These small crustaceans, which aquarists feed fish, are the main and most numerous representatives of aquatic multicellular animals. In addition, copepods are one of the main links in the food chains, the state of which ultimately affects our health. Their abundance and species diversity make up an important part of the planet's biosphere. The biology and life features of copepod mini-crustaceans will be discussed in this article.
Copepods
Copepods call a large group of animals that are united in a subclass of Copepoda crustaceans. This is one of the largest taxa in the animal world and includes about 20 thousand species. Among copepods, free-living (Calanoida and Cyclopoida orders) and parasitic forms are found.
Free-living crustaceans are one of the most important components of zooplankton in saline and fresh water bodies. They form the vast majority of the food supply of most fish and some marine mammals, which is called the generalizing word “krill”. The usual food chain of the seas and oceans looks something like this: marine phytoplankton - copepods - herring - dolphin.
Small crustaceans
The sizes of copepods range from 1 to 30 millimeters. Like all crustaceans, their body consists of three departments - the head, chest and abdomen. Breathing is carried out by the entire surface of the body, no gills.
On the head is the oral apparatus (mandibles), simple eyes and two pairs of antennas:
- One-branching antennals are jointed formations that participate in movement and perform the functions of the senses.
- Bipartite antennals. Their main function is to ensure the flow of water during swimming and nutrition.
Segmental body
The main swimming legs of the crustacean are located on four segments of the chest - flattened and similar to oars, for which these animals got their name. On the fifth segment, modified limbs are located, which in some representatives of copepods play a role in sexual reproduction.
The abdomen of 2-4 segments is usually deprived of limbs and ends in paired mobile appendages. Most species are characterized by sexual dimorphism, which is expressed in the number of segments of the abdomen, the structure of the limbs and the shape of the antennas.
Growth, development and fitness
Copepods have small sizes and growths that increase the area of the body - these features allow these plankton animals to stay in the water column without unnecessary expenses. This is facilitated by a thin chitinous cover and reserves of fat, which accumulates in special fat droplets and often gives color to these crustaceans.
When a sharp change in body position in the water column is required, they swim with the help of limbs or make jet jumps, folding their body in half.
Representatives of almost all types of copepods are dioecious organisms. Despite their simplicity, these copepods mating is preceded by complex sexual behavior. In the process of mating, the male transfers a spermatophore to the abdomen of the female (a special bag), the fertilization of eggs can be both external and internal.
The larval form (nauplius) emerges from the eggs, which, after several molts, turns into an adult crustacean.
The strongest
If you think that the most powerful animals live on land, you are mistaken. Recent studies prove that the smallest copepods can be considered the strongest. These crustaceans are capable of moving a distance 500 times their size in 1 second. Their small legs develop a force of movement that is 10 times greater than the similar forces of other animals.
As you know, copepods also make jumps. The speed that they develop at the same time is 3-6 km / h. Few? This is comparable to if a man of average height could run at a speed of several thousand kilometers per hour.
The main component of plankton
About 20-25% of plankton are representatives of this particular group of crustaceans, united in 3 orders:
- Calanoids (Calanoida) - the dominant group in marine plankton (up to 90%). They are the main food supply of many marine inhabitants. A distinctive feature is very long antennula and short abdomen. Representatives of this order, Diaptomus, live in fresh waters. These copepods feed on algae, filtering them out of the water column.
- Cyclops (Cyclopoida) are benthic (bottom and bottom) crustaceans. The peculiarity of their structure is relatively short antennules, the abdomen is long and separated from the chest, there is only one eye on the head. These crustaceans are predators, their prey are other small crustaceans and protozoa. In addition, it is the copepod cyclops, the inhabitant of fresh water reservoirs, that is the intermediate host of the worm that is a parasitic worm in the human intestinal tract, a wide ribbon.
- Bottom worm-shaped crustaceans (Harpacticoida) are free-living organisms of fresh and salt bodies of water. Antennules are shortened, the thoracic segments remain mobile, and the abdomen is almost no different from the chest. These crustaceans lead a bottom life of filtrators and saprophytes and are found in the most extreme conditions of life - in underground waters, in poisonous moss swamps and at very great depths in the ocean.
Parasitic organisms
Among copepods there are many parasitic forms. Their owners are fish and aquatic invertebrates. Many are characterized by a simplification of the organization, the loss of segmentation. And only by free nauplius is it possible to systematize these organisms.
For example, Lamproglena are copepods (see photo below) that parasitize on the gills of freshwater fish. Many of these parasites glue gill petals and lead to the mass death of infected fish.
Salmon disease is caused by parasitization on the skin, gills and in the mouth of the fish, which returns to spawn in fresh water, the Salmincola crustacean. It leads to violations in the health of fish, but does not pose a danger to humans.
Food for aquarium fish
Cyclops and diatoms are the most famous representatives of these crustaceans that feed aquarium fish. This is a high protein food for fry and adult aquarium inhabitants. In this case, the most nutritious nauplii of cyclops. But do not forget when feeding aquarium fish that cyclops are predators and grow quite quickly. Therefore, from food for fry, they can turn into predators that attack small fish. That is why experienced aquarists do not feed their pets live food, but pre-freeze it.
Depending on what the cyclops ate, crustaceans are red, brown, green, gray. This property to accumulate coloring substances in your body is also used to give aquarium fish a brighter color.
