These small crustaceans, which aquarists feed to fish, are the main and most numerous representatives of aquatic metazoans. In addition, copepods are one of the main links in the food chain, the state of which ultimately affects our he alth. Their abundance and species diversity constitute an important part of the planet's biosphere. The biology and life characteristics of copepod mini-crustaceans will be discussed in this article.
Copepods
Copepods are a large group of animals that are united in a subclass of crustaceans Copepoda. This is one of the largest taxa in the animal kingdom and includes about 20 thousand species. Among copepods, there are free-living (orders Calanoida and Cyclopoida) and parasitic forms.
Free-living crustaceans are oneone of the most important components of zooplankton in s alt and fresh water bodies. They make up the vast majority of the food base 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 sections - the head, chest and abdomen. Breathing is carried out by the entire surface of the body, there are no gills.
On the head is the mouth apparatus (mandibles), simple eyes and two pairs of antennae:
- Single-branched antennules are jointed formations that participate in movement and perform the functions of sensory organs.
- Two-branched antennules. Their main function is to provide water flow for swimming and feeding.
Segmental body
On the four segments of the chest are the main swimming legs of the crustacean - flattened and similar to oars, for which these animals got their name. The fifth segment contains modified limbs, which in some copepods play a role in sexual reproduction.
The abdomen of 2-4 segments is usually devoid of limbs and ends with paired movable 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 antennae.
Growth, development andfitness
Copepods are small in size and have outgrowths that increase the body area - such features allow these planktonic animals to stay in the water column at no extra cost. This is facilitated by a thin chitinous cover and reserves of fat, which accumulates in special fat drops and often gives color to these crustaceans.
When a sudden change in body position in the water column is required, they swim with the help of their limbs or make jet jumps by folding their body in half.
Representatives of almost all copepod species are dioecious organisms. Despite the outward simplicity, mating in these crustaceans is preceded by complex sexual behavior. In the process of mating, the male transfers a spermatophore (special bag) to the female's abdomen, 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 strongest animals live on land, you are wrong. Recent studies show that small copepods can be considered the strongest. These crustaceans are capable of moving 500 times their size in 1 second. Their small legs develop a power of movement that is 10 times greater than that 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 person of average height could run at a speed of several thousandkilometers per hour.
The main component of plankton
About 20-25% of plankton are representatives of this particular group of crustaceans, united in 3 orders:
- Kalanoids (Calanoida) - the dominant group in marine plankton (up to 90%). They are the main food base for many marine life. A distinctive feature is very long antenullae and a short abdomen. Representatives of this detachment live in fresh waters - Diaptomus. 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 is other small crustaceans and protozoa. In addition, it is the copepod cyclops, an inhabitant of fresh water, that is the intermediate host of a dangerous worm that parasitizes in the human intestinal tract - a wide tapeworm.
- Bottom worm-like crustaceans (Harpacticoida) are free-living organisms of fresh and s alt water bodies. Their antennae are shortened, the thoracic segments remain mobile, and the abdomen almost does not differ from the chest. These crustaceans lead a benthic lifestyle of filter feeders and saprophytes and are found in the most extreme living conditions - in groundwater, in poisonous moss swamps and at very great depths in the ocean.
Parasitic organisms
There are many parasitic forms among copepods. Their hosts are fish and waterinvertebrates. Many are characterized by the simplification of the organization, the loss of segmentation. And only by free nauplius is it possible to systematize these organisms.
For example, Lamproglena is a copepod (see photo below) that parasitizes the gills of freshwater fish. Many of these parasites stick together the gill filaments and lead to massive deaths of infected fish.
Salmon disease is caused by parasitism on the skin, gills and in the oral cavity of fish that returns to spawn in fresh water, the crustacean Salmincola. It leads to disturbances in the he alth of fish, but does not pose a danger to humans.
Aquarium fish food
Cyclops and diatomuses are the most famous representatives of these crustaceans, which are fed to aquarium fish. This is a high protein food for fry and adult aquarium inhabitants. At the same time, the nauplii of the Cyclopes are the most nutritious. 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 with live food, but freeze it first.
Depending on what the cyclops ate, crustaceans are red, brown, green, gray. This ability to accumulate dyes in your body is also used to give a brighter color to aquarium fish.
Meaning in nature
These small crustaceans make upa key link in the food chains of marine ecosystems. Modern studies show that the reduction of krill in ocean waters (according to some estimates, it has amounted to 80% since 1976) threatens the existence of not only many fish species, but also penguins, seals and even whales.
In addition, copepods, together with other benthic saprophytes, provide water purification from corpses and waste products. Planktonic crustaceans purify water from mineral suspension, contribute to its transparency, and therefore increase the efficiency of plant plankton. And in the end, it is they who participate in the enrichment of the atmosphere with oxygen and the absorption of carbon dioxide from it. This is how small crustaceans are built into a system common to the planet that regulates the climate and the state of the atmosphere.
