Any way to harvest zooplankton and put them in the aquarium?
Yes one can harvest phytoplankton and zooplankton but the collection materials are not easily obtained. For collecting use a very fine mesh plankton net of the correct mesh size for the size of plankton needed. Plankton nets come in a variety of mesh sizes. Most common plankton nets are in 80-180 micron mesh size. Newly 1st feeding fry are eating very small plankton in the size close around 20-40um, several sizes smaller than the common plankton nets. I have a small filter bucket with 35um mesh to collect rotifers. Smallest mesh netting can be 10um.
When in high school I raised tropical zebra fish from eggs. I fed the fry an egg emulsion and managed to get several of them to survive to adult size.
Our PB forum member Azteca recently provided a link about feeding new fish fry using an egg emulsification method. This is a readily available fairly simple method to try as fry food. After the fry are growing 6-10 days I would blend in some fine powdered fish food.
https://www.fao.org/3/x5738e/x5738e0p.htm
