Daphnia... darkness or light?

[melr70]

Hi,
Can someone tell me if Daphnia prefer to be in darkness or light? My culture came with instructions that specifically said darkness but having just read an article on here, it seems darkness is bad and they prefer light. Do different types prefer different things? Do I need to get them out of the cupboard before they all peg it?
Thanks

 

[Jennewt]

Do you know what species of Daphnia? Are you sure you aren't mis-reading the instructions? Can you tell us who sold them to you? I'm not sure to what extent light matters, but raising them in the dark sounds crazy to me!

 

[Salamanderfire]

AW: Daphnia... darkness or light?

Hi,

my own experience with Daphnia pulex and Dapnia magna says that they need light if you want that they reproduce. So for breeding these two species you need light, either artificial light or sunlight.
Maybe there are other species that prefer darkness, but that certainly are not the common ones.

If you only want to store the Daphnia till you feed them to your newts or salamanders then you can keep them cold and dark. But their number won't increase much then.

Peter

 

[melr70]

Re: AW: Daphnia... darkness or light?

Right. Thanks guys. I figured as much. Have taken them out of the cupboard. Not sure what species they are, I ordered them from ebay. The instructions said daphia live in deep ponds and so don't require light. I thought this was a little strange and now I'm sure of it. I'll bin the instructions.

 

[Molch]

Re: AW: Daphnia... darkness or light?

those instructions are nonsense. Daphnia live in all kinds of ponds, deep or shallow, and you'll observe that they'll have a strong tendency to move toward the light, in part because that's where their food, small algae, is hanging out.

My Daphnia will sit near the bottom of the tank at night and swarm out and feed actively during light hours.

 

[eyrops]

In lakes, Daphnia like many cladocerans, typically migrate toward the surface at night, and deeper in the daytime. Light seems to be one trigger in this movement. Warmer, more food-rich water is often near the surface. Cooler water, usually with a lower concentration of food items, is deeper. This vertical migration has been the subject of a lot of scientific papers investigating the physiological mechanisms involved and the reasons it has developed. This link is to an interesting paper that summarizes some of that work:

http://myweb.facstaff.wwu.edu/shulld/ESCI 432/Lampert1989.pdf

-Steve Morse

 

[BioNut]

I tested this some time ago in 4 containers with green water. These are my basic results but I must disclaim that this was not done under true scientific guidelines.

Group A. was under light 24/7.

B. was under 12 hours light.

C. was under 6 hours of light.

D. was under no light at all and was blacked out.

(All variables constant with the exact same green water source. Temp stable 70 deg F. Full spectrum lighting 23W compact. All done in dark basement. 10 Daphnia Magna to start seed cultures.)

Findings after 2 weeks as follows:

A. Exponential growth with ample die off left at the bottom. (note daphnia seem smaller than all other groups.

B. Exponential growth little to no die off. (note typically stay small... 1 dozen large Daphnia per this group.) {side note: if left for longer or started with bigger seed culture many larger daphnia in population.}

C. Less growth than 12 hours but still adequate population with little die off. (note larger population of larger daphnia)

D. Little growth in population with some die off. (note many large females with black epiphia under carapace. Exponential growth in smaller ostracod population that differs from all other groups.)

My conclusion: 12 hours of natural light is beneficial in yielding lager populations but is optional in keeping Daphnia alive. If you want more little daphnids from Magna keep the lights on. If you want larger daphnids than go with less light. No light is not beneficial but is not necessarily needed and is apparently key to producing large populations of ostracods.

(Remember these where my simple experiments many other factors could have been addressed and maybe will be by others experimentation's)

 

[Salamanderfire]

AW: Daphnia... darkness or light?

Hi Steve,

according to my (limited) knowledge there are only a few freshwater species of Daphnia that show a vertical migration behavior like this and go deep down during daytime.
One of them is D. hyalina in Lake Constance. But as far as I know they only do it during those times of the year when there is a high populaton density of daphnia in the lake and there is not enough food availabe for all of them. In spring while there is a much more lower population densitiy and there is enough food available, they don't migrate to deeper water levels during daytime.
The paper that you linked to says that the very similar D. galeata, which also lives in Lake Constance, doesn't vertically migrate at all. It stays near the surface all day and it is much more productive than the migrating D. hyalina. And the paper also says that even D. hyalina reproduces faster if it doesn't migrate in laboratory experiments.

We breed daphnia as food and of course we want that they reproduce fast. And the optimal condition for this is the condition near the surface of the water.
That means the water being not as cold as in a depth of 40 meters in Lake Constance and providing enough light. The light also lets floating micro algae grow which in my opinion are the best food for daphnia.
Of course you can breed daphnia at a low light level or even in the dark, for example in a barrel which is dug into the ground.
But the more light they get the faster they breed. That at least is my own experience with these interesting and ecologically so helpful little critters.
And last but not least all daphnia species that I know are surely positive phototactic and don't try to hide from the light at all.
So in my opinion there is absolutely no advantage in keeping daphnia in the dark.

Well, if the sun is too strong and heats up the water too much then of course it's better if the daphnia's habitat is shaded. But that is more related to the temperature (higher temperature can lower the oxygene level dramatically) instead of the question if daphnia should be kept dark or illuminated.

Peter

 

[Salamanderfire]

AW: Daphnia... darkness or light?

Hello BioNut,

that's an interesting experiment.
My supposition why less hours of lighting automatically cause a higher production of black epiphia (so-called "winter eggs") instead of life offsprings is: In nature shorter days mean that the winter is near and then the daphnia have to provide for the following generation that will hatch from the epiphia in spring after most or all of the daphnia have died during winter. That is important because they often live in small ponds or even temporary puddles that can freeze completely to the bottom.
So besides drought and bad water conditions, short days seem to be a trigger to switch from producing life offsprings to producing winter eggs.

Would be interesting to know if it is the same with tropical species that don't need to provide against winter.

Peter

 

[eyrops]

Re: AW: Daphnia... darkness or light?

Hi Steve,

We breed daphnia as food and of course we want that they reproduce fast. And the optimal condition for this is the condition near the surface of the water.

Peter

The existence of a daily vertical migration is a very common pattern across many species of zooplankton. It is interesting that your comment and Bionut's experiment, and other comments from experience posted here support the idea that light is good. The article I cited (because it offered a summary of research) does not conflict with this. It argued that there was little support for the idea that the vertical migration (up at night, down by day) offered a metabolic advantage. The main point of the article as I read it was to support the 'better hungry than dead' argument that the migration was a sight predator avoidance tactic. It's rare that anyone comes up with the final word in these long term discussions, but I thought the paper was prettty well argued.

-Steve Morse

 

[BioNut]

Re: AW: Daphnia... darkness or light?

Would be interesting to know if it is the same with tropical species that don't need to provide against winter.

Peter

If anyone from the States has True tropical daphnia I have the setup to run this experiment (this time with picture documentation). I have a UPS account # so shipping would be a snap for anyone who can provide them for me. I am from Minnesota so true tropical species are impossible to come by.