At the Iwate Prefectural Roes and Fries Distribu- 

 tion Center the gametogenesis of adult abalone was 

 observed, as well as the normal development from 

 fertilized egg to creeping stage larvae (Shibui, 1972). 



Once the artificial production of abalone in Japan 

 progressed to the commercial scale, interest de- 

 veloped in the potential of interspecies crosses. At 

 Chikura Branch of Chiba Prefectural Fisheries such 

 hybrids were made and studied. These were between 

 H. discus and H. gigantea; between H. discus and 

 H. sieboldii; and between H. gigantea and H. 

 sieboldii (Oba, Toyama, and Kaneko, 1972). All 

 were reared through metamorphosis in the labora- 

 tory. Hatching, fertilization abnormalities, and shell 

 form and structure were compared to the parental 

 characteristics. Such hybrids could have advantages 

 over nonhybrids for intensive aquaculture under ar- 

 tificial conditions, or for colonization of a new area 

 in nature. 



Some hybridization work was also conducted at 

 the Kesen-numa Institute (J. W. McBeth).^ 



Pearl Research Laboratory of the Fisheries 

 Agency at Kashiko-jima, Mie-ken 



Research is confined exclusively to study of those 

 mollusks used to culture pearls. Work is ultimately 

 directed at improving the quality of the cultured 

 pearl. All the research appears to be basic. It seems 

 that, because the science and art of pearl culture are 

 well worked out, these researchers have more free- 

 dom to pursue fundamental work. There is a persis- 

 tent near 40% mortality of the pearl oyster, Pinctada 

 fucata, in the trays and racks used to hold them in the 

 pearl farming. Mortality appears to be accepted as 

 part of the business. The demand for pearls has 

 dropped and there is now a government restriction 

 on the amount of pearl farming to be conducted. 

 There are no projects aimed at breeding disease re- 

 sistant organisms, as those for the commercial 

 Crassostrea virginica in the U.S. mid- Atlantic 

 states. 



Research is being carried out on the artificial cul- 

 ture of this pearl oyster's mantle (A. Machii, pers. 

 comm.). Mitosis and cell proliferation have been 

 obtained in vitro. American, European, and 

 Japanese workers can all generally attest to the fact 

 that success in invertebrate tissue culture has been 

 most elusive. A persistent measure of culture suc- 



cess would find application in numerous fields of 

 fishery research. It would apply to work on this 

 epidemic MSX disease of the American oyster, 

 which just about devastated the oyster industry of 

 the U.S. mid-Atlantic states a few years ago (Sin- 

 dermann and Rosenfield, 1967). 



Some inbreeding and some hybridization studies 

 are being conducted on the pearl oyster (K. Wada).^ 

 Also, some studies have been conducted on its 

 chromosomes in spite of technical problems caused 

 by the presence of so much yolky material in the eggs 

 (K. Wada, see footnote 3). This latter work will 

 probably be published soon. It seems that some re- 

 search effort will be directed in the future towards 

 study of biochemical polymorphisms in the wild 

 stock. 



Ocean Research Institute, University of Tokyo — 

 Genetic Polymorphisms of Wild Populations 



In the division. Biology of Fisheries Resources, 

 studies are being conducted on enzyme variation in 

 fish populations (Numachi, 1972a). 



Shortage of genetic markers has been a handicap 

 in the study offish genetics. Now variation in differ- 

 ent enzymes can be used as genetic markers by em- 

 ploying gel electrophoresis followed by histochemi- 

 cal staining methods. This method makes possible 

 an examination of the structure of a population offish 

 in genetic terms. Identification of self-sustaining 

 subpopulations of fish is a most basic problem 

 in fisheries management. 



Enzyme polymorphisms reflect a mutation in the 

 structural gene of the enzyme concerned. A few 

 years ago variants of enzymes were regarded as rare 

 events. It is now known that such variants are very 

 common in most enzymes in various organisms. An 

 increasing number of electrophoretically distin- 

 guishable variants has been discovered in fish, as well 

 as in other organisms. Marine mammals, such as 

 whales, dolphins, and seals, all contain five lactate 

 dehydrogenase forms. Their enzyme "patterns" are 

 similar to those of terrestrial mammals, including 

 man. 



Numachi (1971 , 1972b, c) has specifically reported 

 in the literature on interspecific and intraspecific 

 variation of enzymes in fish species and on analysis 

 of the genetic control of such enzymes in fish — on 



- Communication through Japanese staff member acting as 

 Director at the time. 



^ Personal communication from a fellow staff member. K. 

 Wada was away at a fisheries meeting at the time the laboratory 

 was visited, so more precise information on this work was not 

 obtained. 



129 



