Quantification of waste feed and fish faeces in sediments beneath yellowtail pens and possibility to reduce waste loading by co‐culturing with sea cucumbers: an isotopic study |
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Authors: | Hisashi Yokoyama Daiji Tadokoro Masatsugu Miura |
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Affiliation: | 1. National Research Institute of Aquaculture, Minami‐ise, Mie, Japan;2. Owasebussan Co., Ltd., Owase, Mie, Japan |
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Abstract: | To evaluate environmental impacts of yellowtail culture and to examine the efficiency of the sea cucumber Apostichopus japonicus in reduction of waste loading, surface sediments were sampled and A. japonicus were cultured at a yellowtail farm in Owase Bay, Japan. Waste feed‐ and faeces‐derived organic matter (WOM, FOM) in sedimentary organic matter (SOM) was estimated based on the δ13C and δ15N of the fish feed (?21.7‰, 9.2‰), yellowtail faeces (?20.6‰, 6.2‰) and SOM reference (?24.4‰, 4.4‰). Small WOM (0–22% in SOM) but substantial FOM (28–61%) loadings in the fish farm area and high sulphide concentrations in the sediments (1.0 mg g?1) suggest that reduction in the fish stocks or mitigation of the faeces should be considered. A. japonicus juveniles were cultured in three cages deployed below a pen and growth was assessed after three different periods (62, 107, 181 days). A. japonicus grew well during the first 107 days (daily specific growth rate, 3.7%) and their survivorship was high (80–90%). Growth ceased after 107 days, probably due to fouling on the cages. The δ13C and δ15N of their hypothetical diet (–19.7‰, 5.5‰) were close to the FOM values, suggesting assimilation of FOM. |
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Keywords: |
Apostichopus japonicus
aquaculture waste fish farm integrated multi‐trophic aquaculture sediment stable isotope |
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