1 Abstract 2 The Paddlefish Polyodon spathula is a ram suspension feeding planktivore that resides in fresh 3 water habitats. While there are numerous hypotheses about the external morphology of the Paddlefish, 4 none truly support a definite finding. 5 Context and Content 6 The Paddlefish Polyodon spathula is classified as the following: Kingdom: Animalia, Phylum: 7 Chordata, Class: Actinopterygii, Order: Acipenseriformes, Family: Polyodontidae, Genus: Polyodon, 8 Species: spathula (Ross and Brenneman 2001, Starnes 2016). The order Acipenseriformes includes the 9 sturgeons (family Acipenseridae) and the paddlefishes (family Polyodontidae; Ross and Brenneman 10 2001). The Chinese Paddlefish, Psephurus gladius, is the only other species in the family Polyodontidae 11 (Wilkens and Hofmann 2007) and resides exclusively in China’s Yangtze River (Ross and Brenneman 12 2001). There are a variety of common names associated with the species such as Paddlefish, Spadefish, 13 Spoonbill Catfish, or Duck-Billed Catfish (Ross and Brenneman 2001). Walbaum portrayed the Paddlefish 14 as a shark in 1792; but was corrected by Lacepedѐ in 1797, who classified Paddlefish in the genus 15 Polyodon (McKinley 1984). 16 General Characteristics 17 Paddlefish are an ancient species and exhibit less derived traits. They are typically characterized 18 by the presence of heterocercal caudal fins and the absence of teeth in adults (Ross and Brenneman 19 2001). Polyodon means ‘many teeth’, while Adult Paddlefish do not have teeth, but do have many gill 20 rakers which they use to filter zooplankton from the water column (Ross and Brenneman 2001) and 21 spathula means ‘flat piece’, referring to the long snout, or rostrum, which makes up around one third of 22 the total body length of adults (Wilkens and Hofmann 2007). For the most part Paddlefish have a 23 smooth shark-like exterior appearance and possess a small amount of scales located on the operculum 24 and the bottom lobe of the tail. The Paddlefish skeleton consists mostly of cartilage with the jaws being 25 the only exception (Ross and Brenneman 2001). 26 Distribution 27 Ross and Brenneman (2001) documented Paddlefish in the: Noxubee River system, Pearl 28 drainages of the Gulf of Mexico Basin, and areas of the Mississippi River Basin. Paddlefish have also been 29 documented throughout the Licking, Tennessee, Mississippi, Ohio, Kentucky, and Cumberland rivers and 30 as far north as the Great Lakes (Burr 1980). 31 Form and Function 32 The main theory pertaining to the rostrum of Paddlefish is that it is used as an electrosensory 33 apparatus for locating plankton in aquatic habitats (Wilkens and Hofmann 2007) While earlier writers 34 suggested that the Paddlefish used the elongate rostrum to dig into the benthic layer to locate items for 35 nourishment, later scientific research confirmed that they feed primarily on plankton (Ross and 36 Brenneman 2001). 37 Paddlefish total length is often measured using eye-fork length, taken from the eye to the fork 38 of the tail (Ross and Brenneman 2001). The rostrum of fingerlings and smaller fish account for most of 39 the body length which may increase error if measuring total length from the paddle to the fork of the 40 tail. Eye-fork length (EFL) is the best method for determining an accurate total body length (Ross and 41 Brenneman 2001). 42 Ontogeny and Reproduction 43 Paddlefish journey upstream each spring to spawn. Upon locating areas having an average water 44 temperature of 12ᵒC, Paddlefish spawn over coarse gravel (Ross and Brenneman 2001). The timing for 45 spawning varies with location as more northern populations mature later and have differing thermal 46 regimes. There appears to be a positive relationship between seasonally warming waters and adult 47 Paddlefish abundance (Miller et al 2011), suggesting spawning depends on water temperature. 48 Initially, eggs float, but once the fertilization process is completed the eggs sink, sticking to hard 49 surfaces for up to one week. Eggs hatch when the water temperature ranges from 18-21ᵒC (Jennings 50 and Zigler 2000). Maturity rates seem to vary by location, with males tending to mature at age six (Ross 51 and Brenneman 2001). In most cases females mature later in life around age nine, although a study 52 concluded that half matured by age nine and half matured at age ten (Reed et al 1992). 53 Conservation 54 Paddlefish roe provides a domestic alternative to purchasing expensive imported sturgeon 55 caviar (Clarke-Kolaks et al 2009). However, increased poaching to harvest eggs, driven by the 56 compensation fishers receive for roe, has led to rising concerns Paddlefish conservation. In 2006, fishers 57 could earn as much as $22.50 per pound of roe harvested (Bettoli et al 2009). Although this may be an 58 ongoing problem, management plans have established guidelines for legal harvest regulations, such as 59 regulating areas where harvest is still permitted to prevent over-exploitation. As different habitats can 60 support varying numbers of fish, limits must also vary according to current population status. A 61 commercial harvest of Paddlefish was permitted during the summer of 2006 in Mississippi. Possessing a 62 Paddlefish that was over thirty inches in length was prohibited and the catch limit was two fish per day 63 (Bettoli et al 2009). 64 Paddlefish were plentiful in the Mississippi River drainage before 1900 (Jennings and Zigler 2000 65 However, Paddlefish are listed as vulnerable by the International Union for Conservation of Nature 66 (IUCN) (Grady 2004), largely due to habitat alteration. Paddlefish movement is negatively impacted by 67 the construction of dams as they increase the difficulty of moving upstream to spawn. Increasing river 68 modification, could significantly reduce spawning success and ultimate result in population decline. 69 Coker (1928) participated in a study to determine whether Paddlefish were injured while passing 70 through the Keokuk Dam located on the upper Mississippi River. The results found that Paddlefish were 71 in fact harmed more often than other species of fish, but Paddlefish were able to move through the 72 system at times unharmed (Coker 1928). River modification can result in loss and degradation of 73 spawning habitats due to the destruction of passageways. Jennings and Zigler (2000) cite river 74 modification (along with pollution and over-exploitation) as they discussed environmental issues relating 75 to declines in Paddlefish abundance. Following modification, Paddlefish populations may be confined to 76 an area, resulting in negative impacts on population size, increased competition for resources, and 77 increased rates of disease transmission and mortality. Piers and other channel construction, while not 78 obstructive, may result changes in Paddlefish movement. Wilkens and Hofmann (2007) noted the 79 Paddlefish avoided structures containing steel, perhaps due to abnormal electric signals. Fish in 80 laboratory trials also avoided metal structures. (Wilkens and Hofmann 2007). 81 The Paddlefishes along with sturgeons, are protected by the Convention on International Trade 82 in Endangered Species of Wild Fauna and Flora. This organization was established in order to prevent 83 over-exploitation of any species due to international trade. As extensive concern for Paddlefish 84 populations began to grow people began to get involved with the conservation of the species, as of 85 March 1992 Paddlefish were listed within the Appendix II section titled “Class Actinopterygii” (Jennings 86 and Zigler 2000; CITES 2015). Currently in the state of Mississippi, the Paddlefish is not considered an 87 endangered species, but is listed by Mississippi Natural Heritage Program as a species of special concern 88 (MNHP 2015; Ross and Brenneman 2001). 89 90 Behavior 91 Paddlefish feed on plankton using a method known as ram suspension feeding in which they 92 open their mouths and continuously swim forward, forcing water to flow through their gill rakers, which 93 filter out plankton (Ross and Brenneman 2001). These fish happen to be the only filter feeders in the 94 family Polyodontidae and have adapted specifically for this method of feeding, as their gill arch and jaw 95 configuration produces a wider gape that allows for successful filter feeding (Wilkens and Hofmann 96 2007). 97 Acknowledgements 98 Upon completion of this paper I would like to acknowledge Jason Bies for being a wonderful 99 mentor and teacher throughout the species review. Also, Dr. Mike Colvin who assisted in providing me 100 with a substantial amount of resources and information that led to the successful completion of literary 101 research to make this paper possible. 102 Literature Cited 103 Bettoli, P. W., J.A. Kerns, G. D. Scholten. 2009. “Status of paddlefish in the United States.” American 104 Fisheries Society Symposium, Volume 66. 105 Burr, B.M. 1980. “A distributional checklist of the fishes of Kentucky.” Brimleyana, Number 3. 53–84. 106 Clarke, S. J., J. R. Jackson, and S. E. Lochmann. 2009. “Adult and juvenile paddlefish in the floodplain 107 lakes along the lower white river, Arkansas.” Wetlands, volume 29, number 2. 488–496. 108 Coker, R. E. 1928. “Keokuk Dam and the Fisheries of the Upper Mississippi River.” Bureau of Fisheries. 109 Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). 2015. 110 “Appendices I, II, and III.” Available: https://cites.org/eng/app/appendices.php. (Accessed 111 March 2016). 112 Grady, J. 2004. “Polyodon spathula The International Union for Conservation of Nature and Natural 113 Resources Red List of Threatened Species.” Available: 114 http://www.iucnredlist.org/details/17938/0. (Accessed March 2016). 115 Jennings, C. A. and S. J. Zigler. 2000. “Ecology and biology of paddlefish in North America: historical 116 perspectives, management approaches, and research priorities.” Reviews in Fish Biology and 117 Fisheries. 167–178. 118 McKinley, D. 1984. “History of a Neglected Account of the Paddlefish, Polyodon spathula.” Copeia, 119 volume 1984, Number 1.