Autofeeding Daphnia into Outdoor Mini Ponds

[Lowells Fish Lab]

For the last few months I've been doing an experiment to see if I can both culture and automatically feed daphnia into a couple of outdoor mini ponds. It's been working well so I thought I would share.

Here's one of the ponds containing fish:

 

Notice the pvc pipe on the right side? That's the outlet of an uplift tube coming from a daphnia pond next door:

 

The concept is very simple: the uplift tube is powered by an airpump run on a timer so that daphnia are pulled out of the culture and dispensed into the fish ponds twice a day. A simple overflow return line allows the water pumped into the fish pond to circulate back into the daphnia culture so that there is no net change in water level on either side.

 

I had to make some adjustments. At first, I had to run the pump for 15 minutes twice a day in order to move enough daphnia to be useful. The trouble was, the daphnia culture water is loaded with toxic nitrogenous compounds. It takes a lot of food to keep the culture going, so that's no surprise. I found that moving that much water into the fish ponds was reducing water quality more quickly than I was comfortable with so I had to find a way to increase the efficiency of daphnia moved per volume of water exchanged. To do that, I added a U-shaped attachment to the intake of the uplift tubes that would still give them good depth in the water column (for uplift efficiency) but would be drawing in water from near the surface of the water where the daphnia tend to accumulate.

 

After making this adjustment, I have been able to move enough daphnia by running the pumps for only 2 minutes at a time twice a day rather than 15 minutes twice a day. If I need to, I can further increase the amount of daphnia moved by using a partial cover to darken the center portion of the daphnia pond which would encourage the daphnia to accumulate around the intakes. Since they are light sensitive, it's possible to choose where you want them to hang out. They actually tend to accumulate around the intakes anyway because they are white and reflect light more than the black of the tub.

Here is the yield after holding a sieve under the output for about 10 seconds:

 

In addition to feeding two ponds for me, I am also able to culture enough daphnia to harvest a large amount each day for my indoor tanks.

 

Right now I'm raising celestial pearl danios in one pond and ricefish in the other. Working great so far!

Edited January 9, 2022 by Lowells Fish Lab

[BETTA999]

interest in that for my betta fry

can you geave any tips i had daphnia but it died off

Edited January 9, 2022 by bettta999

[BETTA999]

how do you make the air throw the daphnia ??🤔

[Lowells Fish Lab]

On 1/9/2022 at 12:34 PM, bettta999 said:

interest in that for my betta fry

can you geave any tips i had daphnia but it died off

Just a few. I found dry active yeast blended with water to be a good food but it take some time to learn where the line is between feeding and overfeeding. I think the common recommendation to make the culture water cloudy but not milky is a good place to start.

I also found that my cultures would slow dramatically in reproduction over a couple of weeks despite having plenty of food available and I took a guess that this was because my water is so soft. Not enough minerals for the daphnia to molt and grow properly. I started adding a small amount of seachem equilibrium to the yeast and water mixture each time I fed them and that seemed to solve the problem for me.

I've found that they can survive some pretty low temperatures but reproduction slows to a crawl. I use a heater to keep the pond at least 65F. At that temp or above they seem to do fine.

Last thing I could offer is start with a reasonable volume of water. I keep a small backup culture that is just a few gallons but for producing a useful amount, a 20 gallon pond or tub has been much better than a 5 gallon bucket. Regular harvesting keeps the population in check.

Air is pumped into the bottom of the uplift tube with a length of airline tubing. As air bubbles up through the vertical segments of pvc pipe they rise with enough force that it lifts some of the water up through it and out the horizontal segment. I made these to function like the uplift tube on a matten filter but with a longer horizontal segment.