Assessment of a Newly Designed Rearing Method Using Raceway Tanks in Juvenile Abalone, Haliotis gigantea, without Routine Bottom Cleaning

Abstract

This experiment was conducted to evaluate the effectiveness of a newly designed rearing method using 10 kl raceway tanks in juvenile abalone, Haliotis gigantea, in large scale production. Two different size groups (4.9±0.4 and 6.4±0.5mm in mean shell length ±SD) of juveniles feeding on diatoms were removed from settlement plates, and then the scattered seed rearing method was used at two stock densities of approximately 2, 500 and 1, 800 individuals per square meter for each size. Juveniles were fed on artificial diet once every four days over a period of seven months, eliminating the need for routine cleaning by siphon; instead fecal material from juveniles was carried away through drainage after strong aeration of the tank water. Survival rates in all groups were higher than 95%, and feed efficiency was the same between experimental groups, ranging from 78 to 80%. Total weight gain was 3, 420-3, 760% in the smaller groups and 2, 470-2, 800% in the bigger groups. Abalones growing under lower stock densities showed higher weight gain and grew significantly faster than those in the higher density groups. These results show that the rearing method we developed is effective for juvenile abalone, H.gigantea, with a mean shell length of 5 mm or greater, and to achieve optimum growth the maximum stock density should be less than 2, 000 individuals per square meter.