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Filming nocturnal fish behavior


Rodney Rountree <[log in to unmask]>


Scientific forum on fish and fisheries <[log in to unmask]>


Wed, 21 Feb 2001 21:35:40 -0500





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A few weeks ago I posted a query to the fish-sci and marbio lists about the use of infrared (IR) and other light sources in studies on the nocturnal behavior of fishes. I am working in both laboratory (large 57000-liter tank) and field conditions and am looking for a way to obtain video recordings of fish behavior with a minimal of disturbance. Unfortunately, it appears that we need much better information on fish response to light at different wavelengths to be able to design a lighting system to study the nocturnal behavior of fishes. Infrared lights appear to work well in small aquaria, but due to the heavy absorption in sea water, they are not very effective over greater distances. Some studies have been conducted using red lights, but apparently fish can see well in red light. Several underwater video camera companies now advertise blue and/or green lights for low light conditions, but again, fish can see in these wavelengths. There is apparently some question as to whether some fishes and crustacean can see in IR too. Studies attempting to examine predator-prey interactions in the field at night, therefore, may need to be re-evaluated. Responses (slightly edited) to my original post are provided below. The bottom-line though, is that I'm still looking for information on optimal light sources for nocturnal behavior studies. The best answer I have now is to acclimate laboratory animals to low light levels suitable for filming. Unfortunately, this can't be done in the field.

Richard Fuhrman (of Fuhrman Diversified, Inc.) suggests that studies using a multi-spectrum light controller are needed to determine interactions between light wavelength and intensity on fish behavior. (This has been done for some freshwater fishes, but less is known for marine species). Controlled studies of this type would establish the optimum lighting for studies of the nocturnal behavior of a given fish species AND its potential predators. For example, he cautions that field studies of a crustacean's night behavior might be highly biased if a predator fish is attracted to the lights even if the target species can't see in that wavelength.

1. Jason T. Moore wrote:

My thought is that you might be able to progressively condition the
tank's inhabitant's to a low-light condition. The actual "night" light
level or wavelength requirements will vary according to the species
involved and certain biological limits will be necessary. But as long as
there is still a marked difference between the "day" and "night" portions
of the cycle, it might be possible.
When I say progressively, I mean over a period of weeks or more. I'm
assuming your set-up includes complete control over tank lighting. You
might try introducing a short twilight phase as dusk and dawn (which
might have its own long-term benefits) and then gradually lengthen the
twilight and "squeeze" the night phase out from the ends. With enough
time and patience, I see no immediate reason why this wouldn't work over
a short-term period (a couple months), though completely removing
darkness might be detrimental over longer periods (many months or years).
The gradual conditioning and its effect on the animals might be an
interesting research project on its own!

2. R.C. Marelius wrote:

Hobbyists with crepuscular fish or deep-water fish often find actinic blue
flourescents make the fish reasonably comfortable while allowing them to
still be seen by their person.

3. Steve Jury wrote:

I am very curious on what you find is your best solution as I have been
working with a similar situation to video lobsters in situ in New Hampshire
and FL. We are presently conducting control studies using a heart rate assay
to determine if lobsters are able to detect infrared, far red, near red or
white light. As you mention the literature generally "suggests" that lobsters
(and I assume fish) do not see infrared or red light. We have used infrared
LED arrays (from Fuhrman Diversified, Inc.) to illuminate a relatively small
field of view around a bait bag of a lobster trap to observe entries into the
trap. There are also papers from a New Zealand researcher (I'll try to dig
these up) where they had hardwired lights from shore to observe predation
behavior on tethered lobsters. ...
As I mentioned, we have had little success with infrared for behavioral
observation and some success with red light. I have not heard of anyone using
green but would be interested in how that works. I'm interested in sharing
information to come up with a suitable solution for field and lab studies
that minimize observational artifacts. .....I've spoken to several folks and I think the best

thing may be to get
letters of interest to really push the engineers into seeing that this is a
possible market. Just like you, I really just want the technique to collect
the data but I've had to become part engineer to get what I need.

4. Cliff Ryer wrote:

I have done a fair amount of work using IR in tanks up to 5000
liters. You are correct that IR attenuation will probably be too great for
your tank. With regards to red, it makes people think its dark, but the
fish still see it. Blue has the lowest attenuation in clear water, green
in coastal water (slight turbidity). Green is also the dominant wavelength
at night. How are you going to visualize your fish, by eye or using video
cameras? If by video, the spectral sensitivity of your camera may be
important. In any case, if you use visible light ( to the fish), which it
sounds like you will have to, you will only be making observations under
the upper range of nighttime conditions. On a cloudless night with no moon,
the starlight at the sea surface is about 6 x 10 -6 micro einsteins. You
will not be able to see at light levels below 1 x 10 -3, roughly half to
full moon at the surface. Factor in attenuation with depth and you see the
problem. Hope this has been helpful.

5. Stephen Cotterell wrote:

I did some fish swimming experiments in a 60,000 l tank at the Marine
Laboratory, Aberdeen. We were also filming them. If this is any use to you
contact them. You want the Fish Behaviour Team, which was headed by Dr Clem
Wardle DSc, now retired.

There was a day and night cycle of daylight simulation bulbs. This ran on a
quite complex timer which increased and decreased the intensity over a period
of time. As far as I know this is a commercially available system that was probably
tweaked by someone within the electronics dept.
Fishe's eyes are similar to humans in terms of accommodation to changes
in intensity and response to absolute values. Thus about 10^-4 lux is a starry
night, (less light than this can cause panic in captured fish) and 10^5 lux is
a bright sunny day in clear water. About 40 minutes is the least necessary
for change between the two.

For filming fish in low light levels we used the following system.
A light sensitive camera mounted high in the roof looked down into the annular
tank. From memory we used about 60mm lens, f1.8. The camera was quite
specialist and analogue. Much better than a CCTV but commercially available.
This, now is the clever part. The floor of the tank was coated with 3M
"Scotchlight" the reflective material made into police jackets, road signs,
running shoes etc. Its special property is that it reflects light back to
its source in the same direction from where it came. Very clever. Now,
fitted around the camera lens was an array of red LEDs which shone down into
the tank. The really clever bit was that these were pulsed to coincide with
the camera shutter settings. Thus they were not on all the time, in fact they
gave out very little light, but their pulse was the same as when the
electronic camera shutter was open. This is a much shorter period than the
1/24 s frame. The frame was sustained for the 1/24 but the image was
collected over a much shorter period. I don't know exactly how long, but
probably 1/1000 s or so. The devide which timed the LED to coincide with
the shutter was a bespoke piece of electronics built by Dr Clem Wardle,
who has now retired. I ran it through an oscilloscope and (on a PAL TV
system at least) it matched the first part of the interlaced signal, the
so-called header, then timed the LED pulse to coincide with the start of
the gathering part of the signal. The pulse length was variable by a knob on
the side of the TV black box. I think only one of is kind, but probably if you
know a bit about the way your TV signal works then in theory you could build
something similar.

The real beauty was that you could film the outline of fish swimming in light
levels that would reveal them clearly without them being aware of increased
light levels. Very neat indeed. Hope this is some use to you

Rodney Rountree, Ph.D.
Adjunct Assistant Professor
Dept. Natural Resources Conservation
48 Oregon Rd.
Mashpee, MA 02649
(508) 477-5140
[log in to unmask]

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