Life History of the Swamp Darter, Etheostoma Fusiforme, in Florida

Life History of the Swamp Darter, Etheostoma fusiforme, in Florida

Authors: Flemming, Adania, and Page, Lawrence M. Source: Southeastern Naturalist, 19(2) : 418-435 Published By: Eagle Hill Institute URL: https://doi.org/10.1656/058.019.0222

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Life History of the Swamp Darter, Etheostoma fusiforme, in Florida

Adania Flemming1,* and Lawrence M. Page1

Abstract - Over a period of 18 months, we studied the life history of Etheostoma fusiforme barratti, the southern subspecies of the Swamp Darter, in Hatchet Creek in the Suwannee River drainage of Florida. We found E. f. barratti on sandy and muddy substrates with dense vegetation and woody debris. Field data suggested a lifespan of up to 14 months, although individuals survived 18 months in an aquarium. There was no significant difference between the mean standard lengths of males and females, and the sex ratio was 1:1. The largest specimen collected was a 50-mm SL (59-mm TL) reproductively mature male. Midge larvae (Chironomidae) and water fleas (Cladocera) were the most common food items. Individuals in the smallest size class, 10–19 mm SL, consumed a larger proportion of small food items such as cladocerans and midge larvae, and larger Swamp Darters ate larger food items such as caddisflies, and consumed a larger variety of food items. Approximately one-third of all E. f. barratti dissected were parasitized by a digenean trematode. A large increase in the female gonadosomatic index occurred in January in each of the 2 study years as the darters approached 1 year of age and were at least 25 mm SL. Spawning occurred in January–May 2016 and January–April 2017. In an aquarium, adhesive eggs were attached to aquatic plants by females and fertilized by males. Numbers of mature and maturing ova were extremely variable (4–226), suggesting that E. f. barratti is a batch spawner and lays eggs over several mating bouts rather than during a single spawn. Compared to the northern subspecies, E. f. fusiforme, E. f. barratti reaches a larger size, 59 vs. 55 mm TL, and spawns earlier and longer, from January to April vs. April to May. Males of E. f. barratti, but not of E. f. fusiforme, were aggressive and possibly territorial during spawning. Etheostoma f. barratti may have a shorter life span, 14–18 months, compared to 2 years in E. f. fusiforme. This study provides baseline life-history data for a widespread and common species that has the potential to affect the structure and function of aquatic ecosystems.

Introduction Etheostoma fusiforme (Girard), the Swamp Darter, is a small percid fish distributed from southern Maine along the Atlantic Coast and Gulf Coast to east Texas and north in the former Mississippi Embayment to Kentucky and Missouri (Fig. 1). It is a benthic species found in non-flowing or slow-flowing water over sand or mud, often near live vegetation or woody debris and, as the name implies, is common in swamps (Page 1983). Two morphologically distinct subspecies are recognized, with the northern subspecies, E. f. fusiforme (Girard), being found from Maine to the Waccamaw River, NC, and the southern subspecies, E. f. barratti (Holbrook), occurring throughout the rest of the range (Collette 1962). Etheostoma f. fusiforme is distributed almost entirely below the Fall Line—the geomorphologic break between

1University of Florida, Florida Museum of Natural History, Gainesville, FL 32611. *Cor- responding author - [email protected]. Manuscript Editor: Nathan Franssen

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upland regions of hard rock and the softer sedimentary rock along the Atlantic and Gulf Coastal Plains (Renner 1927)—except for its limited distribution in Con- necticut above the Fall Line. The unusual distribution above the Fall Line prompted life-history studies of E. f. fusiforme in southern New England by Schmidt and Whit- worth (1979) and Schmidt (1983). Little information other than from these studies exists on the life history of the Swamp Darter. To provide additional information on this wide-ranging species, we conducted a study on the southern subspecies in a stream in northern Florida. We examined demographic characteristics, including growth rate, longevity, sex ratio, and age and size at sexual maturity; diet; and reproductive characteristics, including seasonality of spawning, fecundity, and behavior. We also compared our data for the Florida population with what has been reported for E. f. fusiforme when comparable data were available.

Figure 1. Distribution of the Swamp Darter, Etheostoma fusiforme. Map from Page and Burr (2011). The red line represents the approximate boundary between E. f. fusiforme in the northern part of the range and E. f. barratti in the southern part.

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Methods Hatchet Creek (29°41'17"N, 82°12'24"W), in the Suwannee River drainage of Alachua County, FL, supports a large population of E. f. barratti and served as the study area. The creek flows south and east from Austin Cary Forest into Newnans Lake, and we accessed the site at State Road 26. The riparian zone of Hatchet Creek is heavily forested, which provides shade throughout most of the year and consists of floodplain swamp (with Taxodium distichum (L.) Rich. [Bald Cypress] dominant), pine flatwoods, pond cypress domes, and mesic hammocks. Common macrophytes in the stream are species of Juncus (rushes) and Cinnamomum. The creek is typical of the environments inhabited by Swamp Darters (Everhart 1966, Page 1983), with a sandy bottom littered with woody debris—mostly dead leaves and branches from the hillslope canopy, and tree roots along the bank. There were no rocks present in the creek at the study site. We used dip nets (38 cm × 46 cm, 30 cm deep, 3-mm mesh) to make monthly collections in Hatchet Creek from November 2015 to August 2017 to capture individuals throughout the predicted lifespan of a Swamp Darter (~1 year). In addition to dip nets, we deployed seines (3 m × 1.1 m, 3-mm mesh) in July and August 2017 to capture individuals on the floodplain where they had moved during overbank flooding. Sampling continued during each visit until 20 specimens were caught, except in January and February 2016, when fewer specimens were captured as a result of high water, and beginning in December 2016, when we increased the number of individuals collected per month to 25–35 to obtain large enough sample sizes for estimating growth and reproduction. Dip netting was concentrated along the banks of the creek in areas containing root nodules of trees and other vegetation, which have been identified as preferred Swamp Darter habitat (Schmidt and Whitworth 1979, Schmidt 1983). We measured water temperature, water depth, and pH (measured with a Professional Plus YSI meter 10102030; Yellow Springs, OH) monthly at the same site in the middle of Hatchet Creek. We anesthetized captured individuals with MS-222 until limited mobility was observed, then transferred the specimens to 10% formalin to cease ongoing meta- bolic processes and preserve gut contents. We removed the fish from formalin after 5 days and transferred them to 70% ethyl alcohol. We classified individual darters of ≥25 mm standard length (SL) as adults, the smallest size at which the adult color pattern was present and the lateralis system was fully formed.

Demography We measured the SL and total length (TL) in mm of each darter using a Vernier caliper. We plotted SL against the month of collection to examine growth rate, and assigned specimens to size classes based on SL for comparisons of diet at different sizes. We used TL for comparisons with the studies of Schmidt and Whitworth (1979) and Schmidt (1983). We sexed specimens by examining the genital papilla, which was larger and blunter in females, dorsal fin pigmentation, which was darker in males, or when necessary, the gonads. We classified very small specimens as indeterminate if their

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Downloaded From: https://bioone.org/journals/Southeastern-Naturalist on 12 Jun 2020 Terms of Use: https://bioone.org/terms-of-use Access provided by University of Florida 2020 Southeastern Naturalist Vol. 19, No. 2 A. Flemming and L.M. Page sex could not be established using these methods. A two-factor chi-squared (χ2) test between month and gender was conducted, to determine if the proportion of males to females was related to the month of the year data were collected, over the period of 18 months from November 2015 to August 2017. To quantify the lifespan of specimens, we assessed the size of sampled individuals over time (Fig. 2) and removed a scale just below the lateral line and under the origin of the 1st dorsal fin of each specimen in an effort to use annuli to age fishes (Schneider et al. 2000). However, the age of E. f. barratti could not be determined using scale annuli as the annuli were not well marked. We compared morphological characteristics of larvae and juveniles, including pigmentation, squamation, and development of the lateral line, to those of adults. We conducted a two-way ANOVA to determine whether there was an interaction between the mean length of males and mean length of females. Given the interaction was not significant, we removed the interaction term and reran the analysis for the purpose of determining if the mean length differed based on sex of specimens and time period. We sepa- rated specimens into 2 time periods to distinguish between a period influenced by juveniles (period 1) and one consisting of only adults (period 2). Period 1 consisted of specimens collected during the presence of juveniles (May to July), immediately following the spawning period (January to April), while period 2 included specimens collected before and during the spawning period (August to April). Only adults were included in the analysis.

Diet We examined digestive systems of a representative sample (~25%) of the Swamp Darters larger than 25 mm SL from each collection to identify food items and parasites. In collections containing juveniles (≤ 25 mm SL), we also dissected at least 5 juveniles to compare the diet of juveniles to that of adults. We dissected fish by making an incision on the left side from the anus to the operculum and removed the liver, exposing the esophagus, which we cut at the anterior-most point. We then cut

Figure 2. Standard lengths of E. f. barratti males, females, and individuals of undetermined sex by month of collection.

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Downloaded From: https://bioone.org/journals/Southeastern-Naturalist on 12 Jun 2020 Terms of Use: https://bioone.org/terms-of-use Access provided by University of Florida 2020 Southeastern Naturalist Vol. 19, No. 2 A. Flemming and L.M. Page the intestine at its posterior end, which freed the entire digestive system from the body cavity and exposed the gonads, which we also removed from the body cavity. We placed all organs removed from each fish in an individual vial in 70% ethyl alcohol for later examination. We examined the contents of the stomach and intestine under a dissecting microscope, counted each food item, and when possible, identified the items to order (e.g., Odonata, Cladocera) or to the family Chironomidae (an exception because of the large quantity of this food item) using Merritt and Cummins (1996), Smith (2001) and Voshell (2002). We classified items that could not be identified to order as Insecta. We calculated percent occurrence of food categories (number of specimens with each food item divided by all specimens containing food in a given sample) and percent composition of food items (percent each food category contributed to total number of food items) according to the methods used by Schmidt and Whitworth (1979) to allow comparisons between the northern and southern populations. We used both percentages to determine “significance” (S; Windell 1971) of each food category, calculated as: S = √(% occurrence)(%composition)

Reproduction We assessed reproductive condition using (1) gonadosomatic index (GSI), determined as the weight of the gonads as a percentage of the adjusted body weight (weight of fish minus weight of organs removed; Page and Smith 1971), and (2) number of ova in the left ovary (doubled to estimate the number per female). Af- ter removing the gonads, we placed each specimen and its gonads in water for about 30 seconds to avoid the fluctuation in weight from the evaporation of ethanol, then blotted dry with a paper towel and weighed them. The weight of the gonads and adjusted body weight of each fish were determined using a JT-D analytical digital balance scale (JT1003D 100g/1mg Lab Analytical Digital Balance Scale; KUN- HEWUHUA Company, China)) to the nearest 0.001 gram and a Mettler Toledo AJ100 analytical digital balance scale (Columbus, OH) to the nearest 0.0001 gram for smaller specimens. We conducted a correlation test (Pearson’s correlation) to determine if there was an association between mean GSI and monthly temperature readings. We counted ova from adult females caught just prior to and during the reproductive season (January–May 2016 and January–April 2017) and measured their diameters using a dissecting microscope with an ocular micrometer. We se- lected 2 specimens with the heaviest gonads from each month for ova counts following Heins and Baker (1988). We counted and assigned all ova to 3 developmen- tal stages: mature, intermediate (developing), or immature (undeveloped). Mature ova were partially translucent with an invaginated membrane, 1–2 oil globules, and a diameter of 1.0–1.5 mm. Intermediate (developing) ova were also 1.0–1.5 mm but still opaque and with several oil globules, while immature (undeveloped) ova were 0.2–0.75 mm in diameter and lacked oil globules (Hatch 1986, Page 1983). We conducted a correlation test (Pearson’s correlation) to determine if there was a

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Downloaded From: https://bioone.org/journals/Southeastern-Naturalist on 12 Jun 2020 Terms of Use: https://bioone.org/terms-of-use Access provided by University of Florida 2020 Southeastern Naturalist Vol. 19, No. 2 A. Flemming and L.M. Page relationship between SL and total number of ova. We tested the total number of ova, and not individual stages, because the number in each stage of ova development in a female changes in relation to the number in the other stages. For spawning observations, we used a 150-L aquarium containing all substrates known to be used for spawning by other darter species: sand, gravel, sticks, plants (in this case Microsorum pteropus (Blume) Fraser-Jenk. [Java Fern]), and rocks (Page 1985). Sand and gravel were in roughly equal amounts, with sticks, plants, and rocks scattered over each. We added 6 reproductively mature individuals (3 males and 3 females, all ≥40 mm SL), as evidenced by swollen abdomens in the females and dark colors in the males, to the aquarium on 1 March 2016. The aquarium temperature varied from 21 to 23 °C, the span of temperatures at which other darters are known to have spawned (e.g., E. gracile (Girard) [Slough Darter]; Braasch and Smith 1967), and the aquarium light was set on a 12-hour cycle approx- imating day length in northern Florida in March. We fed the Swamp Darters frozen blood worms and brine shrimp daily. To record spawning, we videotaped the individuals in the aquarium daily using a GoPro® camera (Hero 4; San Mateo, CA) between 8:00 and 17:00 from 1 March 2016 to 1 May 2017, and from 8 January 2017 to 1 May 2018. Recording was discontinued on 1 May each year as spawning activity was no longer observed. To compare our observations in the laboratory with those observed in a field set- ting, we obtained videos of E. f. barratti spawning at 21.8 °C in an effluent of Hart Spring (29°40'35"N, 82°57'10"W) in the Suwannee River drainage at 10:30 on 2 March 2016 from Kirsten Work (Stetson University, DeLand, FL, unpubl. data). All statistical analyses were conducted using SPSS version 25 (IBM, Armonk, NY).

Results During the study period, we collected 475 Swamp Darters, of which we dissected 431 to examine diet, gonads, and parasites. In average flow conditions, individuals were mainly found along the banks of the creek, and during floods they were collected on the floodplain. The maximum water depth measured at base flow was 114.3 cm. The pH varied from 6 to 7.8, while the water temperature varied from 11.3 °C in March 2017 to 25.1 °C in July 2016 (Fig. 3). We collected a total of 15 species of fishes (Table 1).

Demography The SL of specimens varied from 13.1 to 50.1 mm (Fig. 2). We conducted a two-way ANOVA to determine if the mean SL of fish collected in the study differed based on sex of specimens and time period. The assumptions of normality and equality of variance were met. There was no interaction between period and sex in relation to SL. Thus, the interaction term was removed, and the analysis was rerun. The results indicated there was no significant mean difference in SL of Swamp

Darters due to sex (F(1) = 0.009, P = 0.935), but there was a significant difference in SL due to period (F(1) = 50.2, P = 0.001). When observing the effect of SL on sex,

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Downloaded From: https://bioone.org/journals/Southeastern-Naturalist on 12 Jun 2020 Terms of Use: https://bioone.org/terms-of-use Access provided by University of Florida 2020 Southeastern Naturalist Vol. 19, No. 2 A. Flemming and L.M. Page the mean SL was 33.8 mm (SD = 0.36) for female specimens compared to 33.8 mm (SD = 0.38) for males. When observing the effect of SL between the 2 time periods, the mean SL was 35.8 mm (SD = 0.25) for period 1 compared to 31.7 mm (SD = 0.52) for period 2. Of the 475 Swamp Darters collected, 442 were identified to sex (220 males, 222 females), and 33 were classified as indeterminate. Three percent were 10–19 mm SL, 13% were 20–29 mm SL, 64% were 30–39 mm SL, and 20% were 40–50 mm SL. The largest Swamp Darter collected was a 50-mm SL, 59-mm TL male. There was not sufficient evidence to support a relationship between the proportion of male 2 and female Swamp Darters to month of the year data were collected (χ (20) = 14.7, P = 0.792). Thus, there was not a significant difference in the proportion of male to

Figure 3. Variation in temperature and mean GSI values of female and male E. f. barratti by month of collection.

Table 1. The fish diversity collected at Hatchet Creek. *Fishes collected only in July 2017 after heavy rains and probably entered Hatchet Creek from Newnans Lake. Percent occurrence is number of collections in which a species was collected.

Scientific name Common name % occurrence Gambusia holbrooki Girard Eastern Mosquitofish 100.0 Etheostoma f. barratti Swamp Darter 100.0 Lepomis macrochirus Rafinesque Bluegill 76.2 Lepomis gulosus (Cuvier in Cuvier and Valenciennes) Warmouth 76.2 Lepomis auritus (L.) Redbreast Sunfish 71.4 Heterandria formosa Girard Least Killifish 61.9 Noturus gyrinus (Mitchill) Tadpole Madtom 42.9 Elassoma okefenokee Böhlke Okefenokee Pygmy Sunfish 38.1

Elassoma evergladei Jordan Everglades Pygmy Sunfish 28.6 Aphredoderus sayanus (Gilliams) Pirate Perch 23.8 Notropis chalybaeus (Cope) Ironcolor Shiner 23.8 Fundulus chrysotus (Günther) Golden Topminnow 19.0 Esox americanus Gmelin Redfin Pickerel 19.0 Lepisosteus platyrhincus Dekay* Florida Gar 9.5 Hoplosternum littorale (Hancock)* Brown Hoplo 9.5

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female Swamp Darters due to month. Monthly variation in SL (Fig. 2) indicated that no E. f. barratti in Hatchet Creek live much beyond their first (and only) spawning season as an adult. A few individuals lived 1–2 months beyond the anniversary of their hatching, suggesting a maximum lifespan of 14 months.

Diet Stomach contents of 431 darters (0 empty) included a diverse array of organisms, with the composition varying by size class (Tables 2, 3; Fig. 4). Midge larvae (Chironomidae) and water fleas (Cladocera) were the most numerous food items for all size classes, with significance values of S = 42.4 and S = 57.4, respectively (Fig. 4, Table 4). The lowest rate of consumption occurred in July and March 2016, and the highest rate occurred in December 2016 (Tables 2, 3, 4; Fig. 5). Chi- ronomidae were consumed monthly throughout the study period, and Cladocera, Trichoptera, and Ephemeroptera were consumed nearly monthly. Approximately one-third of all Swamp Darters dissected during gut-content analysis contained at least 1 specimen of an apparently undescribed fluke (digenean trematode) of the genus Crepidostomum (Allocreadiidae). A total of 676 digeneans was removed from 130 Swamp Darters.

Reproduction The individual GSI values for males varied from 0.5 to 1.5, with the highest values occurring in November 2015, January–March 2016, and February–April 2017 (Fig. 3). In breeding males, testes were white, large, and spongy in appearance compared to translucent and stringy in non-breeding males. Large males became very dark in early spring with distinctive dark blotches, absent in females, in the membranes between the first 4 dorsal spines (Fig. 6). Tubercles were present on

Table 2. Mean number of each food item found in the stomach of E. f. barratti by size class (mm) of Swamp Darter. Numbers in parentheses are numbers of Swamp Darters in each size class.

Swamp Darter size class Taxon 10–19 (17) 20–29 (23) 30–39 (64) 40–49 (27) Cladocera 8.2 7.2 18.0 5.0 Chironomidae 4.5 5.0 4.5 3.8 Copepoda 1.9 0.1 1.4 0.4 Trichoptera 0.5 0.6 1.3 2.7 Amphipoda 0.4 0.2 0.1 0.0 Odonata 0.1 0.5 0.2 0.5 Annelida 0.0 0.0 0.0 0.0 Coleoptera 0.0 0.2 0.3 0.1 Diptera 0.0 0.0 0.0 0.4 Ephemeroptera 0.0 0.2 1.0 0.5 Gastropoda 0.0 0.0 0.0 0.0 Hemiptera 0.0 0.1 0.0 0.0 Insecta 0.0 0.0 0.0 0.1 Isopoda 0.0 0.0 0.1 0.2 Nematoda 0.0 0.0 0.0 0.0 Ostracoda 0.0 0.0 0.0 0.4

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- 0.2 - Jun (10) 31.9 - (11) May (8) 1.0 Apr - - - - 0.5 0.1 - 1.3 - - 0.1 0.5 - (9) 3.9 5.3 7.0 1.7 4.1 0.2 0.4 1.5 0.5 0.1 0.9 0.1 0.8 0.4 0.1 - 0.8 0.2 1.5 0.5 3.0 0.1 1.6 4.3 4.2 1.5 0.5 0.1 0.4 0.2 ------0.4 3.4 0.4 1.6 0.6 0.2 2.2 0.4 Feb Mar ------(6) (5) 1.7 0.2 0.3 0.3 0.3 0.2 Jan ------6.8 0.4 0.3 0.2 2.0 0.6 Dec ------(5) 4.2 0.3 0.8 0.4 Nov Chironomidae Table 3. Mean number of food organisms per stomach on each collecting date from November 2015 through May 2017. Numbers of specimens examined per stomach on each collecting date from November 2015 through May 2017. Numbers of specimens examined 3. Mean number of food organisms Table are in parantheses. Nematoda Odonata Ostracoda Cladocera Food items Food Isopoda Trichoptera Annelida Coleoptera Copepoda Ephemeroptera Amphipoda Diptera Gastropoda Hemiptera Insecta

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the branched rays and the membranes between the rays of the anal and pelvic fins of mature males during the reproductive season. Individual GSI values for females varied from 0.7 to 21.7, with the highest values occurring during the spawning period, January–April in 2016 and January– April in 2017 (Fig. 3). The highest GSI in 2016 was 19.3 for a female (34.8 mm SL) collected in February, and in 2017 it was 21.7 for a female (37.5 mm SL) collected in April. Females with mature ova (Table 5) had GSI values above 5 (Fig. 3). The number of mature ova in 18 females varied from 4 to 226 (Table 5). A weak relationship was observed between SL and the total number of ova (r = 0.451, P = 0.060). Additionally, a linear relationship was observed between mean GSI and monthly temperature, with normal distribution and equal variance. Moderately strong negative correlations between mean monthly temperature and GSI values were observed for both females (r = -0.698, P < 0.001) and males (r = -0.644, P = 0.003). The smallest specimen collected, a 13.1-mm-SL juvenile, had a morphology similar to an adult, but without the adult pigment pattern, incomplete squamation, and an incomplete lateralis system. The lateral line and scales were not visible,

Figure 4. Percentages of the 7 most common food items by size class of E. f. barratti. Num- bers in parentheses are numbers of Swamp Darters in each size class.

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Table 4. Significance of food items of E. f. barratti and E. f. fusiforme. Data for E. f. fusiforme from Schmidt and Whitworth (1979). Signicance (S) in diet Taxon E. f. barratti E. f. fusiforme Cladocera 57.4 51.5 Chironomidae 42.4 23.8 Trichoptera 17.9 <1.0 Copepoda 12.1 19.8 Ephemeroptera 8.9 <1.0 Odonata 5.1 - Amphipoda 3.5 14.4 Coleoptera 3.1 - Isopoda 1.5 - Diptera 1.0 - Ostracoda 1.0 18.7 Hemiptera 0.7 - Insecta 0.7 - Nematoda 0.5 - Gastropoda 0.3 - Annelida 0.2 -

Figure 5. Number of food items in all E. f. barratti stomachs by season; y-axis is a logarith- mic scale. Food items which occurred less than 3 times in any season were removed from this figure.

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Figure 6. Etheostoma f. barratti adult male, 46.0-mm-SL (top) and female, 44.0-mm-SL (bottom). Black bands in the 1st dorsal fin and a more pronounced dark pattern are present on the male. Photograph © Zachary Randall.

Table 5. Weights, lengths, and ova counts for individual females of E. f. barratti collected just prior to and during the reproductive season (January–May 2016, January–April 2017). Adjusted body weight is weight of female minus ovaries, stomach, and intestines.

Adjusted When body Gonad Standard Immature Intermediate Mature collected weight (g) weight (g) length (mm) ova ova ova January 16 0.62 0.10 42.5 920 174 4 January 16 0.39 0.04 37.6 614 72 24 February 16 0.59 0.05 42.1 1100 90 24 February 16 0.45 0.05 39.2 400 180 0 March 16 0.47 0.07 41.0 300 180 128 March 16 0.18 0.01 29.2 150 80 10 April 16 0.47 0.05 42.4 560 200 0 April16 0.54 0.06 42.0 740 320 0 May 16 0.78 0.06 46.8 480 0 190 May 16 0.50 0.04 40.2 280 300 0 January 17 0.44 0.04 38.7 680 214 0 January 17 0.45 0.05 39.6 720 162 2 February 17 0.38 0.01 37.0 600 272 0 February 17 0.47 0.07 41.0 460 220 140 March 17 0.35 0.03 38.0 600 20 18 March 17 0.44 0.03 38.8 580 168 0 April 17 0.40 0.07 38.5 800 240 198 April 17 0.39 0.09 37.5 540 26 226

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Discussion Comparisons with the New England population of E. f. fusiforme studied by Schmidt and Whitworth (1979) and Schmidt (1983) are in Table 6 and described below in more detail. In Hatchet Creek, as elsewhere (Page 1983, Schmidt 1983, Schmidt and Whitworth 1979), Swamp Darters were found in habitats with sandy and muddy substrates, emergent vegetation, and deep piles of undecomposed leaf and woody debris where they presumably hide from predators and find the invertebrates on which they feed.

Demography Schmidt and Whitworth (1979) found aging based on scale examination agreed well with the length–frequency distribution. Young-of-the-year were categorized as individuals <30 mm TL and lacking annuli. Yearlings were categorized as individuals

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Downloaded From: https://bioone.org/journals/Southeastern-Naturalist on 12 Jun 2020 Terms of Use: https://bioone.org/terms-of-use Access provided by University of Florida 2020 Southeastern Naturalist Vol. 19, No. 2 A. Flemming and L.M. Page with annuli (30.5–55 mm TL) or large breeding individuals collected in May and June but lacking annuli (32–46 mm TL), and the lifespan was estimated to be about 2 years. Although age could not be estimated using scale annuli in the present study, monthly variation in SL and GSI values indicated that Swamp Darters in the southern population live up to 14 months (Figs. 2, 3). Our largest recorded specimen of E. f. fusiforme measured 55 mm in TL and was thought to be in the second fall of life. Our largest specimen of E. f. barratti was a 59-mm-TL reproductively mature male in the first spring of its adult life. Although the northern subspecies may live longer, to 2 years, it reaches a smaller maximum size than the southern subspecies. Three (2 males and 1 female) of the 6 individuals of E. f. barratti placed in the aquarium on 1 March 2016 were still alive 18 months after their first spawning event. Although E. f. barratti rarely if ever lives longer than 14 months in nature, the species is capable of living at least 1.5 years when held in captivity where lack of predation and a steady food source contribute to long-term survival.

Table 6. Summary of life-history information on the Hatchet Creek population of E. f. barratti (this study) and that of a southern New England population of E. f. fusiforme (Schmidt 1983, Schmidt and Whitworth 1979).

Characteristic E. f. barratti E. f. fusiforme Principal habitat of and young Slow flowing water near stream Same as E.f.barratti; less and adults banks with live and dead often a rocky bottom littered vegetation; deep leaf piles with sticks and leaves Size at reaching sexual maturity ~25 mm SL (= 30 mm TL) ~30 mm TL Age at sexual maturity 10 –12 months 10 –12 months Sexual dimorphism During breeding season, male has Male same as E. f. barratti; black blotches on fins and body, female not described. tubercles on anal and pelvic fins; genital papilla enlarges on female Number of mature ova 4–226 Unknown/not studied Diameter of egg 1.5 mm Unknown/not studied Spawning period January to April April and May Spawning habitat Leaves of plants, logs Same as E. f. barratti Spawning position Both male and female inverted, Same as E. f. barratti head to head Egg guarding No; eggs abandoned after spawning Same as E. f. barratti Sex ratio 1:1 male to female Unknown/not studied Longevity in nature 1+ year ~2 years Maximum size 59 mm TL 55 mm TL Aggression In breeding males None reported Diet Aquatic insect immatures and Same as E. f. barratti but crustaceans with much less variety Parasites Crepidostomum sp., nematode None reported

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Diet Small individuals (10–29 mm SL) consumed a greater amount of smaller food items such as cladocerans and midge larvae than did larger individuals, which fed on larger food items such as caddisflies (Table 2). The diets of the larger size classes were more variable, presumably because their larger mouths facilitated consumption of a greater variety of food items. Seasonal variation in composition of the diet (Fig. 5) was probably more related to availability of particular food items than to variable characteristics of the population of Swamp Darters. For example, the abundance of cladocerans, a large component of the diet of Swamp Darters of all sizes (Fig. 4, Table 2), is dependent on the abundance of algae, itself dependent on weather (Choi et al. 2014). Our data do not indicate that seasonal variation in diet was closely related to variation in the size classes of Swamp Darters present (Figs. 2, 5). Schmidt and Whitworth (1979) reported only 6 food categories for E. f. fusiforme, compared to 17 found for E. f. barratti (Table 4). Both studies reported cladocerans to be the most significant food item, followed by midge larvae. InE. f. fusiforme, copepods and ostracods were the only other items with a significance value greater than 1.0. In E. f. barratti, copepods (S = 12.1) were also significant, but ostracods (S = 1.0) were much less significant than caddisflies (S = 17.9), mayflies (S = 8.9), and damselflies and dragonflies (S = 5.1).

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Downloaded From: https://bioone.org/journals/Southeastern-Naturalist on 12 Jun 2020 Terms of Use: https://bioone.org/terms-of-use Access provided by University of Florida 2020 Southeastern Naturalist Vol. 19, No. 2 A. Flemming and L.M. Page The greater complexity in the diet of E. f. barratti in Hatchet Creek relative to that of E. f. fusiforme could be the result of variation in invertebrate diversity and abundance in the study areas rather than selection of certain food items by the Swamp Darters. Hatchet Creek is much further south, and species-level diversity in many groups of organisms is higher at southern latitudes. However, studies of the relationship between insect diversity in streams and latitude have produced in- consistent results (Boyero et al. 2011, Vinson and Hawkins 2003), and the variation in invertebrate diversity in the 2 darter study streams may be more dependent on the ecological characteristics of the streams than on latitude. Whether the substan- tial differences in the diets of Swamp Darters in the 2 study areas is a function of the selection of certain food items by the fish studied or the result of variation in the diversity of food available would require a much larger study focused on measuring the diversity and abundance of invertebrates in the 2 streams. Schmidt and Whitworth (1979) hypothesized that the lower significance of midge larvae compared to that of cladocerans was because Swamp Darters could not physically contain more than 5 midge larvae in their stomachs, whereas they found the much smaller cladocerans to be as numerous as 140 per stomach. Al- though there was a high significance value for cladocerans in our study (S = 57.4), there was also a high significance value for midge larvae (S = 42.4). As many as 15 midge larvae were found in specimens of E. f. barratti.

Reproduction The weak relationship between SL and the total number of ova is likely a con- sequence of the type of spawning undertaken by E. fusiforme. As an egg-attaching species (Page 1983), E. f. barratti deposits 1–2 eggs on each successful mating bout over a period of a few minutes or hours, leaving some mature or maturing ova in the ovaries to be spawned later. This type of batch spawning leaves variable numbers of mature ova in the gonads, as suggested by the counts in Table 5. For example, 2 females—both ~38.0 mm SL—had substantially different numbers of intermediate and mature ova in March 2017. One individual had 600 immature, 20 intermediate, and 18 mature ova, while the other had 580 immature, 168 intermediate, and 0 mature ova. It is likely that the second individual had recently spawned, reducing the number of mature ova compared to the first individual. The minimum size for reproductive maturity for female E. f. barratti, defined as the length at which an individual had intermediate (developing) ova present, was ~25 mm SL. The negative correlation between temperature and mean GSI for females and males is likely a function of the early spawning period of this southern species of darter. Unlike E. f. fusiforme and other northern species which spawn later in spring (Page 1983), E. f. barratti spawns in late winter and early spring, from February to April. As gonads increase in size between November and February, temperatures are generally decreasing (Fig. 3). Thereafter, as temperatures increase from spring to summer (Feb- ruary to August), spawning occurs and then the size of gonads decreases. The spawning behavior observed was similar to the behavior described by Fletcher (1976) for E. f. fusiforme and for that of other species of darters that attach eggs to plants or other objects above the substrate (Page 1985). The change

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Acknowledgments Gratitude is expressed to Jason Fraser-Nash, William Fraser-Nash, Hannah Owen, and Cathleen Bester for their assistance in collecting specimens; to Danielle Diaz for her assistance in sorting and identifying invertebrates; to Kevin Love for his guidance with learning R programming and technical support; to Zachary Randall, Jarred Randall, Cathleen Bester, and Gustav Paulay for their assistance with photographing specimens; to Jann Macinnes for her assistance with statistical analyses; to Lillian Hendrick for her editorial feedback; to Kirsten Work for video footage of E. f. barratti spawning behavior; to Steven Ash Bullard and Anindo Choudhury for identification of the digenean parasite; to Master's Degree com- mittee members (for A. Flemming) Daryl Parkyn, Max Nickerson, and Jimmy Liao for their guidance; and to lab mates John Pfeiffer, David Boyd, Randy Singer, Rob Robins, Lindsay French, and Samara Nehemia for their support. Distributional data for the Swamp Darter were downloaded from iDigBio, supported by NSF EF 1115210 and DBI 1547229.

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