2010 SOUTHEASTERN NATURALIST 9(2):347–358
Life-history Aspects of the Rainbow Shiner, Notropis
chrosomus (Teleostei: Cyprinidae), in Northern Georgia
D. Sean Holder1 and Steven L. Powers2,*
Abstract - The life history of Notropis chrosomus (Rainbow Shiner) was investigated
using 12 monthly collections from Moore Creek (Etowah River Drainage) at
GA Highway 140 in Cherokee County, GA. Specimens were collected by electroshocking
and seining primarily from runs and flowing pools and examined to identify
feeding habits, age, growth, and reproductive patterns. Notropis chrosomus are opportunistic
insectivores with gut contents largely consisting of Chironomidae larvae,
unidentified insect parts, unidentified Diptera adults, and Collembola. Spawning occurred
in spring with 400–896 (mean 708.92, SD = 162.90) mature oocytes ranging
from 0.7 mm to 1.22 mm (mean = 0.90 mm, SD = 0.167 mm) present in specimens
collected in April, May, and June. Sexual maturity occurred at approximately one
year of age. The maximum age of both males and females was estimated at approximately
24 months (females = 25 months, males = 23 months). The largest female
collected was 66.71 mm SL and 5.515 g total weight. The largest male collected was
60.19 mm SL and 3.691 g total weight.
Introduction
Notropis chrosomus (Jordan) (Rainbow Shiner) was described in 1877
from specimens collected in a tributary to the Etowah River near Rome, GA
(Gilbert 1998). Hypothesized close relatives include N. leuciodus (Cope)
(Tennessee Shiner) and N. nubilus (Forbes) (Ozark Shiner) (Mayden 1987)
as well as N. rubricroceus (Cope) (Saffron Shiner) and N. lutipinnis (Jordan
and Brayton) (Yellowfin Shiner) (Mayden et al. 2006). Notropis chrosomus
is often abundant in small streams throughout the tributaries of the Etowah,
Oostanaula, Cahaba, and Coosa River drainages of Northwest Georgia and
Northeastern Alabama, and is distinguished from other cyprinids within its
range by a red upper half of the eye; nuptial males possess a reddish stripe
above the midlateral stripe and powder blue below with iridescent flecks
of lavender, pink, and silver over the body (Boschung and Mayden 2004).
Little is known of the biology of N. chrosomus other than the associated
spawning with Nocomis leptocephalus (Girard) (Bluehead Chub) and Campostoma
oligolepis Hubbs and Greene (Largescale Stoneroller) occurring
from May to June, as determined from observations and the physical condition
of museum specimens (Johnston 1991, Johnston and Kleiner 1994). The
primary objective of this study is to elucidate some of the aspects of the life
history of N. chrosomus and briefly compare them to those of hypothesized
close relatives.
1 Department of Fisheries and Allied Aquaculture, Auburn University, 203b Swingle
Hall, Auburn, AL 36849. 2Biology Department, Roanoke College, 221 College Lane,
Roanoke, VA. *Corresponding author - powers@roanoke.edu.
348 Southeastern Naturalist Vol. 9, No. 2
Study Area
Specimens were collected from Moore Creek upstream of its confluence
with Shoal Creek (34.3240ºN, 84.5636ºW), near Waleska in Cherokee
County, GA (Fig. 1). Moore Creek is an upland second order tributary of the
Etowah River between 3.1 and 6.4 m wide and less than 1.0 m deep at normal
flows. Substrate is primarily gravel to cobble with sporadic bedrock in
riffles, with gravel to sand in runs, and sand and silt in pools. Most N. chrosomus
collected during this study were taken from runs to flowing pool habitat
near the riffle edges. Upstream of the study area, the Moore Creek watershed
is mostly forested with moderate agricultural use and sparse residential
development. Water temperatures during times of collection ranged from 4
ºC in January 2006 to 25 ºC in June 2006. The species richness found for
fishes within the study reach was relatively high, with 30 species collected.
A complete list of species collected from Moore Creek near its confluence
with Shoal Creek can be found in O’Kelley and Powers (2007).
Methods
Notropis chrosomus and vouchers of associated species were collected
by sampling near the middle of each month using a 3.3-m x 1.3-m seine and
a Smith-Root model 24 backpack electrofisher from January to December
2006. A total of 200 specimens were collected, preserved in 10% formalin,
rinsed with water, and transferred into 70% EtOH for long-term storage.
Specimens were accessioned into the University of Alabama Ichthyological
Collection (UAIC 15027–15038). Observations for spawning behavior of
Figure 1. Map of
Notropis chrosomus
study area in Moore
Creek (34.3240ºN,
84.5636ºW), near
Waleska in Cherokee
County, GA.
2010 D.S. Holder and S.L. Powers 349
N. chrosomus were conducted in 10-minute intervals on 16 May 2007 by
snorkeling and bank observations lasting approximately one hour.
The standard length (SL) of each specimen was measured using digital
calipers and recorded to the nearest 0.01 mm. Sexual size dimorphism was
detected using a two sample t-test of SL; therefore all analyses regarding
age and growth were performed separately according to sex. Specimens
were blotted dry and total weight (TW), eviscerated weight (EW), and gonad
weight (GW) were measured using a digital analytical balance and recorded
to the nearest 0.001 g. Standard length and EW were plotted against month
to provide length and weight frequency distributions to illustrate age and
growth data. All statistical analyses were executed using Data Desk 6.0
(Data Description, Inc., Ithaca, NY) with alpha for all tests equal to 0.05. In
reference to regressions, independent variables are listed first and dependent
variables second unless otherwise noted.
Standard length was plotted against month. Gaps of approximately 5 mm
or more in the SL of specimens from a single month were considered indicative
of different age classes. Frequency distributions of SL from selected
months were also examined for peaks adjacent to categories lacking specimens
to corroborate indications of different age classes by SL data (Fig. 2).
Using May as an example, the frequency distribution category 45–50 mm
entirely lacked specimens, but adjacent categories (40–45 mm and 50–55
mm) contained 3 or more specimens each suggesting two separate age
classes in specimens collected in May.
Due to high GSI values found in specimens collected in April and May, as
well as spawning behavior observed on 19 May 2007, we assumed spawning
occurred in spring and used May as the month of spawning for age estimates.
Figure 2. Frequency distribution of standard length (SL) in categories of 5 mm increments
for Notropis chrosomus collected in January, May, and September 2006 from
Moore Creek, Cherokee County, GA.
350 Southeastern Naturalist Vol. 9, No. 2
Specimens less than 12 months of age were counted as age 0+, specimens
12–23 months were counted as age 1+, specimens, and 24–35 months were
counted as age 2+. The proportion of total specimens collected represented
by each age class was calculated to approximate the age class distribution of
the population. A Mann-Whitney test of age in months was used to test differences
in lifespan among sexes. Regressions by least sum of squares were
performed for SL and the natural log of EW.
The anterior third of the gastrointestinal track was opened and its contents
were removed and weighed using a digital analytical balance and recorded
to the nearest 0.001 g. Weight of gut contents for specimens with empty guts
was recorded as “0.” An ANOVA was performed to detect mean differences
in weight of gut contents between months. Food items were identified to the
lowest taxonomic category possible following Thorp and Covich (1991) and
Merritt and Cummins (1996) and enumerated. Due to mastication by pharyngeal
teeth, most gut contents were not identifiable below the family level,
and some could only be identified to order or class.
Gonadosomatic index (GSI), was calculated by dividing GW by EW. An
ANOVA was performed to detect mean differences in GSI from different
months for males and females. Mature oocytes were categorized as latent,
early maturing, late maturing, and mature (see Heins and Machado 1993). In
gravid females, mature oocytes were enumerated and diameters of five representative
mature oocytes were measured. The regression of SL was used
as a predictor of the number of mature oocytes to test the influence of size
on fecundity.
Results
The smallest specimen collected (19.28 mm SL and 0.095 g TW) was in
July and presumed to be the earliest capture of a young-of-the-year specimen.
The largest female collected was 66.71 mm SL and 5.515 g TW. The
largest male collected was 60.19 mm SL and 3.691 g TW. The ratio of females
to males collected was 0.96:1. Sexual size dimorphism was detected
(P = 0.006) with mean SL of 47.83 mm (SD = 9.87) for females and 44.43
(SD = 8.35) for males. Due to this sexual size dimorphism, the following results
are presented for females and males respectively unless otherwise noted.
As age in months increased, so did SL (r2 = 67.5%, P < 0.001; r2 =
66.4%, P < 0.001). Visual inspection of the data suggested a curvilinear
relationship between SL and EW, so before regressing it with SL, we log
transformed EW (r2 = 72.3%, P < 0.001; r2 = 69.3%, P < 0.001). Growth
rates appear to increase in spring as indicated by length and weight increases
in specimens approximately 1 and 2 years of age (Figs. 3–4). Of the
200 specimens collected, 44.2% were 0+, 54.3% were age 1+, 1.5% were
age 2+. Mean age in months was different between the sexes (P < 0.001)
with a mean age for males of 11.70 months (SD = 5.63) and for females of
13.46 (SD = 6.34). Maximum age of specimens captured was 23 months for
males and 25 months for females.
2010 D.S. Holder and S.L. Powers 351
Chironomidae larvae made up 44.6% of all gut contents of N. chrosomus
examined. Unidentified insect parts, Diptera adults, and Collembola made
Figure 3. Standard length (SL) in mm ± one standard deviation by age in months
for Notropis chrosomus collected from Moore Creek between January 2006 and
December 2006.
Figure 4. Eviscerated weight (EW) in g ± one standard deviation by age in months
for Notropis chrosomus collected from Moore Creek, Cherokee County, GA from
January 2006 to December 2006.
352 Southeastern Naturalist Vol. 9, No. 2
up 14.39%, 9.15%, and 6.1% of all food items, respectively (Table 1). Of
all specimens examined, 54.76% of GI tracks were empty. Feeding was not
uniform across all months (F= 4.77, df = 11, P < 0.0001) and appeared to
be greatest in taxa richness of food items in February and March (n = 5)
and peak weight of gut contents (0.031g, SD = 0.014), occurred in March.
Feeding appeared to decrease during August with a low mean weight of
gut contents (0.006 g, SD = 0.004), taxa richness of food items (n = 2), and
68.75% of GI tracks were empty. In January, 76.5% of all guts were empty
with 4 specimens (23.5%) containing detritus, unidentified insect parts, and
a single Chironomidae larva. Eviscerated weight explained a low proportion
of the variation in the weight of gut contents (r2 = 9.3% for females and 2.9%
for males), but the relationship was significant (P < 0.001 for females, P =
0.029 for males). Eviscerated weight explained an even lower proportion of
the variation in taxa richness of food items as regressions were not signifi-
cant (P = 0.196 for females, P = 0.052 for males).
On 16 May 2007, behaviors associated with spawning in other species
(Johnston 1991) were observed for an aggregation of 7 individuals with 3
males in nuptial condition engaging in circle swims and leading the 4 females
to a nest of a Semotilus atromaculatus (Mitchill) (Creek Chub) at the
downstream end of a pool. This behavior was observed for approximately
1 hour in the afternoon. No behaviors directly associated with the expelling
of gametes were observed. Mean and individual female GSI peaked
in spring, with values greater than 0.15 in specimens from April and May
(Fig. 5). Males showed a similar pattern, with GSI values greater than 0.03
Figure 5. Gonadosomatic index (GSI) by month of the year (1 = January, 2 = February,
etc.) ± one standard deviation by months for Notropis chrosomus females
collected from Moore Creek, Cherokee County, GA between January 2006 and
December 2006.
2010 D.S. Holder and S.L. Powers 353
Table 1. Gut contents of Notropis chrosomus from Moore Creek, Cherokee County, GA by month. Numbers for each food item indicate the total number of individual
items of that food type in all guts examined; detritus and unidentified insect parts are exceptions due to the difficulty quantifying them and are noted by
occurrence within a single specimen (e.g., the occurrence of detritus in two specimens from a month is denoted as “2”).
Month
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total % of total
# of specimens 16 13 15 13 15 17 22 16 15 24 14 20 200
Detritus 3 9 7 5 3 3 2 2 3 5 6 49 10.68
Sand 2 1 3 6 1.31
Ova/eggs 22 22 4.79
Nematoda 2 2 0.44
Mollusca
Physa sp. 2 3 0.65
Insecta
Unidentified parts 3 6 7 3 7 8 10 4 4 8 2 2 66 14.38
Ephemeroptera 5 13 1 1 20 4.36
Collembola 28 28 6.10
Coleoptera 1 1 1 3 0.65
Lepidoptera 1 1 0.22
Hymenoptera 1 1 1 1 4 0.87
Hemiptera 3 3 0.65
Trichoptera 3 1 1 5 1.09
Diptera
Chironomidae larvae 1 6 27 91 21 47 1 1 2 205 44.66
Unidentified adults 14 15 2 10 42 9.15
Number empty 13 5 6 6 8 7 11 11 10 13 8 11 115
% empty 81.25 38.46 40.00 46.15 53.33 41.18 50.00 68.75 66.67 41.76 57.14 55.00
Total number of items 7 51 82 101 49 70 27 9 8 26 4 12 459
Mean items/gut 0.41 3.92 5.47 14.43 6.13 4.12 1.23 1.80 0.53 1.08 0.29 0.60
354 Southeastern Naturalist Vol. 9, No. 2
in specimens from March to June (Fig. 6). The water temperatures of the
April, May, and June collections for this study were 20 ºC, 16 ºC, and 25 ºC,
respectively. The highest GSI for a single specimen was 0.349 in a female
of 53.03 mm SL collected in May. For females, GSI was not uniform among
months (F = 10.48, df = 11, P < 0.0001), but male GSI was not significantly
different among months (F = 1.48, df = 11 P = 0.155). April had the highest
mean GSI for females (0.278, SD = 0.047), and March had the highest mean
GSI for males (0.048, SD = 0.023). Male GSI in April was also high, with a
mean of 0.039 (SD = 0.01). The lowest mean GSI were in January (0.0166,
SD = 0.003) for females and October for males (0.009, SD = 0.004). Gravid
females were collected from April to June and contained between 400 and
896 (mean 708.92, SD = 162.90) mature oocytes ranging from 0.7 mm to
1.22 mm in diameter (mean = 0.90 mm, SD = 0.167 mm). Ovaries of mature
females appeared to contain one class of mature oocytes, and SL was a significant predictor of the number of oocytes (r2 = 26.4%, P < 0.0001).
Discussion
Maximum age appears to be approximately 2 years and is similar for both
sexes. The female-to-male ratio (0.96:1) combined with a similar maximum
age suggests a similar life span for both sexes. This sex ratio by age class
suggests that both males and females have very similar patterns of survival.
Very few specimens of either sex appear to reach maximum age, with only
1.5% of all sexed specimens reaching age class 2+. The relatively low number
of 0+ specimens collected is likely due to the ease with which specimens
Figure 6. Gonadosomatic index (GSI) by month of the year (1 = January, 2 = February,
etc.) ± one standard deviation by months for Notropis chrosomus males collected from
Moore Creek, Cherokee County, GA between January 2006 and December 2006.
2010 D.S. Holder and S.L. Powers 355
less than 35 mm in SL pass through the 9.5-mm mesh of the 3.3-m x 1.3-m
seine. Increases in size as specimens approach 1 and 2 years of age (Figs.
3–4) coincide with increases in feeding and indicates an increased growth
rate in the spring.
While the relationship between EW and weight of gut contents was significant, the low r2 values for these relationships, and the lack of significant
relationship between EW and taxa richness of food items suggests size has
little impact on diet in N. chrosomus. The increase in feeding during late
winter and spring months coincides not only with increases in growth, but
also slightly precedes the increased energy requirements of gamete production
and courtship behaviors. Feeding continues at an increased level
through spawning season, declines sharply in late summer, and appears to
be nearly absent in January, with 81% of guts empty (Table 1). Not only
did mass of gut contents increase as spawning approached, but taxa richness
of food items also increased during these months. This pattern may
suggest that N. chrosomus become less selective in their food items during
periods of high caloric demands. Alternatively, as the diet of the syntopic
Notropis xaenocephalus (Jordan) (Coosa Shiner) also increases in variety
during spring (Jolly and Powers 2008), seasonal changes may be due to food
availability rather than selectivity of specific food items by N. chrosomus.
The variety of food items available likely increases during spring due to
increased reproductive activity by aquatic invertebrates making them more
susceptible to predation (see Thorp and Covich 1991). Increased energetic
input by terrestrial insects during summer (and to a lesser extent spring) has
been documented in other streams in the Southeast (Cloe and Garman 1996).
The increased abundance of terrestrial insects during a period of increased
energetic demands provides a relatively simple explanation for these data.
Occurrence of ova in the gut of two specimens collected in March is consistent
with the observation of N. chrosomus eating “loose” eggs by Johnston
and Kleiner (1994), and also suggests that N. chrosomus are opportunistic
feeders during these periods of increased energetic demands.
While Chironomidae (44.6%) are the predominate food item of the gut of
N. chrosomus, this value is intermediate between the 88.8% of gut contents
as Chironomidae in Hypentelium etowanum Jordan (Alabama Hog Sucker),
a hypothesized bottom feeder (O’Kelley and Powers 2007), and 19.5% as
Chironomidae in N. xenocephalus, a hypothesized drift feeder (Jolly and
Powers 2008), within the same study stretch. This intermediate value also
suggests N. chrosomus are not particularly selective in their feeding compared
to other syntopic species, but rather are opportunistic feeders.
High GSI values in female specimens collected in April and May and low
values from July (Figs. 5–6) indicate spawning most likely occurs between
late April and early June. All specimens from fall and winter months were
latent or maturing (see Heins and Machado 1993), indicating a single spawning
season. The water temperatures of the spring collections for this study
suggest spawning occurs in 16–25 ºC water. Our observations of spawning
356 Southeastern Naturalist Vol. 9, No. 2
behavior were consistent with the findings of Johnston and Kleiner (1994)
and indicate that spawning occurs in habitat similar to that used throughout
the year, but within this population, egg deposition likely occurs in
Semotilus sp. nests, as Nocomis sp. are absent from Moore Creek and large
Campostoma sp. are not common.
Examination of gonads and length-frequency distributions (Fig. 2) indicated
that sexual maturity occurs by 12 months of age for most individuals,
and the maximum age of a little over 24 months suggests no more than 2
spawning seasons for any individual. The occurrence of two specimens over
the age of 12 months that did not possess mature gonads suggests that some
individuals do not reach sexual maturity until their second spawning season.
It is unknown whether this variation in maturation is linked to lifespan. The
positive relationship between SL and number of mature oocytes suggests
that larger specimens produce more eggs. The positive relationship between
age and SL then suggests that older specimens have greater reproductive
potential than younger specimens.
Comparison to hypothesized close relatives
Breeding of N. chrosomus is comparable to other hypothesized closely
related species, N. leuciodus, N. lutipinnis, N. nubilus, and N. rubricroceus
in each having a single breeding season peaking in spring to early summer in
water temperatures up to 25 ºC (Boschung and Mayden 2004, Clayton 2000,
Etnier and Starnes 1993, Fowler et al. 1984, Outten 1958). Little is known
of the biology of N. leuciodus, but both N. chrosomus and N. nubilus appear
to reach sexual maturity mostly at 12 months of age (with a few individuals
not reaching maturity until 24 months) and have a maximum lifespan of
less than 3 years. Notropis lutipinnis and N. rubricroceus differ in having
maximum life spans of 5 years and sexual maturity occurring at two years
of age (Clayton 2000, Outten 1958). All hypothesized close relatives spawn
over nests of Nocomis sp., Campostoma sp., or Semotilus sp. These associations
are hypothesized to be mutualistic relationships (Johnston 1994a, b),
with host species benefiting from predator dilution and associative species
benefiting from the parental care of the host. The observed range of mature
oocytes size (0.97–1.22 mm) in Notropis. chrosomus appears to be smaller
than that of N. lutipinnis, N. rubricroceus and N. nubilus at 1.4–1.7, 1.6, and
2.1 mm, respectively (Clayton 2000, Fowler et al. 1984, Outten 1958). While
methods of quantifying fecundity are variable across studies, N. lutipinnis
examined by McAulliffe and Bennett (1981) had up to 286 eggs, Clayton
(2000) estimated up to 786 eggs per female, and Outten (1958) reported up
to 1174 eggs per female.
The diet of N. chrosomus appears to be similar to that of hypothesized
close relatives in feeding habits as 83% of food items were invertebrates
with ova, detritus, and inorganic materials consisting of the rest of the gut
contents. As with N. lutipinnis and N. rubricroceus, the bulk of the invertebrates
were aquatic and terrestrial insects. However, as insects represent
the bulk of available food items, all species are hypothesized to be largely
opportunistic feeders. (Clayton 2000, Outten 1958)
2010 D.S. Holder and S.L. Powers 357
Acknowledgments
We thank K. Edberg, S. Barton, and C.K. Ray for assistance with field and lab
work. We thank Reinhardt College for field and lab equipment used in this study.
Fishes were collected under Georgia Scientific Collecting permit 16494 issued to
S.L. Powers. This study was conducted in part as an undergraduate independent
research project by D.S. Holder while at Reinhardt College.
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