From microscopic to meters in size!
Most zooplankton are small or even microscopic organisms, such as copepods, water fleas, rotifers, and krill. They live their entire lives as plankton because they stay small. But small fish fry and other larvae also count as plankton until they grow strong enough to propel themselves against the water currents. There are also large zooplankton!
Most zooplankton are small organisms but there are exceptions. Many jellyfish are also zooplankton, as is the four-metre-long and thousand-kilo-heavy ocean sunfish. Zooplankton eat phytoplankton. Many animals in the oceans and seas eat zooplankton. The world’s biggest animal, the blue whale, only eats the zooplankton krill.
The ocean sunfish - a zooplankton that weighs up to a ton!
Jellyfish, like these common jellyfish, are also zooplankton.
Photo: Laika-ac-CC-BY-SA
Different kinds of small crustaceans - also zooplankton.
Fish fry, like this newly hatched salmon fry, are also zooplankton.
Photo: Uwe-Kils-CC-BY-SA
A daphnia - commonly known as water flea - similar to the ones in our tank.
Photo: Anatoly-Mikhaltsov-CC-BY-SA
The Aquarium’s water fleas
This tank is home to zooplankton belonging to the order of small crustaceans known as Cladocera or water fleas. These specific water fleas belong to the genus Daphnia. They eat phytoplankton by filtering out the plankton from the water. Most Daphnia are female and can reproduce without mating. Daphnia mostly live in fresh water but can also live in the brackish water of the Baltic Sea.