Daphnia are well renowned as being a great supply of food for fish and have been used by many fish keepers for years but are usually given to the fish in frozen or dried form, culturing these aquatic creatures provides a fresh food that gives your fish plenty of nourishment, once researched they are not that difficult to culture and it can also be rewarding as well as saving money which is always a bonus with this hobby.
It does help if you understand these creatures and their needs so hopefully this article will provide you with all of the information that you require and encourages to start out on this project.
So the best place to start is a brief description of the Daphnia and their life cycle.
There are many species of Daphnia and as the name suggests they all belong to the genus of Daphniidae, they are a small crustacean, females only reach an adult size of 0.5 cm-1 cm dependant on the actual species and the males are usually smaller than this at an adult stage. They have a primitive organ system and the bodies are kidney shaped with primitive eyes. They have earned the common name of “water fleas” due to the jerky and uneven movement as they swim through the water column but note that actual water fleas belong to a different species and are copepods, bear this in mind when purchasing Daphnia to culture.
The most common daphnia that are available and used by fish keepers are the Daphnia magna and Daphnia pulex.
Their bodies are transparent with their interior organs clearly visible and they are found naturally in many continents throughout the world.
They can be found in slow moving waters and lakes but due to their small size and transparent body colouration are often difficult to see with the naked eye.
Daphnia are very adaptable when it comes to reproducing and can quickly colonise the water column if given the correct conditions. The good news is that you do not need to ensure that you have both males and females, in fact males are only produced when conditions are adverse, under normal conditions the Daphnia will reproduce asexually making the need for males non-existent. If conditions are not perfect then males are produced but the eggs that are laid will become dormant until conditions are right and then only will they hatch out for the next generation of Daphnia.
Females start to produce eggs from a very young age due to their short lifespan, eggs will be produced from the age of 4 days, the batches will be small in number initially, increasing in size as the female gets older. A female will produce a batch every 3 days but as the expected lifespan is approximately 75-80 days on average, each female can only produce up to 25 batches.
Setting up your culture tank for Daphnia
Firstly you do not need a large aquarium to produce Daphnia, 5 gallons will suffice to produce a decent colony that will provide plenty of nutritional food for your fish. You don't even need to use an aquarium, a plastic container can be used but ensure that it is food safe and will not leach any impurities into the water over a period of time. Surface area is very important compared to the volume as dissolved oxygen in the water column is essential to produce a healthy colony and a larger surface area provides a higher rate of gaseous exchange from the atmosphere, running an airline in the container or aquarium can have detrimental effects on the colony growth. Gentle agitation of the water surface via a filter outlet will increase the gaseous exchange, air bubbles from air stones can get trapped in the Daphnia making them unable to leave the surface of the water thus resulting in them not being able to feed properly. Sponge filters are ideal for these cultures as the flow can be turned right down plus they will maintain the water quality although in this situation actually filtering the water is the second priority, keeping the oxygen levels high is the main concern.
The water should be filtered as like all other aquatic creatures, the Daphnia are intolerant of ammonia, nitrites and nitrates although having said that a reasonable amount of nitrates will not be so detrimental as the latter in the tank.
The pH is also not critical as they do tolerate a wide range of pH ranging from acidic conditions with the pH settling at a level of 6.5 right up to alkaline conditions where the pH may reach 8.5, for optimum conditions you should aim for a pH range between 7.0-8.0, at these levels th Daphnia will be fine.
Temperature of the water can play a part in your success, higher temperatures are tolerated by the Daphnia but aim for a temperature set between 18-22 ° C (64-72 ° F), this will also keep the oxygen in the water column better as well.
The key to successful colonies is to try to keep all of the parameters at a constant level, this will involve performing partial water changes. Views on the amount of water changes do vary, at the end of the day do what is best for your culture. You may find that smaller changes does not keep the water quality high so increasing the volume of the water changes will correct this problem. Some people will say perform 50% water changes on a daily basis, others will swear by performing 75% water changes every other day, you will find out by trial and error the best method to use but test the water on a regular basis to ensure that ammonia or nitrites are not allowed to rise at all.
You can purchase starter cultures of Daphnia on the internet or some local aquatic suppliers may even be able to help you, some keepers are lucky enough to live near natural water ways that the Daphnia inhabit and can retrieve the initial stock from the water using a fine sieved net.
Feeding the Daphnia is also very simple, they love micro algae and this can be propagated very easily by leaving water in sunlight or even starting off a basic Infusoria culture and leaving this in a sunny windowsill. The Daphnia will relish the algae but you can also supplement the diet with a weekly feed of yeast which the Daphnia will also consume. Be careful which yeast you use as some contain compounds that can be harmful to the Daphnia in the long term. Brewers yeast is ideal and bakers yeast can be used but it must be an active yeast, the inactive yeasts should never be used for feeding.
Harvesting the Daphnia
The harvesting process is crucial to keeping your colony going, if the population of Daphnia rises too far then the colony can crash and you may have to start all over again. Think carefully about the volume of Daphnia that you will require as this can affect the decision you make as to the size of the tank/container that you will be using. If you do finish up with surplus daphnia to your requirements, do not worry you will still need to harvest but the excess will need to be disposed off to keep the colony population down to the correct level.
So how do we harvest these little creatures? Very simple to perform, the first step is to turn off any lighting that you are illuminating the colony with, this will encourage the Daphnia to rise to the surface of the water. Turn off any filters etc. that you may have running so that the water settles and leave the tank for a few minutes so that the Daphnia have had time to reach the surface.
You can collect the Daphnia with a fine net, what you are trying to achieve is to remove the larger daphnia so that the younger daphnia pass through the net and back into the tank.
You will need to wait until the daphnia have been in the tank for a couple of weeks before harvesting, this allows time for the colony to have grown slightly and ensures that you leave enough daphnia behind in the colony to keep the numbers at a satisfactory level. You should harvest approximately a quarter of the colony in each session but no more, as mentioned above any unused daphnia will have to be disposed off but bear in mind that you can keep some of the harvested daphnia in water for a couple of days before feeding them to the fish.
Just prior to harvesting I always like to ensure that the daphnia are well fed, this is sometimes referred to as “gut loading”, not only does this keep the daphnia healthy but also provides a bit of extra nourishment to your fish as they consume your harvest.
Daphnia make a great food source for fish, juvenile fish especially as they provide a high fat content which is good for growth. They are on a level par with newly hatched brine shrimp and in my opinion once a colony has been established they are far easier to maintain in the long run.
If your colony does crash ie. overpopulates and produces dormant eggs you can re-start it by removing a percentage of the original culture and adding these to a new set up.