Development studies of microalgae-based closed recirculating bivalves adults conditioning system: Ⅰ. Induction of the gametogenesis
Chung Yoo Kim, Young Baek Hur, Jong Chul Han and Young chul Park
Southeast Sea Fisheries Research Institute, NIFS, Tongyeong 650-943, Korea
Techniques were developed for holding and conditioning of Pacific oysters, Crassostrea gigas, in a closed recirculating system. Experimental adults were used 500 oysters ( x two system, total 1,000 oysters) which were collected in 20th March 2016 from long-line aquaculture farm at the south coast of Korea. During conditioning periods concentrated live microalgae as Isochrysis sp. 15 × 107 cells/mL, Tetraselmis sp. 2 × 107 cells/mL and Pheaodactylum sp. 18 × 107 cells/mL were added 5 L every day, respectively which micro algae were functioned as diets and biological filter. Over all experimental periods total water exchange rate was 21.3% (daily 0.5%). Over 42 days conditioning, female and male oysters were maturated 90.9% and 94.4%, respectively. Survival rate was 98.7%. Mean shell hight (8.3 mm), total wet weight (19.2 g), meat wet weight (5.0 g) and shell wet weight (13.6 g) were significantly increased (P〈 0.05). Water quality parameters including the water temperature (22.1 ± 0.4℃), salinity (24.9 ± 04), dissolved oxygen (5.1-7.9 mg/L) and pH (7.93 ± 0.15) were kept stable. Concentration of dissolved inorganic nutrient as ammonia (1.96-0.35 mg/L), nitrite (0.03-0.16 mg/L), nitrate (1.34-0.47 mg/L), DIP (0.42-0.03 mg/L) and silicate (3.83-0.00 mg/L) were significantly decreased throughout experiment except nitrite which was increased (P〈 0.05), but nitrogenous components stayed below toxic levels (ammonia 0.0-5.5 mg/L, nitrite 0.0-460.0 mg/L) which indicated that closed recirculation system with microalgae based bio-filter could supply sufficiently environment condition to holding and conditioning of oyster. 
  
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