Legand, M. - Some biometric data on the albacore of the region west of New 

 Caledonia 



The discussion was divided into three 

 main categories depending on the methodology: 



A. Chemical methods 



1. Biochemical 



velopment of a suitable method for use in the 

 identification of larval forms of tuna. The study 

 has shown that the method of diffusion precipitin 

 analysis demonstrated the presence of species - 

 specific differences in serum antigens of adult 

 tuna. 



2. Immunochemical 



B. Morphometrical methods 



C. Serological methods 



A. (1) Discussion centered on the bio- 

 chemical studies on the races of tuna by analysis 

 of the base composition of testis DNA (deoxyri- 

 bonucleic acid). It was brought out that DNA is 

 implicated as the substance primarily responsi- 

 ble for the transmission of hereditary character- 

 istics at the molecular level. In most samples 

 of DNA, four heterocyclic bases predominate. 

 For the purines, these are adenine and guanine, 

 and for the pyrimidines, they are thymine and 

 cytosine. These bases are bound together on a 

 chain of deoxyribose sugar together with certain 

 phosphate residues, and the chain forms the 

 chemical backbone of the DNA molecule. 



It has been demonstrated that the values 

 of the base pairs adenine and thymine divided by 

 the values of the base pairs guanine and cytosine 

 yield ratios which are quite different for some 

 tunas. Studies on bigeye, yellowfin, Indo - maguro 

 and Goshu-maguro yielded ratios which ranged 

 from 1. 26 to 1.75. 



The conclusion was reached that the 

 ratio of the base pairs of the DNA molecule may 

 in the future provide an indication of the racial 

 relationships of the tunas . 



It was noted that a similar study of differ- 

 entiating the racial stocks of tuna by electron - 

 micrographic comparisons of tuna spermatozoa 

 was being carried on by the Inter-American 

 Tropical Tuna Commission. In this study the 

 potentiality of telling racial stocks apart depends 

 on differences in sperm morphology. 



Cushing endorsed further exploration on 

 the subject of DNA as a tool for differentiating 

 subpopulations of tunas . A paper model of the 

 DNA molecule was shown the conferees, and its 

 structure was briefly explained. 



A. (2) Discussion centered on the im- 

 munochemical method. The study involved de- 



The study has revealed that there is at 

 least one distinctive antigen which may be used 

 as a diagnostic antigen for individual species of 

 tuna. 



The conclusion was reached that there 

 are definite possibilities in the application of 

 immunochemical methods to the problem of iden- 

 tifying larval forms. The usefulness of this 

 method, however, depends on the development 

 of species specificity in antigenic constitution 

 early in embryological development. 



Discussion brought out that immuno- 

 chemical methods may be useful in studying the 

 taxonomic relations between species of fishes. 

 Their use may provide additional information in 

 distinguishing species and, when combined with 

 red blood cell studies, may be a very sensitive 

 and useful tool in taxonomic studies. 



The question was raised whether this 

 method would be useful in distinguishing the tuna 

 larvae, which have only a very small amount of 

 blood. It was stated thatthereare refined tech- 

 niques for dealing with organisms with a small 

 amount of blood, but the techniques are very time- 

 consuming and expensive. It was stated that 

 fresh specimens should be used in immunochem- 

 ical studies, and sample size should be as large 

 as possible so that statistical tests can be made. 



The conclusion was reached that sero- 

 logical studies can be useful in verifying the con- 

 clusions reached by systematic studies. The 

 suggestion was made that a study of the American 

 and European eel problem be carried out by 

 these methods. 



B. Hiyama noted that there were only 

 small differences in the body characters of the 

 northwest Pacific albacore which form the basis 

 of the Japanese winter longline and summer live- 

 bait fishery. When northwest Pacific albacore 

 were compared to the albacore from the equa- 

 torial and southwest Pacific areas, there were 

 distinct differences. The albacore from the 

 equatorial and southwest Pacific were morpho- 

 metrically similar. The Indian Ocean albacore 

 were found to b e distinct from the northwest 



