Title Quantification of Waste Feed and Fish Feces using Stable Carbon and Nitrogen Isotopes
Authers Hisashi YOKOYAMA, Yuka ISHIHI, Katsuyuki ABO, and Toshinori TAKASHI
Keywords fish farm, stable isotope, waste feed, fecal matter, feeding
Citation Bull. Fish. Res. Agen. No.31, 71-76, 2010
For improving the economic and environmental sustainability of fish farming, it is necessary to optimize feeding regimes and to decrease waste feed. We developed a method to quantify waste feed and fecal matter in sediment trap materials and sediments beside and beneath fish cages using stable carbon and nitrogen isotope ratios. The contribution ratio of three sources (waste feed, fecal matter and natural organic matter) in sedimentary organic matter in and around a red sea bream (Pagrus major) farm in Gokasho Bay, central Japan, was estimated using an isotopic mixing model. The result showed that waste feed (29% in the bulk organic matter) exceeded fecal matter (12%) in the fish farm area, suggesting the overfeeding in this farm. Then we monitored the growth and mortality of red sea bream, C and N fluxes and sediment chemistry at two commercial fish cages; cage 1 (conventional satiation feeding) and cage 2 (restricted feeding: same feeding frequency but 18% reduction in the feed amount) for 276 days. The restricted feeding achieved normal growth, increased feed conversion efficiency and reduced mortality of red sea bream and reduced contents of waste feed-derived organic matter in the sediment. Determining the relative amount of waste feed and fecal matter in settling and sedimentary organic matter is effective for the evaluation of the optimum ration level from the viewpoint of the minimization of waste feed.
URI http://www.fra.affrc.go.jp/bulletin/bull/bull31/31-3-3.pdf