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Life-history Aspects of Thoburnia rhothoeca (Torrent Sucker) in Southwestern Virginia
Alexandra Tarasidis and Steven L. Powers

Northeastern Naturalist, Volume 21, Issue 1 (2014): 108–118

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Northeastern Naturalist 108 A. Tarasidis and S.L. Powers 22001144 NORTHEASTERN NATURALIST 2V1(o1l). :2110,8 N–1o1. 81 Life-history Aspects of Thoburnia rhothoeca (Torrent Sucker) in Southwestern Virginia Alexandra Tarasidis1 and Steven L. Powers1,* Abstract - Life-history aspects of Thoburnia rhothoeca (Torrent Sucker) were investigated using specimens from the Roanoke College Ichthyological Collection and from recent collections to examine age, growth, food habits, and reproductive cycle. The largest specimen collected was a female aged 37 months, of 165.1 mm standard length and 73.73 g total weight. Spawning occurs from February to May, with a mean of 782.6 mature oocytes, and an oocyte diameter of up to 2.02 mm. Sexual maturity is reached at 1–2 years of age, with a maximum lifespan of between 3 and 4 years. Chironomidae and detritus composed the bulk of the diet. Mass, number, and variety of food items peaked in spring and early summer. Introduction Thoburnia rhothoeca (Thoburn) (Torrent Sucker) was described by Thoburn in 1896 from specimens collected at an uncertain locality, most likely in the Upper James River drainage in southwestern Virginia (Jenkins and Burkhead 1994, Jordan and Evermann 1896). It inhabits swift creeks and streams of the James, Roanoke, Potomac, Rappahannock, and Chowan drainages of central Virginia, and it is distinguished from other catostomids within its range by its torpedo-shaped body with ventrolaterally-blotched coloration and plicate-papillose lips (Jenkins and Burkhead 1994). It is sister to Thoburnia hamiltoni Raney and Lachner (Rustyside Sucker, Chen and Mayden 2012), but the monophyly of Thoburnia is uncertain due to the ambiguous phylogenetic position of Thoburnia atripinne (Bailey) (Blackfin Sucker, Harris et al. 2002). The hypothesized sister relationship of Thoburnini to Moxostomatini (Chen and Mayden 2012, Harris et al. 2002), suggests that a clear understanding of the life-history of Thoburnia is key to interpreting the considerable variation in life-history of the Moxostomatini in an evolutionary context. Despite the need for additional data to clarify relationships within the genus, little has been published on the life-history of Thoburnia. Timmons et al. (1983) published a thorough life-history study of Thoburnia atripinne, but investigations of T. hamiltoni and T. rhothoeca are less complete. Information on their biology is restricted to a report to the US Fish and Wildlife Service (R.E. Jenkins, Roanoke College (RC), Salem, VA, unpubl. data); information in Jenkins and Burkhead (1994) based on 21–22 specimens of each species; and papers based on a few collections made primarily in spring, and investigating only specific components of life-history (Raney and Lachner 1946), and on other aspects of stream ecology (Flemer and Woolcott 1966, Neves and Pardue 1983). Information about the 1Roanoke College, 221 College Lane, Salem, VA 24153. Corresponding author - powers@ roanoke.edu. Manuscript Editor: Rudolf G. Arndt Northeastern Naturalist Vol. 21, No. 1 A. Tarasidis and S.L. Powers 2014 109 diet and the gonad condition for T. rhothoeca is particularly sparse; quantitative comparisons of specimens collected throughout the year do not exist. The primary objective of this study was to document these and other aspects of the life history of T. rhothoeca based on specimens collected in all months of the year. Methods We examined Thoburnia rhothoeca specimens (n = 314) from the Roanoke College Ichthyological Collection and from recent collections. The recently collected specimens were those we obtained on 18 November 2010 using a 3.3-m x 1.3-m seine with 9.5-mm mesh and a Smith-Root model 24 backpack electrofisher. We initially preserved all specimens examined in 10% formalin, rinsed them with water, and transferred them to 45% isopropanol for long-term storage. Collection details for our specimens—collection sites, collection dates, numbers of specimens taken, collector field numbers—are available from the authors upon requ est. We collected and analyzed data largely following recently published fish lifehistory investigations (Barton and Powers 2010, Edberg and Powers 2010, O’Kelley and Powers 2007). We measured standard length (SL) of preserved T. rhothoeca specimens to the nearest 0.01 mm using a digital caliper. We blotted specimens dry, and measured the total weight (TW), eviscerated weight (EW), and gonad weight (GW) to the nearest 0.001 g using a digital analytical balance. We used Data Desk 6.0 (Data Description, Inc., Ithaca, NY) with alpha equal to 0.05 for all statistical analyses. We present results of regressions with independent variables listed first and dependent variables second, unless otherwise noted. We plotted SL and EW against month. We assigned specimens collected within a single month with gaps of ≥10 mm in the SL to different age classes (e.g., for January, all specimens were 47.74–87.83 or 117.75–129.54 mm SL with each cluster lacking gaps approaching 10 mm). If 10-mm gaps in SL did not occur in a particular month, we delineated age classes by extrapolating lines from gaps in adjacent months. For selected specimens, we removed three scales from the right dorsolateral portion of the body, mounted them on a slide and examined them under 40x magnification for the presence of annuli. Annulus formation occurs at the transition from a period of slow growth to rapid growth that occurs each spring; annuli persist on scales throughout the life of a fish and are used to corroborate hypothesized age classes (Bond 1996). If the three scales removed did not have the same number of annuli, we continued removing scales until both authors arrived at a consensus on the number of annuli. We examined 4 specimens from February, 1 from April, 2 from June, 2 from August, 2 from October, and 2 from November for annuli and used the results to perform a linear regression of age in months and SL to further corroborate the age class extrapolations by comparing r2 values of models for ambiguous specimens. For example, if different methods of aging produced a different age in months for a single specimen, we assigned whichever value produced a higher r2 in a regression of age in months and SL. To determine reproductive state, we calculated gonadosomatic index (GSI) by dividing GW by EW to allow for quantitative comparison of the proportion of the Northeastern Naturalist 110 A. Tarasidis and S.L. Powers 2014 Vol. 21, No. 1 body mass represented by the gonads. We used one-way analysis of variance to test for differences in GSI among specimens collected from different months. In gravid females, we counted greatly enlarged (>0.75 mm in diameter), fully yolked, mature oocytes, and we measured 5 representative oocytes to provide an approximation of ovum size and number (Heins and Baker 1988). We used regression of SL as a predictor of number of mature oocytes to test the influence of specimen size on fecundity. Due to the high GSI values we calculated for specimens collected in February–May, and a precipitous decline in June, we assume spawning occurred in the spring of each year, and assigned March as the month of spawning for estimating specimen age. We classified specimens less than 12 months of age as age 0+, specimens of 12–23 months as age 1+, specimens 24–36 months as age 2+, and specimens older than 36 months as age 3+. We calculated the proportion of the total number of specimens collected represented by each age class to approximate the age-class distribution of the population. We tested differences in lifespan among sexes using a Mann-Whitney test of age in months. To examine the relationship between length and weight, we did regressions by least sum of squares for SL and the natural log of EW We opened the anterior third of the gastrointestinal tract of all specimens and removed and weighed its contents using a digital analytical balance, and recorded weights to the nearest 0.001 g. For specimens with empty guts, we recorded the weight of the gut contents as 0. We counted food items and identified them to the lowest taxonomic category possible following Merritt and Cummins (1996) and Thorp and Covich (1991). Due to mastication by pharyngeal teeth, we were unable to identify most food items below the level of order or family. To test for differences in feeding throughout the year, we performed one-way analysis of variance on weight of gut contents/EW and for variety of food items. To test the influence of size on feeding, we performed regressions by least sum of squares for EW and weight of gut contents as well as for EW and variety of gut contents. Results The smallest specimen examined was a female of 29.22 mm SL and 0.402 g TW taken in December. The largest specimen examined was a female of 165.1 mm SL and 73.726 g TW taken in April. The July collection provided the earliest capture of young-of-the year specimens. These specimens ranged from 38.62 to 41.3 mm SL (mean = 39.96, SD = 1.9). Standard length and EW by month are presented in Figs. 1 and 2, respectively. Standard length increased with the natural log of EW (r2 = 94.3%, P < 0.0001) and is represented by the model SL (0.039) -1.32 = ln EW. The ratio of male to female specimens collected was 0.9:1, with no sexual size dimorphism detected in SL (P = 0.12); the mean SL for females and males was 85.26 and 77.69 mm, respectively. Scales from the two largest specimens (149.8 and 165.1 mm SL) examined contained three annuli each, while the smallest specimens examined for annuli (37.56 and 51.39 mm SL) contained no annuli or a single annulus located at the edge of the scale. Standard length increased with age in months (r2 = 84.1%, P < 0.0001) and is represented by the model SL = age in months(3.02) Northeastern Naturalist Vol. 21, No. 1 A. Tarasidis and S.L. Powers 2014 111 Figure 1. Standard length (SL) in mm by month (1 = January, 2 = February, etc.) for Thoburnia rhothoeca. Figure 2. Eviscerated weight (EW) in g by month (1 = January, 2 = February, etc.) for Thoburnia rhothoeca. Northeastern Naturalist 112 A. Tarasidis and S.L. Powers 2014 Vol. 21, No. 1 + 30.44 (Fig. 3). Of all specimens collected, 36.1% were age 0+, 39.4% were age 1+, 23.2% were age 2+, and 1.2% were age 3+. Hypothesized maximum age of specimens captured was a female of 39 months; age did not differ between the sexes (P = 0.66). Mean female GSI was not uniform across all months (F = 5.43, P < 0.0001). Mean female GSI and individual female GSI were greatest in February (0.10, SD = 0.034 and 0.15, SL = 129.33 mm, respectively); lowest mean GSI (0.0083, SD = 0.0086) was in July (Fig. 4). Mean male GSI was not uniform across all months (F = 3.48, P = 0.0003). The highest mean male GSI (0.034, SD = 0.001) was in April, and the highest individual male GSI was from a specimen collected in May (0.061, SL = 71.06 mm). The lowest male GSI values were from June to August, with means of 0.0087 (SD = 0.0096), 0.0040 (SD = 0.0026), and 0.0019 (SD = 0), respectively (Fig. 5). Mature oocytes measured up to 2.02 mm in diameter, and the relationship between SL and number of oocytes was not significant (r2 = 8%, P = 0.27). The mean number of mature oocytes in mature females was 782.6 (SD = 627.1), with the largest number of oocytes observed in a 32-month old female (135.58 mm SL) that had 5174 oocytes. Weight of gut contents (F = 4.61, P < 0.0001) was not uniform across all months, and the greatest mean weight of gut contents was in June (0.10 g, SD = 0.06) and Figure 3. Standard length (SL) in mm by age in months for Thoburnia rhothoeca. Northeastern Naturalist Vol. 21, No. 1 A. Tarasidis and S.L. Powers 2014 113 April (0.081 g, SD = 0.15), while the lowest mean weight was found in August (0.00025 g, SD = 0.0005) and December (0.007, SD = 0.012). The lowest number of items per specimen (0.25) and highest percent of empty guts (75%) occurred in August. The largest number of food items per specimen was in March (48.43; Table 1). Chironomidae was the most abundant individually identified food item, comprising 82.5% of all food items, and was found in all months except August. Detritus was found in 99.97% of specimens containing gut contents and was found in every month. Other food items identified from specimens are listed in Table 1. Of all specimens examined, 8% of GI tracts were empty. The variety of food items Figure 4. Gonadosomatic index (GSI) by month (1 = January, 2 = February, etc.) for Thoburnia rhothoeca females. Figure 5. Gonadosomatic index (GSI) by month (1 = January, 2 = February, etc.) for Thoburnia rhothoeca males. Northeastern Naturalist 114 A. Tarasidis and S.L. Powers 2014 Vol. 21, No. 1 Table 1. Food items identified by month of collection and related stomach content data for Thoburnia rothoeca collected between 1963 and 2012. Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total % of total Detritus 6 11 13 7 25 7 35 1 47 15 33 16 216 Acarina 2 2 0.085 Branchiopoda 1 1 2 0.085 Insecta Unidentified parts 1 1 2 2 6 0.26 Coleoptera larvae 1 1 0.043 Diptera Diptera pupae 9 6 2 1 18 1.5 Blephariceridae 2 2 0.085 Chironomidae 25 48 741 206 282 173 233 204 28 13 1 1954 82.5 Culicidae 1 1 0.043 Simulidae 5 2 2 11 1 40 61 2.5 Ephemeroptera 2 2 3 7 11 1 26 1.1 Hemiptera 1 1 0.043 Plecoptera 2 2 4 0.17 Trichoptera 3 1 3 1 3 1 12 0.51 Unidentified eggs 3 1 4 0.17 Sand 2 2 4 1 17 4 1 4 35 1.5 Number empty 2 1 1 0 0 0 5 3 1 2 0 4 19 0.8 Total items 36 62 775 228 323 193 303 1 267 49 53 58 2348 # of stomachs 11 12 16 7 25 7 40 4 49 17 33 20 241 Items/stomach 3.27 5.17 48.43 32.57 12.92 27.57 7.58 0.25 5.45 2.88 1.6 2.9 % empty 18.18 8.33 6.25 0 0 0 12.5 75 2.04 11.76 0 20 Northeastern Naturalist Vol. 21, No. 1 A. Tarasidis and S.L. Powers 2014 115 (F = 10.18, P < 0.0001) was not uniform across all months, with April having the highest variety of food items (mean = 3.0, SD = 1.4) and August having the lowest (mean 0.25, SD = 0.5). Weight of gut contents increased with EW (P < 0.0001), but there is not a strong relationship between the two variables (r2 = 10.5%). Variety of food items also increased slightly with EW (P = 0.003), but the relationship is weak (r2 = 3.5%). Discussion Thoburnia rhothoeca appears to grow to a maximum size of 165 mm SL in a pattern well predicted by the models SL(0.039) -1.32 = ln EW and SL = age in months(3.02) + 30.44. Scales indicate that annuli form near the end of winter or early spring as suggested by Raney and Lachner (1946). The largest T. rhothoeca specimen examined (165.1 mm SL) had three annuli indicating, along with length and weight frequencies, that four different age classes were present in our samples. Neves and Pardue (1983) suggested that there were five age classes in the T. rhothoeca population they examined in a small, cold-water (less than 18 °C) stream in Rockbridge County, VA (from which none of our specimens originated). Raney and Lachner (1946) suggested T. rhothoeca males live up to five years and females to seven years, based exclusively on examination of scales. The differences among these studies may be due to different maximum ages in different populations, or to the well-documented problems in estimating maximum age of fishes (see Summerfelt and Hall 1987). Our hypothesized maximum age of between three and four years is consistent with the hypothesized maximum age of T. atripinne (Timmons et al. 1983), T. hamiltoni (Jenkins and Burkhead 1994), and other similarly-sized Catostomidae such as Hypentelium etowanum (Jordan) (Alabama Hog Sucker) and Moxostoma cervinum (Cope) (Blacktip Jumprock) (see Bentley and Powers, in press; O’Kelley and Powers 2007). The low proportion of age 3+ specimens suggests that very few individuals survive to the maximum age, as is typical of most fishes (Matthews 1998). However, the low number of juvenile specimens collected and present in collections may be due in part to the difficulty of collecting smaller specimens using a seine with 9.5-mm mesh because small, young fish may pass through the mesh. Another possible explanation for the relatively few small specimens housed in the RC collection is the historical retention of larger specimens, which are more useful for systematic studies (R.E. Jenkins, Roanoke College, Salem, VA, pers. comm.), thus leading to the disproportionate release of juveniles. The GSI values for both males and females were highest from late winter to early spring. The precipitous drop in GSI values in June and low values through the summer suggest that spawning occurs from February to May and is finished by June. Thoburnia rhothoeca specimens in reproductive condition during late March and early April were reported by Raney and Lachner (1946) and from late February to late May by Jenkins and Burkhead (1994). Our finding of increased GSI in both males and females during the fall months initially appears puzzling because all previous reports suggest that Thoburnia spawns in late winter or early spring (Jenkins and Burkhead 1994, Raney and Lachner 1946, Timmons et al. 1983). However, the Northeastern Naturalist 116 A. Tarasidis and S.L. Powers 2014 Vol. 21, No. 1 only mention of specimens examined from fall or winter months by these authors is a report of a non-tuberculate male collected in December that was emitting milt (Timmons et al. 1983). While there is little evidence that Thoburnia spawn any time other than late winter to spring, O’Kelley and Powers (2007) reported an increase in GSI during fall for Hypentelium etowanum. Additionally, Moxostoma cervinum gonads dramatically increase in size during the fall prior to spring spawning (Bentley and Powers, in press). The report of clearly mature Moxostoma ariommum Robins and Raney (Bigeye Jumprock) from September to April (Jenkins and Burkhead 1994) also indicates increased size of gonads during the fall months. Collectively, our data and the work of others suggest that for small catostomids, a period of low GSI during the summer is normally followed by an increase in GSI in the fall prior to actual spawning in the subsequent late winter or spring. Sexual maturity apparently begins for some T. rhothoeca as they approach one year of age because two of the females we examined were approximately one year of age and had mature oocytes and elevated GSI values (>0.08), and three males approximately one year old had elevated GSI values (>0.02). However, the vast majority of specimens approximately one year old did not have mature oocytes or elevated GSI values, and it appears that sexual maturity usually does not occur until the fish approach two years of age. Because we found the maximum lifespan to be approximately 39 months, it appears that most T. rhothoeca that reach maximum age will go through two spawning cycles, with a very small number of individuals that spawn at approximately one year old spawning three times. Raney and Lachner (1946) suggested that spawning does not occur until age 2 or 3 years for males and 3 years for females, but this difference between their findings and ours can likely be attributed to differences in hypothesized age of specimens because their reported average of 71.1 mm TL for specimens 2 years of age is within the range of specimens hypothesized to be 1 year of age in our study and the Timmons et al. (1983) study of T. atripinne. The maximum number (5174) of mature oocytes in a single specimen found in our study is much larger than the 1749 eggs reported by Raney and Lachner (1946) and the 1755 eggs reported by Timmons et al. (1983). The difference is most likely explained by our inclusion of all oocytes of larger than 0.75 mm, whereas the previous authors counted only what they considered to be maturing eggs. The maximum oocyte diameter of 2.02 mm in our study is slightly smaller than the maximum egg size of 2.5 mm as reported by Timmons et al. (1983). Thoburnia rhothoeca feeding varies widely throughout the year. The mass, variety, and the number of food items per specimen peaked in the spring and the early summer. Increased feeding coincides with greater energetic requirements associated with spawning, and the higher metabolic rate associated with increased water temperatures. The prevalence of Chironomidae in the diet of T. rhothoeca (82.5% of food items) is less than the 100% occurrence of Chironomidae in T. atripinne as noted by Timmons et al. (1983). These numbers may indicate selective feeding by Thoburnia, but they may also be explained by the high density of chironomids (>20,000 individuals/m2) present in the substrate of streams (Benke et Northeastern Naturalist Vol. 21, No. 1 A. Tarasidis and S.L. Powers 2014 117 al. 1984). The inferior mouth of Thoburnia suggests that feeding occurs at or near the substrate, as is typical of most Catostomidae (Jenkins and Burkhead 1994). A large proportion (89.63%) of specimens examined for this study contained detritus. Jenkins and Burkhead (1994) reported that detritus composed the bulk of the diet of T. hamiltoni, and detritus was found in 67% of the T. atripinne examined by Timmons et al. (1983). Throughout the year, chironomids and detritus make up the bulk of the diet of T. rhothoeca, but larval blackflies, mayflies, and caddisflies are also common foods during the non-winter months. The presence of these other food items in our samples may indicate a decrease in selectivity of feeding during the warmer months, but it may also indicate that as feeding increases, the variety of items eaten is also likely to increase even if selectivity does not change. The significant relationships between weight of gut contents and EW, and variety of food items and EW suggest that as T. rhothoeca grow, they consume more and a greater variety of foods. However, the very low r2 values associated with these relationships suggest that any changes in diet throughout the life of T. rhothoeca are not pronounced. Acknowledgments We thank R.E. Jenkins and his previous students for access to specimens in the Roanoke College Ichthyological Collection. All other fish were collected under a Virginia Department of Game and Inland Fisheries Scientific Collecting Permit issued to S.L. Powers. We also thank J.S. Bentley for help in collecting specimens for this study. Several anonymous readers made helpful comments during manuscript review. This study was part of an undergraduate independent research project at Roanoke College by A. Tarasidis. Literature Cited Barton, S.D., and S.L. Powers. 2010. Life-history aspects of the Cherokee Darter, Etheostoma scotti (Actinopterygii: Percidae), an imperiled species in northern Georgia. Southeastern Naturalist 9(4):687–698. Benke, A.C., T.C. Van Arsdall, Jr., D.M. Gillespie, and F.K. Parrish. 1984. Invertebrate productivity in a subtropical blackwater river: The importance of habitat and life history. Ecological Monographs 54(1)25–63. Bentley, J.S., and S.L. Powers. In press. Life-history aspects of Moxostoma cervinum (Blacktip Jumprock) in the Roanoke River, Virginia. Northeastern Naturalist. Bond, C.E. 1996. Biology of Fishes. Second Edition. Saunders College Publishing. Fort Worth, TX. 750 pp. Chen, W.J., and R.L. Mayden. 2012. Phylogeny of suckers (Teleostei: Cypriniformes: Catostomidae): Further evidence of relationships provided by the single-copy nuclear gene IRBP2. Zootaxa 3586:195–210. Edberg, K.M., and S.L. Powers. 2010. Life-history aspects of the Southern Studfish, Fundulus stellifer (Actinopterygii: Fundulidae) in northern Georgia. Southeastern Naturalist 9(1):119–128. Flemer, D.A., and W.S. Woolcott. 1966. Food habits and distribution of the fishes of Tuckahoe Creek, Virginia, with special emphasis on the Bluegill, Lepomis m. macrochirus Rafinesque. Chesapeake Science 7:75–89. Northeastern Naturalist 118 A. Tarasidis and S.L. Powers 2014 Vol. 21, No. 1 Harris, P.M., R.L. Mayden, H.S. Espinosa Perez, and F. Garcia de Leon. 2002. Phylogenetic relationships of Moxostoma and Scartomyzon suckers (Catostomidae) based on mitochondrial cytochrome b sequence data. 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Life-history of the Alabama Hog Sucker, Hypentelium etowanum (Actinopterygii: Catostomidae), in northern Georgia. Southeastern Naturalist 6(3):479–490. Raney, E.C., and E.A. Lachner. 1946. Age and growth of the Rustyside Sucker, Thoburnia rhothoeca (Thoburn). American Midland Naturalist 36:675–681. Summerfelt, R.C., and G.E. Hall (Eds.). 1987. Age and Growth of Fish. Iowa State University Press, Ames, IA. 544 pp. Thorp, J.H., and A.P. Covich. 1991. Ecology and Classification of North American Freshwater Invertebrates. Academic Press, Inc. San Diego, CA. 911 pp. Timmons, T.J., J.S. Ramsey, and B.H. Bauer. 1983. Life history and habitat of the Blackfin Sucker Moxostoma atripinne (Osteichthyes: Catostomidae). Copeia 1983(2):538–541.