Growth of juvenile Pinna nobilis in captivity conditions: Dietary and pathological constraints

Abstract

The fan mussel, Pinna nobilis, is an endemic Mediterranean species, whose populations have been seriously affected by infectious diseases. The effect of diet composition on growth and survival rates, and on nutritional metrics including ingestion and absorption rates, together with food preferences were investigated in 48 juveniles. Individuals were initially acclimated to conditions of captivity with a mixed diet of three species of microalgae cultured in situ and riverine sediment. Then, they were changed to different diets based on combinations of commercial phytoplankton gels and riverine sediments except for a control group that was maintained under the acclimation conditions. Diet A consisted of Tetraselmis chuii; diet B on a 2 species mix of T. chuii and Isochrysis aff. galbana (T-ISO), diet C on a 3 species mix T. chuii, T-ISO and Phaeodactylum tricornatum, diet D on riverine sediment without microalgae, and diet E on T. chuii and riverine sediment. Individuals under experimental diets were fed ad libitum once per day and the water with food excess replaced before the next ration. The control diet showed the highest survival and growth (50% vs. 2.5% survival and ca. 6 mm vs. <1 mm shell growth· month−1), but rates were much lower than those of field animals (by ca. 30–40%). Mortality was ultimately associated to presence of Vibrio mediterranei, but our results suggest that diet quality is an important factor mediating host condition and disease resistance. Individuals fed sediments showed the lowest levels of nutritional performance, with higher ingestion (up to 5.5 times higher) and lower absorption rates (by approx. 60%), suggesting a poor adaptation to feed on detrital material. Additionally, individuals showed a significantly higher consumption of less voluminous microalgae (T-ISO and P.tricornatum) during food preference assays. The experimentation suggests that the development of new diets nutritionally similar to those available in the field and the finding of new food supplements promoting disease resistance is a research priority for the optimal maintenance of the species under long-term captivity conditions.