28 MARCH 2015 • WORLD AQUACULTURE • WWW.WAS.ORG at a farming site in Ailian Bay, Yellow Sea (Ge et al. 2007). Seabass Lateolabrax japonicus (72 percent) and black rockfish Sebastodes fuscescens (28 percent) cultures were fed iced trash fish. The production period occurs from April to January with an annual production of 3250 kg for this site (5.6 km2). Based on biological characteristics, Laminaria and Gracilaria were selected as extractive species. These two seaweed species were cultured sequentially, with kelp from December to May (winter-spring) and Gracilaria from June to November (summerautumn). Nitrogen was selected as the parameter to balance the seaweed absorption and fish production. Assuming the nitrogen in feed residue and fish faeces could be completely converted to dissolved inorganic nitrogen, including direct conversion and microbial degradation, then the nitrogen balance equation can be represented as follows: Nseaweed = Nfish excretion+ Nfeed residue+ Nfish feces, where feed residue and feces are 1.5 and 0.1 times the nitrogen excretion by fish, respectively (Jiang et al. 2010). Nitrogen quantities released by the combined fish culture of sea bass and rockfish represented 510 kg N in winter-spring and 5874 kg N in summer-autumn. To balance the nitrogen release, the estimated optimum co-culture proportion is 1:0.44 for Laminaria in winterspring and 1:1.12 for Gracilaria in summer-autumn, where fish is expressed in kg wet weight and seaweed in kg dry weight. Growth and origin of food sources of the Pacific oyster Crassostrea gigas integrated with seabass Lateolabrax japonicus culture were studied in Ailian Bay, Yellow Sea, during a field study from April to October (Jiang et al. 2013). Both shell and tissue growth of the oysters were enhanced by 30-40 percent at the fish farming site compared to a control site where fish farming was absent. Stable isotope signatures in oyster tissue showed enriched values at the farming site, indicating that the difference in growth performance between the cage and the control area resulted from utilization of organic matter derived from fish aquaculture. Several other studies have reported that mussels and oysters can effectively remove fish wastes and increase their growth when cultured in proximity to finfish (Chopin et al. 2008, Handå et al. 2012). Suspended, open-water culture of abalone, kelp and sea cucumber. Sea cucumber is a detritivorous species that feeds on decaying organic matter generated by biodeposition of fecal material by abalone and decaying plant material from the kelp cultures. In this study, sea cucumbers were added directly to abalone cages without any modification of the culture equipment to allow simple and low-cost production. Cages were suspended from kelp longlines. The study indicated that 1 kg of sea cucumbers can be produced per cage and that the majority of sea cucumbers will reach market size (Fang et al. 2009). The high overall observed growth rate of sea cucumbers (0.33 percent/day; Table 3) showed that adding them directly to abalone cages may be a feasible production technique. Compared to production in land-based facilities, tidal ponds or extensive bottom culture, this method is simple and requires a minimum of extra labor or additional investment. TABLE 3. Comparison of sea cucumber growth at different densities. Treatment Initial BW (g) Final BW (g) SGR (% day-1) Total growth (%) 1SC 98.7±5.3a 186±11.51 0.32±0.07 89.2 1SC 60.6±3.6b 137.8±5.72 0.40±0.04 129.2 2SC 63.4±5.3b 120.3±4.12 0.32±0.02 90.4 4SC 66.2±2.8b 132.4±9.62 0.34±0.05 100.0 6SC 63.4±5.7b 118.5±13.12 0.30±0.01 78.3
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