Importance of biofilm as food source for shrimp (Farfantepenaeus paulensis) evaluated by stable isotopes (δ13C and δ15N)

The contribution of biofilm and artificial feeds for the growth of the pink shrimp Farfantepenaeus paulensis reared in tanks and net cages were evaluated by using stable isotope (delta C-13 and delta N-15) analysis. In the net cage experiment, mass balance and mixing equations showed that the biofilm contribution to shrimp growth was over 49% of carbon and 70% of nitrogen. These data suggest that the artificial feed offered in this experiment, although ingested, was not properly incorporated in the shrimp tissue. In contrast, biofilm growing in tanks contributed little to the nitrogen incorporated by the shrimp (maximum of 29%). In this experiment, shrimp presented an unusually large isotope fractionation. These results imply that the shrimp are selectively ingesting some items from the biofilm, or differentialty assimilate specific items of the artificial feed, due to differential digestibility. The hypothesis of selective feeding of biofilm microorganisms was corroborated in the experiment with net cages, where shrimp preferentially consumed centric diatoms. This study also demonstrated that shrimp biofilin consumption and the presence of artificial feed largely influenced biofilm formation. The consumption of centric diatoms by shrimp seem to stimulate biofilm chlorophyll-a, while biofilm delta 15N values measured in tanks indicate that microorganisms present in the biofilm absorbs nitrogen released by artificial feed after its decomposition. (c) 2007 Published by Elsevier B.V.