Karyotype of the Giant Abalone, Nordotis madaka

genus are frequently found along the coasts of Yamaguchi, Ehime, Tokushima, Mie, Akita, and Niigata Prefectures.1-4) Karyological analyses are useful for clarifying systemat ic relationships and provide fundamental information for animal breeding in artificial crosses. Chromosomes of the genus Nordotis (=Haliotis auctt.) have been described in the works of Arai et al.,3,5) Arai and Wilkins,6) Minkler,7) Nakamura,8,9) Okumura et al.,*3,*4-10) and Miyaki et al.11) In formation on the chromosomes of the giant abalone N. madaka has not been previously reported. The purpose of this paper is to report the karyotype of N. madaka from trochophore larvae. Adult specimens were collected from the coast of Iki Island in Nagasaki Prefecture, Japan. Spawning was in duced by ultraviolet irradiated sea water 12) and larvae were obtained by the artificial insemination of specimens at the Nagasaki Prefectural Institute of Fisheries. Trochophore larvae were treated with 0.1% colchicine in seawater for two hours, transferred to 0.075 M KCl solution for 40 minutes, then fixed in Carnoy solution containing three parts ethyl alcohol and one part acetic acid. The chromo some preparations were made by a chopping method in fish embryos by Yamazaki et al.13) with little modification as follows. Cell suspension was made on a slide glass by chopping several fixed larvae with a scalpel in 60% acetic acid, expanded by dropping Carnoy solution, flamed, and stained with 5% Giemsa solution for 30 minutes. The diploid chromosome number was determined from five well-spread metaphase plates. The karyotype analysis was carried out on the metaphase, in which all the elements were clearly visible. Classification of the chromosomes fol lowed Levan et al.14) To determine the fundamental num ber, metacentric and submetacentric chromosomes were re garded as bi-arm chromosomes. The diploid chromosome number of N. madaka was 36 (Fig. IA). The karyotype consisted of 10 pairs of metacen tric chromosomes and eight pairs of submetacentric chromosomes (Fig. 1B) and the fundamental number was determined as 72. The diploid chromosome number, Fig. 1. Mitotic metaphase chromosomes(A) and karyotype(B) of Nor