| Summary: | Few suitable genetic characteristics for studying herring population structure are available, and the main aim of the study reported here has been to reveal traits which display useful genetic variations for application on more extensive population studies of herring in Northeast Atlantic waters. Esterase is aften found to be highly variable among fishes, but often the phenotypes are difficult to discern and thus the genetic background for the observed variation is difficult to reveal. In the present report isoelectric focusing of blood esterases has been used as an analytic tool for revealing and describing variations and their genetic background. Material has been collected from coastal and offshore Norwegian waters, and more than 1500 specimens of 24 samples have been analysed at two pH ranges (3.5-9.5 and 4.0-6.5). Four groups of esterase components were found, each probably representing at least one polymorphic locus. Two of these groups were clear enough for proper classification of the individuals, and at least one seemed useful for further studies of herring population structure. Clear variations were seen in phenotype distributions between samples, and especially the samples of autumn spawning herring deviated from the bulk of the spring spawners.
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