The Age and Growth of the Silverjaw Minnow, Ericymba Buccata Cope

The Age and Growth of the Silverjaw Minnow, Ericymba buccata Cope

DALE C. WALLACE

•

Reprinted from THE AMERICAN MIDLAND NATURALIST Vol. 86, No. 1, July, 1 971, pp. 116127 University of Notre Dame Press Notre Dame, Indiana The Age and Growth of the Silverjaw Minnow, Ericymba buccata Cope

DALE C. WALLACE Department of Biology, Eastern Michigan University, Ypsilanti 48197

ABSTRACT: A study of the age and growth of Ericymba buccata Cope in Vigo Co., Indiana, was based on calculated increments of growth as well as length frequencies observed through the year. The annulus is a valid year mark. Annulus completion takes place over VA to 3 months with older individuals completing the annulus later. Young- of-the-year continue growth later in the autumn and commence growth earlier the following spring than older fish. Growth compensation by later-hatched young is indicated. In their third summer of life males grow to a larger size than females. The maximum life span for this species is about 4 years. A poor year of growth in 1963-64 is apparently correlated with lower mean spring and summer air temperatures during that period. INTRODUCTION A study of the age and growth of the silverjaw minnow, Ericymba buccata Cope was undertaken as a part of an investigation of the ecology and life history of this species (Wallace, 1969) . No previous investigation of the age and growth of this species has been reported. The study was conducted in a 7.5-mile section of the North Branch of Otter Creek, a tributary to the Wabash River in Vigo Co., Indiana. The stream flows through Illinoian drift which includes much sand, fine gravel, considerable silt and some clay. Its gradient is approximately 6.7 ft per mile and water depths are commonly between 6 inches and 3 ft Ericymba buccata was the most abundant fish species. METHODS AND MATERIALS Collections were taken from October 1964 through October 1965. During each month random plots 25 ft long, extending from shore to shore, were blocked off and sampled with seines. The percentages of the study area sampled by season were 5.2 for spring, 6.7 for summer, 6.5 for autumn and 2.8 for winter. The seines were 1/4-inch mesh, 15 and 30 ft long and 4 ft deep. A total of 2465 Ericymba were taken. A large collection of 301 specimens taken on 28 March was utilized for the calculation of growth. All specimens were utilized in comparing the growth of males and females and in the analysis of observed growth through the year. At least four scales were removed from the scale row just above the lateral line and just anterior to the dorsal origin. They were cleaned and mounted in water between two glass slides. All scales utilized for calculating growth were examined and measured with the aid of a microprojector at the magnification of 112X. All other scales were examined under a binocular microscope at magnifications of 7 to 30X. Scale radius was measured from the focus to the posterior edge of the scale. Standard length was measured from the tip of the snout to the posterior edge of the hypural plate. Sex was determined by examination of the gonads. Growth was calculated following procedures outlined by Hile 116 1971 WALLACE: GROWTH OF SILVERJAW MINNOW 117

(1941). The one-tailed t-test was used to test the hypothesis that the mean length of one group of fish was equal to or less than that of another group (Steel and Torrie, 1960). RESULTS AND DISCUSSION Validity of the annulus as a year mark.-The annulus is indicated by "cutting over" of circuli in the lateral fields and by a rather abrupt change from close to more widely spaced circuli, especially in the posterior field. Those hatched late in the year had less growth to the first annulus, and on these fish this annulus was often not as clearly defined as in specimens hatched earlier. Harrington (1948) noted in Notropis bifrenatus (Cope) that the first annulus is progressively less clear-cut in bridled shiners hatched near the end of the season. Larimore (1957) and Hile (1941) outline the important argu- ments in determining the validity of the annulus as a year mark. The following evidence indicates that the scale method of age determina- tion is valid for Ericyrnba: (1) There is reasonable agreement between calculated lengths and observed lengths of fish at corresponding ages (Tables 2 and 3). (2) The number of annuli increases consistently with increase in length (Table 3). (3) Calculated growth increments among those from different year classes in the same collection are similar for any given year of life (Table 2). (4) There is agreement among the different year classes as to the goodness or poorness of growth in a given growth period (Table 8). Time of annulus completion.-The time of annulus completion was determined from the examination of the scales of 139 specimens collected between 28 March and 31 August (Table 1). The smaller specimens (mostly yearlings) (22 to 37 mm S.L.) laid down their annulus approximately 6 weeks earlier than larger ones (39 to 47.5 mm S.L.) which were in their third or fourth summer of life. Some 60% of the larger fish from the 12 June collection had completed their first annulus. Scales from specimens collected later in the year showed

TABLE 1.-Percentage of Ericymba with new annulus and with a given number of circuli beyond the new annulus during given periods

Range No. Percentage with noted number in of Percentage of circuli beyond new annulus Date length speci- with new More collected (mm) mens annulus 1 2 3 4 than 4 28 March 39-47 10 0 ...... 30 April 42-45 6 0 ...... 22 May 40-45 10 20 -6.0 0.0 0.0 0.0 0.0 29 May 41-45 10 10 0.0 0.0 0.0 0.0 0.0 12 June 42-48 10 60 0.0 0.0 0.0 0.0 0.0 19 June 41-47 10 100 10.0 0.0 0.0 0.0 0.0 29 July 39-49 11 100 54.5 18.2 0.0 0.0 0.0 26-31 Aug. 39-46 11 100 27.2 27.2 0.0 0.0 0.0 28 March 22-34 10 0 - 30 April 23-34 9 67 11.1 16 May 23-34 13 100 30.5 30.5 0.0 0.0 0.0 22 May 26-36 11 100 0.0 63.6 27.3 0.0 0.0 29 July 27-37 18 100 0.0 0.0 0.0 16.7 83.3

118 THE AMERICAN MIDLAND NATURALIST 86(1) a clear trend toward added circuli. Thus the median period of annulus completion for fish in their third and fourth summers of life was the 1st week in June. Approximately 67% of the smaller specimens from the 30 April collection had completed the first annulus and the median time of annulus completion for those beginning their second summer of life was probably the 3rd week in April. 1 Thus annulus completion extended over a period of about 2 /2 to 3 months for all sizes and about 4 weeks for each of the two size groups considered. The later period of annulus completion in larger specimens was related to the later resumption of growth by larger fish. Nikolsky (1963) cites examples of this in pike perch, Lucioperca lucioperca L. and the bream, Abramis brama bergi Grieb. In the latter, the new year's growth is added in the autumn in older fish. Length as an index of age.—In the analysis of growth, calculations of length, length frequencies of fish collected throughout the year, and length frequencies of aged fish taken from March through September

20- 4. Males

10-

/ • \ I • 14,/ 0--0, 0 0•—•---0 • 'A.," N., ....Jo

FREQUENCY 30-

Females

20 •

10 A c.

. ._.r , 514 113 22 26 30 34 38 42 46 50

STANDARD LENGTH (mm) Fig. 1.—Age frequency distribution of 142 male and 159 female Ericymba collected on 28 March 1965. Broken line represents specimens which had completed one winter of life; solid line with dots, two winters; dotted line with triangles, three winters; and solid line with squares, four winters of life 1971 WALLACE: GROWTH OF SILVERJAW MINNOW 119

were considered. The length frequencies in the 28 March collection indicates that length is a poor index of age after the first summer of life. This is mainly due to the long breeding season (Wallace, 1969). A considerable proportion of the late-spawned young of 1963 over- lapped in size with the early-spawned young of 1964 (Fig. 1). The same overlap is evident in comparing those spawned in 1962 and 1963. A similar phenomenon was described by Stone (1940) in Notropis spilopterus (Cope) and Notropis analostanus (Girard), and by Van Cleave and Markus (1929) in Pimephales notatus (Rafinesque) . Although a 1/8-inch mesh seine was used, it is possible that large numbers of small fish were lost in sampling. Hence the smaller individuals (17-22 mm S.L.) of the 1964 year class may have been poorly represented in the 28 March collection. Of the 301 individuals collected on this date, 26.1% had completed their first summer, 37.5% their second summer, 34.1% their third summer and 2.3% their fourth summer of life. Since the latter age group made up an even smaller percentage of collections taken later in the year, they were not included in the analysis of growth through the spring and summer. Relationship of body growth to scale growth.—The relationship of body growth to scale growth was studied in 92 males and 80 females from the 28 March collection. This relationship is expressed for males by the equation L=5.653 mm+0.250 R, where L=standard length in millimeters and R=scale radius (mm X 112). For females the relationship was expressed by: L =5.271 mm+0.257 R. The correlation coefficient in both cases was 0.98. Inspection of the plot of these two variables indicates that a rectalinear model best represented their relationship. These relationships were utilized in calculating growth from annulus to annulus. Comparison of growth in males and females.—Using the 28 March collection, calculated growth increments for the sexes were compared ( Table 2). For each age group the last year's growth was computed to 28 March and hence is an underestimate. According to these data, males and females had comparable increments of growth during their first 2 years of life. In their 3rd year the male increment exceeded that of females by 2.7 mm. However, this difference was not statis- tically significant. This was also true of a comparison of the mean lengths of the four males and three females which had completed their fourth summer of life. Data from the observed lengths of aged fish taken on 28 March indicated the same trends (Table 3). Thus, it appeared that males may grow at somewhat faster rates. Further investigation indicates that males in fact do grow to a significantly larger size. The monthly length frequencies of 2465 Eric ymba were compared by sex. Too few specimens were available from the months of Febru- ary and April to warrant analysis. For each season and sex the mean standard length of large adults and small adults was calculated and compared (Table 4). In consideration of large adults only, males were larger on the average in all seasons. The differences in mean length of the sexes were significant for all seasons except winter. The lack of a significant difference between the sexes in the winter and among the older fish from the 28 March collection discussed above 120 THE AMERICAN MIDLAND NATURALIST 86(1) may be attributed to greater winter mortality of larger, faster-grow- ing males. Calculated growth increments with sexes combined.-Because there was some growth between 28 March and the time of annulus completion, the mean length of aged specimens from May collections was used as an estimate of the length at the last annulus for each year class. These data indicate that this species grew to an average length

TABLE 2.-Calculated growth increments (mm) in male and female Ericymba from 28 March collection Number Males Year of Calculated standard length at end of class speci- indicated year of life mens 1 2 3 4 1961 4 26.2 34.0 45.2 49.1 1962 44 27.1 38.4 41.7 1963 52 21.9 31.6 .... 1964 42 25.0 .... Weighted mean: 24.6 34.6 42.1 49.1 Increment: 24.6 10.0 7.5 7.0 Percentage of growth to 3rd year: 58.5 23.8 17.4 TABLE 2.-((continued) Number Females Year of Calculated standard length at end of class speci- indicated year of life mens 1 2 3 4 1961 3 21.9 38.4 43.9 45.1 1962 60 26.0 38.7 40.0 -••• 1963 60 21.9 31.4 .... 1964 36 25.3 .... Weighted mean: 24.5 35.8 40.6 45.1 Increment: 24.5 11.2 4.8 4.5 Percentage of growth to 3rd year: 60.3 27.3 12.4

TABLE 3.-Observed mean standard length of aged male and female Ericymba from 28 March collection Number of Males winters Number of Mean Growth of life specimens length increment 1 42 25.0 25.0 2 52 31.6 6.6 3 44 41.7 10.1 4 4 49.1 7.4 TABLE 3.-(continued) Number of Females winters Number of Mean Growth of life specimens length increment 1 36 25.3 25.3 2 60 31.4 6.1 3 60 40.0 8.6 4 3 45.1 5.1 1971 WALLACE: GROWTH OF SILVERJAW MINNOW 121 of 23 7 mm during the 1st year of life. This constituted 52.9% of its growth to the end of the 3rd growth year (Table 5). Growth increments for subsequent years were 13.4 mm, 7.7 mm and 2.0 mm from the 2nd to the 4th year, respectively. Although the aquarium conditions were not specified, Hankinson (1919) raised the eggs of Ericymba collected on 25 April. One individual grew to 19.1 mm (total length?) by 5 August of that year and another to 31.8 mm by 19 December. History of growth through the year by age groups.-Growth during the spring and summer was estimated from length frequencies of aged specimens (Table 6) . All young-of-the-year were included but a

random sample of older specimens was used. The young-of-the-year• were hatched from late spring to late summer. Because the early- hatched young constituted a distinct group measuring between 26 and 34 mm by September, the standard lengths of young for this month was calculated from this group.

TABLE 4.-Comparison of the mean standard lengths (mm) of the sexes of Ericymba at each season No. of Size group Season Sex speci- Length S.D. t1 mens

SMALL ADULTS Spring 102 34.6 3.86 2.654** ,

(30-40.5 mm) -=1.4 153 35.9 3.78

Summer , 147 36.3 2.94 0.052" , 14

.. 186 36.3 3.01 Autumn 89 34.3 3.72 2.078** ,

=14 104 35.4 3.72 Winter 63 35.8 3.42 0.113"

=14 82 35.8 3.59 ..

LARGE ADULTS Spring 4 163 44.3 2.74 2.303*

(41+ mm) '' 115 43.3 2.42 Summer 203 45.0 2.68 ;i.377** 167 43.7 2.58

Autumn 4°T14 95 44.1 2.26 2.110*

'' 81 43.3 2.64 Winter 44 43.9 2.41 1.044ns--

'14 22 43.1 2.72 ..

1 t values are one-tailed tests on the differences in means at N, + N2 - 2 degrees of freedom, * = larger mean significantly greater at the 95% level, ** = same test at 99% level, ns = no significant difference

TABLE 5.-Calculated growth increments (mm) in Ericymba (sexes combined) from 28 March collection' Number Calculated length at end of indicated Year of year of life class specimens 1 2 3 4 1961 7 23.8 36.4 44.5 46.8 1962 104 22.6 38.5 44.8 ---- 1963 112 21.9 35.8 1964 78 27.9 ---- .... ---- Weighted means: 23.7 37.1 44.8 46.8 Increments: 23.7 13.4 7.7 2.0 Percentage of growth to the 3rd year: 52.9 29.9 17.2 1 The last year of growth is corrected to include growth through May 122 THE AMERICAN MIDLAND NATURALIST 86(1)

Based on data presented in Table 6, individuals in their second and third summers of life begin growth between May and June and have completed much of the year's growth by the end of July (Fig. 2) . The apparent decrease in mean length of fish in their second and third summers of life taken in August and September was not significant. Young specimens grew faster between June and July than between July, August and September. Because there is no evidence of autumn or winter growth for fish in their second and third summers (see below), the changes in mean length between May and July should be a reasonable estimate of growth from annulus to annulus. Based on these estimates, growth increments were 10.1 mm for the second summer and 8.5 mm for the third summer. Both estimates agree well with calculated growth increments (Table 5) . The lengths attained by the 1963 year class in July and August (Table 6) are reasonable estimates of the average maximum lengths at the end of the third summer of life. Those young (1965 year class) which measured 26 to 34 mm in September represent early-hatched young, while those measuring between 12 and 24 mm represent later- hatched young. Early-hatched young averaged 30.5 mm by the end of September and grew to between 64% and 67% of the length finally attained by the end of their third summer of life (Table 6) . Those hatched later in the summer averaged 18.0 mm in length in Septem- ber and grew to about 40.6% of their final third summer length. The growth of young-of-the-year and older fish from October through March was compared. This was based on length-frequency data from those periods (Table 7). Specimens were designated as young-of-the-year if they measured from 10 to 32 mm in length. The overlap in length between young-of-the-year and older fish was not extensive within this range (Table 6) . There was no increase in length of older fish between October 1964 and March 1965 (Table 7). However the mean length of young-of-the-year increased significantly between October and November (t=4.518, df 408) and between

50 .0 ...... 0 0 ...... o ...... 0 • 30 0..... 0 ......

MAR MAY JUN JUL AUG SEP Fig. 2.—Change in the mean standard length of aged Ericymba collected in 1965 (March through September) (see Table 6). Open dots and dotted line represent the 1963 year class; solid dots and dashed line the 1964 year class; triangles and solid line, young-of-the-year 1971 WALLACE: GROWTH OF SILVERJAW MINNOW 123

January and March (t=7.481, df 259). From November through January the mean length did not change significantly. Thus there is no evidence of growth in older fish from midautumn through the winter but young-of-the-year apparently continue growth to late autumn, grow little during the winter, and commence growth early the following spring. Compensatory growth. —That individuals with initially slower growth tend to grow at increased rates in later life has been noted for several fish species such as striped bass (Tiller, 1943), lake herring (Van Oosten, 1929, 1937), rock bass (Hile, 1941) and warmouth (Larimore, 1957). Compensatory growth was investigated using 59 Ericymba of the 1962 year class from the 28 March collection. Specimens were sep- arated into three groups based on their calculated length at the end of the 1st year. These groups were designated as small (18-24 mm standard length), moderate (25-28 mm) and large (29-35 mm). The average growth increment for each year of life was calculated for each group. Based on data presented in Table 8, smaller Ericymba of the 1962 year class had a greater growth increment (15.9 mm) in their second year of life than did moderate or large individuals of the same year

TABLE 6.—Frequency distribution for each year class of Ericymba buccata collected from March to September 1965 Month collected: March May Year class 1964 1963 1962 1964 1963 1962 St. L. 56 .... 54 .... 52 ---- 2 50 .... 4 48 5 46 .... 7 --1 9 44 10 6 11 42 -.5 23 6 12 40 7 50 .... 7 .... 38 9 12 5 36 .... 3 1 - 2 12 34 .... 6 .... 5 19 32 6 18 14 15 30 9 38 8 3 28 23 20 13 .... 26 10 7 18 24 13 .... 4 22 4 5 20 7 .... 18 6 16 .... 14 12 10 No. spec. 78 113 104 69 74 43 Mean 25.2 31.4 40.7 27.9 35.8 44.8 St. error 0.427 0.404 0.206 0.424 0.493 124 THE AMERICAN MIDLAND NATURALIST 86(1) class. There was little difference in growth increments during the following growth period (1964-1965). The observed decrease in the ranges in lengths between young in September (22 mm) and yearlings in March (14 mm) is probably due at least in part to this compensatory growth (Table 6). History of successive years of growth.—Based on the time of annulus completion, a year's "growth period" was designated as starting at the beginning of May. The growth increments of each age group during each growth period from 1961 to 1965 were calculated (Table 9) . Reading this table diagonally from left to right, the growth increments of each year class are obtained. Increments in the first of these diagonal rows indicate growth of the 1961 year class. In this case, these increments are based on only seven specimens and so their reliability is questionable. Reading across the table, the growth during a given year of life for a given "growth period" (1 year) is obtained. The third "growth period" (May 1963 to April 1964) was a rather poor one for growth. The average increment of growth for the young- of-the-year was 21.9 mm as compared with 26.6 mm for the preceding growth period and 27.9 mm for the following growth period. The second year of growth during the third growth period was 11.9 mm compared with 13.9 mm for the 1964-65 growth period.

TABLE 6.—(continued) Month collected: June July Year class 1965 1964 1963 1962 1965 1964 1963 1962 St. L. 56 .... 2 54 ------i - 2 52 .... i: 1 50 4 3 .... 10 1 48 13 .... 2 14 - 46 - 26 2 25 2 44 2 23 11 10 25 1 42 11 29 7 14 20 .... 40 14 16 .... 15 12 38 22 1 17 .... 36 24 .... 21 34 23 .... 2 32 14 5 30 3 2 4 28 ...... 10 .... 26 7 24 3 6 22 3 1 20 4 3 18 5 2 16 6 1 14 4 1 12 5 .... 10 1 No. spec. 31 113 112 26 33 90 107 9 Mean 12.9 36.0 43.5 44.7 24.1 38.0 44.3 50.6 St. error 0.617 0.309 0.259 0.668 0.394 0.273 1971 WALLACE: GROWTH OF SILVERJAW MINNOW 125

AN EXAMINATION OF THE MEAN MONTHLY TEMPERATURES IN THE STUDY AREA MAY OFFER AN EXPLANATION OF THIS POOR GROWTH DURING THE 1963-64 GROWTH PERIOD. AIR TEMPERATURE RECORDS OBTAINED FROM THE DUNROVIN METEOROLOGICAL STATION, LOCATED 7 MILES SW OF WEST TERRE HAUTE, INDIANA, AND APPROXIMATELY 15 AIR MILES FROM THE STUDY AREA, ARE SUMMARIZED FOR EACH GROWTH YEAR IN TABLE 10. EACH GROWTH PERIOD WAS DIVIDED INTO CALENDAR PERIODS WHICH WOULD REFLECT SEASONAL TEM- PERATURE CONDITIONS. BOTH THE EARLY- AND LATE-SUMMER MEAN AIR TEM- PERATURES WERE LOWER DURING THE 1963-64 GROWTH PERIOD THAN FOR PREVIOUS OR FOLLOWING PERIODS. AS NOTED ABOVE, THESE WERE THE PERIODS OVER WHICH THE MAJORITY OF THE YEAR'S GROWTH TAKES PLACE (FIG. 2). A CORRELATION BETWEEN AIR TEMPERATURE AND GROWTH UNDER NATURAL CON- DITIONS WAS FOUND BY HILE (1941) IN AMBLOPLITES RUPESTRIS (RAFINESQUE) AND IN NOTROPIS HUDSONIUS ( CLINTON) BY MCCANN (1959).

ACKNOWLEDGMENTS.—I AM THANKFUL FOR THE MANY WAYS IN WHICH DR. EDWARD C. RANEY HELPED ME DURING THE COURSE OF THIS STUDY. SUPPORT WAS PROVIDED IN PART BY NATIONAL SCIENCE FOUNDATION FELLOWSHIP 66312 AND BY PUBLIC HEALTH SERVICE FELLOWSHIP 1-FL-GM-37,924-01.

TABLE 6.—(CONTINUED)

MONTH COLLECTED: AUGUST SEPTEMBER YEAR CLASS 1965 1964 1963 1962 1965 1964 1963 1962 ST. L. 56 54 2 52 ...... -__. 50 ...... 1 48 ---- 5 1 .... 5 .... 46 11 .... 8 4 44 --3 13 1 22 2 42 5 9 10 25 .... 40 13 2 8 3 38 .... 15 ...... 4 1 36 .... 13 4 .... 34 7 6 5 3 32 9 1 8 .... 30 6 .... 4 28 8 5 26 4 24 2 22 2 9 20 1 7 18 1 5 16 .... 5 14 5 12 1 10 _...

NO. SPEC. 40 56 40 1 58 30 64 9 MEAN 28.6 37.6 44.0 .... 23.1 39.0 43.1 47.3 ST. ERROR 0.646 0.340 0.332 0.432 0.474 0.253

126 THE AMERICAN MIDLAND NATURALIST 86(1)

TABLE 7.-Change in the mean standard length of large and small Ericymba from October through March Size group October November December January March 30+ mm N 45 109 128 47 141 X 40.5 39.5 40.0 38.0 40.3 14 to 32 N 157 253 46 100 161 mm X 21.2 23.5 23.7 23.2 27.3

TABLE 8.-Comparison of the growth increments for Ericymba with initially different standard lengths - 1962 year class Calculated Number Calculated length at Increments of growth length at of end of period between periods 1st annulus specimens 1963 1964 1965 1963-64 1964-65 18-24 mm 18 22.0 37.9 40.5 15.9 2.6 25-28 mm 22 26.4 38.3 41.0 11.9 2.7 29-35 mm 19 31.3 39.5 41.7 8.4 2.2 Maximum difference: 9.1 1.6 1.2 Weighted mean: 26.6 38.6 41.1 Increment: 26.6 12.0 2.5

TABLE 9.-Growth history of Ericymba (1961-1965) Growth periods Growth increments for indicated year of life 1 2 3 4 May 1961-April 1962 23.8 May 1962-April 1963 26.6 12.6 May 1963-April 1964 21.9 11.9 May 1964-April 1965 27.9 13.9 6.3 2.3

TABLE 10.-Mean air temperatures during several growth years of Ericymba Growth period May 1962- May 1963- May 1964- April 1963 April 1964 April 1965 Calendar Mean 2 Mean Mean period" temp. Dev. temp. Dev. temp. Dev. March- April 50.8 +3.0 49.3 +1.5 44.5 -3.3 May- June 71.0 +2.4 66.6 -2.1 69.0 +0.4 July- August 73.5 -3.1 70.8 -5.8 72.9 -3.7 May- August 72.2 -0.4 68.7 -3.9 70.9 -1.7 September- November 54.9 -1.4 56.2 -0.1 54.5 -1.9 December- February 23.8 -8.5 27.7 -4.4 29.9 -2.4 1 Periods are inclusive 2 Dev. = Deviation from normal 1971 WALLACE: GROWTH OF SILVERJAW MINNOW 127

REFERENCES HANKINSON, T. L. 1919. Notes on life-histories of Illinois fish. Trans. Ill. State Acad. Sci., 2:132-150. HARRINGTON, R. W. 1948. The life cycle and fertility of the bridled shiner, Notropis bifrenatus (Cope). Amer. Midl. Natur., 39:83-92. HILE, R. 1941. Age and growth of the rock bass, Ambloplites rupestris (Rafi- nesque) in Nebish Lake, Wisconsin. Trans. Wis. Acad. Sci. Arts Lett., 33:189-337. LARIMORE, R. W. 1957. Ecological life history of the warmouth. Ill. Natur. Hist. Sure. Bull., 27:1-83. McCANN, J. A. 1959. Life history studies of the spottailed shiner of Clear Lake, Iowa, with particular reference to some sampling problems. Trans. Amer. Fish. Soc., 88:336-343. NIKOLSKY, G. V. 1963. The ecology of fishes. Academic Press, New York. 352 p. STEEL, R. G. D. AND J. H. TORRIE. 1960. Principles and procedures of statis- tics. McGraw-Hill Book Co., New York. 481 p. STONE, U. B. 1940. Studies on the biology of the satinfin minnows, Notropis analostanus and Notropis spilopterus. Unpublished Ph.D. Thesis, Cornell Univ., Ithaca, New York. TILLER, R. E. 1943. Indications of compensatory growth in the striped bass, Roccus saxatilis Walbaum, as revealed by a study of the scales. Publ. No. 57, Chesapeake Biol. Lab. 16 p. VAN CLEAVE, H. J. AND H. C. MARKUS. 1929. Studies on the life history of the blunt-nosed minnow. Amer. Natur., 43:530-539. VAN °OSTEN, J. 1929. Life history of the lake herring (Leucichthys artedi LeSueur) of Lake Huron as revealed by its scales, with a critique of the scale method. Bull. Bur. Fish., 4,4:265-428. . 1937. The age, growth, and sex ratio of the Lake Superior longjaw, Leucichthys zenithicus (Jordan & Evermann). Pap. Mich. Acad. Sci. Arts Lett., 22 : 691-711. WALLACE, D. C. 1969. A study of the ecology and life history of the silverjaw minnow, Ericymba buccata Cope (Pisces, Cyprinidae). Unpublished Ph.D. Thesis, Cornell Univ., Ithaca, New York.

SUBMITTED 11 MAY 1970 ACCEPTED 31 AUGUST 1970