The 11th Pacific Symposium on Flow Visualization and Image Processing
1-3 December 2017,Kumamoto, JAPANEFFECTS OF MAGNETIC FORCE ON SWIMMING BEHAVIOR OFISOLATED ZACCO PLATYPUS IN STATIC WATER
K. ONITSUKA1, J. AKIYAMA1, K. KUNISAKI2 and T. TAKEDA1
1Department of Civil and Architectural Engineering, Kyushu Institute of Technology
1-1 Sensuicho, Tobata-Ku, Kitakyushu 804-8550 Japan
2Kimitsu Works, Nippon Steel & Sumitomo Metal Corporation
1 Kimitsu, Kimitsu, 299-1141, JapanABSTRACTIt becomes quite problematic in fishery that a lot oflarval fish are lost due to enter intake gates of weirs anddams. Some techniques with air bubble, electricity and lighthave been developed to avoid fish from entering intakegates. In recent years, action control techniques of fish withmagnet are evaluated. Hutchinson et al. achieved a certain
result to prevent the entrance of several species of sharks
into longlines by mounting magnets on longlines. Smith &O’Connell showed that magnet worked on Raja clavata toprevent alike. Ward et al. reported the research that Daniorerio which belongs to fresh water fish changed theswimming speed and the swimming direction near themagnets. However, few studies about action control
techniques of fresh water fish with magnet have beenconducted. In this study, the magnetic flux density of themagnets put on the bottom of the side wall in the circularpool is changed to make clear effects of magnetic force on
the swimming behavior of the isolated Zacco platypus instatic water. The swimming position, the swimming speed,
the fish direction and the turning angle are analyzed bycapturing the swimming in the experiment. As a result,Zacco platypus is unaffected by magnet force under thecondition of this experiment.
INTRODUCTION
It becomes quite problematic in fishery that a lot oflarval fish are lost due to enter intake gates of weirs anddams. Some techniques with air bubble, electricity and lighthave been developed to avoid fish from entering intake
gates. Patrick et al. (1985) showed that Osmerus mordax
dentex and Alosa pseudoharengus avoided the air-bubble
barrier with the oval pool. Sekiya et al. (2005) observed theswimming behaviors of Plecoglossus altivelis altivelis,
Cyprinus carpio and Carassius when the potential gradient
was systematically changed in the 0.1 (V/cm) to 1.0 (V/cm)
range under the definite condition that the pulse length was
1/100 s and the pulse interval was 10 Hz. As a result,
Plecoglossus altivelis altivelis didn’t changed theswimming behavior, however Cyprinus carpio andCarassius avoided the electric screen. Ono & Simenstad(2014) showed that Oncorhynchus changed the swimming
behavior under the condition that the lighting system onlyilluminated the area shaded by the river structures. Dawson
et al. (2006) pointed out that the combination of the electric
screen and the air bubble was more effective in limiting themovement of Gymnocephalus cernua than using electric
screen only.

Walker et al. (1997) found that Oncorhynchus mykissbore the organ that could feel the magnetic field of the earth.
It is generally recognized that calcium, iron which belongs
to magnetic material and zinc which belongs to diamagnetic
material are absorbed into the ear stone of fish (see Haradaet al., 2001). Therefore, in recent years, action control
techniques of fish with magnet are evaluated. Hutchinson etal. (2012) achieved a certain result to prevent the entranceof several species of sharks into longlines by mounting
magnets on longlines. Smith & O’Connell (2014) showedthat magnet worked on Raja clavata to prevent alike. Ward
et al. (2014) reported the research that Danio rerio which
belongs to fresh water fish changed the swimming speed
and the swimming direction near the magnets. However,few studies about action control techniques of fresh water
fish with magnet have been conducted. In this study, themagnetic flux density of the magnets put on the bottom of
the side wall in the circular pool is changed to make clear
effects of magnetic force on the swimming behavior of theisolated Zacco platypus in static water.
EXPERIMENTAL SETUP AND CONDITION
Figure 1 shows the schematic of the experimental setupthat is circular pool, in which D =1.83 m is the diameter ofthe circular pool. Table 1 shows the experimental
condition, in which  is the diameter of the cylindricalmagnet and S is the diameter of the sphere magnet. The
values of magnetic flux density B are changed 0.1, 0.2,0.3 and 0.4 T. Besides, it is pointed out that earthmagnetism is 5×10-5 T (see Harada et al., 2001). Figure 2
shows the picture of the used magnets. The circular pool isdivided into normal area or magnet area in line symmetry.
32 magnets are put on the bottom of the side wall ofmagnet area at equal spaces. The experiment is performed
5 cases in the situation whether the magnets are put on ornot. The used fish is Zacco platypus and the averaged
body length BL is about 0.07 m.
The water depth h is 0.04 m. The circular wire net
0.15 m in diameter is placed in the center of the circularpool and the isolated Zacco platypus is put into thecircular wire net. After it is confirmed that the isolated
Zacco platypus settled down, the circular wire net is taken
up. The swimming behavior of the isolated Zacco platypus
are recorded with a digital video camera fastened to theceiling for 1 minute. In this way, the experiment isperformed 30 times in each case. After recording, theswimming position, the swimming speed, the fish

The 11th Pacific Symposium on Flow Visualization and Image Processing
1-3 December 2017,Kumamoto, JAPAN

top-view

normal area

0.15m

initial positionof fishmagnetmagnet area

42%

45%

47%

47%

50%

normal

1

58%

55%

53%

53%

50%

D=1.83m

magnet0B0.3(T)
00.1
0.2
0.4
Figure 3. Time ratio of swimming area

Figure 1. Experimental setup

1

Non-dimensional distance
between fish and side wall
divided by averaged body length

Table 1. Experimental condition

TypeMagnet
Shapend B

Size

Cylinder φ 12mm×3.2mm
SphereS φ 6mm
Neodymiumφ 10mm×2mm
Cylinderφ 10mm×5mm
FerriteB (T)00.1
0.20.30.4

LNd B

L

Zacco Platypus
BL =70mm

0.6
0.4

0.2T
2000G

0.3T
3000G

0.1T

0.2T

0.3T

0.4T

0.2
0.1T
1000G

0T

0.4T
4000G

00246d BL

10Figure 4(a). Normal area1

Non-dimensional distance
between fish and side wall
divided by averaged body length

nd B

LFigure 2. Used magnets

Nd B

L

Zacco Platypus

direction and the turning angle are analyzed every 0.5
seconds.

0.6

EXPERIMENTAL RESULTS AND ANALYSIS

0.4

Swimming position
Figure 3 shows the time ratio of swimming in normal
area or magnet area in each case. There are few changes inthe time ratio of swimming area associated with magnetic
flux density B .
The non-dimensional distance between the fish and theside wall divided by the averaged body length d / BL iscalculated. Figure 4(a) shows the frequency distribution ofd / B L in each case regarding normal area. The
distribution profiles that have a high frequency in low
value and decrease with increase of value are described. In
addition, there are few changes in the distribution profiles
and the peak positions associated with increase ofmagnetic flux density B . Figure 4(b) shows the frequency
distribution of d / BL in each case regarding magnet area.

BL =70mm

0T

0.1T

0.2T

0.3T

0.4T

0.2
002

4

6d BL

10Figure 4(b). Magnet area
Figure 4. Frequency distribution of d / BL
The distribution profiles are similar to those of normal
area. In other words, there are few changes in thedistribution profiles and the peak positions associated withincrease of magnetic flux density B .
Judging from these results, it is found that presence orabsence of the magnets has few effects on the swimming
position in the range of this study.

The 11th Pacific Symposium on Flow Visualization and Image Processing
1-3 December 2017,Kumamoto, JAPAN

1nV B
s

1Swimming speed
divided by averaged body length

Swimming speed
nV B divided by averaged body length

Ls

NV B Zacco Platypus
BL =70mm0.6s

L

NV B Zacco Platypus
BL =70mm0.6Ls

0T

L

0T

0.1T
0.4

0.1T
0.4

0.2T
0.3T

0.2

0.2T
0.3T

0.2

0.4T

0.4T

000246Vs B L

100246

Vs B L

10Figure 5(a). Normal area
Figure 5(b). Magnet area
Figure 5. Frequency distribution of V s / BL11magnetn
49%

51%

56%

56%

54%

Angle between
body axis and tangentw

N

Zacco Platypusw

0T

BL =70mm

0.1T

0.6

normal

0.2T
0.4
51%

49%

44%

44%

0.3T

46%

0.4T
0.20(T)
00.1
0.2 B 0.3
0.4
Figure 6. Selected ratio of fish direction

Swimming speed
The swimming speed divided by the averaged bodylength V s / BL is calculated. Figure 5(a) shows thefrequency distribution of V s / BL in each case regarding
normal area. The distribution profiles that have a highfrequency in low value and decrease with increase ofvalue are described. In addition, there are few changes inthe distribution profiles and the peak positions associatedwith increase of magnetic flux density B . Figure 5(b)shows the frequency distribution of V s / BL in each caseregarding magnet area. The distribution profiles are
similar to those of normal area. In other words, there arefew changes in the distribution profiles and the peak
positions associated with increase of magnetic flux density
B.
Judging from these results, it is found that presence orabsence of the magnets has few effects on the swimming
speed in the range of this study.
Fish direction
The selected ratio of the fish direction is defined as theratio of the number of the intersection between theforward extension of the body axis and the side wall of
normal area or magnet area. Figure 6 shows the selected00

 4

 2

 w (rad.)Figure 7(a). Normal area

1nAngle between
body axis and tangentw

NZacco Platypusw

0T

BL =70mm

0.1T

0.6

0.2T
0.4

0.3T
0.4T

0.2
00 4

 2 w (rad.)Figure 7(b). Magnet area
Figure 7. Frequency distribution of  w
ratio of the fish direction in each case. There are few
changes in the selected ratios of the fish direction
associated with magnetic flux density B .

The 11th Pacific Symposium on Flow Visualization and Image Processing
1-3 December 2017,Kumamoto, JAPANThe angle between the body axis and the tangent  w isdefined as the angle that formed by the intersection
between the forward extension of the body axis and thetangent to the circular pool. Figure 7(a) shows thefrequency distribution of  w in each case regarding
normal area. The distribution profiles that have a similarfrequency in any value are described. In addition, there arefew changes in the distribution profiles associated withincrease of magnetic flux density B . Figure 7(b) shows
the frequency distribution of  w in each case regarding
magnet area. The distribution profiles are similar to thoseof normal area. In other words, there are few changes inthe distribution profiles associated with increase ofmagnetic flux density B .
Judging from these results, it is found that presence orabsence of the magnets has few effects on the fishdirection in the range of this study.
Turning angle
It is observed that there is little difference in thefrequency of the turning direction to right or left.
Therefore, the absolute value of the turning angle  t iscalculated. Figure 8 shows the frequency distribution of
 t in each case. The distribution profiles that there are
the peak positions within the 20° to 40° range and have a
low frequency in high value are described. In addition,
there are few changes in the distribution profiles and thepeak positions associated with increase of magnetic flux
density B .
Judging from these results, it is found that presence orabsence of the magnets has few effects on the turning
angle in the range of this study.
CONCLUSIONSIn this study, the magnetic flux density of the magnets
put on the bottom of the side wall in the circular pool ischanged to make clear effects of magnetic force on theswimming behavior of the isolated Zacco platypus instatic water. As a result, there is little difference in theswimming position, the swimming speed, the fishdirection and the turning angle associated with the changeof magnetic flux density B . Therefore, it is found that
Zacco platypus is unaffected by magnet force under thecondition of this experiment.
NOMENCLATURE
D diameter of circular pool, m diameter of cylindrical magnet, mS diameter of sphere magnet, m
B magnetic flux density, TB L averaged body length, mh water depth, md distance between fish and side wall, mV s swimming speed, m/s
 w angle between body axis and tangent, rad t turning angle, rad1nTurning angle

Zacco PlatypustN

BL =70mmt

0T
0.1T

0.6

0.2T
0.4

0.3T
0.4t

0.2
00

 4

 2

 t (rad.)Figure 8. Frequency distribution of  t
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