Kenneth G. Ostrand, Gene R. Wilde, and Randy Young,
Department of Range, Wildlife, and Fisheries Management, Box 42125, Texas Tech University,
Lubbock, Texas 79409
Richard R. Strauss, Department of Biological Sciences, Box 43131, Texas
Tech University, Lubbock, Texas 79409
Keywords: sexual dimorphism; plains minnow; fish; Texas
During routine examination of fish collections from several southwest
Texas streams, we noted an apparent dimorphism in the length of pectoral and dorsal fins
in specimens of plains minnow Hybognathus placitus. Although sexual dimorphism in
morphological characters other than color and the presence of nuptial tubercles is
uncommon in minnows, sexual dimorphism in length of fins (longer in males) has been noted
in some species. Here, we present an analysis of this dimorphism and test the hypothesis
that plains minnow specimens with longer fins are males. We digitized 16 external
morphological landmarks on 62 plains minnows ranging in total length from 7.1 to 8.4 cm.
These landmarks were used to generate 21 external length measurements. We used
discriminate function analysis to differentiate between males and females based upon 21
measurements. Preliminary identification of males and females was based on dorsal and
pectoral fin characteristics. Of the 21 measurements, ten had significant (P < 0.05)
discriminant coefficients. The first dorsal fin ray had the greatest loading (0.83)
followed by the pectoral fin length (0.56). The male plains minnow predominantly have
larger heads and peduncle regions whereas the females have larger abdomens. After analyses
were complete we verified sex by evisceration of the gonads and histological inspection.
Sixty-one of 62 fish were correctly sexed based on pectoral and dorsal fin characters.
