Malacological Society of Australasia

Molluscan Research

Volume 18, Issue 2 (Australasian Abalone): 31 October 1997 Edited by S.A. Shepherd, P.E.McShane and F.E.Wells

Contribution of diatoms as food sources for post-larval abalone Haliotis discus hannai on a crustose coralline alga.

Hideki Takami*, Tomohiko Kawamura and Yoh Yamashita

Tohoku National Fisheries Research Institute 3-27-5, Shinhama, Shiogama, Miyagi 985, Japan,
*Corresponding author. E-mail: htakami@myg.affrc.go.jp

Survival and growth rates of post-larval abalone Haliotis discus hannai reared on a crustose (non-geniculate) coralline alga (CCA) Lithophyllum yessoense with diatoms (CCA + diatoms) and without diatoms (CCA - diatoms) were compared in the laboratory in order to determine the contribution of diatoms on CCA as food sources for post-larvae and the dietary value of CCA themselves. Experiments were performed for 5 weeks with two groups of different developmental stage, newly metamorphosed stage (younger post-larvae) and over 1 mm stage (older post-larvae). Both stages of post-larvae reared on CCA + diatoms grew well (53.4 +/- 2.4 µm/day; mean +/-SE and 85.0 +/- 4.0 µm/day; mean +/- SE, respectively). Younger post-larvae grew to over 2 mm in 5 weeks, and older ones reached over 4 mm in 5 weeks. There was no difference in shell length of younger post-larvae reared on CCA + diatom and CCA - diatom at the week 1. However, the mean growth rate of abalone on CCA - diatoms from the second to fifth week (24.4 +/- 1.9 µm/day; mean +/- SE) was significantly lower than that of individuals on CCA + diatoms and the younger post-larvae on CCA - diatoms reached only 1 mm shell length in 5 weeks. The older post-larvae also did not grow well (27.8 +/- 3.3 µm/day; mean +/- SE) on CCA - diatoms and did not reach 3 mm by the end of the experiment. On CCA + diatoms, 74.6 +/- 2.0 % (mean +/- SE) of the younger post-larvae survived for the 5 weeks experiment. In contrast, the survival rate of the younger post-larvae reared on CCA - diatoms decreased rapidly until the second week, and 25.0 +/- 12.6 % (mean +/- SE) of the individuals survived by the fifth week. The results of this study indicate that diatoms are essential for the rapid growth of post-larval abalone on the CCA. It is considered that the CCA L. yessoense itself is not a principal food source for post-larval H. discus hannai from approximately 500 µm to at least 3 mm shell length.Molluscan Research

pp. 143-151