These small, usually 1 mm or less, white or somewhat transparent crustaceans or "bugs" makeup about 90% of the zooplankton in the oceans. Most of the 8000 or more species are beneficial and feed on detritus and plant matter, e.g., microalgae in the wild and aquarium. In turn, fish feed upon them. In the aquarium they are mostly seen on the lower aquarium side panels or sand surface areas. Most are free living, however, there are some parasitic copepods that use their anchoring appendages to deeply penetrate flesh and can cause severe tissue damage. Yet, parasitic copepods are very rare in the aquarium.
Copepods are considered an excellent live food source for small fishes, e.g., damselfish, mandarinfishes, wrasses, and small angelfishes. Since they feed on detritus and microalgae, they can somewhat help keep unwanted algae blooms in check. Generally, their appearance in the aquarium should be considered an advantageous situation. Often can be seen with the aid of a flashlight or moonlight after the regular system lights go out. The below species may be in the genus Calanus.
These small crustaceans occur in marine and freshwater environments. Mysis relicta, an excellent freshwater mysis shrimp is widely used as a frozen food source for marine animals. In the wild they make nightly vertical migrations of about 360 feet to the surface to eat, then return downward at daybreak. These migrations require enormous amounts of energy, which is stored as animal fat, i.e., naturally occurring fatty acids such as Stearic, Palmitic, Oleic, Omega-3 and Omega-6. They are also very high in protein (about 70%), adding to their value as an excellent foodstuff. Always look for a product that contains whole specimens when thawed, as pieces leach the valuable fatty acids into surrounding water. Mysis also contain little in the way of sodium making it easier for marine animals to maintain their osmotic balance.
Krill are small, basically translucent 2 inch (5 cm) long crustaceans that have a life span of about seven years. They go through five stages of changes during the three to four years it takes to reach adulthood. They can go 200 days without food and must continually swim or sink to the bottom. Swimming in dense clouds, they can sometimes number a half million more or less in one cubic yard. It is estimated there are hundreds of million metric tons of krill in the Antarctica.
There are 85 species that represent the term "Krill." They are difficult to locate and require processing within a half-hour after capture. Yet, Krill is highly sought after by many nations. But it is the Antarctic species Euphausia superb that the whale feeds upon, and is the most commonly known and utilized species
Krill is half protein and very high in Vitamin A and is the worlds richest source of pure protein. Dried Krill is fed to many animals, e.g., cattle, fish, and poultry. They also contain high levels of fluoride in their shells and it is difficult to separate shell from flesh. Due to the processes involved in producing dried and freeze-dried foods their taste and nutritive value is not as good as fresh, live or frozen foods. Therefore, in my opinion, dry food including Krill, should be enhanced with a vitamin/mineral additive. Also, care should be exercised as to the amount fed at any one time. Dry foods begin decaying almost immediately upon contact with water, either leaching vitamins or going to waste.
Isopods are a free-living mostly nocturnal crustacean found in both the freshwater and marine world. They live from intertidal zones down to the deepest regions of the oceans. Those near coastal areas emerge at night and descend upon the shoreline to browse upon seaweed. Typically the body is dorsally flattened, the limbs are without well-developed claws and the last pair of abdominal limbs is modified into stylets or flat blades. Creature size varies from about 4 mm to some reaching over a foot (30 cm) in length. Yet most seen in the aquarium trade is usually less than a half inch (1 cm).
Most marine isopods are bottom dwellers and their dull colored leathery body provides for excellent camouflage. Most feed upon organic debris, yet some do feed upon algae or smaller animals. There is even one family that bores into marine timbers/pilings and causes severe damage. Rarely seen in the aquarium, however, a few species are noted below so you can get an idea of what they look like.
Amphipods are mainly free-living bottom dwelling crustaceans in intertidal zones, generally having laterally compressed bodies. Antennae vary in size and shape, and the eyes are unstalked. Size varies with species, e.g., a few millimeters to a few centimeters. They inhabit live rock and seaweed areas and are basically omnivores, although many are herbivores. They are naturally brought into aquaria on live rock and generally graze at night on filamentous algae, diatoms and cyanobacteria.
This is included here because this species is certainly a strange looking amphipod that I thought you might find interesting, both because it is similar looking to a mantis shrimp, yet "extremely" small.
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