Effects of Transverse Width Pattern of Interception Constructed in Open-channel
on Swimming Characteristic of Ayu, Plecglossus Altivelis Altivelis
Kouki Onitsuka a, Juichiro Akiyama a and Keisuke Kasugai aa

Department of Civil Engineering, Kyushu Institute of Technology, Kitakyushu, 804-8550, Japan

Abstract
It is important to secure the rest area for fish. Fish has the ordinary and dark muscle. When fish uses
ordinary muscle, fish got tired. In such a situation, fish needs a rest. In this study, rest characteristic of Ayu(Plecglossus altivelis altivelis) with changing the width and the number of interception was researched. The
migration rates of Ayu were obtained with the aid of a digital video camera. It was found that the swimming
speed increased with an increase of flow velocity, because Ayu swims in keeping with flow velocity forpreventing to be drift towards downstream. The total time of the rest increased with an increase of flow
velocity.
Keywords: rest area; ordinary and dark muscle; flow velocity; migration speed

1. Introduction
Ecosystem conservation is necessary for river maintenance business. It is necessary toprotect the river resources. Ayu is protected as edible fish in Japan. Ayu migrates from the sea tothe river in spring. Ayu has to migrate in a river for spawning. There are rest areas for fish in theriver which is not artificial. It is important to secure the rest area for Ayu. However artificial
structure made in river like fishway may not has appropriate rest area. Most of fishways constructedbeside of weirs and dams in Japan. It is important to install the rest area in fishway. When fishway
is made, it is necessary to investigate rest characteristic of Ayu to protect them. Likewise it isimportant to understand the relationship between fish behavior and flow characteristics againstinterception. Some researchers investigated on such relationships. However, the detailed
parameters such as instantaneous swimming direction and instantaneous swimming speed have notbeen investigated. In this study, rest characteristic of Ayu with changing the width and the numberof interception was researched.
2. Materials and Methods
2.1. Experimental device
Fig. 1 shows the open-channel. Pool length (L) was 4.0m and width (B) was 0.6m. x, y andz were the coordinates of the streamwise the vertical and the spanwise directions, respectively.
Thickness of interception wall (Δx) was 0.015m. Fig. 1 shows location of interception walls.
Interception walls were installed at even intervals.
Tab. 1 Experimental case
0.015mtop-view

insert interceptionBinterception

flow

0.15mzx 1.0m

Lx

1.0m
side-viewyx

LFig. 1 Open-channelBipattern of interception
2B
3

1
B
3

2
B
91B
6

Number ofU m / BL (1/s)
Biinterception247
10
1(2/3)B C1-02 C1-04 C1-07 C1-102(1/3)B C2-02 C2-04 C2-07 C2-103(2/9)B C3-02 C3-04 C3-07 C3-104(1/6)B C4-02 C4-04 C4-07 C4-10

0.8z (m)z (m)0.8z (m)0.8z (m)

0.8

0.4

0.4

0.4

0.4

1.0x (m)2.0 0 0
0.8

0.4

0.4

0.4

0.4

0.4

0
2.0 0
0.8

C2-07

1.0x (m)

0
2.0 0
0.8

0
2.0 0
0.8

0.4

0.4

0 C1-101.0x (m)

0
2.0 0

C2-10

1.0x (m)0
2.0 0C4-021.0x (m)

2.0

C4-04

1.0x (m)

2.0

C4-07

1.0x (m)

2.0

C4-10
9.20x (m)1.0
12.27 (1/s) 15.34

2.0

1.0x (m)2.0

1.0x (m)2.0

1.0x (m)2.0

1.0x (m)

2.0

0.4

C3-04

1.0x (m)2.0 0 0
0.8

0.4

0.4

00
2.0 0
0.8

0.4

z (m)

x (m)

x (m)

z (m)

1.0

1.0z (m)0 C1-07
0
0.8

C2-04

x (m)

z (m)

0
2.0 0
0.8

1.0z (m)

x (m)

z (m)

1.0z (m)0 C1-040.80

C3-02z (m)

C2-02

C3-07

1.0x (m)02.0 0
0.8z (m)2.0 0 00.8z (m)

x (m)

z (m)

1.0z (m)0 C1-02
0.80

0.4

1.0

C3-10

downstream direction

0.00

x (m)
3.07

0
2.0 0
6.14

Fig. 2 The contour figure of flow velocity for each case
0.8

0.8z (m)

z (m)

z (m)

0.8z (m)

0.8

0.4

0.4

0.4

0.4

1.0x (m)0
2.0 0 C3-02
0.8

1.0x (m)2.0 0 0 C4-02
0.8z (m)0
2.0 0 C2-020.8z (m)

x (m)

z (m)

1.0z (m)0 C1-02
0
0.8

0.4

0.4

0.4

0.4

1.0x (m)2.0 0 0 C3-04
0.8

1.0x (m)0
2.0 0 C4-04
0.8z (m)0
2.0 0 C2-04
0.8

z (m)

x (m)

z (m)

1.0z (m)0 C1-04
0.80

0.4

0.4

0.4

0.4

00 C1-10

1.0x (m)1.0x (m)2.0 0 0 C3-07
0.8

1.0x (m)2.0 0 0 C4-07
0.8z (m)0.40
2.0 0 C2-07
0.8z (m)

x (m)

z (m)

1.0z (m)0 C1-07
0.80

0.4

0.4

0.40
2.0 0 C2-10

1.0x (m)2.0 0 0 C3-10

downstream direction

1.0

2.0 0 0 C4-10x (m)Rest Area

Fig. 3 The distribution of rest area for each case

2.2. Experimental methodology
Tab. 1 shows experimental conditions. Flow velocity divided by averaged body length ofAyu was set to four patterns within the range from 2 to 10. Number of interception was set to fourpatterns within the range from 1 to 4. Ayu was used for the experiments. The number of used fish
was 1 in one recording. The recording has been carried out for 50 conditions in each case and 800
conditions in total. 800 of Ayu were used for the experiments. Averaged body length was about
60mm. A circular wire net of 0.25m in diameter was set up 2m downstream from upstream edge
and a quintet of Ayu is inserted. After it is confirmed that the Ayu settled down, the circular wire
net is taken up. Further, trajectory of Ayu was recorded with a digital video camera set up the upsideof the open-channel. The number of pixel of the digital video camera is 1440×1080, and recording
speed is 30fps. The migration rates of Ayu and the rest rates were obtained with the aid of the digital
video camera.

50
Plecoglossus altivelis altivelis

C1t RA
N40RAs C230

1t RATC1C2C3C4C30.5

Plecoglossus altivelis altivelis

20C4

10002

4U m B7L (1 / s)

210Fig. 4 The ratio of rest time divided by test duration
2Plecoglossus altivelis altivelis
1nnNr
1.5RA

4U m B7L (1 / s)

10Fig. 5 One stay time in rest areaPlecoglossus altivelis altivelis
C1C2C3C4
10.5

C1C20.5

C3C40024U m B7L (1 / s)

210Fig. 6 The relation of frequency of use and flow velocity

4U m B7L (1 / s)

10Fig. 7 One rest number of times

3. Results and Discussion
3.1. Definition of the rest
Fig. 2 shows contour figure of three components of flow velocity for each condition. Fastflow velocity is observed in just below gap of interception walls. Slow velocity flow is observed injust below interception walls. In addition, when the number of interception wall increases, flow
velocity becomes slow. Fish has the ordinary and dark muscle. Fish gets more and more tired whenfish uses ordinary muscle. In such a situation, fish needs a rest. It is thought that the fish takes arest in the state that is lower than cruising speed without the accumulation of fatigue when using
the dark muscle. Generally, the cruising speed V fC is defined as follows:
V fC /BL = 2～4(1)Ayu has a characteristic that swimming to a course of upstream when there is flow to thedownstream. The “rest area” is defined as the area where the flow velocity divided by the bodylength is less than 2. Rest time was defined as the time when Ayu swims at swimming speed ( V f )2 1/s which is divided by the averaged body length ( BL ) and less in rest area. Coloring area in Fig.
3 shows the demarcation that Ayu can take a rest. It is understood that when the number ofinterception wall increases, fast velocity flow area increases.
3.2. Characteristic of Ayu to take a restFig. 4 shows ratio of rest time ( t RA ) divided by test duration ( T ). The increase of numberof interception wall is not influential on the ratio. Fig. 5 shows relation of rest time ( t RA ) divided byentering number of times to rest area ( N RA ) and flow velocity ( U m / BL ). When the flow velocity
and the number of interception wall increases, stay time of one rest area decreases. It is understoodthat when the number of interception wall increases, entering number of times to rest area increases.
This is because that Ayu went from rest area to fast velocity flow area and came back. Frequency

11OR Area

IR Area

0.8

The number of use OR or IR Area/amount number of use Rest Area

The number of use OR or IR Area/amount number of use Rest Area

OR Area

0.6
0.4
0.2

IR Area

0.8
0.6
0.4
0.2
0024 U m B7L (1 / s) 104 U m B7L (1 / s) 102(a) C3(b) C4Fig. 8 The ratio of the entering number of times divided by the total number of times of entering rest area
10060024rest

OR Area20202000U m B7L (1 / s) 10rest

404040

not rest

Total time of rest or not rest/
total time using OR Area

6060(%)
80

Total time of rest or not rest/
total time using IR Area(%)
80

IR Area

Total time of rest at OR or IR Area/
total rest time

(%)
80

100
not rest

100

24U m B7L (1 / s) 10

24 U m B7L (1 / s) 10

20
0
24U m B7L (1 / s) 10not rest

(%)
80

60

60

4040rest

OR Area40(%)
80

Total time of rest or not rest/
total time using IR Area

60100rest(%)
80

100Total time of rest or not rest/total time using OR Area

Total time of rest at OR or IR Area/
total rest timeIR Area

100not rest(a) The ratio of rest time in OR Area or (b) Rest vs non-rest time in OR (c) Rest vs non-rest time in IR
IR Area divided by the total rest timeFig. 9 The relation of rest area and rest time in C3

20200024U m B7L (1 / s) 1024U m B7L (1 / s) 10(a) The ratio of rest time in OR Area or (b) Rest vs non-rest time in OR(c) Rest vs non-rest time in IR
IR Area divided by the total rest time
Fig. 10 The relation of rest area and rest time in C4of use for rest area is defined as follows:
Frequency of use 

The number of the experiment s using rest area( nRA )Number of run( n  50)(2)

Fig. 6 shows relation of frequency of use and flow velocity ( U m / BL ). In C1, frequency ofuse is about 50%, when flow velocity ( U m / BL ) is 2～7. C1 is the case that each side of theinterception wall contacts with a sidewall alone. Because there was much Ayu which swam alonga sidewall, Ayu went up without entering in the rest area. In other cases, more than 70% of thenumber of the experiments using rest area. Fig. 7 shows relation of the rest number of times ( N r )and flow velocity ( U m / BL ). The increase for numbers of interception walls is not influential on therest number of times.
3.3. Comparison of the use by the position of rest area
In this study the rest area below interception wall which contacted with a sidewall is definedas “Outside Rest Area (OR Area)”. Rest area existing in the central part is defined as “Inside RestArea” (IR Area). Fig. 8(a), (b) shows ratio of the entering number of times to OR Area and IR Area
divided by the total number of times of entering rest area in C3 and C4. A ratio of approach numberof times to OR Area rises. Fig. 9(a) shows ratio of rest time in OR Area or IR Area divided by thetotal rest time in C3. Fig. 9(b), (c) show ratio of rest time divided by the total stay time in OR Area
and IR Area. A stay in OR Area occupied 90% or more. Fig. 10(a) shows ratio of rest time in OR
Area or IR Area divided by the total rest time in C4. Fig. 10(b), (c) show ratio of rest time divided
by the total stay time in OR Area and IR Area. A stay in OR Area occupied 90% or more. OR Area
is used in a rest purpose, and IR Area is used for the purpose of evading fast velocity flow area or
the movement to the crossing direction.
40050

Plecoglossus altivelis altivelis
C1

L fx
300
BL200

C2

L40fz
BLC330400

Plecoglossus altivelis altivelis

Plecoglossus altivelis altivelis
Lf300
BL

C1C2C4C3200

20C2100C4C110100

C3C4024U m B7L (1 / s)

02104U m B7L (1 / s)0

10Fig. 11 The relation of swimming Fig. 12 The relation ofdistance and flow velocityof the x-axis direction

8V fxBL 16 s

4

Plecoglossus altivelis altivelis

V fz
BL 12 s

C2C3C4U m B7L (1 / s)

10distance and flow velocity

834Fig. 13 The relation of swimming

swimming distanceand flow velocity ofthe z-axis direction

Plecoglossus altivelis altivelis
C12VfBL61 s

C1C2C3C44

Plecoglossus altivelis altivelis
C1C2C3C412200024U m 7BL (1 / s) 10

24U m B7L (1 / s)

10

24U m B7L (1 / s)

10Fig. 14 The relation of swimming

Fig. 15 The relation ofFig. 16 The relation of swimming

speed and flow velocityof the x-axis direction

swimming speed
and flow velocity ofthe z-axis direction

speed and flow velocity

3.4. Characteristic of swimming distance and swimming speed of Ayu
Fig. 11, 12 and 13 show relation of swimming distance ( L fx , L fz and L f ) divided by theaveraged body length ( BL ) and flow velocity ( U m / BL ).When flow velocity ( U m / BL ) and thenumber of interception wall increase, swimming distance becomes increase. This is because thatthe number of interception wall and the number of times of entering rest area increase. Fig. 14, 15
and 16 show relation of swimming speed ( V fx , V fz and V f ) divided by the averaged body length( BL ) and flow velocity ( U m / BL ).When flow velocity ( U m / BL ) and the number of interception wall
increase, swimming speed becomes( V fx ) increase. This is because that Ayu swims for purpose ofevading the fast flow velocity in the rest area.
4. Conclusion
The rest characteristic of Ayu was found with changing the width and the number ofinterception wall. When the flow velocity and the number of interception wall increases, swimming
distance becomes increases and swimming speed becomes increase. This is because that Ayu swims
for preventing to be drift towards downstream when Ayu swim out of rest area.
Acknowledgements
This study was received assistance from Grants-in-aid for Scientific Research when the study
conduct.
References
Onitsuka, K., Akiyama, J., Takeuchi, H., Ono, A., Swimming Behavior of Isolated Ayu in Running Water.
Annual Journal of Hydraulic Engineering, JSCE. 54, 2010; 1309-1314.
Webb, P.W. Hydrodynamics and energetics of fish propulsion, Bull. Fish. Res. Bd Can., Vol.190, pp.,
1975, 190: 1-159