Preliminary studies on increased survival and accelerated growth of overwintering juvenile abalone, Haliotis discus hannai Ino

Factors concerning the survival and growth rates of juvenile Haliotis discus hannai in winter were investigated during the winter of 1984 and spring of 1985. The results indicated that the small size of juveniles and low water temperatures were important contributing factors to high mortality in northern sea areas of China. A shell length (SL) of 8-10 mm was the critical limit for survival. Most animals less than 8 mm died in winter whether they were held in indoor tanks at ambient temperature or in the sea. Minimal growth occurred during the 5-month period from December to April. Two recirculating systems using elevated temperature control were used to overwinter abalone, with good results. One system consisted of active carbon, coral debris and ultraviolet light (AC.CD.UV) and the other a biomembrane grown on plates of glass-fibre-reinforced plastic (GFRP). The survival rates in the two systems were similar and several times higher than previous reports. After 163 days, the survival rate in the AC.CD.UV system was 66% for 7.1 mm SL (4.0-9.5 mm) juveniles. After 165 days, the survival rate in the GFRP system was 63.4% for 7.3 mm SL (5.0-10.5 mm) juveniles. The daily growth rate was higher in the AC.CD.UV system: 102 mu m day(-1) for the entire period and 137 mu m day(-1) during the last 50 days. Thus, at the end of the experiment the abalone were 23.1 mm SL, the biological mass was 16.8 kg m(-3) and the density was 3300 individuals m(-2). The growth rate in the GFRP system was 54 mu m day(-1), producing juveniles of 13.2 mm SL.