Inter-and Intrapopulational Variation of Vertebral Numbers of the Yoke Darter, Etheostoma juliae

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Roentgen-ray photography was used to analyze the inter- and intrapopulational variation of vertebral numbers of the yoke darter. Etheostoma juliae. Means of vertebral numbers between river systems, among age groups, and within an age group are compared. Significant differences of mean vertebral numbers exists among populations within a river system, and means of vertebral counts from the most downstream collection are significantly lower than those of other collections. Size-vertebrae correlations are significant within some age groups. Comparisons of mean vertebral counts among different intrapopulational age groups give significant differences, and vertebral counts are frequently different between the same age groups of interpopulational samples. The differences observed are considered to signify different or changing environments during the sensitive period of development and genetic diversity. Racial investigations and resulting systematics, based on vertebral numbers, have become important techniques in applied fishery bi- ology. Bailey and Gosline (1955) demonstrated that vertebral counts are of systematic significance in the American fishes of the family Percidae. However, they noted differences between populations that could be of environmental origin and Thning (1944 and 1952) and Gabriel (1944) have shown that the environment can modify the number of vertebrae of other fishes. The primary objective of this study was to determine whether variation of mean vertebral numbers existed among populations within a river system, among age groups within a population, and within an age group. Six samples of the yoke darter, Etheostoma juliae (Meek), collected from six collection sites during the summer of 1962 (Fig. 1), are dealt with here. This study presents information on the degree of variation among these fish and provides data for future research work. The family Percidae, which includes E. juliae serves advantageously for studies of this nature. Some of the advantages favoring the use of darters include: fishermen do not object to the taking of large samples, all are small fishes and do not require a vast amount of storage space,