Optimum Stocking Density of 3-year-old Pacific Abalone, Haliotis discus hannai Reared in Net Cage Culture

Abstract

The effects of different stocking densities on the growth and survival rate of the 3-year-old pacific abalone, Haliotis dicus hannai were investigated in marine net cage for a year. Stocking densities in net cage (2.4 × 1.2 m) was set 15, 30, 45 and 60 percentage (= per)/sq m (square meter, m 2 ) with share to cross-sectional area per shelter. The water temperature during the testing period was 8.2℃-22.1℃, and salinity is 33.5 ± 0.6 psu, and dissolved oxygen is 7.87 ± 0.86 mg/L. In the shell length (initial size : 71.50 ± 2.28 mm) growth and shell breadth (initial size : 46.43 ± 2.28 mm) of the test abalones, the absolute growth rate (ARG), daily growth rate (DGR) and specific growth rates (SGR) of the 15 per/sq m and 30 per/sq m were higher than those of 45 per/sq m and 60 per/sq m density group (P < 0.05). Also in the weight (initial weight : 35.7 ± 8.1 g), it showed the same results. In survival rates, it were that 15 per/sq m and 30 per/sq m is significantly higher than 45 per/sq m and 60 per/sq m. Therefore, it was that the 15 per/sq m is optimized stocking density in marine net cages about the 3-year-old pacific abalone over 70 mm size. The result shown that total cross-sectional area under the shelter is based on 15 per/sq m (2.4 × 2.4 m, 354 number in a net cage) is suitable for fast growth and survival. But if the economy consider, optimized stocking density would be appropriate to accept 30 per/sq m (2.4 × 2.4 m, 710 number in a net cage).

Temperature-Dependent Food Consumption Rates of the Sea Urchin Mesocentrotus nudus and Top Shell Turbo sazae: Potential Impacts on Seaweed Beds

“…T. sazae is a sub-tropical species found in subtidal habitats with water temperatures of 14 • C to 25 • C [35,37], which suggests that it can withstand higher temperatures than M. nudus. In our study, it showed a gradual increase in the food consumption rate with an increase in temperature, with a peak at 25 • C. In such gastropods, increases in temperature lead to higher metabolic demand, thus increasing food consumption [59][60][61][62]. For example, the rate of Turbo samaticus gradually increases with increasing temperature, peaking at 25 • C [63]; in Haliotis midae, the rate doubles at 15 • C compared to 22 • C [64].…”