a single year -class at a time. Furthermore, 

 although it may be obvious that mixing is taking 

 place, the number and location of the areas be- 

 tween which mixing is taking place will general- 

 ly be much less obvious. In this connection, 

 they point out that the power of this tool will be 

 greatly increased by a concurrent tagging experi- 

 ment, which would yield supplementary and 

 complementary information. 



In spite of these limitations, however, 

 application of the method proposed by Widrig 

 and Taft, should provide useful quantitative and 

 qualitative information about availability changes 

 in many fisheries . 



Perhaps one of the most exciting poten- 

 tialities in the study of subpopulations is the 

 application of biochemical techniques borrowed 

 from other fields . These methods are extremely 

 promising because the characteristics which can 

 be examined are either known to be genetically 

 determined or can be examined experimentally 

 to see if they are genetically fixed. 



One of these techniques is the determina- 

 tion of tissue (muscle, for example) amino acids 

 by the use of paper chromatography. Farris 

 has briefly reviewed the method and some of the 

 results that have been achieved to date. He also 

 points out examples of non-genetic differences 

 that have been observed under certain circum- 

 stances. Farris concludes that while systematic 

 chromatography theoretically holds great prom- 

 ise, its general and specific applicability need 

 to be critically evaluated. It might also be ex- 

 pected that the higher one goes along the chain 

 of biochemical complexity, the more specific 

 will the compounds become . For example, the 

 occurrence of certain enzyme systems is more 

 specific than is the occurrence of amino acids. 



Another group of biochemical techniques, 

 if they may be so termed, are those borrowed 

 from the field of immunology. Ridgway has re- 

 viewed blood characteristics which may be 

 useful in the identification of subpopulations. 

 These include (1) differences in red cell antigens, 

 (2) naturally occurring hemaglutinins and (3) 

 the antigenic properties of serum proteins . 



Of these three possibilities, the hema- 

 glutinins hold the least promise, since they are 

 of irregular occurrence and doubt has arisen 

 over their genetic determination. The antigenic 

 properties of blood serum are somewhat more 

 promising, although intraspecific differences 

 have only rarely been demonstrated. Ridgway 

 suggests that the application of the agar diffusion 

 technique may be useful here. The use of serum 

 has advantages over the use of blood cells in 

 that serum can be easily frozen and held for long 

 periods . On the other hand, the technological 

 problems associated with preserving red cells 

 have not yet been satisfactorily resolved. Never- 

 theless, the use of red cell characteristics holds 

 the most promise among the immunological pos- 

 sibilities of attacking the subpopulation problem. 

 Differences in the antigenic composition of red 

 cells have been shown to be genetically con- 

 trolled wherever they have been examined by the 

 appropriate methods . Furthermore, individual 

 differences have been found among diverse groups 

 of animals . 



Thus, the requisites of a useful tool for 

 the study of subpopulations seem to be found in 

 the red cell characteristics. The main problems 

 in this regard are those involved in the applica- 

 tion of the technique to specific situations. 



After briefly considering new techniques 

 and techniques borrowed from other fields and 

 before reviewing recent studies that have been 

 made of particular species, it is instructive to 

 examine in retrospect some previous studies of 

 the subpopulations of several species of fishes. 

 Ahlstrom has done this for eight Pacific species, 

 including one clupeid, four engraulids and three 

 scombroids . 



For all of these species the meristic 

 and/or morphometric approach has been used. 

 Interestingly, meristic studies have been largely 

 confined to the clupeid and engraulids, while 

 morphometric studies have been made of the 

 scombroids. None of these studies have been 

 definitive, owing to the inability of the investiga- 

 tors to distinguish between phenotypic and 

 genotypic characters. In two studies, those of 

 the Pacific herring and Pacific mackerel, 



