Nutritional role of natural productivity and formulated feed in semi- intensive shrimp farming as indicated by natural stable isotopes

The natural productivity of semi-intensively managed shrimp ponds is frequently represented by a diverse trophic structure that forms part of the diet of farmed organisms. As in natural ecosystems, these dietary components exhibit differing isotopic signatures that vary with diet and trophic level. These isotopic differences can be used to infer the transfer of nutrients, as the isotopic values of prey items and consumers can be integrated in mass-balance mixing models, allowing the quantification of the relative contribution of multiple nutritional sources to the growth of a specific organism. By applying such methodology, it has been possible to estimate the relative dietary contribution of several elements that belong either to the biota of the farming environment or that are part of formulated diets. Careful sampling methods and isotopic analysis of these samples provide valuable information, not only in terms of what the consumer organism has selected, captured and ingested, but also in terms of the proportions of assimilated nutrients in the consumer's tissues. Results from several studies indicate that the natural productivity found in semi-intensively managed ponds frequently supplies higher proportions of dietary carbon and nitrogen to shrimp growth than the formulated feed, emphasizing the nutritional relevance of the former. A synthesis of field and laboratory studies applying isotopic techniques to determine the relative contribution of nutrients derived from different biota elements and formulated feeds to the growth of farmed shrimp is presented.