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Benthic fluxes of carbon dioxide (CO 2 ) and methane (CH 4 ) were evaluated in grass carp Ctenopharyngodon idella (G), silver carp Hypophthalmichthys molitrix (S), and bighead carp Aristichthys nobilis (B) polyculture systems, to which topmouth culter Erythroculter ilishaeformis (T), Pacific white shrimp Litopenaeus vannamei (P), or common carp Cyprinus carpio (C) were added. These systems, GSBT, GSBP, and GSBC, respectively, were monitored over 5 mo (May to September 2014). The presence of L. vannamei and C. carpio increased CO 2 and CH 4 emissions in GSBP and GSBC, respectively. From June to August, CO 2 and CH 4 fluxes increased in the 3 systems, and in July and August these fluxes were significantly higher in GSBC than in GSBP and GSBT, and significantly higher in GSBP than in GSBT. The metabolisms of L. vannamei and C. carpio contributed to decrease dissolved oxygen, pH, and oxidation−reduction levels, and the bioturbation of the upper sediment layers caused by these species increased organic matter degradation rate, resulting in a significant increase in particulate and dissolved organic carbon in the overlying water. Our results indicate that improving feeding efficiency and reducing organic carbon accumulation on the bottom of aquaculture ponds, as well as increasing dissolved oxygen and decreasing bioturbation across the sediment−water interface during farming seasons, is likely to reduce CO 2 and CH 4 release from aquaculture pond sediment, especially in July and August.

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In order to meet the demand of salmon market, Chinese scientists and entrepreneurs are working on salmon mariculture far offshore in the Yellow Sea, China. Rainbow, steelhead trout and Atlantic salmon were selected as the main culture species. The aims of the present study were as follows: (a) investigate the effect of the salinity acclimation method on the growth, osmoregulation and energy budget in two forms of Oncorhynchus mykiss, rainbow and steelhead trout and (b) explore the optimal size of steelhead trout for the seawater entry. In trial I, rainbow (mean = 99.44 g) and steelhead trout (mean = 99.01 g) were reared for 40 days after undergoing salinity acclimation at three rates: an abrupt increase in salinity from 0 to 30 g/L (T30); an abrupt increase in salinity to 14 g/L, followed by a daily increase of 2 g/L (T2) or 6 g/L (T6) until reaching 30 g/L; and no salinity exposure (control treatment) (T0). In trial II, steelhead trout with body weights of approximately 100 and 400 g were cultured for 60 days with two treatments, T0 and T2, and the specific growth rate (SGR) was calculated every 10 days. In trial I, in both kinds of fish, the optimal growth performance, survival rate, osmoregulation and energy budget were observed in the T0 treatment, followed by the T2 treatment. These results indicate that O. mykiss with a body weight of approximately 100 g can adapt to sea water with a gradual transition (T2), but they are still not suitable for the seawater entry because of low growth. Based on the recorded SGRs in trial II, our formulated regression formula revealed that approximately 200 g is the optimal size of steelhead trout for the transition to sea water.