Abs!racl.-Length ofconhnemcni in a dip net affected subsequent pcrfi)rnmancc oT2-3-ywr-old
striped bass M o r o n ~ s a x u f i l i in
s a swimming clrallcnge. Fsh that wcrc not confined or wereconhned
Tor only 5 min could consistently swim for 10 min at 100 cm/s, whereas fish confined Tor longer
than 15 win o h m could not. Average swimming time was signihcrantly 1cs.s Tor striped bassconfined
Tor 15 rnin or longer than for unconfined conrrols. Plasma cortisol. glumsc, and lncwte conentrntions were always higher in fish after a swimming challcngc than in rating fish sampled from
the holding tank, although length of net confincment belorc swimming had little e f k t on postchallcnge plasma variables. Timc of postchallenge blood sampling. howcvcr, had a signifimnt effect
on all three plasma variablcs: glucose and cortisol conccntralions were higher in striped bass
immediately after they wcrc removed from the swimming chamber, whereas laclate concentration
e
variables rcsembld
was higher aficr 45 rnin of rccovcry. Kcsting and stress levels d t l ~ plasma
thosc measured in other fishcs, except Tor thc extremely largc and-rapid rise in plasma cortisol
concenlradon from less than 50 ng/rnL in resting 6sh to ovcr 500 n'JmL in fish that lrnd swum
Tor 10 min.
Culturc a n d managcrncnt practices oiien rcquire thc handling.and confinement of tish, a procedure which, if t o o stressful, m a y be lethal (scc
rcview by Parker 1984). If the fish d o not die,
howevcr. thc extent t o which their future performance may be compromiscd is unknown. Three
physiological changes routinely found in stressed
hsh a r c thc clcvations o f plasma cortisol, glucosc,
a n d lactate coriccntrations (c.g., Nikinmaa c t al.
1984; Woodward a n d Strange 1987). T h c question
thcn ariscs whethcr such changes indicate s o m e
s ~ ~ b l c t h but
a l dcletcrious cffkct, o r simply rcflcct
succcssfi~laccommodation t o thc stressor hat w r rics n o mcasurablc futurc cost.
To addrcss t11c problcm o f evaluating sublclhal
strcss in fish, Wedcmcycr and M c k y ( I 9 8 I) descrilxd Lhc concept o f the challcngc tcst. This requires n sequence o f two d i f i r c n t stressors, the
sccorrd nnc hcine amplilicd by the clfcct o n the
hsli o r the first. Although rainbow trout Otlcmrl~.vr~chc.v
n7jkiss had a greater cortisol rcsponsc to
confincnicnt if thcy hati previously h c n cxposcd
lo acidic coridilions ( I h n o n c t al. 1985). they
s l ~ o w c dno enipirical cvidcncc o f rcduccd pcrlornlancc. According t o Wedcrricycr and McLcay
(IORI). appropriate clrallcntl.cs include a first
slrcssor that mimics t l ~ cp r w c d u r c k i n g cvalu; ~ t c d;lnd ;I scconti strcssor (challcngc) thaf has an
empirically disccrni blc endpoint o f recognizcd
adaptive significance. O u r objective was t o evaluatc thc cKect of net confincmtnt o n striped bass
Moronc samfilis in a test with a meaningful challenge (high-spced swimming) while making physiological measurements hclprul in defining the
strcss level.
Methods
Two- and 3-ycar-old striped bass (500-1,600 g
live wcight) from thc California Department o f
Fish and Game's Ccntral Vallcys Hatchcry wcrc
raised a t Ihc I k p a r t n i c n t o f Wildlifc and Fisheries
Biology, University oC California, Davis. T h i s
study was pcrforrncd during the sumrncrs o r 1988
and 1989. Although thc weight of thc fish varied
considerably, a n a l y s i s o f v a r i a n c c ( A N O V A )
showed no significant dillcrencc irr average wcigt~t
orstriljcd bass used in 1988 or 1989 (P = 0.82).
Fish wcrc held in acratcd, 5 10-1, fikrglass tanks
supplied with flowing, norrchlorinatcd, air-cquilibratcti well watcr a t 25°C. Fish wcrc s u b j c c ~ c dto
nn initial strcss by confining lhcni in a rcclangular
(40 x 25 cni) 3 0 x n i - d c c p d i p rmcl submereed just
below lhc surfacc o f t h c walcr-; 1I1cwatcr was vigoruusly ;~cratcdIxncath thc net. T h c dcpth o r 11rc
rlct was ndjustcd r o yiclrl n conrpacrblc dcgrcc o f
ronlincrncnf to varying si/cs of fish. Slripcd bass
wcrc c:irnlir~cdli)r 5. 15. 25, or 35 niin.
Aftcr net conlincnlcnl, lish wcrc subjcctcd to a
swirnrninl: challcngc by k i n g placed in a 34-cmciixmclcr, clear acrylic swirnniirrg clran1bc1cquippcd with n variable-slxcd motor-irnpellcr
:~sscmhly.The swimming apparatus was wlihratcd by rclnting watcr velocity mcasured in thc
swimn~ingclramkrhy a clcctromagnctic now mctcr to motor shaft spccd measured by a variahlcfrcq~rcncystroboscopic light. ARcr a fcw scconds
of low water vclocity that allowcd thc fish to bccomc oricntcd, velocity was increased to 100 cm/
s. G3ch fish rcmaincd in thc chamber for 10 min
or until it Fdikd lo swim against the current. Control fish (0-min initial strcss) wcrc not confined in
the nct, but wcrc placed directly into thc swimming chamber. Cross-sectional area of each fish
was less than 10% of the area of the swimming
chamber; thus, no swimming velocity correction
was necded (Rtarnish 1978). In the summer of
1988, 20 fish (4 from cach confincrnent period or
treatment group) were challcngcd. In the summcr
of 1989, 40 fish (8 from each treatment group)
werc challenged.
Timing of blood sampling differed bctwecn
ycars. In 1988, blood samples wcre taken 45 rnin
aftcr the swin!ming challcnge, while the fish rccovercd in watcr containing 10% NaCI. Also in
1988, [our fish wcre bled immediately aAcr being
removed from thc holding tank to provide rcsting
valucs. In 1989, blood sarnplcs werc takcn immcdiatcly aftcr fish were rcrnovcd from thc swimming. tank. Samplcs wcrc obtaincd by cardiac
puncture with a heparinized syrinec. Aftcr hematocrit valucs were obtained (1989 only), rcmaining blood was centrifuged and the plasma
was withdrawn and frozen until further analysis.
Iactatc and glucose concentrations in the thawed
plasma wcrc measured with a calibrated analy~er.
Plasma cortisol cotrccntntion was determined at
thc CJnivcrsity of Tcnncssce by "Coat-/\-Count"
ratiioimrnunoassay fr-om Diagnostic Products
Corporatiori. T h c assay uscd 1251-labelcdcortisol
lo dctertninc pcrccnt binding over a rangc of standards of 0.25-1 2.50 n d t u b e . Depending on cortisol coruxntration, cilhcr 5 or 25 PI- of plasma
wcrc ass:~ycd pcr tuhc. An intcrnal standard of
poolcd stripcd bass plasma was run with each of
five assays and yicldcd a mean of 253 ng/rnL and
an SE of I(;. Cross-reactivity with other naturally
occurring stcroids was lcss ~ h a nl.SO/o. Stalistiwl
difli-I-cnccs wcrc tictcrnlincd by A N O V A and
analysis of coval-ii~ncc( A N C O V A ) .
Nct-con6ncmcn1 timc nlli-ctcd subscqucnt perror~nariccin thc swimming challcngc (Figurc I ) .
Fish wcrc trmlcd cxactly the sanlc way both ycnrs
in this portion ofthc study and thcrc was no sign i k i n t diKcrcncc hctwccn ycars (ANOVA, 1' =
0.239). Stripcti bass that wcrc not conlincd (controls) orconfincd Toro~ily5 mi11could consistcnlly
nicct thc cliallerigc (swim at 100 cm/s fix I0 min)
wllcreas fish conf~ncdfor 25 or 35 rnin oftcn could
nor. Avcragc swimming timc kll to about 7 min
aflcr 15 rnin coniincmcnt in the net and to lcss
than 6 niin for the longer confincrncnt pcriods
(Figurc 1).
Data from both years analyzed togethcr indicate
a signifiant (ANOVA, P = 0.058) elfcct oflcngth
of confincment on swimming timc; fish confincd
for IS min or longcr swam for a shorter time than
unconfined controls. After the longer confinemcnts, individual performances varicd widcly:
some fish met the 10-min challcnge and others
failed aftcr 2nly a fcw scconds in thc chamber.
Rcgrcssion gnalysis rcvealcd no relationship between weight (wt) of fish and swimming time Cy):
y -0.003 wt + 10.2; r 2 = 0.059; slope was not
significantly different from 0, P = 0.063.
All thrcc plasma constituents (cortisol, glucose,
and lactatc) were significantly (P < 0.05) highcr
in striped bass after the swimming challengc than
in rcsting fish sampled from the holding tank (Figurc I). Plasma cortisol concentration incrcascd
from 45 ng/mL in unstressed animals to betwecn
500 and 800 ng/mL immediately arter tbc swimming challcnge. Striped bass sampled during thc
recovery period (45 rnin postchallcngc) had significantly (ANCOVA, P < 0.001) lower plasma
cortisol than fish bled on rcmoval from the chamber. Longer confinement before thc challenge test
tcndcd to rcsul~in slightly highcr plasma cortisol
conccntrations in fish sampled immediately after
swimming, though this effcct was not significant
(ANCOVA, I'
0.238).
Plasma glucose increased Crom 75 rr~g/dLin animals in thc holding tank to ktwccn 150 to 300
nrg/dl. in fish aftel- swimming. Thcrc was a significant (ANCOVA, P = 0.029) cKcct of lirnc of
blocd sampling on glucosc cotrccntration: glucosc
was highcr in fish blcd imnlcdiatcly aftcr rcmoval
rrom thc charnbcr than aftcr 45 min I-ccovcry in
thrcc out of fivc trcatrncnts. Ixrrgth of confincrilcnt had a significanr cffcct only on fish blcd immcdiatcly aftcr rcrrinvnl frorrl thc chnn-rkr-;longcr
conhncrricnt (25 rnin and 35 win) ~ ~ s u l t cind sig-
-
-
Time in Net
(min)
FIGURE1.-Average swimming time and plasma cortisol, ducosc, and lactate concentrations in striped bass
confined for different times in a dip net and then challengd by forced swimming a1 a 100<m/s water velocity. H
indicates fish sampled directly from the holding tank and C indicates controls thnt wcrc not confind k f o r c
swimming. Solid circles represent 1988 fish sampled For blood 45 min nfter Uley wcrc removed from the swimming
SE, N = 4). Open circlcs n-present 1989 fish samplcd [or blood imrncdintcly ancr thcy wcrc
chamber (mean
rcmnvcd frorr~t l ~ cswimming chnmlxr (mean + SE. N = 8).
n i f i w n t l y highcr glucosc lcvcls ( A N C O V A , P
=
0.03 1).
Plasrna lactate c o r r c c r r ~ r a t i o irrcrcascd
r~
f r o m 0.6
~ n m o l / Lin rcsting stripcd bass t o k l w c c n 1 0 and
25 rnrnol/L in fish a r t c r t h e challenec. Lactatc conccntratiorr w a s corlsistcntly liighcr in Irsh blcd 45
nrin a r t c r rurnoval rrom t h e c h a r n h c r thari ill l h o s c
tdcd irnrncdiatcly (sij:nifimntly diKcrcnt b y A N COVA, /' .-; 0.00 I) c x c c p t Tor Irsh subjcctcd t o thc
lnngcst n e t c o n f i n c m c n l (35 min). Lcnetlr o r c o n fincrncnt a p p c a r c d t o h a v c liltlc cfTcct o n laclalc
concenmation m m s u r c d irnrncdiatcly after s w i m ming.
Hcrnalocrit ( r n c a ~ rYo with SE) n ~ ~ s u r cimd
mediately aflcr s w i m m i n g t c n d c d t o incrcasc w i t h
C'onlincmcnt (rnin)
I tcrnatocrit (%)
0
5
30.8 (3.4)
15
25
35
31.5 (3.1)
33.6 (0.9)
33.0 (2.0)
34.3 (4.4)
co~liincmcntIxror-c swinlririn~;lind a signific;~nr
cllbct or1 plasm;r glucoso cinly i l l san~[)lcswc look
cndcd and tl~cnonly
Wc found ;I dosc-dcpcndcril rcli~lior~sliip
Ix- iniriicdi;itcly aftcr swin~rnin~;
twccn initial confiricnicnt and subscqucrrt swi~ri- wit11 the longcsl conlinc~ncntlimes (25 and 35
niing pcrforniancc Tor striped bass (Figurc I ). Fish min). This may IK duc to thc tilnc (c.g.. >30 min
that wcrc not subjjccrcti lo confincmcnt, or con- in clianncl catfish: Strangc 1980) ncccssary lor hyfined only 5 min, ~ l ~ n oalways
st
swam thc r d l 10 pcr~lyccniiato appcar alicr thc oriscl of stress.
Mciin plasnra lactalc conccntratiorr bcforc our
min al 100 c d s . For our fish. h i s watcr vclocity
10-niin swinrniin~challcngc (0.6 nrmol/L) was
approxiniatcd t l ~ c3.3 and 2.9 body IcnptIrs/s thal
Frcadman (1979) tietcrmined as thc rnaximtm similar to resting mean blood lactalc conccnlrasustainable swimming spccd for striped bass forccd tion n ~ u s u r c din cannulatcd stripcd bass (Nikinto swim Tor 30 and 45 min, rcspectivcly. T h u s . i t maa ct al. 1984). Swimming time a p w r s to inis not surprising that our unstrcsscd fish had littlc fluencc lactatc conccnlrations in this species
problcm swimming at that rare for 10 min, al- bcwusc Nikinmaa et al. (1984) measured 8.2
though the appearancr. of lactate in the plasma mmol/L lactalc in stripcd bass blood artcr 5 rnin
indicated that white rnusclc was being uscd (Rob- of vigorous cxcrcisc, and we rncasurcd 12.2-23.3
mrr,oVL lactatc in the plasma aftcr ner wnfinccrts and Graham 1979).
Striped bass confined for 25 rnin or longer were mcnt and 10 min of vigorous swimming. On the
unable to meet the swimming challenge consis- othcr hand, we did not find lcngth of confinemcnt
tently. Wc suspcct that prolonged nct cclnfinemcnt to have a significant cffcct on lactate concentraincreased maintcnancc metabolic demands and tion. Presumably, lactate was produced primarily
decreased active metabolic capacity (see revicws as a consequcncc of s w i m m i n ~rather than of netby Fry 197 1 and Brett and G r o v e 1979). Wc con- confincd struggling. Thc slight dccreasc in lactatc
cludc that slight handling stress equivalent to 5 scen in fish bled during recovery a t longcr conmin o r less of confinemcnt docs not impair the hnemcnt timd'may be rclatcd to their lowcr mean
ability of striped bass to swim at high spccd, swimtning time.
whereas stress cquivalent to confinemcn~of 25
Timing of the blood sampling influenced lhc
rnin or longer does compromise high-speed swirn- blood chancteristics; cortisol was higher immerning.
diately aftcr fish wcre rcrnoved from the swimI'lasma cortisol conccntration in striped bass ming chamber than aftcr 45 rnin o r recovery,
from thc holding tank (45 ng/mL) was comparable whereas lactatc was highcr aftcr 45 rnin. Thesc
lo thc rangc of 1 M 0 npJmL measured in adult findings probably resultcd from thc rapid secrcstripcd bass collected by clectrofishing from fresh tion of cortisol rrom interrcnal tissue into thc blood
water (Tim et al. 1983). I'lasrna cortisol measured of the closely associated posterior cardinal veins,
in our stripcd bass imnlcdiatcly aftcr removal from whcrcas lactate must diruse into the blood from
thc swimming chamber showed a slight, though the poorly vascularized white rnusclc (Bone 1978;
not statistically signifiwnt, incrcasc with longer Grornan 1982). Cortisol was lower arter 45 min
confinemcnt. Striped bass confined for 25 mi11and of rccovcry than immediately aftcr fish wcrc rcbled immcdiatcly artcr removal from the swini- movcd from the swimming chamber cven though
rning charnbe? had a mean plasma cortisol con- the rccovcry took placc in 10467 NaCI. This concentration of 860 ng/mL. Fingerling striped bass centration ofsalt har k c n shown to incrcasc plassubjected to transport in frcshwatcr had conccn- ma cnflisol in striped bass (Davis ct al. 1982).
Finally, as a practiml conclusion d o u r study.
tra~ionsorabout 1.000 n d m L aftcr 3 11 (Mazik el
wc sug.gcst that fishcrics managers lakc a r c not
31. 1991).
I'lasma glucosc concentration of striped bass 11) to introduce s t r i ~ dbass into situations that rcour holding tank (75 rng/dL) was slightly lowcr quirc fast swimn~iny,aftcr handling stress of over
than coruxnlrations rcportcd Tor lr-csliwatcr511-ipcd 5 win.
1m.c collcctcd rrorn thc wild (80-1 20 mpJdL; Tim
ct nl. 1983). Aftcr corihncmcnt and swininiing,
Wc acknowlcdgc the Univcrsity of Tcr~r~csscc
our stripcd Imss had plasma glucose conccnlralions i n the r:ingc of 200-300 mg/dL, which is and thc Univcrsity oTGlifornia A&ricultur-nlEx.sirnilat to tho coriccr1t1-aliens Mazik ct al. (1991) pcrirncnl Stations Qnnt 3455-11) and thc Califorr,cportcd lion1 fingerling str-ipcd bass a k r porid nia Ikparlrncnt o r Fish and Gamc (conlract
11;lr-vcstand ;I fcw hours into tr;t~lsport.LcnglI~ul' (3- 1733 Lo J.J.C.) for rcscarch supl)ort. Wc thank
(;roman, I). H . 1082. Ili5tolo~yof- tllc s l r i p d h:iss.
A~ncriwnFislicncs Socicly Moncrgr:~ph3
Mazik, 1'. M., 1%. A. Si~nco.and N. C. I':~rkcr. I99 1 .
lnflucncc o f w:lrcr Ii:~rdncssand s ; t l h or1 s u w i v d
and pliysioloeiml chat-ac~cristicsofslripcd bass during and aflcr Imnspon. Tranwclians of lhc Arncrican I~ishcricsSociety 120: 12 1- 126.
Nikinmaa, M.. J. J. Ccch, Jr.. and M . McEnroe. 1984.
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Rcccivcd January 14, 1991
6 . Acadcmic Prcss. New York
Accepted Augusr 29. 199 1
:~ss;iy,wlricl~was pcrlbrlncd in lhc lalx)ratory of
I I. K a l ~ c s l l ,I k p a r l r n c n t oCAnimal Scicncc. IJnivcrsity ol'Tcnncsscc. W c also thank K . I lashagcn
and M. Cclchran o r t h c Calirornia Ucparlnrcnt oT
Fish a n d Gamc for stripcd hass, a n d W. Ucrg a n d
A . ficath Tor critical readings o f t h e manuscript.