WO1999044057A1

WO1999044057A1 - Device and method for measuring the action potential of aquatic organisms

Info

Publication number: WO1999044057A1
Application number: PCT/FI1998/000168
Authority: WO
Inventors: Erkki Aalto
Original assignee: MICROVOLT Oy
Current assignee: MICROVOLT Oy
Priority date: 1996-08-26
Filing date: 1998-02-25
Publication date: 1999-09-02
Anticipated expiration: 2000-08-25

Abstract

A device for measuring the action potential of aquatic organisms, using two electrodes enclosing between them the whole space in which the aquatic organism, preferably a fish, is free to move. The first electrode floats on the water surface and the second is, e.g. on the floor of the measuring aquarium. The device can be built so large that the stress due to cramped conditions, usually influencing the fish, does not have any effect on the measurement. A device according to the invention can also be located directly in a natural water system. Further, a method is disclosed for monitoring the quality of water and investigating aquatic organisms using a device assembly according to the invention.

Description

Device and method for measuring the action potential of aquatic organisms

Technical field

The present invention relates to a device for a measurement system for aquatic organisms, e.g. fish, useful for monitoring the vital functions of organisms e.g. for research purposes or surveillance of water systems. The invention further relates to methods for basal research directed to said organisms and for monitoring of water quality by measuring the vertical component of the action potentials generated by aquatic organisms, whereby the freedom of movement of the aquatic organisms is considerably great.

Technical background Increasing attention is paid to the monitoring of the environment and water systems. Fish and other aquatic organisms are used in different ways for research and monitoring, but an often-encountered drawback when collecting data in this way is the time lag involved. There is a clear need to provide quick information by means of continuous measurements, for example about environmental damage in water systems.

The action potential offish has been measured by, e.g. direct connection of sensor wires. .Another method has been to cut the fish open and investigate the function of the live heart suspended from a string, providing nutrient solution. A third method has been to confine a fish to a narrow tube or container restricting its movement, and measure longitudinal action potentials by means of electrodes placed in the vicinity of the fish.

In US Patent 5,140,855, a measurement aquarium is disclosed having water tanks with a volume of about 0,5 litres for confining fish, , in which tanks the fish cannot turn around. Electrodes are provided at the ends of the tanks and the horizontal component of the action signals is measured.

In Japanese laid-open publication 61-234202, a device of a similar type is disclosed, wherein the mobility of the fish is practically zero. 2

In French Patent application 2 518 265 an aquarium arrangement is disclosed, where sheet- formed antennae are provided on the bottom of the container and near the surface to receive radio signals from a transmitter surgically connected to the fish' head. Probes for sensing the reactions of the fish' olfactory organs are connected to the transmitter. This causes several problems due to the weight of the transmitter and to the emitted radio waves, not to mention the infection risk and the surgical competence required.

Public opinion has been increasingly directed to the treatment of animals. Cutting fish open, connecting leads to them and/or confining them to restricted compartments poses ethical problems. The measurement arrangements themselves cause a stress factor which influences the result and is hard to estimate. Further, part of the prior art methods requires the use of highly trained personnel, thus causing additional costs.

A way of avoiding use of the earlier measuring containers which confine the fish to a cramped space is to measure the vertical component of the action signals. Thereby electrodes are provided above and below the fish. Patent application GB 2 195 543 discloses how small plate electrodes are fitted horizontally on different levels into an aquarium for measurement of the vertical component. According to another known solution, three horizontal electrodes having a grid structure are provided on different levels and covering the whole area of the aquarium. Using this method, a good quality signal is acquired, from which e.g. the heart pulse of salmon-related fish is clearly measurable. The aquarium may be of a spacious construction and a fish is able to move with considerable freedom, whereby stress caused by the measurement situation is decreased or eliminated. For the preferable test fish, lake trout of more than two years of age, lack of appetite has been observed in container sizes of up to 170 litres; only in aquariums of over 400 litres appetite is preserved, according to observations.

In the device described above, action potentials propagate from the fish through the water to the horizontal grid electrodes. The vertical component of the action signal is thereby independent of the position of a fish in its normal, horizontal posture. A dying fish turns on its back, whereby the vertical heart pulse also turns 180 °, which can be observed when monitoring. 3

In the three-grid-electrode aquarium described, the middle electrode causes some inconvenience for the mobility of the fish. Cleaning of the electrodes and the container calls for netting of the fish and relocating during cleaning operations. Transfer of the fish causes handling stress, and during recovery measurement results are not reliable. Further, transfer of the fish easily causes damage to the mucosa, rendering the fish susceptible to parasites, viruses and other pathogens.

Enlarging the aquarium using the state of the art arrangement is expensive, as the manufacture of electrode grids necessarily requires the construction of a separate tool for each possible size. In addition, grids are mechanically difficult to handle and to give a structure which is sufficiently durable for field conditions. These deficiencies have been an obstacle for the extensive use of the device.

Disclosure of the invention With a device according to the present invention, an essential improvement is reached with respect to the aforementioned deficiencies. Thus, a device according to claim 1 has been invented, wherein the vertical component of the fish action potentials is measured by means of two electrodes, and said electrodes are adapted to enclose between them the whole volume in which the fish is free to move during measurement. Preferably the lower electrode rests on the floor of the aquarium or container, or a river bed, while the upper electrode floats on the water surface.

The following may be considered the main advantages of the invention: The construction of the measurement container better fulfil the requirements of animal treatment, fish stress may be diminished, larger containers can be used, maintenance of the measurement aquarium is easier, and construction is simplified. A fish does not have to be removed during cleaning, and thus stress and injury can be avoided. Cleaning can be carried out with the electrodes in place, or they can be removed from the aquarium for cleaning. Further, the mechanical strength of the construction allows locating it, for example, directly into natural water systems. According to another embodiment of the present invention, methods are provided for monitoring the quality of water or investigating an aquatic organism by measuring the vertical component of the action potentials caused by an aquatic organism in such a way 4

that the measurement is equally performed in the whole volume where the organism is free to move.

Via the measurement of water quality, the quality of air can also be monitored, whereby air to be tested is pumped into the device's inflowing water, and simultaneously the influence of water quality is standardised by using either a closed, filtered and temperature normalised water return loop, or a control arrangement which is identical but for the feed of air to the inflowing water.

In the cited publications as well as in the description of the present invention, measurement of vital functions offish is described. A device according to the present invention can naturally be used for monitoring or studying other aquatic animals causing action potentials useful as indicators of water quality.

Brief description of the drawings

The invention is disclosed in detail below, with reference to the attached drawings. Fig. 1 shows a side view of a device according to the present invention. Fig. 2 shows an end view of the device shown in Fig. 1.

Fig. 3 shows an assembly of electrodes in a very large container according to another embodiment of the present invention.

Disclosure of the preferred embodiments

A preferred embodiment of the invention is described below with reference to the enclosed drawings. Figure 1 shows a fish swimming in a measuring aquarium comprising end walls (2), side walls (3, Figure 2), and bottom (4). Said parts are preferably made from neutral, electrically non-conducting or isolated materials. Water enters through pipe connection (5) and exits through opening (6) to the sink (7). Threshold opening (6) determines the level of water in the aquarium. A sandwich-structured upper electrode plate (8) floats on the water surface and consequently sets on a level according to the aquarium water level. The conducting lower part (9) of the electrode plate functions as the electrode proper, the light cellular material (10) works as a buoyancy component, and surface plate (11) gives the structure, which is lighter than water, the required rigidity. Preferably, lower part (9) can be metallic, for example acid-resistant steel; cellular material (10) is an isolator giving the electrode plate floating capacities, i.e. sufficient buoyancy to keep components heavier than 5

water on the surface; preferably such a material is, e.g. a hard PVC foam like Divinycell^® or equivalent. The surface plate is made from an appropriate material which can be either metal or for example a glass/graphite/kevlar fiber laminate material. In the embodiment shown, section (12) of the upper electrode plate (8) is fitted with hinges (13) to form a lid, which can be opened as shown, to form a maintenance opening in the upper electrode plate.

Conducting lower electrode (14) has the size of the container bottom on which it rests. No particular fastening arrangement is required for the lower electrode in the embodiment shown, where the flow rate of water is low. Also the lower electrode (14) is preferably made from metal like acid-resistant steel. Other possible materials for electrode manufacture are sintered or metal oxidised materials.

The action potentials produced by the fish are carried through the water to electrodes (14) and (9). From the electrodes, the signal is transferred via connectors to isolated cables (15) and (16), of which the latter is connected to the lower electrode and, in the embodiment shown, led isolated through the upper electrode plate. From hinged hatch (12) the signal is carried via a cable (not shown) connecting brackets (17) and (18) to the body of upper electrode (9). Cables (15) and (16) carry the signal to a DC-switched low-noise amplifier, known to those skilled in the art, which amplifier is adapted to eliminate offset voltages of the electrodes and the amplifier itself, noise voltages of the surrounding network, possible aliasing of the AD converter, and optionally saturation of the amplified signal due to the considerable dynamics of the signal caused by intense movement of the fish. Preferably, the amplifier is equipped with galvanic signal separation for eliminating noise currents. The amplified signal is linked to a system for data logging and processing, for example a PC- based system freely available on the market.

When located in a natural water system, the aquarium ends (2) can be replaced by water- permeable structures like grids letting through water but confining the fish.

According to another embodiment adapted for use in a natural water system, a container can be located in a channel and the ends (2) removed, allowing any fish to register when swimming through the measuring chamber so formed. Several chambers may thus be coupled in series, for example in fish ladders. 6

The size of a device according to the invention depends on the size of the organism used and, as pointed out above, the size must be sufficient for the conditions not to affect the reactions of the organism. If necessary, electrode units can be coupled together in order to provide a suitable size. Figure 3 shows how the electrode assemblies are installed in large containers. The floating upper electrode (18) is assembled from several sandwich units (19); in the case shown, the lower electrode (20) is also assembled from several units. The action signals are carried by cables (21) and (22). The electrode units are interconnected with couplings (23) which preferably may be, e.g., screw-fastened flexible metal leads with cable connectors. The upper electrode floats on the water surface and the bottom electrode rests on the container floor.

In case the device is installed in a natural water system, it may naturally be necessary to arrange fastenings and supports to keep the electrodes in place. The location of the lower electrode is thereby naturally dependant on the bottom profile and water depth. The distance between electrodes should not, however, vary substantially.

Claims

7Claims

1. Device for measuring the action potential of freely swimming and moving aquatic organisms, said device forming a three-dimensional structure enclosing a water volume, in which the vertical component of an aquatic organism's action signal is measured, characterised by having a conducting lower electrode (14) arranged on the floor of the device, an upper electrode (8) having a conducting lower section and being arranged to float on the water surface, and leads (15, 16) for the signal; and that the electrodes are arranged to enclose between them the whole volume in which the fish is free to move.

2. Device according to claim 1, characterised by additionally having a maintenance hatch (12) in the upper electrode.

3. A device according to claim 1 or 2, characterised by the electrodes being metal electrodes.

4. A device according to any claim 1-3, characterised by having an overflow threshold (6), causing the water surface to set on a level according to said overflow threshold, thus automatically setting the upper electrode to the correct level according to the water surface.

5. A device according to any claim 1-3, characterised by the end walls (2) allowing a throughflow of water.

6. A device according to any claim 1-3, characterised by having open ends (2).

7. A device according to any claim 1-6, characterised by the upper and/or lower electrodes being assembled by flexibly or rigidly connecting together at least two smaller units (19, 20).

8. Device for measuring the action potential of freely swimming and moving aquatic organisms, characterised by a plurality of devices according to any claim 1-6 arranged in series.

9. Method for monitoring the quality of water by measuring the vertical component of the action potential generated by aquatic organisms, characterised by the measurement being accomplished by means of two electrodes, between which the aquatic organism can move freely, and where the volume between the electrodes covers the whole volume where the organism is free to move.

10. Method for investigating aquatic organisms by mea.suring the vertical component of the action potential generated by aquatic organisms, characterised by the measurement being accomplished by means of two electrodes, between which the aquatic organism can move freely, and where the volume between the electrodes covers the whole volume where the organism is free to move.