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The number of cyclops increases starting in April, as soon as the sun really warms up and the water temperature in the ponds rises above +8 °C.
The body of the Cyclops is noticeably divided into a cephalothorax and abdomen. The body length ranges from 1 to 4 mm depending on its type and age. On the head there is an unpaired eye, which gave rise to the name of the crustacean. The organs of movement and soaring are antennae, lined with short hairs and bristles. By simultaneously hitting the antennae and rowing legs, the Cyclops jumps forward. Having jumped, the crustacean spreads its antenna wide, like a parachute, and, as if floating, slowly descends.
Cyclops' food consists of microscopic algae and other small organisms. Cyclops, like all copepods, breathes over the entire surface of the body.
The eggs, when released from the female's oviducts, form two elongated egg sacs, which are positioned at the sides of the end of the body until they hatch into tiny larvae.
The larva swims animatedly in the water, grows and molts. During its transformations, the Cyclops goes through five unsegmented and six segmented stages, the last of which corresponds to an adult sexually mature animal.
For fish, hunting cyclops is also not an easy task, since these crustaceans are very mobile and are not so easy to catch.
Catching a cyclops in a pond
These crustaceans are caught with nets in reservoirs. In order to catch cyclops, you need to lower the net into the water and make movements in the shape of a lying figure eight, creating a whirlpool that will pull the creatures into the net. To do this, curved lines are drawn smoothly with a net, and intersecting lines are drawn sharply and with pressure. Caught crustaceans are transported on wooden frames with fabric pre-stretched over them. The crustaceans are placed on a cloth, which is then lowered in a frame into water and immediately taken out. This is done so that the crustaceans are evenly distributed on it, but their layer should not exceed 3 mm. The frames need to be wrapped in a damp cloth and the crustaceans can be taken home. You can also place them in glass or enamel containers for transportation.
At home, you need to remove the dead cyclops, and the living ones need to be calibrated by size. Cyclops are stored in a cool, dark place, in a wide container with a low water level. If the water level is high, the crustaceans will require aeration. Dead creatures must be removed daily using a hose.
Cyclops can also be frozen or dried.
Cyclops as food for fry
These crustaceans are very mobile, so some fish may have difficulty hunting them. It is worth remembering that if you feed fish fry with Cyclops nauplii, then you should give them in small portions and wait until they are completely eaten, since these nauplii can quickly grow and begin to hunt the fry.
Anatoly Onegov
“Moving in rhythmic leaps, the Cyclops can stay well at one level, rising up and down at angles of varying steepness. A cyclops can swim with equal ease if it turns over on its back. The Cyclops describes arcs well, makes loops, single and multiple, direct and reverse. The Cyclops can make a turn at an angle of 90°, rotate around an axis not only with a descent, reminiscent of the turns of an airplane in a tailspin, but also with an upward movement. The nature of the figures performed by the Cyclops is very similar to aerobatics. Possession of the aerobatic maneuvers necessary for fighter aircraft undoubtedly makes it easier for the Cyclops - an active predator - to ensure its existence by hunting for food. aquatic inhabitants serving him as food." This is how the Cyclops is described in the book “The Life of Animals” (Volume 2, M., Prosveshchenie, 1968).
Cyclops are also crustaceans, but unlike daphnia (cladocerans), cyclops are called copepods.
Daphnia move with the help of so-called antennae, and cyclops, as their name suggests - copepods - use rowing legs-oars to move in the water
Unlike daphnia, Cyclops has not two eyes, but one. Hence another name for the copepod - Cyclops, named after the one-eyed giant from ancient Greek mythology.
In the book “Animal Life” we read further: “When studying the life of every body of water - from a small puddle to the ocean - the researcher encounters these crustaceans. A plankton net stretched at any depth of the ocean, in the hot tropics or in cold polar waters, brings a catch consisting mainly of copepods. These crustaceans also live in streams and lakes, deep dark caves. They swim in masses in all ordinary freshwater bodies of water, often not inferior in number to cladocerans.”
Cyclops are usually smaller than daphnia - the length of a cyclops does not exceed 4 mm. But unlike most daphnia, cyclops are mainly predators - they attack and eat almost all living things that they encounter and do not significantly exceed their size. Therefore, copepods in aquariums can be dangerous not only for fish eggs, but also for fry that have just hatched from the eggs. True, among the Cyclops there are those who feed on plant foods - mainly green filamentous algae.
There is one more thing, very significant difference cyclops from daphnia: it is very difficult to meet daphnia in a reservoir in the cold season, but cyclops live there all year round. This is important for every aquarist to know: after all, fry in an aquarium can appear in winter time- This is where the Cyclops will help us out.
Like daphnia, Cyclops are perfectly adapted to various unfavorable living conditions. When a reservoir freezes through or dries out, the cyclops is enveloped in a special substance that they themselves secrete - a kind of cocoon is formed around the crustacean. In such a cocoon, Cyclops can freeze into ice or remain at the bottom of a dry puddle. Experiments were carried out in which cyclops were preserved in dry silt, which had lain without water for three years. This is why Cyclops appears so quickly in spring and rain puddles.
If you take a closer look at the cyclops through a magnifying glass, you will definitely notice that some crustaceans have small pouches at the end of their bodies - one or two - while others do not. The little sacs are the egg sacs, or egg sacs as they are called. And crustaceans with egg sacs are female Cyclops. Crustaceans without egg sacs are males (it is also impossible to easily distinguish a male from a female in daphnia). From the testicles of the Cyclops comes the Cyclops larva - nauplius, which is also happily eaten by fish, especially juveniles. Reproducing with high speed, Cyclops, like daphnia, quickly populates a suitable reservoir.
Also a Cyclops, but inedible. Cyclops under a microscope (Cyclopidae)
Cyclops under a microscope
Cyclops under a microscope
Another suborder of copepods - Cyclopoida - the largest number species presented in fresh waters.
Freshwater cyclops live in all kinds of bodies of water, from small puddles to large lakes, and are often found in very large quantities copies. Their main habitat is the coastal strip with thickets aquatic plants. At the same time, in many lakes there are thickets certain plants timed certain types Cyclops. So, for example, for Valdai Lake in Ivanovo region 6 groupings of plants with their corresponding groupings of Cyclops species are described.
Relatively few species can be considered true planktonic animals. Some of them, belonging mainly to the genus Mesocyclops, constantly live in the surface layers of water, others (Cyclops strenuus and other species of the same genus) make regular daily migrations, descending during the day to significant depth.
Cyclops swim somewhat differently than calanids. Simultaneously flapping four pairs of thoracic legs (the fifth pair is reduced), the crustacean makes a sharp jump forward, upward or sideways, and then, with the help of the front antennae, can hover in the water for some time. Since the center of gravity of its body is shifted forward, while hovering its front end tilts and the body can assume a vertical position, and the dive slows down. A new swing of the legs allows the Cyclops to rise. These swings are lightning fast - they take 1/60 of a second.
L. Isaev, who has been extensively involved in the biology of cyclops, describes their movements as follows: “Moving in rhythmic leaps, a cyclops can stay well at one level, rise up and fall down at angles of varying steepness. A cyclops can swim with equal ease if it turns over on its back. Cyclops describes arcs well, makes loops, single and multiple, direct and reverse. The Cyclops can make a turn at an angle of 90°, rotate around an axis not only with a descent, reminiscent of the “corkscrew” turns of an airplane, but also with an upward movement. The Cyclops can glide onto the antenna, flip through it, dive headfirst at a 90° angle, and glide onto its tail. The nature of the “figures” performed by the Cyclops is very similar to aerobatics. Possession of the aerobatic maneuvers necessary for fighter aircraft undoubtedly makes it easier for the Cyclops - an active predator - to ensure its existence by hunting for aquatic inhabitants that serve as food for it.”
Most cyclops are predators, but there are also herbivorous species among them. Such common, widespread species as Macrocyclops albidus, M. fuscus, Acanthocyclops viridis and many others quickly swim above the bottom or among thickets in search of prey. With the help of their antennae, at a very short distance, they sense small oligochaetes and chironomids, which they grab with their front jaws armed with spines. The hind jaws and maxillae are involved in transferring food to the mandibles. The mandibles make rapid cutting movements for 3-4 seconds, followed by a minute pause. Cyclops can eat oligochaetes and chironomids larger than themselves. The speed at which prey is eaten depends on their size and the hardness of their coverings. It takes 9 minutes to crush and swallow a bloodworm 2 mm long, and a larva 3 mm long is destroyed within half an hour. The more delicate, although longer (4 mm), Nais oligochaete worm is eaten in just 3.5 minutes.
Herbivorous cyclops, in particular the common Eucyclops macrurus and E. macruroides, feed mainly on green filamentous algae (Scenedesmus, Micractinium), capturing them in approximately the same way as predatory ones capture worms and bloodworms; in addition, various diatoms, peridinia and even blue-green algae are used. Many species can only eat relatively large algae. Mesocyclops leuckarti quickly fills its intestines with colonies of Pandorina (colony diameter 50-75 microns) and almost does not swallow small Chlamydomonas at all.
Freshwater cyclops are very widespread. Some species are found almost everywhere. This is facilitated primarily by adaptations to endure unfavorable conditions, in particular the ability of crustaceans to tolerate drying out of water bodies and passively disperse through the air in the form of cysts. The skin glands of many cyclops secrete a secret that envelops the body of the crustacean, often together with the egg sacs, and forms something like a cocoon. In this form, crustaceans can dry out and freeze into ice without losing their viability. In Camerer's experiments, cyclops were quickly hatched by soaking dry mud, which was preserved for about 3 years. Therefore, there is nothing surprising in the appearance of cyclops in spring puddles that appear when snow melts, in newly filled fish ponds, etc.
Second reason widespread many species of cyclops should be considered the resistance of crustaceans located in active state, in relation to the lack of oxygen in water, its acidic reaction and many other factors unfavorable for other freshwater animals. Cyclops strenuus can live for several days not only in the complete absence of oxygen, but even in the presence of hydrogen sulfide. Some other species also tolerate adverse conditions well. gas mode. Many cyclops thrive in water with an acidic reaction, with a high content of humic substances and extreme poverty of salts, for example, in reservoirs associated with high-moor (sphagnum) bogs.
Nevertheless, species and even genera of Cyclops are known that are limited in their distribution by certain certain conditions, in particular temperature and salt conditions. For example, the genus Ochridocyclops lives only in Lake Ohrid in Yugoslavia, the genus Bryocyclops - in Southeast Asia and in equatorial Africa. TO the last generation Closely related is the exclusively underground genus Speocyclops, species of which are found in caves and groundwater Southern Europe, Transcaucasia, Crimea and Japan. These blind small crustaceans are considered remnants of a once more widespread thermophilic fauna.
Some Cyclops have adapted to life in brackish and even very salty bodies of water. The genus Halicyclops, for example, is quite common in the Caspian Sea and is not found in fresh water. Microcyclops dengizicus is widespread only in brackish and saline reservoirs of the desert zone (Iraq, India, Haiti, Egypt, California, in the USSR - in the Karaganda region, in the Mugan steppe) and lives well even at salinities exceeding sea salinity (up to 41°/ oo) - Many are ordinary freshwater species can also exist in brackish water, such as Mesocyclops leuckarti in the Gulf of Finland and the Gulf of Bothnia.
Marine representatives of the suborder Cyclopoida are less diverse than freshwater ones. Among them, species of the genus Oithona are common and often numerous in marine plankton. Also very characteristic are the large (up to 8 mm) flattened species of the genus Sapphirina, the surface of which has bright blue, golden or dark red tones (Table 31, 1). Another close marine genus, Opsaea (Table 31, 4), has glands that secrete a luminous secretion, and often, together with other organisms, causes the sea to glow.
Animal life: in 6 volumes. - M.: Enlightenment. Edited by professors N.A. Gladkov, A.V. Mikheev. 1970 .
“Moving in rhythmic leaps, the Cyclops can stay well at one level, rising up and down at angles of varying steepness. The Cyclops can swim with equal ease when turning over on its back.
Cyclops describes arcs well, makes loops, single and multiple, direct and reverse. The Cyclops can make a turn at an angle of 90°, rotate around an axis not only with a descent, reminiscent of the turns of an airplane in a tailspin, but also with an upward movement. The nature of the figures performed by the Cyclops is very similar to aerobatics. Possession of the aerobatic maneuvers necessary for fighter aircraft undoubtedly makes it easier for the Cyclops - an active predator - to ensure his existence by hunting for aquatic inhabitants that serve him as food." This is how the Cyclops is described in the book "The Life of Animals" (Vol. 2, M., Enlightenment , 1968).
Cyclops are also crustaceans, but unlike daphnia (cladocerans), cyclops are called copepods.
Daphnia move with the help of so-called antennae, and cyclops, as their name suggests - copepods - use rowing legs-oars to move in the water
Unlike daphnia, Cyclops has not two eyes, but one. Hence another name for the copepod - Cyclops, named after the one-eyed giant from ancient Greek mythology.
In the book “Animal Life” we read further: “When studying the life of every body of water - from a small puddle to the ocean - the researcher encounters these crustaceans. A plankton network stretched at any depth of the ocean, in the hot tropics or in cold polar waters, brings a catch of mainly from copepods. These crustaceans also live in streams and lakes, deep dark caves. They swim in masses in all ordinary freshwater reservoirs, often not inferior in number to cladocerans.”
Ornamental koi carp
Cyclops are usually smaller than daphnia - the length of a cyclops does not exceed 4 mm. But unlike most daphnia, cyclops are mainly predators - they attack and eat almost all living things that they encounter and do not significantly exceed their size. Therefore, copepods in aquariums can be dangerous not only for fish eggs, but also for fry that have just hatched from the eggs. True, among the Cyclops there are those who feed on plant foods - mainly green filamentous algae.
There is one more, very significant difference between cyclops and daphnia: it is very difficult to meet daphnia in a reservoir in the cold season, but cyclops live there all year round. This is important for every aquarist to know: after all, fry can appear in the aquarium in winter - this is where cyclops will help us out.
Like daphnia, Cyclops are perfectly adapted to various unfavorable living conditions. When a reservoir freezes through or dries out, the cyclops is enveloped in a special substance that they themselves secrete - a kind of cocoon is formed around the crustacean. In such a cocoon, Cyclops can freeze into ice or remain at the bottom of a dry puddle. Experiments were carried out in which cyclops were preserved in dry silt, which had lain without water for three years. This is why Cyclops appears so quickly in spring and rain puddles.
If you take a closer look at the cyclops through a magnifying glass, you will definitely notice that some crustaceans have small pouches at the end of their bodies - one or two - while others do not. The little sacs are the egg sacs, or egg sacs as they are called. And crustaceans with egg sacs are female Cyclops. Crustaceans without egg sacs are males (it is also impossible to easily distinguish a male from a female in daphnia). From the testicles of the Cyclops comes the Cyclops larva - nauplius, which is also happily eaten by fish, especially juveniles. Reproducing at high speed, Cyclops, like Daphnia, quickly populates a suitable body of water.
Literature: Onegov A. School of Young People. Living Corner/Art. V. Ra-daev, V. Khramov. - M.: Det. lit., 1990. - 271 p.: ill.
Who would have thought how interesting and mysterious it could be? undersea world! Here you can find not only large and small sea creatures, but also very small creatures with amazing structure bodies. Such animals include an unusual crustacean - the Cyclops. This is a funny arthropod with short and long antennae and a translucent body. We will talk further about what kind of creature this is, why it is called that and how many eyes the Cyclops has.
General characteristics of the Cyclops
Most people associate Cyclops with a huge fairy-tale giant with enormous power and, most notably, a single eye. However, the hero of our today's article has nothing in common with this giant, except for the name and some others external signs, but we’ll talk about them later. On the contrary, it is very small. Its body length is only 1-5.5 mm.
Description of the crustacean body
The elongated and tapering body (in biology textbooks it is said that it is divided into a cephalothorax and abdomen) of this cute crustacean contains four pairs of legs that look more like thin pencil lines. This is how amazing and unique he is - Cyclops (crustaceans). How many eyes it has can only be seen with high magnification of the creature, under a powerful microscope. It is almost impossible to do this while moving in water.
By the way, males also have a fifth pair of legs, but they have a slightly different purpose. The fact is that when communicating with a female, her partner holds her friend near him with these spare legs. This is how he ensures peace of mind and immobilizes his “lady of the heart” at the right moment for him.
When and where can you see a Cyclops?
Don't know how many eyes Cyclops has? We will be happy to tell you about this, but we will do it a little later. Favorite place The habitat of the crustacean is the coastal zone in fresh water, where it appears en masse in early April. It is at this time that the temperature already reaches 8-10 ºС, which is quite acceptable for the reproduction of small flocks of Cyclops.
Towards mid-summer, the number of these crustaceans sharply decreases, and in September it increases again. In winter, the number of arthropods decreases. The baby cyclops themselves become less active. However, they do not go into suspended animation.
How many eyes does a Cyclops have: what do the mythical character and the crustacean have in common?
U small crustacean with antennae and thin legs, only one eye, which, in fact, brings him closer to the mythical character. Externally, these tiny creatures look like a slightly elongated tadpole with antennae and a tail with single-branched antennae. In the middle of their heads they are equipped with short antennules (slightly bent whisker threads). Here there is a single eye, which allows these babies to distinguish objects in fresh water. So if someone asks you how many eyes a Cyclops has, you will find something to answer.
Internal structure of the body
Although the Cyclops belongs to the animal kingdom, it can be spoken of as a simple organism. First of all, he has no heart. Secondly, it has no blood vessels at all, and all internal organs are washed by almost colorless hemolymph.
We have already discussed how many eyes a Cyclops has. By the way, a photo with a schematic representation of this unusual organism can be seen below. However, the question of the number of visual organs in this representative of crustaceans is far from the only one that needs clarification. An important subject for discussion is internal structure crustacean and its work digestive system. So, these copepods have an intestine that is stimulated by the movement of hemolymph.
Respiratory system and level of vision
The crustacean breathes with its whole body. Despite the simplicity of its physique, this extraordinary arthropod has a real nervous system that does not contain nodes. It is presented in the form of a combination of the abdominal cord and the brain “brain”.
In addition, the freshwater organism has good eyesight. If you still don’t know how many eyes the Cyclops crustacean has, we’ll remind you: one. But, despite this fact, this small creature perfectly navigates the terrain, swims quickly and even makes simple maneuvers in the event of a collision with predators.
What and how do cyclops eat?
Despite the simplicity of the body structure and internal organs, Cyclops is considered a predator. Most often they feed on rotifers, small crustaceans, and protozoan microorganisms. But they themselves are a major link in the food chain for the younger generation of fry and fish.
By the way, cyclops themselves can also feed on small inhabitants of aquariums and fresh water bodies. This happens as follows: the crustacean attaches itself to the body of the fish, the length of which is no more than 4-5 mm, and begins to little by little bite off pieces of it. And as soon as the prey chosen by the crustacean weakens, a whole flock of its relatives pounces on it and continues to destroy it. As you can see, appetite does not depend at all on how many eyes the Cyclops has. The animal, despite its inferiority, feels great and easily satisfies its hunger, using all the methods known to it, including collective ones.
Female cyclops and features of bearing eggs
The females of these crustaceans have larger size. In addition, their body contains small bag-like compartments attached to the very base of the abdomen. It is in these unique containers that the already fertilized eggs are placed. On average, their number does not exceed 10-12 pairs. Interestingly, immediately after the birth of the babies, the female sheds her stretched bags, which easily grow anew with each subsequent process of bearing offspring.
Where can it be used and how to catch a Cyclops?
Baby Cyclops can be used as food for aquarium fish. You can catch them using a net. In this case, the tool should be equipped with nylon or fabric made from fine mill gas.
Insect cyclops: who are they?
In addition, some insects are also called. For example, these include moths and nigella butterflies. But, unlike the arthropod baby, they have both eyes. They got their name from the presence of small circles on their wings that resemble an eye. These insects are widespread in China, the Primorsky and Khabarovsk Territories, and they are also found on the Korean Peninsula.
Now you know how many eyes the Cyclops has. An insect from the Lepidoptera family has two eyes, and a crustacean with the same name has one.
Cyclopidae) - a family of copepods with a body length of 1-5.5 mm, having an unpaired frontal ocellus, from which they got their name. Cyclops have short antennae, the antennae used for swimming are single-branched, and there are 4 pairs of developed legs. The fifth pair in males is transformed into an organ for holding the female during the sexual process. They don't have a heart. Blood vessels No. The organs are washed by colorless hemolymph, the movement of which is facilitated by intestinal pulsation. Breathes throughout the entire surface of the body. Nervous system in the form of the head “brain”, the abdominal cord forming a “ladder”, there are no nodes. About 250 species are known, distributed throughout to the globe. They usually live at the bottom of freshwater reservoirs, and only a few live in the water column. Cyclops are predators and feed on protozoa, rotifers, and small crustaceans. They themselves serve as food for many fish and fry. They can serve as intermediate hosts for parasitic worms and others.
The suborder of copepods - Cyclopoida - is represented by the largest number of species in fresh waters. Freshwater cyclops live in all kinds of bodies of water, from small puddles to large lakes, and are often found in very large numbers of specimens. Their main habitat is the coastal strip with thickets of aquatic plants. Moreover, in many lakes certain species of cyclops are confined to thickets of certain plants.
Relatively few species can be considered true planktonic animals. Some of them, belonging mainly to the genus Mesocyclops, constantly live in the surface layers of water, others (Cyclops strenuus and other species of the same genus) make regular daily migrations, descending during the day to a considerable depth. Cyclops swim by simultaneously flapping four pairs of chest legs (the fifth pair is reduced). The crustacean makes a sharp jump forward, up or sideways, and then with the help of its front antennas it can hover in the water for some time. Since the center of gravity of its body is shifted forward, while hovering its front end tilts and the body can assume a vertical position, and the dive slows down. A new swing of the legs allows the Cyclops to rise. These swings are lightning fast - they take 1/60 of a second. Moving in rhythmic leaps, the Cyclops can stay well at one level, rise up and fall down at angles of varying steepness. A cyclops can swim with equal ease if it turns over on its back. Cyclops describes arcs well, makes loops, single and multiple, direct and reverse. The Cyclops can make a turn at an angle of 90°, rotate around an axis not only with a descent, reminiscent of the “corkscrew” turns of an airplane, but also with an upward movement. The Cyclops can glide onto the antenna, flip through it, dive headfirst at a 90° angle, and glide onto its tail.
The second reason for the wide distribution of many species of cyclops should be considered the resistance of crustaceans in an active state to the lack of oxygen in water, its acidic reaction and many other factors unfavorable for other freshwater animals. Cyclops strenuus can live for several days not only in the complete absence of oxygen, but even in the presence of hydrogen sulfide. Some other species also tolerate unfavorable gas conditions well. Many cyclops thrive in water with an acidic reaction, with a high content of humic substances and extreme poverty of salts, for example, in reservoirs associated with high-moor (sphagnum) bogs.
The importance of the Cyclopes in the life of Tanganyika is very great. On the one hand, they serve as food for many fish and their young, but, on the other hand, they act as competitors of the same fish, eating many small animals, both planktonic and bottom.
During the daytime, copepod nauplii is found at depths of up to 25 meters. Juveniles of Diaptomus copepodites are found everywhere at depths of up to 50 meters, and adults - from 75 to 125 meters. Cyclopoid copepodites were found down to 50 meters depth, and adults were found from more than 75 meters. In general, nauplii copepods, in the daytime, are located in the upper layers, copepodites - in the middle layers, and adult, sexually mature individuals - already at depths of one hundred meters. Thus, we can conclude that what larger than the individual, the deeper they are during the daytime. The lower limit of the distribution of zooplankton, including Diaptomus and shrimp, can be considered a depth of 125 meters, below which they practically do not occur. Apparently, in this case, the presence of oxygen in the water is critical, the percentage of which drops sharply after a hundred-meter depth. The vertical distribution of zooplankton in the waters of Miaro and Uvira at night and during the day is approximately the same. It can be noted that there is a significant movement of Diaptomus copepodites into the upper layers of the Lake at night, while Cyclopoids move only slightly. Shrimp also move closer to the surface at night. To summarize, it can be noted that during the daytime, large zooplankton descend to a depth where there is less light and more phytoplankton, and at night, they rise closer to the surface, also following the movement of phytoplankton. The daily vertical migration of crustaceans also allows them to avoid being eaten by fish, such as Ndagalas. Shrimp were widely absent at shallow depths, but were found at depths ranging from 25 to 125 meters. In Lake Tanganyika, the presence of zooplankton is directly related to the presence of phytoplankton, the development boom of which occurs at the beginning of the rainy season (late October - November). In different areas of the Lake, the amount of phytoplankton, even at the peak of the boom, varies in its biomass and it is noteworthy that in areas of the Lake with an insignificant presence of phytoplankton, larger number species of Cyclops than in areas with its abundant presence. In Tanganyika, as in other tropical lakes with year-round high temperature water, zooplankton reproduction occurs throughout the year, changing only in mass in accordance with the presence or absence of phytoplankton.