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448 Southeastern Naturalist Vol. 12, No. 2
First Recorded Occurrence of Oncorhynchus mykiss (Rainbow Trout) in Louisiana
Steven G. George1,*, William T. Slack1, and K. Jack Killgore1
Abstract - An individual of Oncorhynchus mykiss (Rainbow Trout) was collected in a diversion
canal of the Mississippi River known as Davis Pond located at river kilometer (RKM) 191.03 in St.
Charles Parish near Luling, LA. This locality is the southern-most record for Rainbow Trout in the
Mississippi River Basin and represents a range extension of 733.5 RKM south from the previous
southern-most locality at Lake Whittington, Bolivar County, MS. The collection we report here also
represents the first documented record of Rainbow Trout in Louisiana.
Oncorhynchus mykiss (Richardson) Rainbow Trout is native to the Pacific Coast of
North America and has been introduced into suitable habitats over much of the United
States and elsewhere (Robison and Buchanan 1988, Pflieger 1997). Occurrence records
of Rainbow Trout in the Mississippi River are rare however. Waifs in the river have been
reported from the states of Illinois (Smith 1979) and Mississippi (Ross 2001). The Mississippi
records are not represented by voucher material, although an individual taken
from an oxbow in Bolivar County is recognized as a rod and reel record by the State
(Fig. 1:MDWFP 2001; MDWFP 2011). These reports from Mississippi led Douglas and
Jordan (2002) to suggest that Rainbow Trout may occasionally occur in Louisiana. A
394-mm-TL and 245-g Rainbow Trout individual we collected 6 May 2008 from a diversion
canal known as Davis Pond confirms the speculation of Douglas and Jordan (2002).
The Davis Pond diversion is located on the west bank of the Mississippi River in
St. Charles Parish near Luling, LA. It is a US Army Corps of Engineers diversion from
the Mississippi River that reintroduces fresh water, nutrients, and sediment to the saltthreatened
Barataria estuary, which stretches south to the Gulf of Mexico.
Coordinates representing the location of capture are 29.92270ºN and 90.31926ºW. We
(Engineer Research and Development Center [ERDC] personnel, US Army Corps of Engineers,
Vicksburg, MS) captured this individual while conducting systematic sampling
with a small-mesh hoopnet (1.0 m diameter x 4.6 m length; 2.54-cm bar mesh with seven
fiberglass hoops). The net was set approximately 1030 m downstream from the control
structure of Davis Pond. Water velocity at the point of capture was 66 cm/sec, and water
temperature was 19.18 ºC.
The specimen was placed on ice and transported back to the laboratory for further examination.
Otoliths and scales were removed, and subsequent examination suggested the
individual was age 2+. Size-at-age was greater than averages reported for Rainbow Trout
in Missouri (Pflieger 1997) and Tennessee (Whitworth and Strange 1983). Size at age for
this species is known to vary considerably, however, especially with regards to rearing
conditions (Carlander 1969). Examination of gut contents indicated corn was ingested
prior to capture. The specimen was archived as a voucher at the Mississippi Museum of
Natural Science (MMNS 57162) following examination.
This specimen represents the first documented occurrence of Rainbow Trout in Louisiana
and also represents a significant range extension than pre viously reported (Fig. 1).
There are other instances of “northern” fishes occurring at southern latitudes in the
Mississippi River. For example, Suttkus and Conner (1980) reported collecting Osmerus
1US Army Corps of Engineers, Engineer Research and Development Center, Environmental Laboratory
3909 Halls Ferry Road, Vicksburg, MS 39180. *Corresponding author - Steven.G.George@
Notes of the Southeastern Naturalist, Issue 12/2, 2013
2013 Southeastern Naturalist Notes 449
mordax Mitchill (Rainbow Smelt) in the Mississippi River (RKM 421.6 [RM 262], RKM
435.5[RM 270]) during flood conditions in April. Other museum records indicate a similar
downstream occurrence in the Mississippi River for Rainbow Smelt during seasonal
periods generally associated with higher river levels (MMNS 53861, RKM 1105.6, March
2007; MMNS 13200, RKM 825.6, December 1978 [Pennington et al. 1982]; NLU 73573,
RKM 701.4, January 1986; NLU 44817, RKM 440.3, March 1989), thus providing support
for the premise of downstream dispersal of fishes aided by elevated river flows.
The Davis Pond Rainbow Trout specimen we collected was taken while the Mississippi
River was at high stage levels (6.1 m [20.0 ft.]), with a recent high stage of 6.52 m
(21.38 ft.) on 19 April (gage = Mississippi River at Bonnet Carré Spillway, Norco, LA
, RKM 204.23[RM 126.9]; overbank = 4.3 m [14 ft]; USACE 2012). Thus,
downstream dispersal is a likely mechanism for explaining its presence in Davis Pond.
The most plausible origin for the Davis Pond Rainbow Trout would be the White River
in Arkansas, a large tributary of the Mississippi River, where annual stocking in reservoir
tailwaters within the system have been well documented (AGFC 2012, Robison
and Buchanan 1988). Stocked Rainbow Trout in the White River system generally range
229–304 mm TL (Bowman et al. 1994). The most downstream areas where stockings have
been reported are below the Bull Shoals Dam, North Fork River Dam, and Greers Ferry
Figure 1. Natural range of Rainbow Trout (inset) based on MacCrimmon (1971) and Behnke (1992)
prior to introductions within North America. Relative locations of wild-caught Rainbow Trout outside
of its range (solid dots, expanded map) within Arkansas, Mississippi, and Louisiana, including
southern most record (Davis Pond) noted in this study. Shaded triangles note potential dispersal
locations where Rainbow Trout are routinely stocked for recreational fisheries.
450 Southeastern Naturalist Vol. 12, No. 2
Dam (Fig. 1). The distance from these stocking points to the Davis Pond control structure
range from 1186 RKM at Greers Ferry to 1442 RKM at Bull Shoals Dam.
Rainbow Trout exhibit the broadest range of water temperature tolerance among
the trouts that are commonly stocked (0–28.3 ºC; Becker 1983) and thus have a greater
chance of survival at locations they may disperse to. We have recorded Mississippi River
surface water temperatures ranging 5–32 ºC during extensive seasonal sampling in the
vicinity of Davis Pond (ERDC, unpubl. data). These data suggest that water temperatures
are suitable for Rainbow Trout survival when referenced to published literature (Robison
and Buchanan 1988).
The distribution of Rainbow Trout in the lower Mississippi River Basin is unknown.
Despite extensive seasonal sampling for fishes over a 15-year span from New Orleans to
Memphis using trotlines baited with worms, trawls, and gillnets, this record marks our
first Rainbow Trout specimen. Perhaps future sampling during major floods in diversion
canals such as Davis Pond may provide additional specimens.
Acknowledgments. This project was funded by the US Army Corps of Engineers, New
Orleans District. Field assistance was provided by J.J. Hoover, W.E. Lancaster, J.P. Kirk,
C. Murphy, J.A. Collins, B.R. Lewis, and C. Troxler. Permission to publish was provided
by the Chief of Engineers.
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