Large and small shrimp.
Large shrimp species are agile predators. Aside from the fact that very few shrimp species are capable of surviving in freshwater, only a small fraction of them more or less meet the requirements of a “community aquarium.” First, there are large species (some of which resemble crayfish more than shrimp taxonomically) that, when growing in a small indoor aquarium, actively alter the underwater landscape by constantly digging up the substrate and uprooting decorative aquatic plants.
Another problem is the exceptional voracity of large specimens. The large amount of food they require leads to an excessive accumulation of organic matter in the aquarium, which severely disrupts the ecological balance and leads to cloudy water, algal blooms, and ultimately, fish diseases. When kept underfed, even predominantly carnivorous arthropod species are forced to supplement their diet with plants — while soft plants disappear very quickly, the destruction of slow-growing Cryptocoryne and Anubias is just a matter of weeks.
Second, despite the assurances of sellers (imported Asian and domestic Far Eastern freshwater shrimp occasionally appear on the market) that “they are peaceful and unpretentious,” representatives of many even small species are quite aggressive and, from early childhood, constantly try to attack even larger fish. While they might not actually eat a fast-moving fish, they can scratch and nip its fins. They will also quickly “cleanse” the aquarium of snails and other invertebrates that fail to escape. This applies primarily to Leander, Palaemon, and Macrobrachium, which, if hungry, may even attack fish fry. This is most commonly observed when keeping conditions change.
Representatives of the genus Macrobrachium are classified as long-clawed shrimp, with some species having one larger claw and a second normal one. All members of this family are known for their unfriendly nature. Some species reach substantial sizes (up to 15-20 cm) and are used in gastronomy (notably Macrobrachium rosenbergii, which is successfully farmed on an industrial scale).
Fortunately for nature enthusiasts, the genus also includes quite a few relatively compact creatures suitable for home aquariums. Chief among these is Macrobrachium nipponense, the Oriental river prawn. Alongside Macrobrachium nipponense, other members of the genus are also kept in aquariums. Many of them are so morphologically similar that they still lack a definite scientific name. When of equal size, these shrimp get along reasonably well with each other, conflicting only when hiding spots and food are scarce.
Their behavioral pattern is aggressive, and keeping them in mixed aquariums causes a number of problems. Their fights are quite spirited but generally harmless — serious injuries usually occur only when one of the rivals is temporarily stripped of its chitinous armor. Males are quite territorial, and it is common to see males missing claws. This is the result of battles for territory and dominance. It is worth noting that there will usually be only one large male with all its limbs intact — the dominant one. The other males are somewhat smaller. However, this “reign” does not last long, as there are too many contenders for the “throne.”
On the other hand, smaller tank mates (especially those belonging to other genera) are poorly tolerated, and potential competitors are eliminated at the slightest opportunity. They coexist peacefully with Ancistrus and Apistogramma. They hunt at night when they are most active, while resting fish cannot react adequately, nipping the fins and tails of sleeping fish. They should not be kept with small fish or veil-finned varieties.
As for Macrobrachium rosenbergii, if an off-guard fish suddenly finds itself within reach of their claws, the unsuspecting fish stands no chance. Rosenbergs easily have the strength and determination to overpower a fish half their size. Given that these animals reach their natural size of 40 cm within a year even in a 100-liter aquarium, introducing a Rosenberg to fish smaller than 15-20 cm is essentially signing a delayed death sentence within a year. Fortunately, identifying a Rosenberg on the market (where they have become increasingly common and cheaper) is quite easy: despite significant similarities, Rosenbergs are betrayed by a noticeable red “nose” (rostrum) with small serrations.
Thus, most large freshwater shrimp species offered on the market have limited suitability in large “office” aquariums with coarse, lifeless substrate, gypsum-plastic decorations, and large (10-30 cm) fish such as cichlids.
Shrimp of the genus Leander have much in common with crayfish in terms of body structure, behavior, and reproduction. Their antennae are one and a half to two times longer than their body, and their claws are small and weak. The body is translucent, so their coloration depends on the type of food consumed as well as the substrate color. Their coloration is not particularly striking: the pale grayish-brown tones of the translucent body are unlikely to attract aesthetic aquarists. They can be kept in aquariums alongside fish. Leanders pay absolutely no attention to healthy fish, possess enviable hardiness, remain active even during daylight hours, and conflict with each other only in confined spaces. To avoid infighting, there should be no more than 10-15 individuals in a 100-liter aquarium.
In moments of danger, they make sudden, jet-propelled swimming movements through the water column by contracting their tail fan. They can swim backward. However, at high stocking densities due to competition for living space, cannibalism occurs: stronger individuals destroy weaker ones. The female carries over a hundred eggs for about 3 weeks and then abandons the hatched fry to their fate. Raising these shrimp is not easy due to the lack of proper food and the high sensitivity of the fry to water pollution.
Shrimp of the genus Palaemonetes are generally peaceful, except for larger females which are somewhat territorial. They are most active at night, hiding in the shade during the day. They are very active and constantly foraging. At higher temperatures, these shrimp are more active and become aggressive enough to attack fish and prey on smaller shrimp. At lower temperatures, they are less active and become vulnerable to fish attacks.
The aquarium must be heavily planted so they can hide from fish. They are extremely sensitive to scent and locate food on the substrate faster than any fish or other shrimp. They even swim upside down along the water surface to catch flakes and pellets. They often gather in very large groups whenever food is abundant.
Filter-feeding shrimp are not small creatures. They are heavy and clumsy. Two pairs of their thoracic legs are transformed into catching fans, or little brooms, which they use to gather their daily bread. Essentially, the fan is the same claw that terminates the appendages of certain thoracic segments in filter-feeding shrimp. In filter shrimp, the appendages of the 4th and 5th thoracic segments are adorned with fans (the first three thoracic segments bear maxillipeds, while the 6th-8th segments are walking legs). The fan consists of two hemispheres formed by a dense row of elastic setae. The appendages of the sixth thoracic segment (the first pair of walking legs) are transformed into powerful “hooks” that anchor the animal in the current.
Filter-feeding shrimp cannot be called bottom-dwelling animals. They utilize the entire space of the aquarium and can take up positions near the water surface on grottoes, driftwood, and aquarium equipment. To allow a filter feeder to sit more or less constantly in the water current, it is advisable to place a piece of driftwood, a stone, or any other object at the bottom of the aquarium. If the shrimp has no opportunity to settle in the path of a water current, it will try to move closer to the filter, often crawl into filter tubes, and may even climb out of the aquarium. The shrimp position themselves in the current, facing into the flow, and open their fans, which gradually fill with food on their own. If there is a small group of 9 or more shrimp and sufficient open space, they arrange themselves in a neat circle and filter cooperatively.
It is recommended to introduce filter feeders into an established, silted aquarium with live plants, as the shrimp will find a sufficient amount of food there. They do not eat algae such as filamentous, red, brown, or others. As gatherers and strainers, these creatures have an exceptionally mild disposition. They do not bother any tank mates, except perhaps having minor conflicts among themselves over the best position in the filter current. They should only be kept with large fish.
Small shrimp of the genera Neocaridina or Caridina can be the salvation of the inquisitive aesthetic aquarist. The well-known Caridina multidentata (japonica) belong to this group. Small freshwater shrimp are very peaceful inhabitants of decorative aquariums. Most of the time, they leisurely scurry across the substrate and decor elements in search of food. Mature, sexually mature individuals prefer to wait out daylight hours in various hiding spots, and their activity noticeably increases only at dusk. Younger shrimp pay less attention to the light cycle. Usually, these shrimp are colored, with some species displaying quite intense coloration (Cherry, Bumblebee, Tiger).
Keeping and caring for shrimp. 
