Sustainable Swimming Spccds of Striped Bass Larvae
Ahsit-UC~.
-Sustnillnblc swimming speeds, defined as spccds maintnincd in I-h tcsts, wcrc mcabured Ibr three size-classcs (6-6.9 nlm, 7-7.9 mm, and 8-8.9 rnm) of larval striped bass Moronc
MA-uiilis. Probit analysis was uscd to find fnilure velocities (the water vrlocity at which 50% 01-the
Iarvnc fnil to sustain swimming spccd) and confidcncc intervals Ibr cach si~e-class.Failure velocities
wcre 1.7, 1.1, nnd 3.0 cm/s Tor 4-6.9-mm, 7-7.9-mm, and 8-8.9-nim lnrvne, rcspectivcly. Thcrc
'hcrc
.
was no diffcrcncr in swimwas a general improvcmcnt in swimming pc~formanccwith R ~ C
ming ability due lo the prcscncc or nhscnce of nn inflntcd swim bladder. Striped bass larvae
approached the upper rnngc of swimming speeds recordcd for other lnrval fishcs and reachrd
speeds o r 3 4 body lengthsls, which nre cornparablc to adult fish speeds. The relatively high speeds
a~tainedby swiped bass larvnc may improve reeding succrss rates by increasing the volume ol"
wntcr larvnc arc capable oT searching Tor food.
Numbers of striped bass M o t m o n rsuxutilis have
declincd dramalically in he Sucramento-San Joaquin estuary of California (Stevens 1977; Stevcns
ct al. 1985) and Chesapeake Bay (Boreman and
Auslin 1985) sincc thc carly 1970s. In both cases
a reduction in larval food supply is thought to be
a contributing factor (Stcvens et al. 1985; Tsai
199 I). Previous laboratory sludies have quantificd prey densitics rcquired for larval stripcd bass
growth and survival. (Daniel 1976; Millcr 1076:
Eldridge et al. 198 I , 1982; Houdc and Iubhers
1086; Chcsncy 1989; Tsai 1991; Mcng 1993), but
these dcnsities are o k n scvcrul tirncs higher than
prey dcnsities found in lhc ticld in California (Stevens ct al. 1985; Meng 1993). T h e discrepancy
betwl.cn laboratory and held results may be cxplained by the hilure of labornlory studies to adequately cvaluatc thc cffcct of swimming performance o n larval starching ability and feeding
success.
Swimming perfbrmance detcrmincs larval Teeding rules and encrgy expenditures, as well as
wlicther or not larvac rcmain in food-rich areas
(TIunter 198 1; Dabrowski ct al. 1988; Miller et al.
1988). Larvul swimming ability determines prey
encounter rates because Fish larvae altcr their
swimming speeds in response to changing prey
densitics (Kosenthal and Hempel 1970; Hunter
and Thonins 1974; Theilacker and Dorscy 1980;
M u n k and Kiorboe 1985). Fish larvac may increase encounter rates by swimming fastcr at low
prey densities (Theilacker and Dorsey 1980; Munk
and Kiorboe 1985). Cruising o r sustainablc swimming speeds, defined here as speeds sustained Tor
a t least 1 h, are maintained by fish during routinc
uctivi~iessuch as fccding (Hunter 198 1).
Cruising speeds of adult hsh are well documcntod (Beamish 1978), but sustainablc speeds of
larvae have been more d i f k u l t to obtain. Fish
larvae are delicate and easily damaged, and the
low velocities attained by larvae are difficult to
measure. Moreover, there is a large disparity in
reported swimming speeds of hsh larvae. Speeds
of ahout 1 body lengtli/s (BL/s) have heen documented on film or videotape Tor Tree-swimming
larvae (Rosenthal and Hempel 1970; Hunter 1972;
Batty 1984). Whcn larvac are subjected to currcnts
in a furnc, sustainablc swimming spccds of somc
larvac increase lo 3 BL/s o r more (Houde 1969;
Laurence 1972; Doyle el al. 1984). In flunie studics, groups o r striped bass larvae suslained speeds
of 4 BL/s (Doyle et al. 1984) and larvae of largemouth bass Microp1rru.s .s~zlrnoiu'rssustained 5
BL/s (Laurence 1 972). Larvac of chub mackerel
Scombr~rjuporricusswam around thc perimeter oT
a rcaring tank Tor long periods at 3.8 RL/s (Hunter
and Kirnbrell 1980).
Bccause swimming speeds detcrniine the amount
of watcr a fish larva is ublc lo search for h o d ,
swimming speed measurements are needed for inclusion i n feeding models. Such models attcmpt
to synthcsizc information on larval fccding, energy expcnditurc, and growth to quantiry food Icvel? neccssary for larval survival (Blaxtcr 1986).
The goals of my study wcrc (1) to dctcrmine sustainablc swimming speeds (maintnincd in I -h tesls)
for three size-classes o r first-fccding striped bass
larvac (6-6.9 rnm, 7-7.9 imn, and 8-8.9 m m ,
hercufter rererred to as 6 mm, 7 m m , and 8 m m )
in a current flume; (2) to cvaluu~ethe erect of
swim bladder inflation on swimming performance; and (3) to relate swimming performance
SWlMMlNCi SPEEDS OF STRIPED BASS LARVAE
FROM HEAD TANK
valve
needle
Z
H
needle
valve
-,funnel
1
50 crn
swim tube
nitex
SCreenlng
-
-
I
I
I
I .
3
nitex
screening
-
valve to +-,
remove fish
Z
I I
needle
valve
I
needle
valve
10 crr
TO RFTURN TANK
Flc;rr~eI.-Apparatus uscd to tcst swimming ahility of striped bass larvae. Arrows denole direclion of water
flow during swimming tcsts. Swim tube (50 cm long) is clcnr; rcmnindcr of appnrntus is opnquc.
to the volume of watcr a larva is capablc of starching for food.
Methods
Culture methods. -From April to June 1992,
striped bass larvae from thc California Depaament of Fish and Game Central Valley Hatchery
were transferred to laboratory facilities at the LJniversity of California, Davis, 1 4 d after hatching.
I reared the larvae in 32-L circular tanks in a flowthrough system held at 17°C and 3% saiinity. Fish
wcrc maintained at a dcnsity o r 8/L and in a 12
h light :12 11 dark photoperiod. Artemia sp. nauplii
were maintained at a nominal concentration of
lOO/L during duylight hours by aliquot sampling
2-3 timcs pcr day.
E x p ~ r i r n ~ n t udesign.
i
-Experiments were designed to dctcrmine failure velocity (the currcnt
velocity at which 50% of the larvae fail to sustain
swimming specds) in I-h tests. Current velocitics
tcstcd were 0 . 5 4 . 5 cm/s in 0.5 cm/s increments.
Oldcr larvae had a wider range of swimming ability and wcre tcstcd at more velocitics than 6-mm
larvac. I tcsted 6-mm larvae at six velocities, 0.53.0 cm/s; 7-nlm larvae at scvcn velocities, 1.04.0 cm/s; and 8-mm larvac at seven velocitics.
1 . 5 4 . 5 cm/s. Tcn fish in cach size-class were tested individually at cach vclocity. I began testing
fish 8 d posthatch.
Switnming apparatm. -The swimming apparams rollowed the design of Rishai (1960) and
Houde (1969). A rcctanglc was assembled from
19-rnm PVC (polyvinyl chloride) pipe. Four 13nim nalgene needle valves, one at each comer,
regulated the water flow (Figurc I). Fish were tested in n clear tube (50 cm long) that ran across the
middle of the PVC rectangle. Gravity-induced
current flowed in either direction, and both current dircction and vclocity wcrc controlled by valve
adjustment. Air bubblcs wcrc bled out of the apparatus. Nitex fabric screening (900-km mesh)
prevented ihe fish fiom moving out of the swirnming tube and mny havc hclpcd crcatc a laminar
flow. I mcasurcd currrnt velol-itics by timing thc
passage of dyc through the tubc. Tcn vclocitycalibration tcsts wcrc nladc for each vclocity. and
the nican valvc sctting was delcrmined. Watcr was
supplicd to the device from the cullure system
hcad tank, in which temperature and salinity were
constant.
Expritr7cntal p r o t o d . -A larva was introduced into thc water-flled funncl ofthr swimming
T A ~ LI E
.-C:urrent velocitics (calculawd from probil
annlysis) at which 50% of striped hnss larvac in lhrcc
si~c-classcsfailed to rcmain in a swimming tube I'or 1 h
( I -h FV50)at 17°C. Also given arc confidencc limits for
I -h WSO for each size-class. BL is body lcngth.
I-h FVSO
95% confidence
limits
Medinn
vclocity
Vrlvcitlwi In cm/s
1.7
2.1
3.0
1.3 5 FV50 r 2.1
1.6 5 FVSO 2.5
2.6 5 W 5 0 5 3.4
ity can bc viewed as a bioassay experiment (Brctt
1967; Houde 1969). Current velocitics arc dose
rates, and thc vclocity at which 50% of the larvae
fail (FW50) is analogous to the dosc at which 50%
oflest organisms die (LD50). 1 used thc SAS probit procedure (SAS Institute 1990) to calculate W 5 0
and confidence limits for cach size-class. I used a
chi-square test of indcpcndence for a two-way
contingency table (Sokal and Rohlf 198 1) to test
for dilTerenccs in swimming ability attributable to
swim bladdcr inflation.
Vclocilim In BL/a
2.8
3.0
3.8
2.2 r; W 5 0 5 3.5
2.3 < FV50 5 3 . 6
3.3 5 IT50 5 4.3
Results
Failure vclocities (FV50) incrcased with sizc for
stripcd bass larvae and were 1.7, 2.1, and 3.0 cm/s
for 6-, 7-, and 8-mm larvae, respectively (Table
device with a plastic spoon, Kelcasc of thc clamp I). Lack-of-fit tests (Pcarson chi-square) for cach
below the funnel washcd the larva into thc swim- successive size-class showed that the fraction failming tube. The currcnt was immediately shut off, ing to swim for I h at each vclocity fit the probit
and the larva was allowed 10 min to acclimate to model (P * 0.14, 0.43, and 0.89), and confidence
thc tube. 1 incrcused the currcnt gradually up to limits wcre calculated (Table I). Fish tended to
tcst vclocity. Because most fish larvae arc pho- either swim for 1 h or fail within 15 min; intertotactic (Corazza and Nickum 1981) as well us mediate swim times wcrc less common (Figurc 2).
Larval behavior diffcred in thc velocities tested.
rhcotactic (Blaxter 19691, an incandcscent light
source at the upstream cnd oT the tube providcd Aftcr being washed inlo the tube and in thc ahthc larva with an additional orientation cuc. 1 ob- sencc of a current, larvae explored thc tube unless
served thc larva carefully during thc accli~ltation they were damaged. Damagcd larvac lay on the
pcriod and the first 5 min of the test. If therc was bottom and were removed. Whcn the current was
any cvidcnce of damage to a larva from handling turncd on, larvae imnlediatcly swam into it and
or if it did not swini for 5 min. the test was ter- oriented thcmselvcs facing the upstream cnd of
thc tube und near the light. At higher vclocities
minated.
I scorcd a larva as "passed" if it remained in larvae maintained a constant position in the top
the 50 cm swimming tube for 1 h. If the larva half of the tuhe, whcrc the velocities wcre expccted
was washed downstream and impinged on thc to bc near the mean value in the cross section of
Nitex screening in less than I h, it was scorcd as the tuhe. At lower vclocities the fish did not main"Tailed." Occasionally a larva would lie on the tain a constant posjtion and tended to movc ahout
boltom orthe tube whcrc the currcnt was minimal the tuhe, alternately losing and gaining position in
reference to the upstream cnd near the light.
becausc ~Thydrodynamicdrag. If a larva "rested"
Tor morc than 5 min, it was scored as failod. The Whenever a larva approached the darkness o f the
fish was removed from the tubc aner thc swim- downstream cnd of the tube it swam vigorously
ming tcsl and held in a beaker. Afier being oh- upstream. At rai lure veloci tics, larvae tendcd to
servcd in the beakcr Tor at Icasi 1 h, the fish was losc tubc position incrementally and spent scveral
mcasured (standard length), and thc prescnce vr minutes at the downstream cnd fighting to stay in
absence of an inflated swim bladdcr was recorded. the lit portion of the tubc. Failure was morc unObservations were recorded on fish activity at predictable at lower velocities; at low vclocities, a
15-niin intervals throughout thc swimming tcst. I larva could bc swept away (or swim downstrcam
recorded position of thc larvae in the tubc (cross- or simply stop swimming) from any position in
scctional and lengthwise) as wcll as tail-heat fre- the tube. The rraction of oldcr larvac complcting
the 1-h tests was more prcdictablc and more closequcncy (slow or fast).
Stufirticul anui.v.ci.v. -I used probi t analysis, ly related to velocity than that of 6- and 7-nim
which is based on the ]incur transformation of a larvac (Figurc 3).
Failurc to sustain swimming in thc current was
sigmoid-type curve (Hubert 1984). to analyze the
swimming data. Determination of swimming abil- not permanently dcbilitating. All larvae survived
SWIMMING SPEEDS OF STRIPED BASS LARVAE
Swim time (mln)
FIGIIRE
2.-Duration of sustnincd swimming (min) by striped bass larvae of three size-classcs in n laborntory
swim chamber, all vclocitics combined.
the tests and swam nornlally in beakers for at least
I h after bcing removed from the tube.
There was no difference in sustained swimming
ability between thc larvae due lo the prescncc or
0.20,
absence of an inflatcd swim bladder (I'
0.70, and 0.35 for 6-, 7-, and 8-mm larvac, respcctively). Observations during the swim test
suggested that larvae with uninflated swim bladders swam w i ~ hgreater tail beat frequency.
-
Discussion
Striped bass larvae of 6-9 mm approach thc
uppcr range of sustainable swimming speeds that
havc been deterrnincd for larvae o r other percihi^ fishes in this size range (Table 2). The speeds
(BL/s) I mlculatcd for striped bass larvae arc
slightly lower than those of Doyle et al. (1984).
but our methods diffcrcd and the larvae in my
study werc smaller. Doyle el al. (1984) begun thcir
experiments with 9-1 1.9-rnm larvaf and tcstcd 10
fish a1 a time at three velocities: 3.0 cm/s, 6.0 cm/
s, and I8 cm/s. All 9-1 1.9-mm larvae failed at 18
cm/s. Neither water temperature nor number of
replicates were specified by Doyle et al. (1984). In
addition, because 10 fish wcrc tcstcd at the same
time. ihcre may have been a schooling effect.
Striped bass larvae from both studies, however,
were able to attain 3 4 BL/s (Table 2).
Cruising spccds become asymptotic at 3 4 BL/s
Ibr many spccies of adult fish (Bainbridge 1960).
I did not rcach the asymptote in my study, but
my objcctivc was lo study swimming speeds o r
the youngest larvae at the age that thcy are switch-
ing to exogenous roods. Doyle ct al. (1984) recorded speeds of 10 BWs for 12-20-mm larvac,
but Doyle el al. included fish that occupied areas
of reduced flow along the edges of thc flume. Critical swimming speeds, the maximum velocity fish
can maintain Tor a precisc time period (Beamish
1978), of3-4 RL/s have bccn measured for striped
bass juveniles (Young and Cech, in press); adults
reach critical swimming spccds of 2.9-3.3 BL/s
(headman 1979). Sisson und Sidcll (1987) reported sustainable swimming spceds of 1.8-2.4
BL/s for striped bass adults by measuring thc speed
FICILIKE
3.-Frnction of striped bass larvac of cach
size-class [bat rontinucd t o swim for I h in laboratory
swimming tests as a function of watcr velocity.
TAME2.-Average sustninablc swimming spccds for
seleclcd fish larvac (stnndnrd lcngth 5-10 mm). BL is
body length.
Tcmpar-
nlurc
Species
Paciljc
Study
melhud
("r)
Speed
(BWs)
10
0.83
Film
Kownlhal
and Hcmpcl
(1 Y 70)
10
1.3
Videotape
Batty (1984)
17
1.7
Film
Hunicr
hcrringn
Northern
nnchovy"
Slripcd
bass
Lirgcmouth
bass
Rcfcrcnce
(1 972)
noyle
et al. (1 984)
This study
Laurence
(1972)
Yellow
perchr
Wnlleyed
at which white muscle fiber was rccrui~ed.Swimming performance, expressed in HUs, favors
smaller individuals due to reduced hydrodynamic
drag (Beamish 197R), and this may explain why
the developing larvac wcrc able to rcach adult
speeds according to this measure.
Swimming in a currcnt flume may produce
higher spccds than would normal feeding activity
in a rearing tank. The rorced swimming speeds
did not appear to bc ovcrly stresshl becausc all
fish in my study swam normally Tor at least 1 h
after testing and did not appcar otherwise stressed.
Fish that completed the 1-h tests remained in the
upsiream end of thc tubc und had to bc mancuvered out the tubc after an hour, suggesting that
the spccds reachcd could be sustained Tor longer
than the test period.
Striped bass larvae in this study showcd vanable swimming ability. Thc ability of younger larvae to sustain swimming for 1 h was less closcly
related to velocity than that of 8-mm larvae (Figure 3). Thc more variable swimming ability in
relation to velocity among the youngest fish may
indicate a gencral improvement in swimming performance with age. The greatest variability in velocity-related swimming performancc occurred in
7-mni larvae (Figure 3) and may indicate a transition period in swimming ability.
Methods for measuring swimming speeds of lar-
val fish [all into two categories: observation, including the use of film or videotape, or testing
swimming ability againsl a cument in a flume. Observation techniqucs tcnd to restrict fish to smallcr
containers suitable for photographic purposes and
may explain, in part, the lower velocities attained
in observation studies (Table 2).
The development of swinlniing ability is spccics
specific, and diffcrcnces in swimming spreds for
5-1 0 m m larvae (Table 2) may represent different
stages of development or swimming modes. Walleye larvac arc relatively poor swimmers ni 7-9
m m (Table 2) due to largc yolk sacs and slow
development o r fins, but swimming speeds double
as yolk is absorbed (Houde 1969). Swimming
modes bascd on anatomical differcnccs (Webb and
Weihs 1986) also afrect larval swimming speeds.
The eel-like larvac of Pacific herring swim in a
slow undulating fashion (Rosenthal and Hempel
1970; Batty 1984) whereas northcm anchovy
(Hunter 1972) achieve intermediate speeds with
"beat-and-glide" swimming (Table 2). Chub
mackerel rcach high speeds with continuous tail
beats (Hunter and Kimbrell 1980).
Swimming modes and consequent foraging
ability arc based on energetic tradeoK5 (Huntcr
1981). Swim bladder inflation achieves neutral
buoyancy, increases swimming cfficiency (Doroshov et al. I 981), and might bc expected to aid
sustained swimming. In my study, however, I
found no difference in 1-11 sustainable swimming
spccds due to thc presence or absencc of an inAnted swim bladder. Fish without inflated swim
bladders swam with greater tail beat Trequencics.
Chub mackcrcl larvae attained high speeds with
rapid tail beat frequencies, which overcame negativc buoyancy (Beamish 1978), but thc larvae
paid a high metabolic price (Hunter and Kimbrell
1980). Rapid tail beats and fast swimming help to
increase search area but are not as cncrgetically
favorable as beat-and-glide swimming used by larvae with inflatcd swim bladders (Wcbb and Weihs
1986). Rapid tail beat frequency becomes incrcasingly unravorable as larvac grow and Reynold's
number and inertial forccs increase. Striped bass
larvac with uninflated swim bladders have poorer
reeding success and survival rates than their counierparts (Doroshov ct al. 198 1 ; Meng and Orsi
199 1).
Swimming speeds are important to fceding
models because speeds dctcrmine how much area
larvac are capable of searching Tor food (Hunter
198 1; Dabrowski et al. 1988). Reactivc distance,
the distance at which prey is perceivcd, is com-
SWIMMING SPEEDS OF STRIPED BASS LARVAE
bincd with s w i m m i n g spccd l o d c t e r m i n c t h e volume o f water a larva i s capable o f searching (Rlaxt,, 1986). S w i m m i n g speeds reachcd b y striped
bass in this study suggcst t h a t t h e larvae m a y be
capable o f scarching grcaler v o l u m e s t h a n prcviously believed. R c p o r t c d search v o l u m e s range
from 0.1 L / h lo 1.8 L / h for 6-10-mm fish larvac
(Hunter 198 1). A s s u m i n g a half-circle perceptive
aren a n d u 5-mm reactivc distance similar t o other
larval fishes ( H u n t e r 1 9 8 I), striped bass l a w a c
may be capablc o f searching 4 L/h. T h i s searching
ability suggests the larvac m a y be able t o grow
and survive a t prey densities ohserv-vcd in t h c field.
Special t h a n k s goes t o R. G. O t t o a n d t h e Elcctric Power Research Institute Tor making this study
possible. I t h a n k P. Moylc for his c n t h u s i a s m and
support. D. B. Kclley p r o v i d e d tccbnical assistance a n d careful reviews o r t h e manuscript. I a p preciate c o m m e n t s o n t h e m a n u s c r i p t f r o m R.
Yosbiyama a n d M. G a r d . I a m grateful f o r t h e
ongoing efforts and cooperation o f the Central
Vallcy Hatchery.
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Received
Nuvcmher 20, 1992
Acccplcd April 13. I993