As a sudden drop in the temperature is a problem in terms of e.g. experiment consistency, 17*C (I assume you're talking Celsius) is not a live-threatening for D. magna as it lives in mostly shallow ponds and astatic reservoirs, so I should take rapid temp. shifts OK (unless you have some 'special' clone from a lake in the middle of a desert, or sth. like that).

I can think of three reasons:

1) Water contamination

2) Pathogens

3) Food quality

For (1) - place some of the culture you have in water from a different source you have and see what's happening. For (2) - it's tricky, you may be forded to resort to your stock culture (you have a stock culture, haven't you?). No. (3) ones happened to me - our algae culture was contaminated with protists, food quality dropped, Daphnia had issues with diseases. You can try to have a look at the food culture under a microscope (the proper one) and check what algae are there.

Barbara Pietrzak

Thank you for your time and response Piotr Bentkowski.

At first I though it was the temperature, but as soon as I saw that it was taking too long for them to recover I discarted it. Yes, I was refering to Celsius degrees.

For (1), I thought about the medium also and checked pH, hardness, oxygen and conductivity. It was all right and between the recommended values. Therefore, I changed the destilled water that we used to make ISO, but nothing changed even after 2 weeks (6 medium changes), daphnids are still dying.

Regarding number 2, I think is the most reasonable reason, unfortunately. I looked some daphnias under the estereomicroscope and some presented white eggs and some white dots, indicating probably fungal infection.

For the number (3), I also looked the algae under a microscope and they had a healthy appearance, and I spot no protists.

To get rid of Pathogens I think is more plausable to start culturing again new daphnias and discart all daphnias that I have nowadarys. Do you agree or see another way?

Unfurtunately I don't have a stock culture...how do you used to mantain yours (if you have it), any tips?

Thank you for all the attention.

Regards, Giuliana.

I don't work with Daphnia anymore...

We had a special Daphnia 'stock room' where a technician kept small populations of the most important clones we worked with (Daphnia is the model animal of choice where I worked). If you work in Europe, there are plenty of places to ask if they can share some of their cultures as live animals or ephippia (if you cover the shipment). KULeuven in Belgium, Dept. of Hydrobiology at the University of Warsaw, few places in Italy and Germany. Check the one which is closest to you or your colleagues have friendly relations with.

Thank you Piotr. I have already asked for some new daphnias, they will arrive soon. I was curious about the stock culture so I would not have to keep asking for new ones every time a "surprise" occurs.

Thank you again for your attention.

If you don't need a specific clone, you could also just extract some from the environment ;-) They live out there in the wild around Europe in ponds and even fountain basins.

Yeah, it's worth keeping a fraction of the population somewhere else (different room, use different jar for their plankton feed etc.). As a backup. Because when you loose a clone some experiments are not possible to repeat.

Hallo, Piotr has answered most already I guess. We keep our stocks doubled, few to several individuals in each, and one of the set is kept at 11 degrees C, everything is slower there, stocks are easier to maintain (still, you need to check for and take away ephippia, if they appear). I hope the cultures will go well now! Good luck, Barbara

Hola, trata de evaluar la calidad del alimento, los cultivos de algas deben ser frescos para beneficiar el crecimiento poblacional en las dafnias, algunos protocolos recomiendan adicionar selenito de sodio al medio para promover la reproducción. En general fotoperiodos 16:8 funciona muy bien. Saludos

Hello Barbara.

Thank you so much for your answer...I started keeping a stock culture at 10ºC, let's see what happens! =).

Hola Adriana Janneth Espinosa-Ramírez. Sí, las algas, fotoperiodo y todo estavan bien. Las dafnias ahora están bien y a reproducir normalmente.

Gracias por la respuesta.