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A simple device for measuring minimum current velocity to maintain semi-bouyant fish fish eggs in suspension.

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  • Metro Wastewater Reclamation District

Abstract and Figures

Pelagic broadcast spawning cyprinids are common to Great Plains rivers and streams. This reproductive guild produces non-adhesive semi-buoyant eggs that require sufficient current velocity to remain in suspension during development. Although studies have shown that there may be a minimum velocity needed to keep the eggs in suspension, this velocity has not been estimated directly nor has the influence of physicochemical factors on egg buoyancy been determined. We developed a simple, inexpensive flow chamber that allowed for evaluation of minimum current velocity needed to keep semi-buoyant eggs in suspension at any time frame during egg development. The device described here has the capability of testing the minimum current velocity needed to keep semi-buoyant eggs in suspension at a wide range of physicochemical conditions. We used gellan beads soaked in freshwater for 0, 24, and 48 hrs as egg surrogates and evaluated minimum current velocities necessary to keep them in suspension at different combinations of temperature (20.0 ± 1.0°C, 25.0 ± 1.0° C, and 28.0 ± 1.0° C) and total dissolved solids (TDS; 1,000 ± 300 mg L-1, 3,000 ± 300 mg L-1, and 6,000 ± 300 mg L-1). We found that our methodology generated consistent, repeatable results within treatment groups. Current velocities ranging from 0.001–0.026 needed to keep the gellan beads in suspension were negatively correlated to soak times and TDS and positively correlated with temperature. The flow chamber is a viable approach for evaluating minimum current velocities needed to keep the eggs of pelagic broadcast spawning cyprinids in suspension during development.
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ThePrairieNaturalist45:84–89;2013
A Simple Device for Measuring the Minimum Current Velocity to Maintain
Semi-Buoyant Fish Eggs in Suspension
JULIA S. MUELLER, BRANDON D. CHEEK, QINGMAN CHEN, JILLIAN GROESCHEL, SHANNON K. BREWER, and
TIMOTHY B. GRABOWSKI1
TexasCooperativeFishandWildlifeResearchUnit,TexasTechUniversity,Lubbock,TX79409,USA(JSM,BDC,QC,JG)
U.S. Geological Survey, Oklahoma Cooperative Fish and Wildlife Research Unit, Oklahoma State University, Stillwater, OK
74078,USA(SKB)
U.S. Geological Survey, Texas Cooperative Fish and Wildlife Research Unit, Texas Tech University, Lubbock, TX 79409, USA
(TBG)
ABSTRACT Pelagic broadcast spawning cyprinids are common to Great Plains rivers and streams. This reproductive guild
producesnon-adhesivesemi-buoyanteggsthatrequiresufcientcurrentvelocitytoremaininsuspensionduringdevelopment.Al-
though studies have shown that there may be a minimum velocity needed to keep the eggs in suspension, this velocity has not been
estimateddirectlynorhastheinuenceofphysicochemicalfactorsoneggbuoyancybeendetermined.Wedevelopedasimple,in-
expensiveowchamberthatallowedforevaluationofminimumcurrentvelocityneededtokeepsemi-buoyanteggsinsuspension
at any time frame during egg development. The device described here has the capability of testing the minimum current velocity
needed to keep semi-buoyant eggs in suspension at a wide range of physicochemical conditions. We used gellan beads soaked in
freshwater for 0, 24, and 48 hrs as egg surrogates and evaluated minimum current velocities necessary to keep them in suspension
atdifferentcombinationsoftemperature(20.0±1.0°C,25.0±1.0°C,and28.0±1.0°C)andtotaldissolvedsolids(TDS;1,000
mg L-1, 3,000 mg L-1, and 6,000 mg L-1). We found that our methodology generated consistent, repeatable results within treatment
groups. Current velocities ranging from 0.001–0.026 needed to keep the gellan beads in suspension were negatively correlated to
soaktimesandTDSandpositivelycorrelatedwithtemperature.Theowchamberisaviableapproachforevaluatingminimum
current velocities needed to keep the eggs of pelagic broadcast spawning cyprinids in suspension during development.
KEY WORDS minimum current velocity, pelagic broadcast-spawning cyprinids, semi-buoyant eggs, velocity chamber
At least 12 species of Great Plains cyprinids produce non-
adhesive semi-buoyant eggs that are broadcast into the water
column during spawning (Perkin and Gido 2011). This re-
productive strategy presumably allows eggs to complete de-
velopment while avoiding the risk of abrasive damage from
shifting sandy substrates characteristic of Great Plains rivers
and streams (Moore 1944). However, these pelagic broad-
cast-spawning cyprinids are in decline throughout the Great
Plainsandmost are of conservationconcern(Hoagstromet
al. 2011, Perkin and Gido 2011).Anthropogenic modica-
tions of the landscape, fragmentation of rivers through dam
andreservoirconstruction,andalteredowregimeshaveall
impactedpelagicbroadcast-spawningcyprinids(Dudleyand
Platania 2007, Durham and Wilde 2009, Hoagstrom et al.
2011, Perkin and Gido 2011).
In response to declining populations of pelagic broadcast-
spawning cyprinids, current research has focused on the min-
imum distance eggs require for drifting in order to complete
development(PerkinandGido2011).However,todateinves-
tigations have examined transport dynamics at coarse scales
through analysis of patterns of species presence and absence
or recovery of egg surrogates released during the spawning
seasonofthesespecies.Forexample,PerkinandGido(2011)
evaluated the minimum distance required for egg transport
of eight species of pelagic broadcast-spawning Great Plains
cyprinids by determining the minimum stream fragment
length in which populations of these species have persisted
throughtime.Atanerscale,studiesonRioGrandesilvery
minnow(Hybognathus amarus) and Pecos bluntnose shiner
(Notropis simus pecosensis) suggestthatowvariabilitydue
to channel morphology and complexity may entrain eggs and
shorten the fragment length or reduce water requirements for
persistence(Kehmeieretal.2007,KinzliandThornton2009,
Widmer et al. 2012). There has been little attention directly
givento evaluating transportdynamicsthat might inuence
thedistancerequiredforsuccessfulreproduction(e.g.,mini-
mum current velocity required to keep eggs in suspension)
andphysicochemicalconditions(e.g.,temperature,totaldis-
solvedsolids[TDS])thatmightinuencebuoyancyofeggs.
Recent development of high-resolution models for evalu-
atingdrifttrajectoriesofparticleslikesemi-buoyantsheggs
has encouraged the evaluation of velocity and discharge re-
quirements for successful reproduction. In this study, we de-
scribe a simple chamber and method for assessing current ve-
locitiesnecessarytokeepsemi-buoyantsheggsinsuspension
and provide the initial validation of this approach using gellan
beadsaseggsurrogates(Reinertetal.2004,Kehmeier2007).
The objectives of our study are to describe the creation and
operationforaow chamber that can be used to keepsemi-
buoyant eggs in suspension, while also providing results that
show how this device is capable of obtaining repeatable and
accurate results under different physicochemical conditions.
1 Current Address: Native Fish Lab, Marsh and Associates, LLC, Tempe, AZ 85282, USA
1 Corresponding author email address: t.grabowski@ttu.edu
Mueller et al. • Measuring Velocity to Suspend Fish Eggs 85
METHODS
Design and Construction
Wedesignedaowchamberconsistingoffourmaincom-
ponents: a submersible pump, a riser stem, a ball valve, and
a clear PVC observation and measurement chamber (Fig.
1).WeusedaLagunaPowerjetfountainandwaterfallpump
kit(UnitedPetGroupsInc.,Cincinnati,Ohio,USA)ratedat
56.8 L min-1at1.7mofheadpressure.Theriserstem,tting,
and control valve included with the pump were connected
with a standard 2.09-cm diameter PVC ball valve. The use
oftwo valves allowed for bothne adjustments and main-
tenance of very low current velocities. Our lowest obtained
velocity was 0.001 m s-1,buttheowchamberhasthecapa-
bilities of lower velocities if needed. We cut a 2.09-cm diam-
eter clear PVC pipe to a length of 120 cm and attached to the
ballvalve,formingtheowchambercolumn.Wedrewtwo
circles around the PVC pipe to delineate a length of 100 cm
centered 10 cm from the top and bottom of the PVC pipe. We
drew smaller hash marks every 1.0 cm on the pipe within this
100-cm length. We used these hash marks to calculate current
velocity by calculating the ratio between the time in seconds
(s)forthetubetolltothatpointandthelineardistance(cm)
from the bottom of the chamber to the hash mark. Addition-
ally, we used has marks to estimate discharge. We estimated
discharge by multiplying the area of the tube by the average
velocitywithinthetube.Theowchamberweighedapproxi-
mately 3.2 kg and could be quickly broken down into two
pieces, making it portable and lightweight.
Operation
Prior to placing objects into the column, we closed the
ballvalvetoavoid asuddenjetofwaterwhenthedeviceis
turned on. We then placed the ow chamber into a 37.8-L
plastic tub. Tubs measured approximately 35 cm in depth,
47cmin width, and 47 cm in height, which was sufcient
to keep the pump fully submerged and was wide enough to
catch water as it spilled over the top of the column. We veri-
edtheverticalpositionofthecolumnusingalevelorplumb
bob to ensure accurate and consistent measurements in all
trials.
We started the pump and opened the ball valve approxi-
mately 3–7% of a full turn to allow the column to slowly
beginlling.Weaddedgellanbeadsasthewaterreachedthe
50-cm mark on the pipe then allowed the column to continue
lling while adjusting the ball valve to keep the objects at
equilibrium(±5cm)withinthecolumn.Whenwaterspilled
over the top of the column, we started a 1-min timer and ob-
served the gellan beads to ensure they remained stationary in
thecolumnwithoutanyadjustmentstotheball valve.If the
gellan beads remained stationary, then we recorded the verti-
cal position of each bead. If the objects had moved within
thecolumn,thenweadjustedtheballvalveandrepeatedthe
processuntil theobjectswereable toremainat equilibrium
Figure1.A)Theowchamber,createdusingasubmersiblepondpump,riserstem,ballvalve,andclearPVCchamber,wasusedto
measure the minimum current velocity needed to keep gellan beads in suspension. B) The clear PVC chamber with circles drawn
aroundthepipetorepresent10cmandhashmarksdrawntorepresent1cm.C)Theowchamberfullysubmergedinaplastictub
regulated at a given temperature and total dissolved solid treatment level. Trials were conducted during October 2012 in laboratory
facilities at Texas Tech University, Lubbock, USA.
270
2 cm
A
C
B
86 The Prairie Naturalist•45(2):December2013
during the 1-min test. Once this step was complete, we un-
pluggedthepumpand nofurtheradjustmentsweremade to
the valves for the remainder of the trial. If there was a need to
recoverthetestobjects,weremovedthepipe,valve,andriser
stem from the pump and turned them upside down over a dip
net. After the water was drained out of the pipe, we repeated
thepreviouslydescribed lling procedure and recorded the
timeittookforthechambertolltoeachrecordedposition.
Experimental Design
Weusedredgellan beads (TechnologyFlavors and Fra-
grancesInc.,Amityville,NewYork,USA) totesttheinu-
ence of water temperature and TDS on the minimum veloci-
ties required to keep egg surrogates in suspension. Originally
used in food and drinks, studies have shown these beads have
asimilarshape and specic gravity(SG)assomesh eggs
and do not change physically with the addition of salinity
(Reinertetal.2004,Kehmeieretal.2007).However,gellan
beads are packaged in a preservative solution that can affect
theirSG. Reinertetal. (2004)soakedgellan beadsinwater
for 0, 24, and 48 hrs and found that SG was negatively cor-
related with soak time, presumably due to the absorption of
water. Therefore, the gellan beads were soaked in water for
thesamethreetimeframes(0,24,48hrs)tominimizethein-
uenceofthepreservativesolutionontheresultsofthetrials.
For each soak time treatment group, we ran trials at three
different water temperatures: 20.0 ±1.0°C,25.0±1.0°C,
and 28.0 ±1.0° C.Thetemperature of thewaterwas main-
tained by the addition of one or more 50-W submersible heat-
ers(AqueonProducts,Franklin,Wisconsin,USA).Foreach
soak time and temperature combination, there were also three
different TDS treatment levels: 1,000 mg L-1, 3,000 mg L-1
and 6,000 mg L-1. Total dissolved solid treatment levels were
established through the addition of the appropriate amount of
Instant Ocean seawater mix (Spectrum Brands, Cincinnati,
Ohio, USA). We determined the treatment levels based upon
values observed in the Canadian River during the spawning
season of pelagic broadcast-spawning cyprinids native to the
drainage(Piggetal.1999)andsetupaseparatetubforeach
temperature × TDS treatment group. We placed three gellan
beads from each soak time × temperature × TDS treatment
groupinthe appropriate ow chamberandconductedthree
replicate trials per treatment group using the procedure de-
scribedabove. Weperformedpoweranalyses(Zar 1999) to
determine the appropriate number of trials per temperature,
TDS,soaktime treatment group.Themajority of thebeads
remainedincloseproximitytooneanother(1–2cm)within
the column and in these cases we used a mean vertical posi-
tion for our velocity calculations. There were a few instances
(Table1) where one of the three beads would become sta-
tionaryatadistancefromtheothers(3–5cm).Weconducted
an additional trial in these cases to ensure this was a result
of physical or SG differences that were found among gel-
lanbeads (Reinertetal.2004).Trialswhere thebeadswere
widelyseparatedwithinthechamber(6+cm)wereeliminat-
ed from analysis as visual examination indicated these beads
were damaged or otherwise deformed.
Weusedanalysisof covariance(ANCOVA)toevaluate
the effects of soak time, temperature, and TDS on the mini-
mum current velocity necessary to keep the gellan beads in
suspension with soak time as a covariate and temperature and
TDS as independent variables. We used Dunnett’s multiple
comparison procedure as a post-hoc test to evaluate differ-
ences among treatment groups. We performed all analyses
using SAS 9.2 (SAS Institute, Inc., Cary, North Carolina,
USA)withasignicancevalueofα=0.05.
RESULTS
Our methodology generated consistent, repeatable results
withintreatmentgroups(Table1).Ingeneral,thecoefcient
of variation of the mean minimum current velocities for each
treatmentgroupdidnotcorrelatewithsoaktime(r = 0.02, P
=0.93),temperature(r = 0.22, P=0.28),orTDS(r = 0.30,
P=0.13).Ourminimumdetectabledifferenceinmeanmini-
mum current velocity among treatment groups was approx-
imately 0.002 m s-1 based upon a post-hoc power analysis
(Zar1999).Asexpected,soak timehadaninuence on the
minimum current velocity necessary to keep gellan beads in
suspension(F3,83=6.56,P<0.05;Fig.2).Treatmentsgroups
soaked in water prior to testing required lower current ve-
locities to remain in suspension than those that received no
pre-testsoak(t1≤–16.80;P<0.05;Fig.2).However,there
wasnodifferencebetweenthe24-hrand48-hrsoaktimes(t1
=0.65,P=0.87).
Overall, soak time, TDS, and the interaction between
soak time and temperature explained approximately 83%
of the variation in current velocity required to keep gellan
beads in suspension. There was an inverse relationship be-
tween TDS and current velocity that was independent of soak
time and temperature (F1,83 = 23.08, P < 0.05). However,
temperature interacted with the three soak times differently,
independentofTDS(F3,83=5.05,P<0.05).Theinteraction
of temperature and soak time exhibited a positive relation-
shiptominimumcurrentvelocity(β1 =0.0004,t1=3.18,P<
0.05), while the interaction of the other two soak times with
temperaturedidnotproduceaneffect(24hrs:β1 =−0.004,t1
=–1.65,P =0.10;48hrs:β1=−0.003,t1=–1.85,P =0.07).
DISCUSSION
Ourresultsdemonstratethat theowchamberdescribed
in this paper can be used to estimate minimum current ve-
locities required to keep semi-buoyant eggs in suspension
at any time during egg development and to provide the data
necessaryformodelingtransportdynamicsatnespatialand
temporal scales. The results of our study are consistent with
Mueller et al. • Measuring Velocity to Suspend Fish Eggs 87
gellan bead behavior as predicted by basic physics and work
conductedbyReinertetal.(2004).An increase inTDSre-
sults in an increase in the density of the water medium, which
would increase the buoyancy of the gellan beads and thus
reduce minimum current velocity necessary to keep them in
suspension. Additionally, soaking the beads in water reduced
theirspecic gravityasthey absorbedwaterand resultedin
lower current velocities needed to keep them in suspension.
However, it seemed that the density of water inside and out-
sidethe gellanbeadswereinuenced similarlybytempera-
ture, resulting in relatively minor effect of temperature we
observed on minimum current velocity.
Ourdeviceiscapableoftestingsheggsunderdifferent
physicochemicalconditions such as, temperature and TDS;
however, the chamber may over simplify stream conditions.
For example, minimum current velocities obtained using this
device may be relative as the chamber only measures hori-
zontal rather than vertical movement. Furthermore, current
velocity in a stream is not the only factor that is keeping these
eggs in suspension. Turbulence created by interacting with
channel features and ripples created by sand bed features may
cause the velocity to be pushed in more of a quasi-vertical
motion rather than simple horizontal as in a pipe with lami-
narow.Inessence,theverticaldirectionofthepipeforthis
Table1.Numberoftrials(n)persoaktime,temperature,andtotaldissolvedsolid(TDS)treatmentgroupwiththemean(± SD) and
range of minimum current velocities necessary to keep gellan beads in suspension. Trials were conducted during October 2012 in
laboratory facilities at Texas Tech University, Lubbock, USA.
Soaktime(hrs) Temperature(°C) TDS(mgL-1)n
Mean current velocity
(ms-1)
020 1,000 40.017 ± 0.006
3,000 30.015 ± 0.005
6,000 30.015 ± 0.005
25 1,000 40.017 ± 0.006
3,000 30.018 ± 0.001
6,000 30.013 ± 0.006
28 1,000 30.026 ± 0.003
3,000 30.021 ± 0.009
6,000 30.016 ± 0.007
24 20 1,000 30.006 ± 0.001
3,000 30.005 ± 0.001
6,000 30.002 ± 0.001
25 1,000 50.005 ± 0.002
3,000 30.002 ± 0.000
6,000 30.001 ± 0.001
28 1,000 30.003 ± 0.001
3,000 30.001 ± 0.001
6,000 30.001 ± 0.001
48 20 1,000 30.007 ± 0.001
3,000 30.006 ± 0.001
6,000 40.003 ± 0.001
25 1,000 40.004 ± 0.003
3,000 30.001 ± 0.000
6,000 30.001 ± 0.001
28 1,000 30.005 ± 0.003
3,000 30.001 ± 0.000
6,000 40.001 ± 0.000
88 The Prairie Naturalist•45(2):December2013
Figure2.The effect oftemperatureand total dissolvedsolids (TDS) on the minimum currentvelocityrequiredtokeepgellan
beadssoaked0-hrs(A),24-hrs(B),and48-h rs(C)insuspension.TrialswereconductedduringOctober2012inlaboratoryfacili-
ties at Texas Tech University, Lubbock, USA.
271
Mueller et al. • Measuring Velocity to Suspend Fish Eggs 89
chamber calculates uplift velocity. Regardless, this device
may be appropriate for questions related to magnitudes of
differences when talking about stream velocity.
MANAGEMENT IMPLICATIONS
Past studies have demonstrated the importance of dis-
charge for pelagic broadcast-spawning shes in freshwater
systems(Reinert et al.2004,Medleyet al.2007);however,
there remains a lack of knowledge on the interactions be-
tween semi-buoyant eggs, the physicochemical environment,
and the ow dynamics within a river channel. Researchers
using this chamber can obtain both estimates of the mini-
mum current velocity needed to keep semi-buoyant eggs in
suspension and how physicochemical conditions inuence
this velocity. Understanding how changes in physicochemi-
cal conditions affect egg buoyancy may provide insight for
determining the fragment length necessary for successful re-
production, especially as streams become increasingly frag-
mented due to the creation of dams and impoundments.
ACKNOWLEDGMENTS
Funding was provided by the U.S. Fish and Wildlife
Service Great Plains Landscape Conservation Cooperative.
B. Durham and two anonymous reviewers provided com-
ments and suggestions to improve this manuscript. Cooper-
ating agencies for the Texas Cooperative Fish and Wildlife
Research Unit are the U.S. Geological Survey, Texas Tech
University, Texas Parks and Wildlife, and the Wildlife Man-
agement Institute. Cooperating agencies for the Oklahoma
Cooperative Fish and Wildlife Research Unit are the U.S.
Geological Survey, Oklahoma State University, Oklahoma
Department of Wildlife Conservation and the Wildlife Man-
agementInstitute.Useoftrade,product,orrmnamesisfor
descriptive purposes only and does not imply endorsement
by the U.S. Government.
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Submitted 9 January 2013. Accepted 10 July 2013. Associate
Editor was Melissa Wuellner.
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