Occurrence and Distribution of Asian Carps in Louisiana

239

American Fisheries Society Symposium 74:239–250, 2011© 2011 by the American Fisheries Society

Occurrence and Distribution of Asian Carps in Louisiana

R. Glenn Thomas*School of Renewable Natural Resources, Louisiana State University Agricultural Center

Baton Rouge, Louisiana 70803, USA

Jill a. Jenkins U.S. Geological Survey, National Wetlands Research Center

700 Cajundome Boulevard, Lafayette, Louisiana 70506, USA

Jody david

Louisiana Department of Wildlife & Fisheries 5652 Highway 182, Opelousas, Louisiana 70570 USA

Abstract.—In the 1970s, commercial fishers reported sightings of grass carp Ctenopharyngodon idella in large rivers and associated backwaters of Louisiana; the first specimen in Louisiana Department of Wildlife and Fisheries’ fishery indepen-dent sampling was recorded in 1976. Beginning in the early 1980s, commercial fish-ers noted increasing populations of bighead carp Hypophthalmichthys nobilis and silver carp H. molitrix (together, the bigheaded carps). Populations of bigheaded carps appear to be increasing at a much slower rate than in the Midwest¸ possi-bly due to limited suitability of and access to backwater habitat for juvenile fish. In 2002, harvester reports of sporadic captures of “different-looking” grass carp indi-cated the possible presence of black carp Mylopharyngodon piceus. Because both normal diploid and triploid (in which triploidy has been induced to cause sterility) black carp have been stocked in the Mississippi basin, determination of the ploidy (number of chromosome sets) of these fishes is important. Since 2002, postmortem ploidy determinations using cells from eyeballs removed from six wild black carp captured in Louisiana showed each to be a normal diploid, indicative of breeding capability and potential reproducing populations. Although reported commercial landings of grass and bigheaded carps have been as high as 34,830 kg/year, limited market demand in past years resulted in many captures being discarded. A protocol for obtaining samples for easily determining ploidy is reported here. Accurate data on Asian carp distributions and their reproductive potential provides information to fisheries researchers that will be constructive in documenting the spread of these invasive species and in the assessment of risk to habitats.

* Corresponding author: [email protected]

Introduction

In the 1970s, commercial fishers reported grass carp Ctenopharyngodon idella in large rivers

and associated backwaters of Louisiana ( J. Da-vid, personal communication); the first speci-men in the Louisiana Department of Wildlife and Fisheries (LDWF) fishery independent sampling was recorded in 1976. Commercial

240 thomas et al.

fishers began to report ever-increasing popula-tions of bighead carp Hypophthalmichthys nobi-lis and silver carp H. molitrix beginning in the early 1980s. Silver carp first appeared in LDWF sampling in 1985. Bighead carp captures were not confirmed until 1998, although anecdotal reports of their captures were common in the early 1990s.

In 2002, commercial fisher reports of spo-radic capture of “different-looking” grass carp resulted in the identification of several black carp Mylopharyngodon piceus. Both normal dip-loid and triploid black carp have been stocked in the Mississippi basin (Nico et al. 2005). By the end of 2004, six specimens had been provided to LDWF by commercial fishers.

Triploid fish are generally sterile, and there is evidence that the reproductive potential of triploid black carp is impaired (Papoulias et al. 2011, this volume). Triploid black carp and grass carp have been produced by the aquaculture in-dustry since the 1980s as a control against the possibility that escaped fish might reproduce in the wild (Mitchell and Kelly 2006). For this reason, black carp used in the aquaculture trade to control snails are now always sold as triploids (Conover et al. 2007). However, some black carp captured from the wild have been diploid ( Jenkins and Thomas 2007). Understanding the ploidy of black carp captured from the wild is critical to understanding whether escaped black carp are reproducing or are likely to reproduce in the wild. Attempts by state personnel to identify ploidy with blood samples from the six fish cap-tured by commercial fishers were unsuccessful, primarily because of the degraded nature of the cells. Specimens taken from commercial fishers are seldom alive. Blood cannot be typically ob-tained from dead fish and getting samples to the analytical laboratory in a timely manner was dif-ficult. Therefore, applying a reliably simple and accurate method for ploidy determination using cells within eyeballs—zones isolated from nor-

mal physiologically degradative processes—of Asian carp to inform managers of the likelihood of reproductive populations could be valuable.

The native distribution of black carp is in rivers of China and far eastern Russia (Nico et al. 2005). Importation to the United States oc-curred during the 1970s and early 1980s primar-ily as a means of biological control for nuisance snails in aquaculture ponds (Ben-Ami and Hel-ler 2001). Because black carp are primarily mol-luscivores, there is substantial concern that the fish may become established and detrimentally affect mollusks that are officially listed as en-dangered species by the United States or indi-vidual states (Nico et al. 2005). Grass carp, first imported to the United States in 1963 as a bio-logical control agent for aquatic weeds (Mitch-ell and Kelly 2006), can have multifarious and complex effects when introduced outside their native range (Fuller et al. 1999). Dispersal of Asian carps was facilitated by the 1993 Missis-sippi floods, accidental releases, stocking, and interstate transports (Mitchell and Kelly 2006).

One of the best methods to prevent the establishment of invasive species is proactive assessment of their threat before introduction (Chen et al. 2007). Following introduction, accurate data on distribution and reproduc-tive potential is useful in tracking species dis-persal and in assessing risk. In this chapter, we document Asian carp incidences in Louisiana through 2005 and describe a protocol to obtain and analyze Asian carp eyeballs for ploidy deter-mination.

Methods

Historic Data Review

Fishery-independent samples are routinely tak-en by biologists from the Inland Fisheries Di-vision of the LDWF according to management plans for individual water bodies. For most wa-ter bodies, sampling methods include electro-

241occurrence and distribution of asian carps in louisiana

fishing and gill netting. Since 2002, the LDWF Big River Fish Inventory (USFWS 2003b) has included yearly electrofishing, gill netting, hoop netting, and seining on rivers, including the Sa-bine, Mermentau, Black, Red, Ouachita, Atch-afalaya, and Mississippi (Figure 1).

Commercial fishery-dependent (landings) data have been collected by LDWF via manda-tory trip-ticket reporting since 1999. Prior to that year, dealer reports were collected. Both of these reporting methods identified landings within drainage basins rather than in specific water bodies.

Samples for Ploidy Analysis

Wild black carp used in this study were ob-tained by LDWF from commercial fishers

along the lower Red and Atchafalaya River systems. Eyeballs were removed by scooping from eye sockets using a scalpel, taking care to not puncture them. Eyeballs were placed into a container with a biological buffer of ap-propriate ionic strength, such as phosphate-buffered saline or saline solution. Containers were labeled with the date and location of col-lection. Eyeballs were delivered unfrozen and uncrushed to the National Wetlands Research Center (NWRC) in Lafayette, Louisiana on six separate occasions from April 22, 2004 through June 29, 2006. Cells were removed from the vitreous humor using a 27- or 23-gauge needle and a 1-mL sterile syringe (Fig-ure 2) and analyzed for ploidy within 7 d of fish capture. Eyeballs were stored at refrigera-

Figure 1. Louisiana watersheds where feral Asian carp captures have been reported since 1999.

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Figure 2. A black carp eye with a sampling needle is inserted in an area that is not highly vascularized for aspiration of cells from the vitreous humor.

tor temperatures (4–88C) prior to analysis. On a single occasion (August 13, 2004), an eyeball was frozen until analysis outside of the 8-d cold-storage window, on November 1, 2004. Nuclear DNA was stained with propidium iodide for analysis by flow cytometry.

Flow Cytometry Analysis

Data from approximately 10,000 nuclei per duplicate sample were analyzed. (Allen 1983; Jenkins and Thomas 2007). Internal and ex-ternal DNA standards included thawed blood from Nile tilapia Oreochromis niloticus (~2.164 picograms [pg]; University of Guelph 2007), domestic chicken Gallus domesticus (2.54 pg; Tiersch and Chandler 1989), and triploid black carp (~3.165 pg), where diploid carp genome

size would approximate 2.11 pg ( Jenkins and Thomas 2007). External blood standards were stained similarly for use in instrument setup (Shapiro 1993).

Data Analysis

Because triploids contain 1.5 times the diploid quantity of DNA per cell (Rasch et al. 1970; Allen 1983) and chicken DNA mass is close to that of diploid black carp, ploidy on experimen-tal samples was estimated with these external and internal DNA controls. In particular, peak channels of experimental histograms were com-pared with those of the standards with known DNA content values. However, we report only ploidy values and not DNA mass because high-resolution DNA analysis was not employed.


Results

To date, in the state of Louisiana, Asian carps have been captured in fishery-independent sampling within the Mississippi, Atchafalaya, Red, Ouachita, Barataria, Teche/Vermilion, Sabine (one grass carp), and Terrebonne (one grass carp) drainages (Figure 1). Relatively few Asian carps have been collected in LDWF samples with any type of gear (Figure 3). Grass carp captures (20) peaked in 1996. A trend to-ward an increase in the yearly captures for each species was due at least in part to the imple-mentation of the Big River fish inventory proj-ect in 2002 (USFWS 2003b). When data from fishery-independent captures not related to the river inventory project were tabulated (Figure 4), captures of bigheaded carps (bighead carp and silver carp together) increased, though

not rapidly. No young-of-year Asian carps have been collected from Louisiana waters in LDWF fishery-independent samples. How-ever, bighead and grass carp larvae have been common in spring ichthyoplankton samples taken in the Mississippi and Atchafalaya rivers (D. A. Rutherford, Louisiana State University Department of Renewable Natural Resources, personal communication). While reports of jumping silver carp are fairly common in the shallow floodplain lakes of the Atchafalaya ba-sin, the minimum size reported generally cor-responded with age 1+ fish (Williamson and Garvey 2005).

Commercial landings in Louisiana have been reflective of market acceptance more than availability, that is, far more Asian carp are captured than are sold. The marketability of grass carp has been fairly consistent, with

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Figure 3. Numbers of grass, bighead, and silver carps reported through fishery-independent captures in Louisiana from 1976 to 2005.

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Figure 4. Numbers of grass, bighead, and silver carps reported through fishery-independent sampling outside the Big River Fish Inventory in Louisiana from 1976 to 2005.

about 18,000–32,000 kg landed annually since 2000 (Table 1). Commercial fishers often sell grass carp to local buyers at higher prices than the other carps; indications are that they are shipped to food fish markets elsewhere in the

Table 1. Total kilograms of Asian carp reported from commercial landings in Louisiana during 2000–2005.

Year Grass carp Silver carp Bighead carp

2000 16,750 * 2,1362001 31,500 * 3,1162002 31,020 * 4,8252003 18,330 * 4,7122004 19,660 3,446 12,3402005 22,720 2,115 9,992

* Because fewer than three landings reported poundage, data are not reported.

United States. Until recently, few bigheaded carps have been saleable, but river fishermen are now finding more consistent markets for them.

Commercial landings also reflect the inci-dental nature of captures (Figure 5; reported in monthly percentages to protect confidential-ity). Most Asian carps have been taken in hoop-net fisheries, incidental to targeted species such as buffalo Ictiobus spp., freshwater drum Aplo-dinotus grunniens, and catfish (flathead catfish Pylodictis olivaris and blue catfish Ictalurus fur-catus). Monthly capture patterns for grass carp indicated a trend toward higher capture rates for months coinciding with likely spawning migra-tion (April–June, Figure 5A; Fuller et al. 1999; Nico et al. 2005) while the sporadic market ac-ceptance of the bigheaded carps decreases the reliability of landings data in estimating their capture rates (Figure 5B, 5C).


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Figure 5. Mean monthly percentage of grass carp, bighead carp, and silver carp fishery-dependent or commercial landings in Louisiana from 2000 to 2005. Bars denote years 2000–2005.

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Each of the six black carp taken from the commercial fishery proved to be diploid (Fig-ure 6). In each case, including the frozen eyeball (Figure 6C), the DNA was intact enough for ploidy determination. Coefficient of variations ranged from 1.94 to 8.01. The protocol used for sampling fish from the wild and for the cold or frozen storage of eyeballs was proven to be reli-able for ploidy determinations.

DiscussionA trend toward more fishery-independent captures of grass carp and bigheaded carps is due at least in part to the implementation in 2002 of the Big River fish inventory project through LDWF (USFWS 2003b), though these species are probably underrepresented even in those data. Because Asian carps tend to be net-shy, their populations are poorly rep-resented in standardized sampling programs (USFWS 2003a; Ickes et al. 2005; Williamson and Garvey 2005; Conover et al. 2007). Even though sampling efforts are not comparable between states, it appears that the trajectory of population growth of Asian carps in Loui-siana has been relatively gradual compared to that in more northern parts of the Mississippi basin (Chick and Pegg 2001; Schofield et al. 2005; Irons et al. 2011, this volume). Irons et al. (2007) reported that commercial fishers on the La Grange Reach of the Illinois river land in 1 d nearly the same weight (11,360 kg) of bigheaded carps that is landed in Louisiana in a year (12,107 kg in 2005). Kolar et al. (2007) documented the general preference of low-ve-locity habitats for juveniles of bigheaded carps. Shortage of contiguous backwaters, side chan-nels, and pool habitats may have constrained population growth rates in Louisiana.

Population increases in Louisiana may also be constrained by the fact that most non-channel river habitats are shallow, wooded floodplains. These backwater areas tend to be

flooded in the winter and spring, and in those years when backwaters remain inundated dur-ing the summer months, water temperatures can exceed 308C for long periods and hypoxia is common (Bryan and Sabins 1979; Ruther-ford et al. 2001). While the thermal maximum for juvenile bighead carp in the laboratory has been reported to be more than 388C, the preferred temperature of 258C was similar for both juvenile bighead and grass carps (Bet-toli et al. 1985). Rasmussen (2002) summa-rized a number of studies that reported the temperature range for silver carp as 6–278C and for bighead carp as 4–268C. Additionally, many Louisiana rivers stay within their banks for several years at a time during dry periods, reducing opportunities for use of nonchannel habitats. For these reasons, optimum habitat for juvenile Asian carps is probably limited during most years.

However, the relatively recent damming of the Red River through the northwest and cen-tral regions of Louisiana may have provided some supplementary habitat for juvenile Asian carps. Construction of the Red River Waterway ( J. Bennett Johnston Waterway) navigation project began in 1973, was completed in 1994 and included five dams along 236 river miles (U.S. Army Corps of Engineers 2010). While this project probably increased the amount of suitable habitat for juvenile Asian carps, some of the dams may have also interrupted the “in-cubation distance” needed for suspension of developing eggs (Nico et al. 2005).

The presence of wild diploid black carp in Louisiana is particularly troublesome in light of the high number (30) of mussel species listed as rare, threatened, or endangered in the state (; Brown and Banks 2001; LDWF 2007). Nico et al. (2005) postulated that these large, long-lived molluscivores could impact mussel pop-ulations even in areas where black carp could not reproduce. Correct identification of ploidy


Figure 6. Representative flow cytometric histograms (A–C) generated with vitreous humor cells from black carp eyes collected in the lower Mississippi and Atchafalaya River systems. Fluorescence of DNA (FL2-Area) on the x-axis and nuclei count on the y-axis. (A) DNA peak from a carp captured in April 2004 is on the left (Marker 1 [M1]) and is compared with an internal DNA control from nuclei of chicken red blood cells (M2) having a known DNA content of 2.54 pg. The carp nuclei coefficient of variation (CV) of 2.77 is indicative of cells in very good condition; (B) DNA peak from a carp captured in June 2005 with a coefficient of varia-tion (CV) of 8.05, indicating cells whose ploidy value is easily obtained using an appropriate external or internal DNA control; (C) DNA peak from an eyeball frozen in August until November 2004. Cells are not in optimal condition as noted by the area of DNA degradation to the left of the main nuclei population (M1) with a CV of 8.08, but ploidy can still be determined with an appropriate control.

248 thomas et al.

of wild black carp, as well as the other Asian carp species, will provide science-based information constructive in the accurate understanding of potential environmental impacts.

Use of eyes rather than blood from wild fish facilitates accurate ploidy analyses because eyes stored through 8 d at 48C in a biological buffer allows nuclei to remain intact longer than peripheral blood ( Jenkins and Thomas 2007). Because flow cytometric DNA analy-sis is a common procedure performed by flow cytometrists in veterinary and human-related studies, ploidy determination for any of the Asian carp species should not be problematic if the correct DNA controls (such as blood from chicken or known triploid carp) are used. Appropriate internal controls are those with DNA content that are close in channel number but that do not overlap with the position of the experimental sample (Burns et al. 1986). Al-though many tissues have been used for ploidy analysis and several analysis techniques have been used (Pandian and Koteeswaran 1998), and the common screening method employs cell volume as a determinant of ploidy (Griffin and Mitchell 1992), analysis of DNA content is the most accurate method.

Overall, Asian carp captures are increas-ing in Louisiana. Improved documentation is allowing for better stock assessments. The five recently constructed major dams in the Red River may inhibit the incubation success of Asian carp eggs while improving habitat for Asian carp juveniles. While markets exist for most Louisiana-harvested grass carp, markets for the bigheaded carps could expand through use as crab and crawfish bait. Increased use of Asian carps would improve profitability for river finfish and coastal crab fisheries, as well as for wild and farmed crawfish industries, and would reduce the standing stock of these inva-sive species. Documention of occurrence and distribution of Asian carps, and determination

of ploidy of captured fish, will support predic-tive modeling on potential impacts of these in-vasive species.

Acknowledgments

The authors appreciate the work of C. Bou-dreaux of IAP World Services, NWRC, for Figure 1 and L. Joseph Shepard of LDWF for fishery-independent and fishery-dependent data. Reviewers David Nieland, Allen Ruther-ford, and Rex Caffey Duane Chapman, Robert Hrabik, and two anonymous reviewers provid-ed valuable advice.

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Documents

Occurrence and Distribution of Asian Carps in Louisiana