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Tank Lights - How The Way We Use Them Affects Fish

Author Topic: Tank lights - how the way we use them affects fish  (Read 1168 times)

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Offline Sue

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Tank lights - how the way we use them affects fish
« on: May 05, 2019, 10:28:15 AM »
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When turning tank lights on and off, we must bear in mind the needs of the fish. We need to remember that fish's eyes do not react to light in the same way as our own. And we need to remember that fish are 'programmed' by nature to expect certain things in their environment.



Fish have eyes which are similar to ours. We both have a cornea, iris, retina etc. We both have rod cells in the retina which allow us to see in dim light. We both have cone cells in the retina which allow us to see colour. The main difference between us and fish is the way we control the amount of light getting into the eye.

We have eyelids we can close; except for a very tiny number of fish, they have no eyelids.
Our pupils can get bigger or smaller to allow more or less light into the eye, fish's pupils cannot change.
Fish's rod cells can sink into the retina in bright light and the cones can come nearer the surface in dim light. Our pupils can change size very quickly but it takes about 30 minutes for the cells in the fish's retina to move.

Fish cannot adapt quickly to changes in the amount of light. We should not do anything to the tank for at least 30 mintues after the tank lights come on Ė we should not feed the fish, do a water change, rearrange decor etc during this time.

And we should not turn the tank lights on or off in a dark room. Doing this stresses the fish, and we know that stressed fish have a lower imune system so they get sick more easily.
The room should have some lighting, either daylight or the room's light, for at least half an hour before the tank lights come on, and at least half an hour after the tank lights turn off. An hour is even better.



Humans and fish, like most animals, have a circadian rhythm or "internal body clock". Upsetting this circadian rhythm causes an imbalance which has to be reset Ė this is the cause of jet lag. The circadian rhythm is controlled by light and dark. In humans, our eyes are the main way we detect light and dark, though many of our other cells have a sensitivity to light. In fish, the sensitivity of the other cells is very high.
It has already been mentioned that the cells in fish's retinas move according to the amount of light. But these cells move in anticipation of changes in light. Fish "know" when dawn and dusk are coming and their eyes start to adjust in readiness. In nature, the time of dawn and dusk is very predictable, especially in the tropics where most of our fish come from. But our tank lights are not predictable to the fish if we just turn them on and off to suit us. We should have the lights turn on and off at the same time every day because the fish's circadian rhythm "expects" this.

Fish also have a need for a period of total darkness in every 24 hours. No tank lights, no room lights on, no daylight. In the regions our fish live in the wild, day and night are just about the same length Ė 10 to 12 hours total dark, 10 to 12 hours bright light, with dawn and dusk of half light between.
Tank lights do not need to be on for the same duration as this. The number of hours total darkness and bright light can be shorter or longer than in the wild Ė to the fish this just seems like a longer or shorter dawn and dusk. But they must have some hours of total dark and bright light in every 24 hours, with periods of dimmer light between. These hours of total dark and bright light should be the same length and at the same time of day, every day of the year.

Offline jaypeecee

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Re: Tank lights - how they affect fish
« Reply #1 on: May 05, 2019, 01:34:10 PM »
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Some very interesting stuff there, Sue. The fact that fish can see in colour is of interest to me. I wonder how they perceive LED lighting? When compared with fluorescent tubes that emit a whole strip of white light, LED lighting is different. Instead, they produce spots of relatively intense light, the norm being red, blue, green and white. Swimming under an LED strip must be like speeding along Blackpool promenade when they have the yearly Illuminations on!

In my LED lighting, I have a couple of near-UV LEDs. Apparently, UV light can encourage mating in some species of fish.

Thanks for starting this topic

JPC

Offline Hampalong

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Re: Tank lights - how they affect fish
« Reply #2 on: May 05, 2019, 01:51:36 PM »
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I think in general our tank lights are too bright for the preferences of most fish. We only need bright lighting for plant growth. In many habitats (jungle streams, or anywhere with less than crystal clear water, etc) lighting isnít all that bright.

Offline jaypeecee

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Re: Tank lights - how they affect fish
« Reply #3 on: May 05, 2019, 02:18:59 PM »
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I think in general our tank lights are too bright for the preferences of most fish. We only need bright lighting for plant growth. In many habitats (jungle streams, or anywhere with less than crystal clear water, etc) lighting isnít all that bright.

Hi,

I would agree. That's why it's necessary to provide low-light hiding places for many community fish. I have a Red Lizard Catfish and Clown Pleco that both hide from the light. But, it's a planted tank so the lighting is essential.

JPC

Offline Sue

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Re: Tank lights - how they affect fish
« Reply #4 on: May 05, 2019, 06:18:38 PM »
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I agree, floating plants or some other cover are necessary for so many species. I didn't include this aspect as I wanted to explain how the way we turn lights on and off affect fish, and how we can use the lights better to fit with fish anatomy and instincts. I've modifed the title to reflect this.

Offline Matt

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Re: Tank lights - how the way we use them affects fish
« Reply #5 on: May 06, 2019, 02:22:49 PM »
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A few disconnected thoughts having read this...

A great alternative to floating plants is dwarf Lilly species.

Rooms lights don't matter so much if you use a ramp timer to gradually bring the tank lights on over half an hour (same but reversed in the evening of course).

I believe UV light enhances the colour of our fish much like we can tan in sunlight. I believe this is a trick used by arowana keepers for example...

Offline Sue

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Re: Tank lights - how the way we use them affects fish
« Reply #6 on: May 06, 2019, 05:10:15 PM »
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Those of us who have lights that are either full on or off have to provide another way of going from dark to full tank lights and vice versa. But those of us who have do lights that can be dimmed can use a dimming feature instead of opening curtains or having the room light on.

I've never liked the idea of UV lights anywhere, even shining out at me from a fish tank. Maybe I'm over sensitive but I've had skin cancer and now that I've got two 'new eyes' due to cataract surgery I don't want to risk the effects of UV light on my retinas  ;D Did you know that yellow cataracts protect the inside of the eye from UV?

Offline daveyng

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Re: Tank lights - how the way we use them affects fish
« Reply #7 on: May 06, 2019, 05:27:58 PM »
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I have uv ledís in my led module. I must admit I turned them off as I assumed there was no benefit to using them. I also drastically reduced the output of the blue ledís to counter the problems I had with algae growth.

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