RESEARCH Open Access
Adap i e lexibili y in he eeding beha iou o
b own ou : op imal p ey size
Ja ie Sánchez-He nández
1,2*
and Fe nando Cobo
1,3
Abs ac
Backg ound: B own ou , Salmo u a Linnaeus, 1758, is a species o signi ican conse a ion and socio-economic
impo ance. A consequence o his impo ance is he eno mous amoun o li e a u e ha has been published on
he species in he las ew decades. In gene al e ms, b own ou has been conside ed as a size-selec i e p eda o ,
e en hough i is able o eed on a wide ange o p ey sizes. Ne e heless, he e a e s ill some gaps in ou knowledge, o
example he heo e ical ela ionship be ween p ey numbe s and p ey sizes ea en by he ish need o be add essed. This
esea ch aimed o s udy op imal p ey size in he en i onmen (ben hos and d i ) as well as he po en ial ela ionship
be ween p ey size and wo o he eeding a iables (p ey numbe s and s omach ullness). Addi ionally, on ogene ic shi s
in hese a iables we e add essed.
Resul s: B own ou showed a clea p e e ence o 4- o 6-mm-leng h p ey, al hough he use o p ey la ge han 10-mm
leng h may be easible. The simila i y o he p ey size equency dis ibu ion be ween he en i onmen (ben hos and
d i ) and he die in some cases was conside able ( om 57.7% o 95.9%). Mo eo e , he esul s e ealed ha he eeding
s a egy can be ela ed o p ey size and he numbe s o p ey ea en by he b own ou ; as ood size dec eased, p ey
numbe s inc eased. On he con a y, he co ela ion be ween he a e age p ey size and ish leng h was posi i e bu
s a is ically nonsigni ican . A signi ican on ogene ic shi , in e ms o p ey size so ed by age classes, was ound in only
wo o eigh s udied popula ions. No clea ela ionship be ween p ey size and s omach ullness was ound.
Conclusions: The eeding s a egy o his species is lexible and clea ly in luenced by he size equency dis ibu ion o
po en ial p ey: ou ed on ei he small numbe s o la ge p ey o la ge numbe s o small, and heo e ically low ene gy,
p ey. Ou app oach co e s a gene al subjec in ophic ecology and animal beha iou ha may be applicable o o he
ish species o imp o e ou unde s anding o p eda o eeding beha iou .
Keywo ds: T ophic ecology; Fo aging beha iou ; Flexible beha iou ; Salmo u a; P ey size; A ailable p ey; Ben hos; D i
Backg ound
Ecologis s ha e conside ed he p ey size hypo hesis, he
ela ionships be ween p ey size and handling e iciency
by p eda o s, as one o he main ac o s in ol ed in eed-
ing beha iou (e.g. Mock 1985; Tö ök 1993; Denoël and
Joly 2001). Wi h ega d o ish species, much esea ch
has ocused on he ela ionship be ween p ey size and
handling e iciency (e.g. Mi elbach 1981; Reimchen
1991), and some ishes may be gape-limi ed p eda o s,
especially when hey a e young (e.g. Schmi and
Holb ook 1984; Schael e al. 1991; Sánchez-He nández
e al. 2011a). Indeed, p ey size is a key a iable in he
eeding beha iou o ishes (see Keeley and G an 2001
and e e ences he ein), which is usually conside ed o
be size selec i e (e.g. O'B ien e al. 1976; Bannon and
Ringle 1986). Fo example, s udies unde con olled la-
bo a o y condi ions ha e demons a ed ha ishes show
a clea p e e ence o la ge p ey i ems (Ringle 1979;
We e e 1989), which a e no mally he mos p o i able
in ene ge ic e ms, e en hough handling cos s inc ease
wi h inc easing p ey size (e.g. Gill 2003). Howe e , i is
impo an o no e ha p ey ene gy con en may exhibi
subs an ial a ia ions depending on seasonal de elop-
men , li e his o y s a egies o axonomic g oup
(e.g. Gup a and Pan 1983; Cobo e al. 1999; 2000). Fac-
o s o he han p ey size and handling e iciency, such as
* Co espondence: [email p o ec ed]
1
Depa men o Zoology and Physical An h opology, Facul y o Biology,
Uni e si y o San iago de Compos ela, Campus Su s/n, 15782 San iago de
Compos ela, Spain
2
Depa men o A c ic and Ma ine Biology, Facul y o Biosciences, Fishe ies
and Economics, UiT The A c ic Uni e si y o No way, N-9037 T omsø, No way
Full lis o au ho in o ma ion is a ailable a he end o he a icle
© 2015 Sánchez-He nández and Cobo; licensee Sp inge . This is an Open Access a icle dis ibu ed unde he e ms o he
C ea i e Commons A ibu ion License (h p://c ea i ecommons.o g/licenses/by/4.0), which pe mi s un es ic ed use,
dis ibu ion, and ep oduc ion in any medium, p o ided he o iginal wo k is p ope ly c edi ed.
Sánchez-He nández and Cobo Zoological S udies (2015) 54:26
DOI 10.1186/s40555-015-0107-x
some ish cha ac e is ics (e.g. p io expe ience, loco-
mo o abili ies, s omach ullness and senso y capabil-
i ies) and physical habi a cha ac e is ics (e.g. low
pa e ns and s uc u al complexi y o habi a ) may also
play an impo an ole in he eeding beha iou o ishes
(e.g. Gill and Ha 1994; Ge king 1994; Sánchez-He nández
e al. 2013). Al hough he eeding beha iou o ish species
has ecei ed conside able a en ion om he scien i ic
communi y (see abo e li e a u e), o he bes o ou know-
ledge, he heo e ical ela ionship be ween p ey numbe s
and p ey sizes ea en by ish has no been add essed so a .
B own ou Salmo u a Linnaeus, 1758 (hence o h
simply ou ), is a species o Eu asian o igin bu , a
p esen , is na u alized in many o he a eas all o e he
wo ld (Kleme sen e al. 2003). Fo una ely, he eeding
beha iou o ou has been well s udied (e.g. Foche i
e al. 2003; Oscoz e al. 2008; E angelis a e al. 2014),
and du ing hei li e his o y, ou unde go on ogene ic
die a y shi s (Sánchez-He nández e al. 2013 and e e -
ences he ein). Wi h ega d o changes in p ey size du -
ing on ogeny, mean p ey size usually inc eases wi h bo h
ou size and age (e.g. S eing ímsson and Gíslason 2002;
Mon o i e al. 2006; Jensen e al. 2008; Sánchez-He nández
and Cobo 2012; Sánchez-He nández e al. 2013). In spi e o
his on ogene ic shi , se e al esea che s ha e demon-
s a ed ha he in luence o gape-limi ed p ey inges ion in
his species is insigni ican (Newman 1987; Rincón and
Lobón-Ce iá 1999). No wi hs anding, ou may be used
as a model species in s udies o eeding beha iou , ega d-
less o he appa en lack o a ela ionship be ween mou h
dimensions and p ey size. He e, we s udied op imal p ey
size in he en i onmen (ben hos and d i ) as well as he
po en ial ela ionship be ween p ey size and o he a iables
(p ey numbe s, s omach ullness, ish size and ish age). We
hypo hesized ha p ey numbe s should be low when he
p eda o eeds on la ge p ey i ems, and ice e sa.We u -
he hypo hesized ha p ey sizemaybehighlydependen
on ish size, ish age and s omach ullness.
Me hods
Fo he pu pose o he s udy, and in o de o a oid pos-
sible di e ences in eeding beha iou among popula ions
due o di e ences in physical habi a cha ac e is ics,
samples we e collec ed in wadeable i le sec ions wi h
simila en i onmen al cha ac e is ics. In o al, eigh
neighbou ing i e s o Galicia (NW Spain) we e sampled
(Figu e 1) du ing June 2003 (Rois, San a Lucía, Sa and
T aba i e s) and Sep embe 2007 (Anllóns, Fu elos,
Lengüelle and Tamb e i e s). P io o elec o ishing,
samples o po en ial p ey i ems (ben hic and d i ing in-
e eb a es) we e collec ed o s udy p ey a ailabili y in
he en i onmen . Ben hic in e eb a es we e collec ed
om i les using a 0.1-m
2
Su be sample (n= 3), and a
B undin ne (250-μm mesh size, 1 m long, 30-cm mou h
diame e ) was used o collec d i ing in e eb a es. D i
ne s we e se a sun ise (8:00 a.m.) and e ie ed a e a
leas 2.5 h ( anging be ween 179 and 200 min). A e
collec ion, we ixed samples using 4% o malin and
s o ed hem o la e p ocessing. In o ma ion on p ey
a ailabili y is only p o ided o i e s su eyed in 2007.
Figu e 1 Maps o he Ibe ian Peninsula and no h-wes e n Spain showing he sampling si es.
Sánchez-He nández and Cobo Zoological S udies (2015) 54:26 Page 2 o 9
Table 1 Size equency (%) o he p ey consumed by ou
Size class (mm)
0 o2 2 o4 4 o6 6 o8 8 o10 10 o12 12 o14 14 o16 16 o18 18 o20 >20
Anllóns
0+ (n= 2) 0 10.8 27.0 2.7 13.5 45.9 0 0 0 0 0
1+ (n= 18) 1.3 18.4 23.7 3.0 27.3 24.7 0 0.3 0 0.7 0.7
2+ (n= 9) 0.4 18.9 56.9 1.3 4.7 17.0 0 0.2 0 0 0.6
3+ (n= 6) 0 15.1 52.8 15.1 1.9 11.3 1.9 1.9 0 0 0
Pooled da a 0.7 18.2 43.7 2.8 12.8 20.6 0.1 0.3 0 0.2 0.6
Fu elos
0+ (n= 37) 2.1 3.2 33.5 0 1.9 51.0 0 6.5 0 0 1.8
1+ (n= 19) 1.4 4.8 81.0 0.1 0.2 6.0 0 3.9 0 0 2.6
2+ (n= 5) 0.5 2.8 54.1 0 8.7 4.1 0 8.7 0 0 21.1
3+ (n= 3) 3.2 18.5 15.3 0.8 0 33.1 0 0 0 0 29.0
Pooled da a 1.6 4.8 60.7 0.1 1.5 20.9 0 4.9 0 0 5.4
Lengüelle
0+ (n= 6) 0 2.4 62.9 0 13.7 19.4 0 0.8 0 0 0.8
1+ (n= 13) 0 18.3 37.7 0.4 16.5 20.4 0 0 0 0 6.7
2+ (n= 16) 0.8 7.9 53.1 0.8 4.3 24.1 0 0.2 0 0 8.7
3+ (n= 4) 5.8 1.9 32.7 0 9.6 38.5 0 0 0 0 11.5
Pooled da a 0.7 10.0 48.7 0.5 9.4 23.2 0 0.2 0 0 7.2
Tamb e
1+ (n= 24) 1.6 12.6 59.6 0.7 6.7 17.0 0 0.9 0 0 0.8
2+ (n= 6) 0.3 5.2 56.0 0.9 4.0 28.4 0 2.4 0 0 2.8
Pooled da a 1.4 11.2 58.9 0.8 6.2 19.2 0 1.2 0 0 1.2
Rois
1+ (n= 31) 2.7 7.7 33.8 3.2 14.3 33.9 0 2.7 0 0.2 1.4
2+ (n= 2) 2.0 6.0 28.0 6.0 4.0 46.0 0 2.0 0 0 6.0
Pooled da a 2.7 7.6 33.6 3.4 13.8 34.5 0 2.7 0 0.2 1.6
San a Lucía
1+ (n= 24) 2.2 29.4 34.7 7.0 5.0 7.9 0 8.0 0.3 2.3 3.4
2+ (n= 5) 3.2 20.6 40.2 10.6 4.2 15.3 0 4.8 0 0.5 0.5
Pooled da a 2.4 27.7 35.8 7.7 4.8 9.3 0 7.4 0.2 1.9 2.9
Sa
1+ (n= 25) 0.6 33.8 4.0 0.9 1.1 57.8 0 0.2 0 0.1 1.6
2+ (n= 4) 1.0 17.7 3.0 0.5 3.4 70.4 0 1.5 0 0 2.5
Pooled da a 0.6 32.2 3.9 0.9 1.3 59.0 0 0.3 0 0.05 1.7
T aba
1+ (n= 15) 0.3 4.8 45.5 0.4 14.8 33.8 0 0.2 0 0 0.1
2+ (n= 14) 0.5 7.6 51.5 1.0 10.7 28.1 0 0.2 0 0 0.2
Pooled da a 0.4 5.7 47.6 0.6 13.4 31.8 0 0.2 0 0 0.2
To al (n= 288) 3.44 5.00 44.44 3.42 8.27 31.97 0.01 1.30 0.03 0.17 1.97
Da a a e displayed o each sampling si e, each age class and in o al using pooled da a. P ey we e g ouped in o 2-mm-leng h classes. The sample size (n) o each
age class is shown in b acke s.
Sánchez-He nández and Cobo Zoological S udies (2015) 54:26 Page 3 o 9
T ou we e collec ed using pulsed D.C. backpack
elec o ishing equipmen (ELT60II, Hans G assl GmbH,
Schönau am Königssee, Ge many). Fishes we e killed
immedia ely wi h an o e dose o anaes he ic (benzocaine)
and anspo ed in cool boxes (app oxima ely 4°C) o he
labo a o y, whe e hey we e ozen a −30°C un il p ocess-
ing. In he labo a o y, ishes we e measu ed o o k leng h
(FL; nea es 1 mm) and weighed (nea es 0.01 g), and he
s omachs we e emo ed. Es ima es o ish age we e made
by scale examina ion and by using Pe e sen's leng h-
equency me hod (Bagenal and Tesch 1978). Age-4+ in-
di iduals we e no included in he die analysis because
only one specimen was cap u ed in he Ri e Fu elos.
No emp y s omachs we e ound, and he s omach ull-
ness index ( ) was calcula ed as =(Ws/W) × 100, whe e
Ws is he o al s omach con en mass (g) and Wis he
ish mass (g).
Po en ial (ben hic and d i ing in e eb a es) and ac-
ual p ey i ems we e coun ed and measu ed ( o al
leng h) wi h a digi al mic ome e (0.01-mm esolu ion,
Mi u oyo Absolu e, Mi u oyo Co po a ion, Taka su-ku,
Japan). The numbe o agmen ed o pa ially diges ed
in e eb a es was es ima ed by coun ing body pa s e-
sis an o diges ion. In hose cases, p ey leng h was es i-
ma ed om he wid h o he cephalic capsule (see
Rincón and Lobón-Ce iá 1999), which was no mally
he bes -p ese ed pa .
The simila i y be ween he size dis ibu ions o po en-
ial p ey in he en i onmen (ben hos and d i ) and
hose consumed by ou was assessed using he B ay-
Cu is simila i y index. The da a we e i s ans o med
by Y= log(x+ 1), and he simila i y index was calcula ed
using he PRIMER s a is ical package e sion 5.0 (Cla ke
and Go ley 2001). In he p esen s udy, in o de o as-
sess whe he p ey size selec ion is dependen upon he
size equency dis ibu ion o a ailable p ey, we clus e ed
all ou ega dless o age a each sampling si e. Add-
i ionally, o explo e on ogene ic shi s, he simila i y
ma ix was calcula ed sepa a ely o each age class.
Finally, wi h he aim o explo ing he possibili y o a
nonlinea ela ionship be ween p ey size and he o he
analysed a iables (p ey numbe s, s omach ullness and
ish size), he cu e es ima ion p ocedu e was used using
pooled da a, which compa ed eigh di e en models (lin-
ea , loga i hmic, in e se, quad a ic, exponen ial, powe ,
compound and S-cu e). The model wi h he highes ad-
jus ed Pea son's ank co ela ions coe icien (R)was
chosen. The da a we e no no mally dis ibu ed, so in
o de o analyse di e ences among age classes in he
s udied a iables (p ey size, p ey numbe s and s omach
ullness), nonpa ame ic analyses (Mann-Whi ney and
K uskal-Wallis es s) we e used. The Mann-Whi ney U-
es was used o compa e di e ences be ween wo inde-
penden g oups because in some i e s (Rois, San a
Lucía, Sa , T aba and Tamb e i e s) only wo age clas-
ses we e analysed (1+ and 2+). K uskal-Wallis es was
used o de ec di e ences among ou g oups (0+, 1+,
2+ and 3+) in he o he i e s (Anllóns, Fu elos and
Lengüelle). S a is ical analyses we e conduc ed using he
p og amme IBM SPSS S a is ics 20 so wa e (IBM Co -
po a ion, A monk, NY, USA). All o hese es s we e
conside ed s a is ically signi ican a Ple el <0.05.
Resul s
A o al o 288 ou ( ange = 48 o 300 mm) was examined
in he p esen s udy, wi h 15,131 p ey i ems ( ange = 1.1
Figu e 2 Size equency o he ben hos, d i and ou die .
Size equency o he ben hos, d i and ou die om Anllóns,
Fu elos, Lengüelle and Tamb e i e s su eyed in Sep embe 2007.
Die da a we e pooled ega dless ish age o each sampling si e.
Sánchez-He nández and Cobo Zoological S udies (2015) 54:26 Page 4 o 9
o 60 mm), 3,855 ben hic mac oin e eb a es ( ange = 2 o
60 mm) and 980 d i ing in e eb a es ( ange = 0.5 o
30 mm) measu ed. T ou ed mainly on p ey wi hin he
2- o 6-mm size ange, wi h p ey o 4 o 6 mm being he
mos commonly consumed, excep a wo sampling si es
(Rois and Sa ) whe e i was 10 o 12 mm (Table 1). The
obse ed p ey size equency dis ibu ion in he s omachs
was no iden ical o he po en ial p ey in he en i onmen
(ben hos and d i ) and a ied among sampling si es
(Figu e 2). Howe e , he B ay-Cu is simila i y index
(Table 2) showed ha he simila i y o he size equency
dis ibu ion be ween he en i onmen (ben hos and
d i ) and he die in some cases was conside able and
accoun ed o >55% in all cases, anging om 57.7% o
95.9% (Table 2). In gene al, 4- o 6- and 6- o 8-mm
size ca ego ies we e mo e equen ly encoun e ed in
he die han in he en i onmen , whe eas in e eb a es
la ge han 10 mm we e mo e equen ly ound in he
en i onmen hanin hedie (Figu e2).
Wi h ega d o on ogene ic shi s, he 4- o 6-mm size
ca ego y was gene ally dominan in all age g oups (Table 1),
as p e iously obse ed om pooled da a. The e we e only
di e ences in he a e age p ey size among age classes in
wo i e s (Table 3), whe e p ey size inc eased wi h in-
c easing ish age (Figu e 3). P ey numbe s we e only s a is-
ically di e en among age classes in wo i e s (Table 3),
achie ing he highes alue in 2+ ish in bo h popula ions
(Table 4). In mos cases, s omach ullness a ied among
age classes (s a is ical analysis shown in Table 3), wi h
young-o - he-yea (YOY) ish ha ing he highes alues
and ullness dec easing wi h age (Table 5).
The ela ionship be ween a e age p ey size and s om-
ach ullness was posi i e bu only s a is ically signi ican
o he exponen ial model (R= 0.138, P= 0.019). The
co ela ion be ween mean p ey size and ish leng h was
posi i e bu s a is ically nonsigni ican (P>0.05 in all
cases). A no ewo hy esul o his s udy is he nega i e e-
la ionship be ween p ey numbe s and mean size (P<0.01
in all cases); as p ey numbe s inc eased, p ey size de-
c eased (Figu e 4; loga i hmic eg ession model R=−0.293,
P= 0.001).
Discussion
This s udy demons a ed ha ou ha e a clea p e e ence
o ce ain p ey size ca ego ies acco ding o p ey a ailabili y
in he en i onmen , co obo a ing he heo e ical conside -
a ions p edic ed by Bannon and Ringle (1986) and ield
obse a ions epo ed by se e al esea che s (Newman and
Wa e s 1984; Newman 1987; Rincón and Lobón-Ce iá
1999). In addi ion, he s udy exempli ies he eeding beha -
iou lexibili y o his ish species wi h espec o he ela-
ionship be ween p ey sizes and numbe s ea en.
The size equency dis ibu ion o po en ial p ey can
ha e a s ong in luence on p ey size selec ion. Al hough
Table 3 S a is ical compa isons o he mean p ey size, p ey numbe s and s omach ullness index ( ) among age classes
Mean p ey size P ey numbe s S omach ullness index
Tes P alue Tes P alue Tes P alue
Anllóns H= 3.1 0.373 H= 12.3 0.006 H = 19.7 <0.001
Fu elos H= 8.7 0.033 H = 3.6 0.303 H= 46.2 <0.001
Lengüelle H= 4.3 0.226 H= 1.5 0.672 H= 19.5 0.001
Tamb e U= 41.0 0.108 U= 69.5 0.897 U= 24.0 0.013
Rois U= 18.0 0.327 U= 25.0 0.650 U= 4.0 0.042
San a Lucía U= 43.0 0.326 U= 24.5 0.040 U = 52 0.644
Sa U= 12.0 0.016 U = 38.0 0.448 U= 46 0.800
T aba U= 71.0 0.138 U= 63.0 0.067 U= 33.0 0.002
K uskal-Wallis (H) and Mann-Whi ney (U) es s. Da a a e displayed o each sampling si e. S a is ically signi ican esul s a e ma ked in i alics.
Table 2 Values o he B ay-Cu is index o size equency dis ibu ion simila i y be ween he en i onmen (ben hos
and d i ) and die
Die e sus ben hos Die e sus d i
Anllóns Fu elos Lengüelle Tamb e Anllóns Fu elos Lengüelle Tamb e
0+ 70.6 89.1 88.0 - 85.3 84.8 78.2 -
1+ 69.2 81.4 82.4 75.5 84.5 74.1 84.0 83.7
2+ 68.3 82.7 83.5 71.8 80.7 77.8 83.3 81.6
3+ 57.7 74.6 95.9 - 76.2 88.4 84.8 -
Pooled da a 67.2 88.4 86.2 72.6 82.6 83.4 85.2 83.7
Simila i ies a e shown as pe cen ages. Da a a e only displayed o i e s su eyed in 2007.
Sánchez-He nández and Cobo Zoological S udies (2015) 54:26 Page 5 o 9
he size equency dis ibu ion o p ey in he die was no
iden ical o ha o po en ial p ey in he en i onmen , as
an icipa ed, p ey size selec ion was highly dependen upon
he size equency dis ibu ion o a ailable p ey (Rincón
and Lobón-Ce iá 1999). P edic i e models ha e es i-
ma ed an op imal p ey size o be ween 2.8 and 97 mm o
ou (Bannon and Ringle 1986); howe e , a g ea a ie y
o esul s, wi h espec o p ey size, ha e been obse ed in
he wild (e.g. McLennan and MacMillan 1984; Rincón
and Lobón-Ce iá 1999; Mon o i e al. 2006; Sánchez-
He nández e al. 2011a; 2011b). In ac , s udies ha e dem-
ons a ed ha newly eme ged ou y mainly consume
p ey o 3 o 4 mm (Sánchez-He nández e al. 2011a),
whe eas olde age-0 indi iduals eed on p ey o 5.5 mm
mean size (Sánchez-He nández e al. 2011b). McLennan
and MacMillan (1984) ound ha ou p eyed upon p ey
i ems a ying in leng h be ween 6 and 10 mm. Rincón and
Lobón-Ce iá (1999) demons a ed ha o ganisms o 1 o
2 mm long we e gene ally he mos nume ous in ou di-
e s, while Mon o i e al. (2006) s a ed ha 2 o 3 mm p ey
Figu e 3 Mean p ey size (mm) consumed by ou . E o ba s ep esen he 95% con idence in e als.
Sánchez-He nández and Cobo Zoological S udies (2015) 54:26 Page 6 o 9
a e commonly consumed. S eing ímsson and Gíslason
(2002) ound ha he size o some p ey i ems ea en by
ou a ied be ween 2.5 and 6.5 mm and be ween 1.5 and
12.5 mm o Simulium i a um Ze e s ed , 1838, and
Radix (=Lymnaea)pe eg a (Mülle , 1774), espec i ely.
Howe e , he op imal p ey size may a y on ogene ically,
wi h mean sizes be ween 4.2 and 8.4 mm in 0+ and 2+ ish,
espec i ely (Sánchez-He nández and Cobo 2012). In
addi ion, s udies ha e demons a ed ha op imal p ey size
is highe in lakes han i e s due o he pisci o ous beha -
iou o ou in s ill wa e s (Keeley and G an 2001 and e -
e ences he ein); gene ally, p ey i ems ange om 25 o
87 mm in lakes (e.g. L'Abée-Lund e al. 1992; Sánchez-
He nández and Amundsen 2015). Hence, based on he
e iewed li e a u e and he p esen s udy, he op imal p ey
size o ou appea s o be 2 o 10 mm, al hough p ey lon-
ge han 10 mm can be consumed.
T ou o en unde go on ogene ic die a y shi s, and i
has been demons a ed ha mean p ey size usually in-
c eases h oughou on ogeny (e.g. S eing ímsson and
Gíslason 2002; Mon o i e al. 2006; Sánchez-He nández
and Cobo 2012; Sánchez-He nández e al. 2013). On he
con a y, ou s udy did no e eal consis en , signi ican
inc eases in p ey size wi h inc easing ish leng h (no sig-
ni ican ela ionships) o age (s a is ically signi ican
posi i e ela ionships we e ound o wo o eigh popu-
la ions). The lack o allome ic scaling in his s udy
could pa ly be an a e ac o ou ish samples, which
lacked la ge (>300 mm) indi iduals. Al e na i ely, he e-
sul s may co obo a e he sugges ions o p e ious s ud-
ies (Newman 1987; Rincón and Lobón-Ce iá 1999)
ha , in he absence o e y small specimens, such as
young la ae in which p ey size may a ec p ey inges-
ion (Sánchez-He nández e al. 2011a), gape-limi ed p ey
inges ion may no occu .
The sizes o p ey consumed may a ec he numbe s o
p ey ea en by ou . A no able esul o his s udy was
ha he ela ionship be ween mean p ey size and p ey
numbe s was signi ican and nega i e. A ange o ac o s
can in luence whe he la ge o small ood i ems a e con-
sumed, bu in he cu en s udy, i appea ed ha ou
ed on ei he small numbe s o la ge p ey o la ge num-
be s o small, and heo e ically low ene gy, p ey. S om-
ach ullness, i.e. limi a ions o s omach olume, migh
he e o e be a key a iable in p ey size selec ion. Wi hin
he limi s imposed by gape size, ishes wi h big s omachs
should be able o eed on a wide ange o p ey sizes
han ishes wi h small s omachs (e.g. Gosch e al. 2009),
bu when he s omach is pa ially ull, ish migh choose
small a he han la ge ood i ems (T uempe and Laue
2005). In his s udy, he ela ionship be ween a e age
p ey size and s omach ullness was posi i e, bu was only
s a is ically signi ican o he exponen ial model, sug-
ges ing ha ou may be able o use ela i ely la ge ood
i ems ega dless o hei s omach ullness. This esul
could be because eeding in ensi y was low in he
Table 4 Mean p ey numbe s among age classes
0+ 1+ 2+ 3+ To al (pooled da a)
Anllóns 18.5 (18 o 19) 16.9 (2 o 38) 52.3 (13 o 224) 8.3 (2 o 19) 24.7 (2 o 224)
Fu elos 19.6 (4 o 82) 69.6 (3 o 363) 43.6 (7 o 139) 41.3 (3 o 100) 37.3 (3 o 363)
Lengüelle 20.7 (8 o 55) 22.4 (7 o 38) 30.9 (4 o 173) 13.0 (8 o 17) 24.6 (4 o 173)
Tamb e - 55.7 (1 o 214) 54.5 (6 o 117) - 55.5 (1 o 214)
Rois - 32.8 (7 o 85) 25.0 (24 o 26) - 32.3 (7 o 85)
San a Lucía - 32.8 (7 o 62) 58.4 (32 o 103) - 37.2 (7 o 103)
Sa - 76.6 (12 o 309) 50.7 (33 o 88) - 73.0 (12 o 309)
T aba - 189.2 (8 o 388) 119.9 (11 o 235) - 155.7 (8 o 388)
Da a a e displayed o each sampling si e. Minimum and maximum a e shown in b acke s.
Table 5 Mean eeding in ensi y (%), measu ed as s omach ullness index ( ), among age classes
0+ 1+ 2+ 3+ To al (pooled da a)
Anllóns 5.2 (2.2 o 8.2) 0.7 (0.3 o 1.6) 0.8 (0.1 o 3.5) 0.1 (0.1 o 0.3) 0.9 (0.1 o 8.2)
Fu elos 9.0 (3.4 o 20.6) 1.0 (0.1 o 2.1) 1.0 (0.4 o 1.8) 1.2 (0.7 o 1.4) 5.6 (0.1 o 20.6)
Lengüelle 1.9 (0.5 o 6.6) 1.0 (0.3 o 1.9) 0.6 (0.1 o 2.8) 0.2 (0.1 o 0.3) 0.9 (0.1 o 6.6)
Tamb e - 0.8 (0.1 o 1.9) 0.3 (0.1 o 0.6) - 0.7 (0.1 o 1.9)
Rois - 4.8 (1.5 o 15.8) 1.9 (1.8 o 1.9) - 4.6 (1.5 o 15.8)
San a Lucía - 5.1 (0.9 o 12.9) 4.3 (3.1 o 7.3) - 5.0 (0.9 o 12.9)
Sa - 10.5 (1.7 o 26.9) 7.7 (5.2 o 9.9) - 10.1 (1.7 o 26.9)
T aba - 16.6 (1.3 o 28.2) 7.3 (0.5 o 14.2) - 12.1 (0.5 o 28.2)
Da a a e displayed o each sampling si e. Minimum and maximum a e shown in b acke s.
Sánchez-He nández and Cobo Zoological S udies (2015) 54:26 Page 7 o 9
majo i y o he ishes; 85.1% o he ish had alues o
s omach ullness below 10%. Fu he mo e, he s udy
con i med a p e ious obse a ion (Sánchez-He nández
and Cobo 2013) ha summe eeding in ensi y o ou
may dec ease wi h ish age, being conside ably highe in
ju eniles han in olde age g oups.
Conclusions
The eeding s a egy o ou is lexible and clea ly in lu-
enced by he size equency dis ibu ion o po en ial
p ey: ou ed on ei he small numbe s o la ge p ey o
la ge numbe s o small, and heo e ically low ene gy,
p ey. This s udy co e s a gene al subjec in ophic ecol-
ogy and animal beha iou ha may be applicable owa d
o he ish species, especially o he salmonids, o imp o e
ou unde s anding o eeding beha iou .
Compe ing in e es s
The au ho s decla e ha hey ha e no compe ing in e es s.
Au ho s’con ibu ions
FC pa icipa ed in he design and coo dina ion o he s udy, and JSH
pa icipa ed in ield sampling and conduc ed he labo a o y wo k. FC helped
o d a he manusc ip and JSH inalized he manusc ip . Bo h au ho s ead
and app o ed he inal manusc ip .
Acknowledgemen s
The au ho s would like o hank he s a o he S a ion o Hyd obiology o
he USC ‘Enco o do Con’ o hei pa icipa ion in he ield wo k. We
app ecia e cons uc i e commen s om wo anonymous e e ees, which
conside ably imp o ed he quali y o he manusc ip . Thanks also o A.D.
Nunn o English co ec ions. J. Sánchez-He nández was suppo ed by a
pos doc o al g an om he Galician Plan o Resea ch, Inno a ion, and
G ow h 2011–2015 (Plan I2C) and p omo ed by he Xun a de Galicia.
Au ho de ails
1
Depa men o Zoology and Physical An h opology, Facul y o Biology,
Uni e si y o San iago de Compos ela, Campus Su s/n, 15782 San iago de
Compos ela, Spain.
2
Depa men o A c ic and Ma ine Biology, Facul y o
Biosciences, Fishe ies and Economics, UiT The A c ic Uni e si y o No way,
N-9037 T omsø, No way.
3
S a ion o Hyd obiology ‘Enco o do Con’,
Cas oagudín s/n, 36617 Vilaga cía de A ousa, Pon e ed a, Spain.
Recei ed: 28 Augus 2014 Accep ed: 19 Janua y 2015
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