Eels swim in the anguilliform mode in which the majority of the body axis undulates to generate thrust. For this reason, muscle function has been hypothesised to be relatively uniform along the body axis relative to some other teleosts in which the caudal fin is the main site of thrust production. The European eel (Anguilla anguilla L.) has a complex life cycle involving a lengthy spawning migration. Prior to migration, there is a metamorphosis from a yellow (non-migratory) to a silver (migratory) life-history phase. The work loop technique was used to determine slow muscle power outputs in yellow- and silver-phase eels. Differences in muscle properties and power outputs were apparent between yellow- and silver-phase eels. The mass-specific power output of silver-phase slow muscle was greater than that of yellow-phase slow muscle. Maximum slow muscle power outputs under approximated in vivo conditions were 0.24 W kg(−)(1) in yellow-phase eel and 0.74 W kg(−)(1) in silver-phase eel. Power output peaked at cycle frequencies of 0.3-0.5 Hz in yellow-phase slow muscle and at 0.5-0.8 Hz in silver-phase slow muscle. The time from stimulus offset to 90 % relaxation was significantly greater in yellow- than in silver-phase eels. The time from stimulus onset to peak force was not significantly different between life-history stages or axial locations. Yellow-phase eels shifted to intermittent bursts of higher-frequency tailbeats at a lower swimming speed than silver-phase eels. This may indicate recruitment of fast muscle at low speeds in yellow-phase eels to compensate for a relatively lower slow muscle power output and operating frequency.

REFERENCES

Altringham
J. D.
,
Block
B. A.
(
1997
).
Why do tuna maintain elevated slow muscle temperatures: power output of muscle isolated from endothermic and ectothermic fish.
J. Exp. Biol
200
,
2617
–.
Altringham
J. D.
,
Ellerby
D. J.
(
1999
).
Fish swimming: patterns in muscle function.
J. Exp. Biol
202
,
3397
–.
Altringham
J. D.
,
Johnston
I. A.
(
1990
).
Scaling effects in muscle function: power output of isolated fish muscle fibres performing oscillatory work.
J. Exp. Biol
148
,
395
–.
Altringham
J. D.
,
Wardle
C. S.
,
Smith
C. I.
(
1993
).
Myotomal muscle function at different locations in the body of a swimming fish.
J. Exp. Biol
182
,
191
–.
Avise
J. C.
,
Nelson
W. S.
,
Arnold
J.
,
Koehn
R. K.
,
Williams
G. C.
,
Thorsteinsson
V.
(
1990
).
The evolutionary genetic status of Icelandic eels.
Evolution
44
,
1254
–.
Bastrop
R.
,
Strehlow
B.
,
Jurss
K.
,
Sturmbauer
C.
(
2000
).
A new molecular phylogenetic hypothesis for the evolution of freshwater eels.
Mol. Phylogenet. Evol
14
,
250
–.
Breder
C. M.
(
1926
).
The locomotion of fishes.
Zoologica
4
,
159
–.
Coughlin
D. J.
(
2000
).
Power production during steady swimming in largemouth bass and rainbow trout.
J. Exp. Biol
203
,
617
–.
Coughlin
D. J.
,
Rome
L. C.
(
1999
).
Muscle activity in steady swimming scup, Stenotomus chrysops, varies with fiber type and body position.
Biophys. J
196
,
145
–.
Curtin
N. A.
,
Woledge
R. C.
(
1993
).
Efficiency of energy conversion during sinusoidal movement of red muscle fibres from the dogfish Scyliorhinus canalicula.
J. Exp. Biol
185
,
195
–.
Curtin
N. A.
,
Woledge
R. C.
(
1996
).
Power at the expense of efficiency in the contraction of white muscle from dogfish Scyliorhinus canicula.
J. Exp. Biol
199
,
593
–.
D'Août
K.
,
Aerts
P.
(
1999
).
A kinematic comparison of forward and backward swimming in the eel Anguilla anguilla.
J. Exp. Biol
202
,
1511
–.
Eggington
S.
(
1986
).
Metamorphosis of the American eel, Anguilla rostrata LeSeur. II. Structural reorganisation of the locomotory musculature.
J. Exp. Zool
238
,
297
–.
Ellerby
D. J.
,
Altringham
J. D.
,
Williams
T.
,
Block
B. A.
(
2000
).
Slow muscle function of Pacific bonito (Sarda chiliensis) during steady swimming.
J. Exp. Biol
203
,
2001
–.
Gillis
G. B.
(
1996
).
Undulatory locomotion in elongate aquatic vertebrates: anguilliform swimming since Sir James Gray.
Am. Zool
36
,
656
–.
Gillis
G. B.
(
1998
).
Environmental effects on undulatory locomotion in the American eel Anguilla rostrata: kinematics in water and on land.
J. Exp. Biol
201
,
949
–.
Gillis
G. B.
(
1998
).
Neuromuscular control of anguilliform locomotion: patterns of red and white muscle activity during swimming in the American eel Anguilla rostrata.
J. Exp. Biol
201
,
3245
–.
Gillis
G. B.
(
2000
).
Patterns of white muscle activity during terrestrial locomotion in the American eel (Anguilla rostrata).
J. Exp. Biol
203
,
471
–.
Gray
J.
(
1933
).
Studies in animal locomotion. I. The movement of fish with special reference to the eel.
J. Exp. Biol
10
,
88
–.
Hammond
L.
,
Altringham
J. D.
,
Wardle
C. S.
(
1998
).
Myotomal slow muscle function of rainbow trout Oncorhynchus mykiss during steady swimming.
J. Exp. Biol
201
,
1659
–.
Jayne
B. C.
(
1988
).
Muscular mechanisms of snake locomotion: an electromyographic study of lateral undulation of the Florida Banded Water Snake (Nerodia fasciata) and the Yellow Rat Snake (Elaphe obsoleta).
J. Morph
197
,
159
–.
Jayne
B. C.
,
Lauder
G. V.
(
1995
).
Are muscle fibers within fish myotomes activated synchronously? Patterns of recruitment within deep myomeric musculature during swimming in largemouth bass.
J. Exp. Biol
198
,
805
–.
Johnson
T. P.
,
Syme
D. A.
,
Jayne
B. C.
,
Lauder
G. V.
,
Bennett
A. F.
(
1994
).
Modeling red muscle power output during steady and unsteady swimming in largemouth bass.
Am. J. Physiol
267
,
418
–.
Johnston
I. A.
,
Davison
W.
,
Goldspink
G.
(
1977
).
Energy metabolism of carp swimming muscles.
J. Comp. Physiol
114
,
203
–.
Josephson
R. K.
(
1985
).
Mechanical power output from striated muscle during cyclic contractions.
J. Exp. Biol
114
,
493
–.
Knower
T.
,
Shadwick
R. E.
,
Katz
S. L.
,
Graham
J. B.
,
Wardle
C. S.
(
1999
).
Red muscle activation patterns in yellowfin (Thunnus albacares) and skipjack (Katsuwonus pelamis) tunas during steady swimming.
J. Exp. Biol
202
,
2127
–.
Long
J. H.
(
1998
).
Muscles, elastic energy and the dynamics of body stiffness in swimming eels.
Am. Zool
38
,
771
–.
Rayner
M. D.
,
Keenan
M. J.
(
1967
).
Role of red and white muscles in the swimming of the skipjack tuna.
Nature
214
,
392
–.
Rome
L. C.
,
Choi
I.
,
Lutz
G.
,
Sosnicki
A.
(
1992
).
The influence of temperature on muscle function in the fast-swimming scup. I. Shortening velocity and muscle recruitment during swimming.
J. Exp. Biol
163
,
259
–.
Rome
L. C.
,
Swank
D. M.
,
Corda
D.
(
1993
).
How fish power swimming.
Science
261
,
340
–.
Swank
D. M.
,
Zhang
G.
,
Rome
L. C.
(
1997
).
Contraction kinetics of red muscle in scup: mechanism for relaxation rate along the length of the fish.
J. Exp. Biol
200
,
1297
–.
Wardle
C. S.
,
Videler
J. J.
,
Altringham
J. D.
(
1995
).
Tuning in to fish swimming waves: body form, swimming mode and muscle function.
J. Exp. Biol
198
,
1629
–.
Williams
T. L.
,
Grillner
S.
,
Smoljaninov
V. V.
,
Wallen
P.
,
Kashin
S.
,
Rossignol
S.
(
1989
).
Locomotion in lamprey and trout: the relative timing of activation and movement.
J. Exp. Biol
143
,
559
–.
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