Can light cause fish to stress?

I noticed something weird recently, I had the light on my aquarium off for 4 weeks and the fish (guppies) seemed fine. I then put my light on (8000k T8) and they started flashing soon after. I turned it off and they returned back to normal. I've been slowly trying to reintroduce the light but it doesn't seem to help. Today I saw one of the males with clamped fins, I turned off the light and 30 minutes later he was back to normal again.

Is 8000k lighting just too much for some fish? I'm going to try 6500k tomorrow probably and see if they react the same.

Like us, they are creatures of rhythm. If the light was off for a long time, they would need an adjustment.

But as a longtime livebearer keeper, I am going to ask you what will look like weird questions:

a) what is your water hardness?
b) are you changing 25-30% of your water weekly?

Take a flashlight and look along the backs of your guppies with the light off. Is there anything coppery looking, like a dusting?

Oodinium sp, velvet, commonly affects hardwater fish kept in water that is not rich enough in minerals, and that is not regularly changed. It is a parasite that produces flashing and clamping, and that can be controlled (but not necessarily destroyed) by depriving it of light. It needs light to really flourish. This is all circumstantial, but what you gave adds up to a possibility worth exploring and hopefully rejecting.

GaryE wrote:Like us, they are creatures of rhythm. If the light was off for a long time, they would need an adjustment.

But as a longtime livebearer keeper, I am going to ask you what will look like weird questions:

a) what is your water hardness?
b) are you changing 25-30% of your water weekly?

Take a flashlight and look along the backs of your guppies with the light off. Is there anything coppery looking, like a dusting?

Oodinium sp, velvet, commonly affects hardwater fish kept in water that is not rich enough in minerals, and that is not regularly changed. It is a parasite that produces flashing and clamping, and that can be controlled (but not necessarily destroyed) by depriving it of light. It needs light to really flourish. This is all circumstantial, but what you gave adds up to a possibility worth exploring and hopefully rejecting.

a) what is your water hardness?
I'm not 100% sure, my tap water is around 83ppm. I put about 1 tablespoon of epsom salt per gallon to increase the hardness, but I don't have anything to measure the hardness after I do that.

b) are you changing 25-30% of your water weekly?
I do 50% water changes weekly.

Take a flashlight and look along the backs of your guppies with the light off. Is there anything coppery looking, like a dusting?
Not that I could tell, I'll double check when I'm home tonight.


Also to add to that, I have a 5 gallon that I keep some smaller fry in. They have the same water conditions as this tank, but they do not have a light. If the original tank had a disease, this tank would have gotten it as well because I used some of the original tank water in it when putting the fry in. I have never seen any signs of stress with the fry in that tank. When I had younger fry in the original tank, most of them ended up clamping up and dieing a lot younger then the fry in the 5g tank. There isn't much natural light in the room (it's in the basement, so just a single window that's probably 1.5 feet by 1 foot), it's just enough to light up the room so I can see around in the room without needing to turn on lights.

Maybe I'll put back my 3500k T8 bulb for a week, then switch to a 6500k CFL lamp for a week, and then to the 8000k T8 bulb and see if the slow transition helps them adjust.

The velvet idea was a "shot in the dark". My water is almost the same as yours ppm wise, and if I forget epsom salts (I don't measure either) clamping results quickly. But if you are doing water changes and not grossly overfeeding, you should be clear. I've had trouble when it came in on new fish. I tend to think it is always present, but not necessarily always active with the fish. Velvet is behind a lot of mystery deaths in livebearers, especially fry, as it is hard to spot.

If you've had the lights off for a month - are you now converting to a planted tank?

The key for keeping my fish calm in their small windowed garage is predictablilty and transition. The lights do come on (via timers) in the dark during winter. It's pretty well unavoidable. But I run a low wattage dollar store nightlight in the 18 by 12 room. It comes on when the lights go off, and throws just enough very dim light that the fish no longer crash about - even the rainbows.
I love my rainbows, but they are not intelligent fish.
I try to avoid total blackness as I find fish do get weird in it - in nature, there is almost always some moonlight unless you have a species from under the rainforest canopy. A nightlight is cheap and effective in calming them down. I have a friend with a cellar fishroom and manual lights - when he turns on his lights you hear the fish hitting the glass.

GaryE wrote:The velvet idea was a "shot in the dark". My water is almost the same as yours ppm wise, and if I forget epsom salts (I don't measure either) clamping results quickly. But if you are doing water changes and not grossly overfeeding, you should be clear. I've had trouble when it came in on new fish. I tend to think it is always present, but not necessarily always active with the fish. Velvet is behind a lot of mystery deaths in livebearers, especially fry, as it is hard to spot.

If you've had the lights off for a month - are you now converting to a planted tank?

The key for keeping my fish calm in their small windowed garage is predictablilty and transition. The lights do come on (via timers) in the dark during winter. It's pretty well unavoidable. But I run a low wattage dollar store nightlight in the 18 by 12 room. It comes on when the lights go off, and throws just enough very dim light that the fish no longer crash about - even the rainbows.
I love my rainbows, but they are not intelligent fish.  
I try to avoid total blackness as I find fish do get weird in it - in nature, there is almost always some moonlight unless you have a species from under the rainforest canopy. A nightlight is cheap and effective in calming them down. I have a friend with a cellar fishroom and manual lights - when he turns on his lights you hear the fish hitting the glass.  

If you've had the lights off for a month - are you now converting to a planted tank?

I had the lights off for a month because people suggested it may be velvet disease. I didn't see any copper on the fish when shining a flashlight, but I couldn't figure out what else it could be so I decided to give it a shot and did a dark/heat/salt treatment for 3 weeks. The tank is "semi" planted. I've got a single Hygrophila Corymbosa plant, hornwort (which pretty much died from the salt, but was coming back to life now with the light) and java moss in the tank.

My timer turns the lights on around 11:00am for about 2 hours, then they come back on around 4:30pm until 9:00pm. Night lights or "off hours" lights seem like a good idea, I'll look into setting that up.

I didn't do the epsom salt thing until the same time I started the dark/heat/salt treatment as that was suggested at the time as well.

But if you are doing water changes and not grossly overfeeding, you should be clear.

I MIGHT be overfeeding, Since I pretty much had fry since day one (one female dropped 8 fry the day after I got it) I got into the habit of feeding 3 times a day (morning, when I get home from work, and before I go to sleep). I think I'm going to have to try and break the habit now that I have a separate fry tank, as I usually feed more then I should in hopes the adults aren't hungry and won't hunt the fry. But the food seems to be all eaten in a couple minutes.

The reason I suggested it was that velvet seems to thrive in uneaten food. I don't quite understand how that creature works, but when I feed too much freshly hatched brine shrimp -even one spill - velvet seems to flare up.

But if it's not there, no worries!

I feed my livebearers once daily, unless they are Xiphophorus, who get two. Poecilia like guppies do fine on once daily. I have had a colony of wild caught Trinidad guppies for 6 years now, and have never removed a fry. They just keep coming, growing and thriving.

I also use the 'fast day' method - one day per week, all my adult fish go unfed. That includes tanks full of fry. I have returned from a week away and found just as many young guppies in there as when I left. Obesity is a serious health problem for domestic linebred fancy guppies - you'll see it across the chests of some males. It really shortens lifespans, and fertility.