

7 páginas, 1 figura, 2 tablas

The feeding behavior and the efficiency of the absorption of biochemical components in the diet of specimens of two species of clams, R adit apes decussatus and Ycncruph pullastra fed on natural and carbohydrate-rich diets were studied. Both the natural diet, which consisted of the microalga Isochnsis aff, galhana, clone T-ISO and ashed sediment, and the carbohydrate-rich diet, which consisted of microalgae and corn starch as organic ingredients, and ashed sediment as the inorganic component, were assayed at a concentration of total particulate matter close to 1 mg TPM L _l , and a concentration of particulate organic matter of approximately 0.6 mg POM L _l , which arc similar conditions to those found in the Galician Rias. The feeding behavior of both species for each diet is described with reference to the clearance and ingestion rates, whereas the absorption of the biochemical components of the two diets was determined by biochemical analysis of the diet and the resulting feces. Both ingestion and absorption rates were higher for V. pullastra when the clams were fed on a natural diet. Enriching the diet with carbohydrates led to a notable increase in the ingestion and absorption rates in both species, although this increase was greater in R. decussatus than in V. pullastra, and in consequence the energy absorbed from the carbohydrate-rich diet was greater in the case of R. decussatus. The energy absorbed by R. decussatus fed on this latter diet was three times greater than that absorbed on the natural diet, allowing it to maintain similar rates of protein absorption for both diets. However, in the case of V. pullastra, the amount of total energy absorbed that derived from proteins is 50% lower in the carbohydrate-rich diet than in the natural diet. The energy absorbed from carbohydrates in the carbohydrate-rich diet was greater for R. decussatus than for t' pullastra. The contribution of lipids to the total energv absorbed was found to be almost double in R. decussatus fed on the carbohydrate-rich diet, in comparison with the natural diet, although in V. pullastra this contnbution was lower. Thus, the effect of diet on the feeding behavior of both species, i.e., the increase in the ingestion rate and the corresponding increase in the absorption rate, allows /?. decussatus to compensate for the nutritional deficiencies of the carbohydrate-rich diet, whereas in the case of V. pullastra it does not appear to be sufficient for the clams to maintain the same protein absorption rate as on the natural diet. These results are discussed in relation to the possible existence of major differences in the metabolism of the two species of clams, differences which would be connected to the habitats in which they live.

Funding for this research was provided by Comision Interministerial de Ciencia y Tecnología, Spain, project MAR99-0240- C02.

Peer reviewed