12th ISE 2018, Tokyo, Japan

EFFECTS OF DIAMETER OF PROTRUSIONS AND DISCHARGE PER UNITWIDTH IN FISH LADDER FOR ANGUILLA JAPONICA ON
MIGRATION RATE OF ANGUILLA JAPONICA
KOUKI ONITSUKA
Department of Civil and Architectural Engineering, Kyushu Institute of Technology,
1-1 Sensuicho Tobata-Ku Kitakyushu, Fukuoka 804-8550, JapanJUICHIRO AKIYAMA
Kyushu Institute of Technology, Laboratory of Hydraulic and Water Environmental Engineering,
1-1 Sensuicho Tobata-Ku Kitakyushu, Fukuoka 804-8550, Japan
KOUSUKE IZUMI
Kyushu Institute of Technology, Laboratory of Hydraulic and Water Environmental Engineering,
1-1 Sensuicho Tobata-Ku Kitakyushu, Fukuoka 804-8550, Japan
Studies on biology and environment of Anguilla japonica have been advanced in recent years. However, little is
known about fish ladder for them and migrating characteristics of them. Especially, special fishways arenecessary for demersal fish like young Anguilla japonica. This study was made to evaluate effects on migration
rates of Anguilla japonica by changing diameter of protrusions and discharge per unit width in fish ladder. It was
found that migration rates increase with the increase of discharge per unit width in each diameter of protrusions.
Besides, the migration route sinuosity of them is increasing, and the averaged migrating speed is decreasing with
the increase of discharge per unit width and diameter of protrusions.

1

INTRODUCTION

Anguilla japonica are very familiar with Japanese people and essential fish in food cultures. However,
population of them has been decreasing in recent years, so they were being designated as an endangered species.
As of now, some of studies on their biology has proceeded. Tsukamoto et al. [1] found that spawning areas of
Anguilla japonica are near the west sea of Mariana Islands. Yokouchi et al. [2] discovered that forms of Anguillajaponica differ according to river system, and they tend to become not only many populations of female but also
large-sized as water body size is larger in the river. Besides, Miller et al. [3] pointed out that overfishing of themand the deterioration of the river environment will cause their populations decline. Thus, studies on biology andenvironment of Anguilla japonica are advanced. In the other hands, little is known about studies on migrationand fishway of Anguilla japonica. Fishways have been provided as a means of solving the problem that dams
and weirs impede migration of fish. There are various kinds of fishways; pool-and-weir fishway, vertical slot
fish ladder, ice harbor-type fishway and so on [4,5]. However, many fishways are pool-and-weir fishway, and itis thought that demersal fish is difficult to migrate in this fishway [6-8]. Therefore, special fishways arenecessary for demersal fish like Anguilla japonica.
Studies on fish ladder for Anguilla anguilla and Anguilla rostrata have been started since decades ago.
These fish ladders for Anguilla anguilla have been used by setting brushes and columnar protrusions in bottom
surfaces. Research on fish ladder setting brushes has been conducted. Knights & White [9] reported that larval
Anguilla anguilla migrate the river easily under the condition that spaces of nylon brushes are set to less than
150mm. Besides, Porcher [10] pointed out that the best spaces of brushes in the slope are 7mm for young
Anguilla anguilla and 14mm for small and yellow Anguilla japonica.
In addition, fish ladder setting columnar protrusions has been studied for more than a decade. Solomon &Beach [11] introduced that fish ladder for Anguilla anguilla and Anguilla rostrata in North America setscolumnar protrusions which is diameter 50.8mm and height 101.6mm, and that fish ladder for Anguilla anguilla
in France sets columnar protrusions which is height 30mm. However, it is not a clear whether these standards are
pertinent or not. Vowles et al. [12] showed that when columnar protrusions which dimeter is 4.5cm or 8.5cm set
in each right and left side from a central axis of this fish ladder, Anguilla anguilla migrated at the case ofdiameter 4.5cm more than at diameter 8.5mm. However, this study is the inadequate experience because thedischarge in this experiment is only one case and there are still room to examine other protrusions. Therefore,
while some fish ladders for Anguilla anguilla and Anguilla rostrata are used in Europe and America, little is
known about appropriate columnar protrusions in fish ladder for them. Furthermore, number of fish ladder for
Anguilla japonica in Japan is few, and few reports are available on fish ladder for Anguilla japonica.
This investigation on migration rates of Anguilla japonica was conducted by changing diameter ofprotrusions and discharge per unit width in fish ladder in order to clarify appropriate fish ladder for them.

2

EXPERIMENTAL DEVICE AND METHODS

Figure 1. shows an experimental device consisting of two tanks and the fish ladder. This tank has a length ( Lx ) of
600mm, a width ( Bz ) of 400mm, and a height ( H y ) of 300mm. The fish ladder has a length ( L ) of 1000mm, awidth ( B ) of 300mm, and a height of 150mm in side wall (Δ h ). This fish ladder is painted gray and is connectedby two tanks at a slant angle of 15 degree. Fish ladder width ( B ) was determined referencing fish ladder for
Anguilla anguilla. Besides, many fish ladder for them are at a slant angle of 12°~55° in Europe, so we adopted thegentle angle of 15° in this experiment.
Figure 2. shows an arrangement of protrusions. This bodies are columnar protrusions made of polyvinyl
chloride and are arranged zigzag in each space of 10mm. The diameter of protrusions ( D ) are set to four patterns of
15, 25, 40 and 50 (mm) and the height is 100mm. The origin (0, 0) of the two dimensional (x, y) coordinate is theleft bank of the upper reach in this fish ladder.
Table 1. shows the experimental cases. The diameter of protrusions ( D ) were set to four patterns as above anddischarge per unit width ( qL ) were set to three patterns of 1.2×102, 7.1×102 and 1.64×103 (mm2/s). At this time, thewater depth in this fish ladder ( hL ) was about 2, 6 and 10 (mm), respectively. Water is provided from the upstreamtank and drainage discharge is adjusted in downstream tank, so the water depth in downtown tank ( h ) was about
250mm in all cases. Moreover, the water temperature was about 20°C in all cases.
Figure 3. shows young Anguilla japonica used in this experiment. Averaged body length ( BL ) is about
150mm. They were captured in Japan and reared for 8 months. There is the characteristic to migrate the river
positively in their growth stage. 20 young Anguilla japonica were used for this experiment, and they were used
only once per experiment. They were inserted in the downstream tank. After it is confirmed that Anguilla japonica
settled down, this migrating experiment was conducted for 30 minutes. Trajectory of Anguilla japonica is recordedwith the digital video camera. Number of pixel of the digital video camera is 1440×1080, and recording speed is
30fps. The swimming positions of Anguilla japonica were obtained with the aid of the digital video camera.
Besides, the number of Anguilla japonica migrating was counted.

L
Flow

x
x

Δh

B

θ=15°

Flow

Flow

Polyvinyl chloride protrusions (Diameter D=40mm)

z
z

B

Hy

B
h
Bz

L
Lx

L

Figure 1. Experimental device

Figure 2. Arrangement of protrusions

Table 1. Experimental cases
Water depth
in fish ladderhL (mm)2
6
10Discharge perunit width2
qL (mm /s)

1.2 102
7.11021.64 103

Diameter of protrusions D (mm)

15
25
40
50
D15-2 D25-2 D40-2 D50-2
D15-6 D25-6 D40-6 D50-6
D15-10 D25-10 D40-10 D50-10

Figure 3. Anguilla japonica used in this experiment

3

RESULTS AND DISCUSSION

3.1 Migration rates of Anguilla japonica
Migration rates of Anguilla japonica were calculated as the following Eq. (1).
Migration rate 

Number of Anguilla japonica that migrated in upstream tank n
Number of Anguilla japonica that used to experiment N (  20)(1)

Figure 4. shows the relationship between migration rates ( n N ) and discharge per unit width ( qL ) in eachdiameter of protrusions ( D ). Migration rates ( n N ) in each discharge per unit width ( qL ) have decreased orincreased with the increase of diameter of protrusions ( D ), and there were not a clear tendency to therelationship between migration rates ( n N ) and diameter of protrusions ( D ). On the other hand, Migration rates( n N ) have a tendency to increase with the increase of discharge per unit width ( qL ) regardless of diameter ofprotrusions ( D ). Accordingly, it is suggested that migration rates ( n N ) are effected by discharge per unit width( qL ) rather than diameter of protrusions ( D ).
1
1.0
Migration rate

n
0.8
N

Anguilla japonica

Diameter of protrusions (D):
25(mm)
15(mm)
40(mm)
50(mm)
15

0.6

25
40

0.4

50

0.2
0

0

2.0
20

4.0
40

6.0
60

2
 10140
10 q120
8.0 100
80
L
2(m m s)16
160

Figure 4. Migration rates of Anguilla japonica in each discharge per unit width

3.2 Challenge rates of Anguilla japonica
The number of Anguilla japonica challenging migration ( N c ) is the number of them entering this fish ladder fromthe downstream tank. Challenge rates of them were calculated as the following Eq. (2).

Challenge rate 

Number of Anguilla japonica that challenged Nc
Number of Anguilla japonica that used to experiment N (  20)(2)

Figure 5. shows the relationship between challenge rates ( Nc N ) and discharge per unit width ( qL ) in eachdiameter of protrusions ( D ). It wasn’t confirmed that there are a great difference in challenge rates ( Nc N ) withchange of discharge per unit width ( qL ), as opposed to migration rates ( n N ). On the other hand, there were nota clear tendency to the relationship between challenge rates ( Nc N ) and discharge per unit width ( qL ) in eachdiameter of protrusions ( D ).

1

5.0 51

Challenge rate

N0.8
c0.8
4
N

Diameter of protrusions (D):
25(mm)
15(mm)
50(mm)
40(mm)

Anguilla japonica

0.6
3
0.6
3.0

25

15
15
25
25

40

40

50

50

15

2
0.4
0.4
2.0

1
0.2

0.2
1.0

0000 000

2040

20 4.0
40
2.0
20
40

60

 10 2 2s)
10100 qq120
L L (c m 140

80

60
6.0
60

100

80
8.0
80

120

2140

(m m s)

160

16
160

Figure 5. Challenge rates of Anguilla japonica in each discharge per unit width

3.3 Reaching heights of Anguilla japonica
The number of reaching heights of Anguilla japonica in each case is N rh , and reaching rates ( N rh N c ) are thevalue that the number of reaching heights ( N rh ) is divided by the number of them challenging migration ( N c ).
Besides, reaching heights ( H c ) are counted in every 200mm range from the lower edge of slopes in this fish
ladder. Figure 6. (a)~(c) show frequency distribution of relationships between reaching heights of them a ( H c )and reaching rates ( N rh N c ) in each discharge per unit width ( qL ). When they migrate in the upstream tank,reaching heights of them ( H c ) are 1.0m. The minimum discharge per unit width q L =1.2×103mm2/s shows thatreaching rates ( N rh N c ) are high in H c =0~200(mm) and are drastically decreased as the higher of reachingheights ( H c ). This decreasing trend with the increase of reaching heights ( H c ) has been de-escalating with theincrease of discharge per unit width ( qL ). Therefore, it is assumed that reaching heights ( H c ) have been higher
with the increase of discharge per unit width ( qL ), and migration rates ( n N ) have increased. On the other hand,Anguilla japonica arrive at reaching height H c =0~200(mm) in the low discharge per unit width ( qL ), so it isassumed that there were not a clear relationships between challenge rates ( Nc N ) and discharge per unit width( qL ).
1.0 1

1.0 1
Reaching heights

N rh0.8
Nc

q L  1.2 10 (m m s)
2

Anguilla japonica
Diameter of protrusions (D):
25(mm)
15(mm)
40(mm)
50(mm)

0.60.6

Reaching heights

Anguilla japonicaq L  7.1102 (mm 2 s)
N rh
0.8
Nc

2

15

Diameter of protrusions (D):
25(mm)
15(mm)
40(mm)
50(mm)

0.60.6

15
25

25

40

40
50

0.40.450

0.20.20.20.2
00

0.4

0.4

00
0-20
20-40
40-60
60-80
80-100100
600~800
H c (mm) 1000
200~400
0~200
400~600

0-20
20-40
40-60
60-80
80-100100
600~800
200~400
400~600
0~200
H c (mm) 1000(a) q L =1.2×103mm2/s
1.0 1

Reaching heights

2
3
N rh q L  1.64 10 (m m s)
0.8
Nc(b) q L =7.1×103mm2/s
Anguilla japonica
Diameter of protrusions (D):
25(mm)
15(mm)
40(mm)
50(mm)

0.60.615
25
40

0.40.450

0.20.2
00
0-20
20-40
40-60
60-80
80-100H c (m)
600~800
200~400
0~200
400~600

4

2

100
1000

(c) q L =1.64×10 mm /s
Figure 6. The frequency distribution reaching heights

3.4 Migration routes of Anguilla japonica
Figure 7. (a)~(d) show migration routes of Anguilla japonica in each diameter of protrusions ( D ). It was foundthat they migrated with rolling their bodies around protrusions by their serpentine movement in all cases. Besides, it
is observed that they migrate more serpentine movement with the increase of diameter of protrusions ( D ) anddischarge per unit width ( qL ).
0

00

172
200

344
400

516
600

L688(mm)

860
1000

0

00

0

172
200

344
400

516
600

L688(mm)

860
1000

0

0

516
600

L688(mm)

860
1000

110

165

165

180

180

220
240

220
240

240

D15-2

344
400

120

165

180

275
300

172
200

B
(mm)
55

110
120

110
120

0

0
0

55
B
(mm)

55
B
(mm)

220

275

275
300

D15-6

300

D15-10(a) D =15mm
00

00

200
172

400
344

600
516

L688(mm)

1000
860

0

0

00

172
200

344
400

516
600

L688(mm)

860
1000

0

55
B
(mm)

55
B
(mm)

110
120

120

110

120

180

165

180

180

220

240

220

220
240

D25-2

344
400

516
600

L688(mm)

860
1000

165

275

275

300

172
200

110

165

240

00

0

55
B
(mm)

275

300

D25-6

300

D25-10(b) D =25mm
0

0

00

172
200

344
400

516
600

L688(mm)

860
1000

0

0

B55
(mm)

00

172
200

344
400

516
600

L688(mm)

860
1000

0

110

110
120

180

180

165

180

220

220
240

220
240

110

120

120

165

240
275

D40-2

172
200

344
400

516
600

L688(mm)

860
1000

165

275

300

00

0
55
B
(mm)

B55
(mm)

300

D40-6

275
300

D40-10(c) D =40mm
00

00

172
200

344
400

516
600

(mm)
L688

860
1000
0

0

B55
(mm)
110

120
165

172
200

344
400

516
600

(mm)
L688

860
1000

110
120

165

165
180

180

220
240

220
240

275

D50-2

0

275
300

00

172
200

344
400

516
600

L688(mm)

860
1000

0
55
B
(mm)

110
120

180

300

00

B55
(mm)

220
240

D50-6

275
300

D50-10(d) D =50mm
Figure 7. Migration routes of Anguilla japonica

3.5 Migration route sinuosity of Anguilla japonica
The length of shortest possible path ( Lsp ) is the length of the shortest possible distance for each configuration of
protrusions. The length of actual migrating paths ( S mr ) is the length of actual migrating routes of Anguillajaponica. The migration route sinuosity of Anguilla japonica ( Smr Lsp ) is defined as the following Eq. (3).

Migration route sinuosity 

Length of actual migrating routes Smr(3)
Length of the shortest possible distance for each configuration of protrusions Lsp

Figure 8. (a)~(c) show the frequency distribution of migration route sinuosity of them ( Smr Lsp ) in eachdischarge per unit width ( qL ). The migration route sinuosity of them ( Smr Lsp ) has a tendency to increase with
the increase of diameter of protrusions ( D ) in each discharge per unit width ( qL ). Thus, it is suggested that thelength of their migrating routes has increased for the increase of diameter of protrusions ( D ). In addition, themigration route sinuosity of them ( Smr Lsp ) has a tendency to increase with the increase of discharge per unit
width ( qL ) in each diameter of protrusions ( D ). It was confirmed that they have a tendency to use protrusions by
their serpentine movement because when they linearly migrate with the increase of discharge in fish ladder, they areswept away at the downstream. Therefore, it is assumed that the length of actual migrating routes has increased
with the increase of discharge per unit width ( qL ). Accordingly, it was proven that they migrate while using
protrusions and the migration route sinuosity has increased with the increase of diameter of protrusions ( D ) anddischarge per unit width ( qL ).

1
1.0

nmr
0.8
N mr

Sinuosity
Anguilla japonicaq L  1.2 102 (m m 2 s)D(mm) :

0.6

1.01
Sinuosity Anguilla japonica
nmr q L  7.1102 (mm 2 s)
0.8
N mr

15
25
40
50

1
1.0
D(mm) :

15
0.6
25

nmr
0.8
N mr

15
25
40
50

Sinuosity Anguilla japonicaq L  1.64 103 (m m 2 s)D(mm) :

15

0.6

25

15
25
40
50

15
25

40

40

40

0.4

0.4
50

0.450

50

0.2

0.2

0.2

0

0
1

1.2

1.4

S1.8
Lsp
mr

1.6

3

0

1

2.0
2

1.2

1.4

2

1.6

S mr 1.8
Lsp

3

2.0
2

1

2

1.2

1.4

1.6

S1.8
Lsp
mr

4

2.0
2

2

(a) q L =1.2×10 mm /s(b) q L =7.1×10 mm /s(c) q L =1.64×10 mm /s
Figure 8. The frequency distribution of migration route sinuosity

3.6 Averaged migrating speed of Anguilla japonica
Migrating speed ( V ) was calculated by lengths of their migrating route and their migrating times, and V isaveraged migrating speed. Averaged migrating speed ( V BLm ) is the value that V is divided by averaged bodylength of Anguilla japonica that migrated ( BLm ). Figure 9. shows the averaged migrating speed of them in eachdiameter of protrusions ( D ). The averaged migrating speed ( V BLm ) has a tendency to decrease with the increaseof discharge per unit width ( qL ) in each diameter of protrusions ( D ). Besides, the averaged migrating speed( V BLm ) has decreased with the increase of diameter of protrusions ( D ) in each discharge per unit width ( qL ).
Considering Figure 8., it became a clear that they migrate while using protrusions and the sinuosity has increased
with the increase of diameter of protrusions ( D ) and discharge per unit width ( qL ). Therefore, it is assumed thatthey wind their bodies around protrusions, so the migrating time has increased and the migrating speed had atendency to decrease.
0.6

Averaged migrating speed

Anguilla japonica

V
0.5
BLm

0.4
(1/s)

Diameter of protrusions (D):

15(mm)
25(mm)
40(mm)
50(mm)

0.3
0.2
0.1
0
0

2
qqL L(c140
10m 2 s) 160
2.0 4.0
6.0 808.0 100
10 120
16
40 60
20
2

(m m s)Figure 9. Averaged migrating speed

4

CONCLUSION

This investigation on migration rates of Anguilla japonica was conducted by changing diameter of protrusions
and discharge per unit width in fish ladder in order to clarify appropriate fish ladder for them. As a result, it was
found that following.
(1) Migration rates increase with the increase of discharge per unit width regardless of diameter of protrusions.
On the other hand, there were not a clear tendency to the relationship between migration rates and diameterof protrusions.
(2) Reaching heights of Anguilla japonica become higher with the increase of discharge per unit width.
(3) The migration route sinuosity of Anguilla japonica increases and the migrating speed decreases with theincrease of diameter of protrusions and discharge per unit width.

5

ACKNOWLEDGEMNETSThis study was supported by Grants-in-aid for Scientific Research (17K06580) when the study conducts. Finally,
the authors are grateful to Marusho Corporation for providing Anguilla japonica treated in this paper.
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