- University of Guelph
Summary
Ages determined by counts of apparent annuli on scales, sagittae, vertebrae, pectoral fin ray and dorsal fin spine cross sections of largemouth bass from northern populations, which are older and slower growing fish than in the southern parts of its native range, were compared to establish the accuracy of each method. Linear regression techniques indicated strong agreement (r> 0.9) among ages assigned from the examination of scales, sagittae, and vertebrae. The pattern of growth zones on pectoral fin ray and dorsal fm spine cross sections proved too variable for accurate age determination. Limited data suggest that ages greater than 7+ assigned from scales were more likely to underestimate true ages than the other body parts used, although none of these methods gave satisfactory results. Examination of scales from recovered tagged fish, and the similarity between back-calculated lengths of fish through age 7+ to annulus I and observed lengths of juvenile largemouth bass near the end of their first growing season, support the validity of ages determined from scales.
Despite a very limited amount of habitat suitable for largemouth bass and severe climatic conditions, growth of this species in Tadenac Lake was similar to growth in other waters north of the Great Lakes. Differences in physical characteristics among these waters does not appear to influence growth rates of largemouth bass, but probably affects production and biomass.
Methodology
Data were collected from 98 largemouth bass taken from Tadenac Lake and the adjacent waters of Georgian Bay and Green Bass Lake (45"02'N, 79'55'W) during spring and summer, 1975. Scales were taken from the area immediately posterior to the depressed left pectoral fin. The first spine of the first dorsal fin and the first ray of the left pectoral fin were clipped at their point of insertion into the body, and were then air-dried. Sagittae and the first two trunk vertebrae were removed and stored in glycerin and ethanol respectively. Scales were washed in detergent, mounted between glass slides and viewed on a Eberbach microprojector at 80X if less than 3.5 rnm in anterior radius, and at 40X if larger. The distal surfaces of the sagittae, still immersed in pure glycerin, were examined on a black background with a binocular microscope under reflected light. Pectoral fin ray and dorsal fin spine cross sections cut from the proximal ends of these bones were covered with pure glycerin and viewed with transmitted light at 30X with a compound microscope. Vertebrae were placed on a black background, covered with glycerin, and the central were examined using reflected light with a binocular microscope