p. Biol. (1963), 40, 437-446
437
3 text-figures
Printed in Great Britain
THE REACTION OF FISH TO MOVING BACKGROUNDS
BY F. R. HARDEN JONES
Fisheries Laboratory, Lowestoft
(Received 20 March 1963)
INTRODUCTION
Many species of fish are said to face upstream and swim against a water current so
as to maintain their position relative to the ground. Lyon (1904) showed that optical
stimuli are usually involved in the response. Although the rheotropic response has
often been used to measure a fish's capacity for work (Bainbridge, 1958; and Fry's
(1960) review) there are few data on the minimum stimulus required to elicit the response
and it is not known how fast the fish swims in relation to the speed of the water. This
information is needed as water currents are believed to play an important role in
guiding or directing fish on their migrations. A simple way to simulate the optical
stimuli produced by a water current is to move the background past the fish. Observations have therefore been made on the reactions of fish to moving backgrounds, and
some of the results are described in this paper.
METHODS
(1) The fish. Preliminary observations were made with the following freshwater
species: pike (Esox hiscius L.), three-spined stickleback (Gasterosteus aculeatus L.),
perch (PercafluviatilisL.), trout (Sahno trutta L.), and roach (Rutilis rutitis L.). The
work was then continued with the following marine species: herring (Clupea harengus
L.), smelt (Osmerus eperlamu L.), cod (Gadus morhua L.), whiting-pout (G. luscus L.),
lesser weaver (Trachmus vipera Cuv. & Val.), armed bullhead (Agonus cataphractus
L.), crystal goby (Crystallogobius nilssoni Dub. & Kor.), plaice (Pleuronectes platessa L.),
dab (P. limanda L.), sole (Solea vulgaris Quensel), and dogfish (Scyllium camcula L.).
The freshwater fish were obtained locally or from dealers; the marine fish were caught
in shrimp nets, beach seines or by line, near Lowestoft.
(2) The apparatus. For some preliminary observations a simple system of pulleys,
belts, and a motor was used to drive a striped background round an 18 cm. diameter
glass dish. The device was essentially a simplified version of that used by Wolf and
Zerrahn-Wolf (1936) and need not be described further.
Other observations were carried out in the apparatus shown in Fig. 1. The experimental tank was made of Perspex, 120 cm. square and 30 cm. deep, filled with water
to a depth of 15 cm. Two clear concentric Perspex rings were placed in the square
tank enclosing a channel with an outer diameter of 100 cm. and an inner diameter of
25 cm. The rings prevented disturbance of the water by the rotation of the outer and
inner striped backgrounds. The latter were made from white Perspex with vertical
strips of black Perspex, 2*5 cm. wide, stuck on at 2-5 cm. intervals to produce a
tegular alternating pattern. Both backgrounds were attached to a common Dexion
28-2
438
F. R. HARDEN JONES
angle frame and suspended on a thrust race (not shown in the figure) above the experimental tank. A sheet of white Perspex (not shown in the figure) was placed under the
floor of the experimental tank and a circle of hardboard, painted matt white, mounted
above it and below the Dexion cross-piece.
The driving mechanism for the backgrounds was provided by a ball and plate unit
coupled to a mechanical torque amplifier, which allowed a wide range of speed and a
simple means of reversing the direction of rotation. The drive from the output of the
torque amplifier was taken to the shaft supporting the backgrounds by pulleys and
leather belts.
Dexion angle supporting
striped backgrounds
I
Neoprene
lardboard
Onazote Insulation
Wooden tank
Cooling colls
Fig. 1. The apparatus used to observe the reactions offishto a moving background. One side of the
wooden bath is shown cut away. The channel between the two Perapexringsis 38 cm. wide.
(3) Experimental conditions. The water temperature was controlled by placing the
experimental tank in a large wooden water-bath (Fig. 1), 160 cm. square and 60 cm.
deep, lined with a 2*5 cm. layer of Onazote, hardboard, and a waterproof neoprene
sheet. The bath was filled with fresh water to a depth a few centimetres below the
level of the water in the experimental tank. It was fitted with copper cooling coils,
the refrigeration plant being a Frigidaire Flowing Cold £ h.p. unit controlled by a
'Teddington' model K thermostat made by The British Thermostat Company. The
water in the experimental tank was kept to within ± i° C. of any temperature down to
4 0 C. against higher room temperatures up to 250 C.
The reaction of fish to moving backgrounds
439
*The wooden water-bath was surrounded by high black curtains and lighting was
provided by two 'Cryselco' 40 W. 'warm white' fluorescent tubes. The light intensity
measured just above the water surface with an EEL selenium barrier-cell photometer
was 20 metre-candles. The fish were watched through a small hole in the curtains.
When the experimental tank was filled with sea water the pH was kept within the
range 7-8-8-2 by aeration, and the specific gravity was lowered by dilution with tap
water to 1-015 (normal sea water 1-026) to reduce the osmotic strain on fish that might
have lost some scales when they were caught. All the species did well under these
conditions. Fish were fed regularly with Artemia, Nereis and chopped Mytilus.
(4) Experimental procedure and treatment of results. In the preliminary experiments
fish were placed in the glass dish or Perspex tank and left to settle down for several
hours or days before observations were begun. In interpreting the results it must be
remembered that swimming in the direction of the moving background is equivalent
to swimming against a current and vice versa. Fish were observed singly and in
groups. In some series of experiments observations extended, at intervals, over several
weeks.
Quantitative estimates of the response to a moving background were made by finding
the difference in the proportion of the total swimming time that a fish moved clockwise during successive 15 or 30 min. periods of clockwise and anticlockwise rotation
at the same background speed. The time that a fish spent swimming clockwise or anticlockwise was recorded on a moving paper chart using ink pens and morse keys. Analysis
of the records showed that a fish that appeared, subjectively, to react very well, spent
about 80 % of its swimming time going with the background. The measure of the
response of such a fish would be calculated as follows:
Direction of background
rotation
Clockwise
Anticlockwise
Measure of response
Proportion of swimming
time that fish
went clockwise
(%)
80
20
(80 — 20) = 60
Fish that appeared to react poorly to a moving background spent, at the most, 60-65 %
of their swimming time going with it, and returned scores of the order of 20-30.
Scores of 25 and over have been taken as indicating a positive reaction.
During an experiment the time taken for one rotation of the background was checked
with a stopwatch and care taken to ensure that the same speed was maintained when
the direction of rotation was reversed. The time taken by the fish for one rotation
with or against the background was recorded whenever possible and the position of
the fish along the radius of the experimental tank was noted during each timed circuit.
RESULTS
(1) Preliminary observations. These were carried out in the 18 cm. diameter apparatus
withfivesmall pike, 7-8 cm. long. When a pike had settled down it remained poised in
mid-water. When the background was rotated the fish turned about its vertical axis
and followed the stripes as a compass needle follows the movement of a magnet. The
response was very clear and was often accompanied by rapid fanning movements of the
44°
F. R. HARDEN JONES
pectoral, first dorsal and tail fins. Clear reactions were usually observed to backgrounu
movements as slow as i rotation in 9 min., and one fish followed a background completing 1 rotation in 32 min., which corresponded to a water current of about 0-03 cm./
sec. around the periphery of the dish. The 'compass needle* response was shown by
sticklebacks and whiting-pout.
The more typical response was to swim round the periphery of the glass dish
following the movement of the background. But the fish did not react every time they
were tested. Among the freshwater species pike appeared to be the best and most
consistent performers, followed by sticklebacks, trout, roach and perch. A fish usually
responded when in mid-water, but rarely when a fin was in contact with the side of
the tank and never when resting on the bottom. Under the latter situation, the tail
would often flex towards the side of the body that the fish would turn to if it were to
follow the background, and the eyes showed a nystagmus, a slow movement with
the background being followed by a quick recovery against it. Small dabs, plaice and
soles rarely showed any reaction to a moving background, and then only when hungry,
when they snapped at the black stripes, possibly mistaking them for food. Thus, for
these fish, contact stimuli would appear to inhibit the typical locomotory response to a
moving background.
A number of preliminary observations were made with roach in the Perspex tank.
Two of the fish developed a bias and always swam, or faced, in a clockwise direction.
They showed no reaction to an anticlockwise movement of the background but did
respond to a clockwise movement, swimming faster than the background at the
speeds used. These fish did not react to a background coming towards them from
head to tail, but swam faster than the background when the movement was reversed
so that the stripes came up on them from tail to head. Other roach, cod, whiting and
herring were watched carefully to see if they showed the same behaviour. None of these
fish would necessarily turn about if the background was coming towards it. But they
showed an immediate swimming reaction if the background was reversed, or if they
turned about themselves, so that the background was coming up from behind. These
observations are consistent with the hypothesis that a fish will tolerate being carried
forward by a water current (stripes going head to tail) but will not tolerate being carried
backwards (stripes going tail to head). Other observations fit in with this. When
a fish has been swimming hard, to keep up with or ahead of the moving background,
it will from time to time turn about to face the background and remain poised in the
water, apparently resting. After a few minutes the fish will turn about and again swim
with the background.
The preliminary observations were followed by a more detailed series carried out
with marine fish in the Perspex tank with results that are summarized below.
(2) The responses of different species to moving backgrounds. Cod, whiting, whiting-
pout, herring, smelt, and crystal gobies usually showed a reaction to a moving background when in midwater but often failed to do so when resting on the bottom of the
tank. Plaice, dabs, soles, the lesser weaver, armed bullhead and dogfish failed to show
a response. There appeared to be a real difference in behaviour between the mid-water
or pelagic species and those which spend more time on the bottom. However, even
among thefirstgroup the response was variable. For instance, of seven whiting examined,
two failed to react, and, of six herring, only two showed a consistent response. When the
The reaction of fish to moving backgrounds
441
w o whiting that failed to react were tested in a group with another whiting that did
respond, all three of them swam round with the background together. Similar
results were obtained with herring.
Many experiments were made to find out why a fish would react at one time and not
at another, and why some fish would react while others of the same species would not.
There seemed to be no correlation of response with length of fish within the size
range used for the different species. Fish rarely took any notice of a background movement when feeding. A fish that did respond behaved better when well fed, but feeding
would not change a bad performer into a good one. Temperature may be important;
one cod failed to show any response in five experiments carried out at 12-5° C. but
did so consistently after the temperature was dropped to 50 C.
The response of herring no. 6 (8*2 cm.) appeared to be related to temperature, as
shown by the following experiments:
Date of
experiment
1961
19 July
25 J"ly
26 July
i8 July
29 July
30 July
30 July
1 August
Temp, in experimental tank
(°C)
US
13-5
II-S
80
80
7-5
Response score
-as-2
+ 14-7
Very poor
+ 43-2
+ 43-5
+ 34-8
IO'O
-
n-7
+ 7-7
2-5
The fish only swam with the background at the lower temperatures. The result
obtained on 19 July suggested that there might be a reversal of behaviour at higher
temperatures, but this was not confirmed in the subsequent experiments. But on the
whole there appeared to be no satisfactory explanation to account for the day-to-day
variation in the performance of individuals, or for the differences between individuals of
the same species. This made work on the threshold of the response both tedious and
lengthy, as it was difficult to know what significance to attach to a negative result unless
a large number of experiments had been made under a variety of conditions. The lower
threshold is best taken as the slowest background movement (or its equivalent in terms of
a water currentflowingat so many cm./sec.) at which a positive response wa3 observed.
(3) The threshold for a positive response. The results are summarized in Fig. 2,
where the differences in the proportion of the total swimming time that the fish moves
clockwise during equal periods of clockwise and anticlockwise rotation of the background have been plotted against the time taken for the background to complete one
rotation. In these experiments thefishinvariably swam close to the outer Perspex wall
and appeared to take little notice of the inner striped background. The water current
that would produce the same optical stimulus would therefore move round the circumference of the outer Perspex ring (diameter 100 cm.), at the same speed but in the
opposite direction to that of the background. In Fig. 2 a second scale shows the
water currents equivalent to the background rotations and it can be seen that positive
responses (when the fish went for 62-5 % or more of its swimming time with the background, and a response score of 25 and over) were sometimes observed with background
movements equivalent to currents of 1-2 cm./sec. Plaice, dabs, soles and the other
442
F . R. HARDEN JONES
bottom-living species failed to respond to background movements equivalent to wateP
currents up to 24 cm./sec.
100
Whltlng-pout
~ O 1 14-7 cm.
• 2 14-0 cm.
+ 3 1S'5cm.
Cod
"O 1 36-5 cm.
• 2 10-3 cm.
80
•v
O
O
60
40
o
o
20
- o
0 -T7-
I.
IM
!-»
J> 10O
* 8°
|
X
O
60
-x Dogfish 29-0 cm?
o
A
X
O
"(P
2
40
I
20 "O1
• 2
Herring
10-5 cm.
6-1 cm.
-+4
"5
"5 _20 A 6
•
In il
Whiting
O1 13-0 cm.
80 - • 2 120 cm.
+ 3 170 cm.
60 -
A
+ *
S-9 cm.
8-2 cm.
i
V
100
O Smelt 12-0 cm.
. • Weaver S-S cm.
+ Dogfish 27-5 cm.
O
O
iV
i
A
-
-
40 -
hill
i
+
+
Whiting
o4
-•5
+ 6
x 7
15-8 cm.
20-8 cm.
16-2 cm. +
16-3 cm.
x+
+
+
t
20 -
—^yi-
0
«CD
o#
i
•
-20
1
+ 1.1
100
1 1 1
I
I
i
10
10
100
Time In seconds for one rotation of the background
1
2
4 6 8 1 0
2 0 4 0
1
2
4
6 810
20
40
Equivalent water current in cm./sec
Fig. a. The orientated response of fish to a moving background. A score of 23 and over
indicates a positive response (see text).
(4) The speed of swimming in relation to background movement. When a fish showed
a positive response, it gained on the background at slow rotational speeds but lost
ground and lagged behind at fast rotational speeds. The results are summarized in a
series of graphs in Fig. 3. In these graphs the variable on the abscissa represents the
water current equivalent to a particular background rotation expressed in fish lengths
The reaction offish to moving backgrounds
443
XL) per second. The ordinate represents the quotient obtained dividing by the time in
seconds for the background to complete one rotation by the time taken by the fish
to swim once round the periphery of the tank with the background. When the fish is
keeping pace with the background this quotient will be numerically equal to 1. It will
be more than 1 when the fish gains ground and less than 1 when the fish lags behind.
With the exception of herring, the fish gained on the background at speeds of less
10
Whiting
O1 13-0 cm.
. • 2 12-0 cm.
+ 3 170 cm.
1
0-1
i i il
10
10
I Whiting
- o 4 15-8 cm.
• S 20-8 cm.
- + 6 16-2 cm.
x 7 16-3 cm.
1 I 1 1 I
0-1
1-0
Whltlng-pout
01 1+7 cm.
- • 2 1+0 cm.
+ 3 15-5 cm.
i
I 0-1
0-1
i 1 1 I
10
1-0
10
Smelt
120 cm.
10
0-1
1-0
i I
10
_ Herring
- O1 10-5 cm.
- • 2 6-1 cm.
+ 4 60 cm.
- x 5 5-9 cm.
A 6 8'2 cm. I
1 il
1 1 il
i
i i i I
1 I
0-1
10
10 0-1
1-0
Equivalent water current In fish lengths/second.
Cod
O1 36-5 cm.
• 2 10-3 cm.
0-1
001
1
1
t
10
Fig. 3. The kinetic response of fish to a moving background. The background speed is given
as the equivalent peripheral water current in fish lengths per second, and the kinetic response
of thefishis measured by the quotient obtained by dividing the time in seconds for one rotation
of the background by the time in seconds for one circuit of the tank by the fish. For further
explanation see text.
than 1 L/sec., held their own at speeds of 1-2 L/sec., but lost ground at higher speeds.
Herring did better and appeared to gain ground on the background at rotational speeds
equivalent to water currents up to 3-4 L/sec.
Detailed observations were made on the swimming of whiting, whiting-pout, and
herring at different background speeds. At speeds equivalent to less than 1 L/sec.
they swam intermittently round the tank. A fish would gain on the background with
a short burst of swimming, then glide forward and gradually lose way until it was
moving slower than the background. The stripes then moved past the fish from tail to
444
F- R- HARDEN JONES
head and appeared to stimulate another burst of swimming. If the speed of backgrouna
rotation was slowly increased the gliding movements became shorter and the fish swam
faster. Swimming became continuous at rotational speeds equivalent to currents of
i L/sec. Fish seemed reluctant to maintain swimming speeds faster than 3-4 L/sec.
for more than 10 min. After a period of rapid swimming a fish would turn about to
face the background and remain poised in the water or swim slowly against the moving
background. One whiting-pout and one herring tested at a fast background speed
(3-4 L/sec.) gave up swimming round the periphery of the channel after several
minutes and moved into the centre and swam round the much shorter path, apparently
following the inner striped pattern.
DISCUSSION
Clausen (1931) showed that the response of a fish to a moving background differed
according to its natural habitat, stream dwellers (fast water) reacting better than lake
dwellers (slow water). My observations show a difference in response between midwater or demersal and bottom-living species. A contact stimulus appeared to inhibit
the response and plaice, soles, dabs, the armed bullhead, lesser weaver and dogfish,
which spent most of their time resting on the bottom of the experimental tank, showed
no locomotory response to a moving background- Some preliminary experiments
have been carried out on the reactions of plaice to water currents. The fish did not
show any reaction unless the current was strong enough to displace them, whereupon
they orientated head upstream and tried to dig into the bottom. If unable to hold their
own they swam upstream against the current. Plaice did not respond to a strong jet
of water played over the body surface or on to the lateral line and only reacted when the
jet lifted the margins of the dorsal and ventral fins off the bottom. These observations
support the suggestion that a contact stimulus has an inhibiting role.
It is difficult to find a satisfactory explanation to account for the fact that some fish
responded to a moving background while others of the same species did not. If the
response is under hormonal control those that failed to respond may not have been in
the appropriate physiological state. On the other hand, the stimulus may be one to
which a fish becomes conditioned to respond and these individuals may never have
had the opportunity to associate a moving background with a water current. Two of
the herring that failed to react to the moving background were tested for their response
to a water current produced by pumping water into the experimental tank. Neither of
the fish showed any reaction and they allowed themselves to be carried around with
the current. It has been shown that the response to a moving background may be
affected by temperature, both cod and herring responding positively at lower temperatures. Northcote (1962) has suggested that temperature may be one of the environmental factors which control the rheotropic responses of juvenile trout in Loon Lake,
British Columbia.
The results show that the response to a moving background has an orientating and
kinetic component. Cod, whiting, whiting-pout, smelt and herring appeared to
orientate to current as low as 1-2 cm./sec., and responded very well to currents of
10 cm./sec. This is in good agreement with Brawn's (i960) observations. She gave a
current speed of 3-9 cm./sec. as the apparent threshold for a rheotropic response in
herring. On the continental shelf, tidal currents run up to 1-2 knots (50-100 cm./sec.)
The reaction offish to moving backgrounds
445
and even at 'slack water' the velocity is still 5-10 cm./sec. This means that these fish,
and possibly similar species, should be able to orientate themselves to the current if
they have a fixed visual reference point.
When the fish is orientated, the kinetic component of the response to a moving
background becomes important. At low rotational speeds a fish gains on the background, which means it will make headway against a current. Again this is in agreement with Brawn's (i960) observations that herring swim upstream in slow-moving
currents. In my laboratory experiments cod, whiting-pout, whiting and smelts
started to lag behind the background when the speed of rotation corresponded to
water currents of the order of 1-2 L/sec., although it was within the swimming capability of the fish to keep pace with the background. Herring did better, and still kept
up with the background at speeds equivalent to water currents of 3-4 L/sec. Fish
can cruise for long periods at speeds corresponding to 2-3 times their own length per
second (Bainbridge, i960) and when the background was rotated faster than this my
fish swam at speeds which would have allowed them to maintain their position
relative to the background when it was moving slower. It is strange that a fish should
have allowed itself to be overtaken by the background while it was still able to swim
faster and keep pace with it. Under the conditions of my experiments thefishwould not
tolerate this at background speeds less than 1 L/sec. A fish may have some protecting
mechanism which makes it swim well within its individual limit. On the other hand,
the visual stimulus may have been inadequate to elicit a complete response. Under
natural conditions, optical stimuli will probably be reinforced by tactile stimuli if the
fish is stemming the tide close to the bottom.
The results are of some interest in connexion with those theories of fish migration
according to which water currents are thought to provide the directional clue to the
fish on passage. The results of the experiments described here suggest that it is unlikely
that a fish is going to gain ground against a current flowing faster than 2-3 times its
own length per second, although a herring may do so against currents up to 3-4 L/sec.
The average tidal velocity in the southern North Sea is about 1-5 knots (75 cm./sec.).
Thus a 10 cm. sprat will gain ground against currents of up to 20-30 cm./sec. (well
below average tidal speed); a 25 cm. herring will gain ground against currents of up to
75-100 cm./sec. (about equal to the maximum tidal speed); and a 70 cm. cod will
gain ground against currents of up to 140-210 cm./sec. (well above the average tidal
speed). Clearly a sprat is not going to make any headway, a herring will make some
headway, while a large cod will make rapid headway against the tide. It is difficult to
see how a simple contranatant theory of migration can account for the movements of
the sprat or the herring in the southern North Sea. The sprat must be carried about
more or less passively by the tide while the herring, if it swims against the tidal current
all the time, should stay in about the same position. With regard to the herring in the
southern North Sea, this is certainly not the case. In the autumn the Downs
spawners move through the Southern Bight to spawn on the banks in the eastern
Channel (Cushing, 1955). It is clear that any relation between migration and current,
if one exists, is likely to be complex.
446
F. R. HARDEN JONES
SUMMARY
1. An apparatus is described to study the response offish to moving backgrounds.
2. Observations were made on pike, three-spined sticklebacks, trout, perch and
roach; cod, whiting, whiting-pout, smelt, herring, armed bullhead, lesser weaver,
plaice, dabs, soles and dogfish.
3. Pike followed a moving background equivalent to a water current of 0-03 cm./sec.
Pike were the best and most consistent performers among the freshwater species,
followed by the three-spined stickleback, trout, roach and perch.
4. The marine species fell into two groups. The cod, whiting, whiting-pout, smelt,
and herring responded to background movements equivalent to water currents of
1-2 cm./sec. The other fish failed to respond to movements equivalent to currents up
to 24 cm./sec. and it is thought that this may have been due to contact with the
bottom.
5. The fish that orientated to a moving background also responded kinetically.
Cod, whiting, and whiting-pout gained on the background (swam upstream) at
rotational speeds equivalent to water currents less than 1 fish length/sec., but started
to lag behind at speeds equivalent to currents faster than 1-2 L/sec., although the fish
were shown to be capable of swimming fast enough to keep pace with the background.
Herring gained on the background up to rotational speeds equivalent to water
currents of 3-4 fish lengths/sec.
6. The results are discussed in relation to the contranatant theory of fish migration.
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BRAWN, V. M. (i960). Underwater television observations of the swimming speed and behaviour of
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