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Alternative spawning strategy and temperature for larval emergence of longfin dace (Agosia chrysogaster) in stream mesocosms.

The longfin dace (Agosia chrysogaster, Girard 1856) is a small (<80 mm in total length) cyprinid endemic to the Gila River drainage of southern Arizona, southwestern New Mexico, and northern Sonora, Mexico. The habitat of longfin dace ranges from clear, cool mountain streams to intermittent desert streams with sand or gravel substrate (Sublette et al., 1990). Longfin dace reach sexual maturity in their first year of life and live to a maximum age of 3 years (Sublette et al., 1990). The spawning season of longfin dace is protracted, lasting from December-July and peaking in April (Lewis, 1978), but little is known about the preferred temperature for spawning and larval emergence. Observations by previous investigators of longfin dace reproducing in streams in Arizona indicated that reproductively active males construct saucer-shaped depressions (saucer-nests) in fine to coarse sand along margins of streams at depths ranging from 5-20 cm (Kepner, 1982; Johnston and Page, 1992). Following construction of saucer-nests, females deposit eggs which are fertilized by males and then buried in sides of the saucer-nest during the act of spawning. Less frequently, longfin dace have been observed spawning over gravel. In these cases, saucer-nests are cleaned of fine sediments and detritus and are shallower than those constructed in sand (Minckley and Barber, 1971; Lewis, 1978). According to Johnston and Page (1992), construction of saucer-nests is a derived spawning strategy among cyprinids and no other cyprinid species is known to construct saucer-nests; however, little is known about how access to adequate spawning substrate influences reproductive strategy and spawning success of longfin dace. Our objectives were to test if longfin dace were able to spawn in the absence of sand substrate using an alternative spawning strategy and to identify the temperature at which larval emergence occurs. understanding the response of longfin dace to substrate and temperature might help predict how these species respond to changes in thermal regimes and sediment-dynamics associated with anthropogenic modifications to lotic systems.

We collected 16-25 individuals of age 1 or older longfin dace (>50 mm in total length) from each of four sites in the upper Gila River basin in southwestern New Mexico from 18-22 March 2013. These sites represented the diversity of habitats used by longfin dace in the upper Gila River basin. Two sites (Little Creek at 33[degrees]11034.5"N, 108[degrees]13038.3"W and Sapillo Creek at 33[degrees]2027.6"N, 108[degrees]13041.1 00W) were located on high-gradient tributaries of the Gila River. The other sites (Gila River 1 at 32[degrees]50053.5"N, 108[degrees]35036.2"W and Gila River 2 at 32[degrees]42056.8"N, 108[degrees]42038.9"W) were located further downstream on the lower-gradient mainstem of the Gila River near the town of Cliff, New Mexico. Brood stocks were transported to the stream mesocosms located at the Konza Prairie Biological Station in Riley County, Kansas. Fish from the four sites were stocked in four separate outdoor stream-mesocosms on 24 March 2013. Each mesocosm consisted of a 2.54-[m.sup.2] pool (1.8 m in diameter, 0.5 m in depth) connected to a 0.84-[m.sup.2] riffle (1.8 m in length, 0.45 m in width, 0.25 m in depth) through which water was circulated with an electric motor at 4-6 L/s and a riffle current velocity of 6-8 cm/s. Substrate consisted of quarried river rock (mean diameter = 51.8 mm, SE = 4.8 mm). See Matthews et al. (2006) for a detailed description of mesocosms. Each mesocosm was filled with water from a nearby spring 12 days prior to stocking, and water was replaced at a rate of 10 L/h throughout the study. Temperature was recorded every 60 min in the four mesocosms from 10 April-28 May 2013 using submersible temperature-loggers (Onset Computer Corporation, Bourne, Massachusetts). Temperature differed among mesocosms by <0.9[degrees]C throughout the experiment. Mesocosms were observed daily for the presence of saucer-nests, larvae, or both from 24 March-28 May 2013 after which brood stock were euthanized with a lethal dose of MS-222 (tricane methanosulfonate). From mesocosms in which larvae were observed, 10 individuals/ mesocosm were euthanized for measurement of length and the remaining live larvae were collected and used in a separate study.

Mortality of brood stock was low ([less than or equal to] 2 individualsmesocosm) throughout the duration of the study. Larvae emerged from three of the four mesocosms at a mean total length of 5.9 mm (SE = 0.09). Larvae emerged from mesocosms stocked with fish from the two sites in the Gila River on 30 April 2013 at temperatures (mean hourly temperature for 3 days prior to larval emergence) of 23.6 and 24.0[degrees]C, respectively. Larvae from Little Creek emerged on 9 May 2013 at a temperature of 19.2[degrees]C (Fig. 1). By comparison, water temperatures throughout the upper Gila River basin during the previously reported peak spawning month of April (Lewis, 1978) typically range from 9.4-19.0[degrees]C (JEW, pers. observ.). No evidence of saucer-nests, cleaning of cobble, or any other sign of preparation of the substrate by adults was observed in the mesocosms at any time during the study. This observation suggests that longfin dace can spawn over cobble substrate with no pre-spawning preparation of the substrate, which demonstrates that this species can spawn using an alternate and more primitive spawning strategy (Johnston and Page, 1992) and successfully produce viable larvae. Spawning may have been accomplished via broadcasting of eggs or depositing eggs in the crevices between the cobbles; however, direct observations of the spawning act would be necessary to confirm which behavior was used in this environmental context. Similar switching of spawning strategies has been observed in other cyprinids when provided with different media for spawning (Vives, 1993) and suggests that longfin dace may be more adaptable with regard to spawning strategy than previously reported (Minckley and Barber, 1971; Lewis, 1978; Johnston and Page, 1992). We cannot assert that this alternate strategy is preferred by longfin dace from these sites in the upper Gila River because the brood stock in our experimental mesocosms did not have access to sand substrate where construction of saucer-nests typically takes place (Minckley and Barber, 1971; Lewis, 1978). Previous to this study, saucer-nests of longfin dace have been observed at all four sites (KBG, pers. observ.), indicating that this species in these locations uses the typical saucer-building strategy when sand substrate is accessible. Two factors may account for the lack of construction of saucer-nests in our mesocosms. First, the large cobble substrate in the mesocosms may have precluded longfin dace from constructing saucer-nests because cobbles were too large to move. Further observation of spawning behavior, particularly by males prior to and during the act of spawning, would be necessary to test this hypothesis. Second, release from egg predation or the lack of siltation in the mesocosms may have circumvented the benefit of nest-spawning observed in other cyprinids (Peoples et al., 2011). Further experimental manipulation of substrate and nest-predators would be necessary to test this hypothesis. Regardless of the proximate and ultimate causes, flexibility in spawning behavior and use of substrate may explain the success of this species in rapidly colonizing recently rewetted reaches of streams and occupying a variety of habitats in desert streams (Minckley and Barber, 1971). Moreover, this species may be able to adapt to changes in sediment-dynamics, such as the trapping of sediments behind dams.

Submitted 7 December 2013. Acceptance recommended by Associate Editor Mark Pyron 27 February 2014.

We thank J. Perkin for assistance with collection of brood stock and K. Kirkbride for assistance with observations of brood stock. This study was funded by research grants from the Southwestern Association of Naturalists, Kansas Academy of Science, Prairie Biotic Research Inc., National Science Foundation (DEB no. 1311183) and Bureau of Reclamation Water Smart program. Longfin dace were collected and housed under the permission of the New Mexico Game and Fish Department (permit no. 3351), Konza Prairie Biological Station (permit no. 221), and the Institutional Animal Care and Use Committee (permit no. 2996).

LITERATURE CITED

JOHNSTON, C. E., AND L. M. PAGE. 1992. The evolution of complex reproductive strategies in North American stream minnows (Cyprinidae). Pages 600-621 in Systematics, historical ecology, and North American freshwater fishes (R. L. Mayden, editor). Stanford University Press, Stanford, California.

JOHNSTON, C. E. 1994. Nest association in fishes: evidence for mutualism. Behavioral Ecology and Sociobiology 35:379-383.

KEPNER, W. G. 1982. Reproductive biology of longfin dace (Agosia chrysogaster) in a Sonoran Desert stream. M.S. thesis, Arizona State University, Tempe.

LEWIS, M. A. 1978. Notes on the natural history of the longfin dace, Agosia chrysogaster, in a desert rheocrene. Copeia 1978:703-705.

MATTHEWS, W. J., K. B. GIDO, G. P. GARRETT, F. P. GELWICK, J. G. STEWART, AND J. SCHAEFER. 2006. Modular experimental rifflepool stream system. Transactions of the American Fisheries Society 135:1559-1566.

MINCKLEY, W. L., AND W. E. BARBER. 1971. Some aspects of the biology of the longfin dace, a cyprinid fish characteristic of streams in the Sonoran desert. Southwestern Naturalist 15:459-464.

PEOPLES, B. K., M. B. TAINER, AND E. A. FRIMPONG. 2011. Bluehead chub nesting activity: a potential mechanism of population persistence in degraded stream habitats. Environmental Biology of Fishes 90:379-391.

SUBLETTE, J. E., M. D. HATCH, AND M. SUBLETTE. 1990. The fishes of New Mexico. University of New Mexico Press, Albuquerque.

VIVES, S. P. 1993. Choice of spawning substrate in red shiner with comments on crevice spawning in Cyprinella. Copeia 1993:229-232.

MATTHEW J. TROIA, * JAMES E. WHITNEY, AND KEITH B. GIDO

Division of Biology, Kansas State University, Manhattan, KS 66506

Present address of MJT: Oak Ridge National Laboratory, Oak Ridge, TN 37830

* Correspondent: troiamj@ornl.gov
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Author:Troia, Matthew J.; Whitney, James E.; Gido, Keith B.
Publication:Southwestern Naturalist
Article Type:Report
Geographic Code:1USA
Date:Jun 1, 2014
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