Recently I asked on here whether anybody had experience cultivating the green algae Chlorella vulgaris in freshwater for use in feeding Moina macrocopa cultures. The species is often used in saltwater phytoplankton systems, and is the preferred food for industrial scale Daphnia and Moina production on fish farms in the far east, but nobody seemed to have any details on small scale cultivation for freshwater livefood systems.
I've done some experimentation and found an incredibly simple and easy method for producing useful amounts of highly nutritious greenwater with an absolute minimum of effort - and using products that are easily and cheaply obtained in the UK.
Why Moina? and why Chlorella vulgaris?
Moina species are cultivated in exactly the same way as Daphnia but are smaller, reproduce faster, and can tolerate much higher culture densities than larger Daphnia species. They are also more nutritious than larger daphnia with a higher protein and fat content.
Culture Techniques of Moina : The Ideal Daphnia for Feeding Freshwater Fish Fry highlights the fact that
Cultures can be very easily maintained on dried bakers yeast but this doesn't provide optimal nutrition and more crucially it's very easy to crash cultures by overfeeding with yeast, particularly in small scale systems or when you're initially working with smaller numbers of Moina. Chlorella vulgaris does not foul the culture water in the same way and contains far more nutrition than yeast. In fact Chlorella is commonly used as a health supplement for humans as it is 50-60% protein and contains all nine essential amino acids as well as vitamin A, Zinc, Magnesium, Iron, Phosphorus, B vitamins and healthy omega 3 as well as caretenoids.High population densities of Daphnia can result in a dramatic decrease in reproduction, but this is apparently not the case with Moina. The egg output of Daphniamagna drops sharply at a density as low as 95-115 mature individuals per gallon (25-30/L). The maximum sustained density in cultures of Daphnia reported is 1,900 individuals per gallon (500/L). Moina cultures, however, routinely reach densities of 19,000 individuals per gallon (5,000/L) and are, therefore, better adapted for intensive culture........
..........Although variable, the protein content of Moina usually averages 50% of the dry weight. Adults normally have a higher fat content than juveniles. The total amount of fat per dry weight is 20-27% for adult females and 4-6% for juveniles
Materials and method
You can find many instructions online for constructing a photobioreactor for intensive phytoplankton cultivation but like me you may be looking for a simpler approach. The primary result of my experimentation is that I've found a cheap and readily available organic fertiliser than can be used to produce healthy uncontaminated Chlorella cultures without any additional equipment. Most of the phytoplankton media offered for sale are prohibitvely expensive - reefphyto.co.uk offers 1000ml of 'Guillards F/2 medium' for £36.98 before delivery and this would make approximately 666 litres of culture water whilst Blades Biological offers just 20ml of 'Algagrow concentrate' sufficient to make only 2 litres of culture water for £7.66 before delivery!
The good news is that I've discovered 'BioBizz fish mix', with an N-P ratio of 5-1 is a sutable organic alternative that can be bought from amazon.co.uk for just £10 delivered and 1 litre of this is sufficient to produce 1000 litres of culture water.
To get started you will need:
1. Two 2 litre bottles of still water. I used coop own brand water, it doesn't need to be fancy and in most cases tap water will suffice. It's the bottle you're really after.
2. One 1000ml bottle of BioBizz fish mix
3. A small starter culture of Chlorella vulgaris. This can be obtained either from Blades Biological (30ml of Chlorella £10.84 + delivery) or from Seahorsebreeder.co.uk in the form of a 'phyto disc' culture on Agar for £18.17 + delivery. I've bought both, and although the phytodisc is more expensive, it represents much better value for money and can be preserved in the fridge as a backup once you've started your culture. Interestingly Chlorella vulgaris can be grown in either salt or freshwater so don't be confused by retailers offering it for use in reef systems.
Once you've got these three things you're good to go and this is really all you need. I was surpised to discover that an air pump to agitate the water seems not to be necessary but may result in faster growth.
All you have to do is add 2ML of your fish mix to 2L of water in a plastic bottle and then innoculate with a small amount of Chlorella and you're set. I place the bottles on a windowsill and shake them for a minute or so a couple of times a day. Once the water is a nice opaque green colour you simply add 95% of it it to your Moina or Daphnia culture before using the remainder to innoculate your second bottle of culture water. In this way you can easily maintain a constant supply of Chlorella with a minimum of effort and by incorporating more bottles or larger 5L containers you can easily scale up production to match the amount of Daphnia or Moina you need to produce.
You must agitate the bottles every day to avoid the culture 'clumping' but If you don't want the hassle then the addition of a cheap air pump avoids this necessity and may boost production. The first starter culture I obtained from Blades biological didn't appear to be 'greenwater' at all as all the chlorella had clumped out and formed a dusty sediment on the bottom of the glass vial. At first it continued to grow in this manner but with daily shaking it quickly seperates and begins to grow as suspended 'greenwater' again.
I'm just sharing this information as it removes a lot of the hassle associated with feeding yeast. Using greenwater you can feed a much more concentrated solution without the same water fouling issues - this means you can perform a large feeding of greenwater every few days or even once a week depending on your culture density and whatever Cladoceran species you're producing will have much higher nutritional value for your fish.
The advantages over an outdoor greenwater bucket or pond is that you avoid contamination with rotifers or any undesirables and know that the single species of algae you're producing has excellent nutritional value whilst many that naturally occur in eutrophic water may not.
Culturing the Moina themselves is equally straightforward and in my experience an air pump is also unnecessary if you use wide flat containers that provide plenty of surface area for air exchange. Moina are well known to thrive in oxygen poor environments due to their capacity to produce haemoglobin so I have no problem producing large amounts in non oxygenated water.
I hope this might prove useful to some of you here. I'm totally sure the method described can be improved upon and I welcome any suggestions but this technique seems valuable purely based on it's simplicity and relatively low startup cost. I found a poorly translated suggestion from an Asian fish breeder that adding some small limestone chips as a 'carbon source' in the Chlorella culture is beneficial and may try it out but I'm not sure of the science behind that.