How do shrimp reproduce?
When a female shrimp reaches sexual maturity, eggs appear under her tail, resembling a green-yellow mass that makes up about a third of the size of the shrimp 
itself. The mating ritual is the same for all shrimp. When a female is ready to carry eggs, she releases special odoriferous substances into the water—pheromones. If you suddenly notice that some of the shrimp are frantically rushing around the aquarium from corner to corner, making their way through moss thickets, it means that one of the females has molted and is calling for sexual partners with pheromones. Sensing them, the males rush around the aquarium like crazy.
One of the males, having made several circles around the female, climbs onto her back. Then, if she does not chase him away, the male slips under her abdomen and deposits his sperm. The fertilization procedure takes a few seconds. However, it is not uncommon for several males to seize the female, resulting in “communal” fertilization. Accordingly, if the amusing commotion has stopped, the deed is done. If you have a large herd of shrimp, you will observe such male races every day.
Then eggs appear under the females’ abdomen. After fertilization, the embryonic development of the shrimp begins. By ventilating the clutch, the female actively works her pleopods, ensuring a continuous supply of water and dissolved oxygen to the eggs. In addition, the caring mother cleans her load from adhered dirt several times a day, getting rid of unfertilized or fungus-affected eggs. Initially monochrome eggs become increasingly contrasting and change their overall color tone almost daily.
The normal development of embryos can be judged by the fact that the so-called eye spots—the visual organs of the future shrimp—become visible in the egg. Sometime later, tiny limbs can already be discerned, and soon the exciting moment of hatching arrives. The animals are born fully formed and represent a miniature copy of their parents. At the proper time, hatching (practically simultaneous) of the offspring occurs. They immediately scatter and wander around the aquarium and begin to feed independently in the same way as their parents.
The pattern of population change in cherry shrimp. The term “reproduction” is more suitable for shrimp than “breeding”. The fact is that if you managed to create favorable conditions in the shrimp tank, its inhabitants will multiply regardless of whether you aim to get offspring from them or not. At first, their number grows. Upon reaching the maximum allowable population, growth does not stop, and by inertia, the shrimp still breed for some time, but at a decreasing rate. At this moment, it seems as if the aquarium is simply swarming with these bugs.
Further, the population drops. And by inertia, it flies past again, dropping well below the optimum. Then the shrimp begin to actively breed again, and their population soars above the norm again. In general, their number constantly fluctuates around a certain value, which is characterized by the volume of the tank and other keeping conditions.
Sex differentiation in shrimp occurs when they reach a length of 8-10 mm. However, large shrimp become sexually mature only at the age of about one year. External distinguishing features of males include a longer first pair of pleopods and an additional appendage on the endopodite of the second pair of pleopods. Females are, in most cases, larger than males.
In dwarf shrimp, the male can often be distinguished from the female by body shape. Females have enlarged abdominal segments that facilitate carrying eggs. When females become sexually mature, you can easily distinguish them from males, primarily by the wide carapace on the abdomen and their curved lower abdomen, as well as by their larger size compared to males. Females carrying eggs are particularly bright. Males usually have longer antennae. This is especially pronounced regarding the second pair of shorter antennae.
Female signs: 1. – Curved lower abdomen. 2. – Saddle with eggs.
Often you can observe that during activity in the shrimp tank, males swim and crawl in all layers of water, while females prefer to gracefully move along the bottom or the surface of plants. However, in some species, this approach is insufficient for sex determination, and for reliability, one has to focus on the genital openings. In females, they are located in the lower part of the sixth body segment, and in males, between the sixth and eighth segments. However, in shrimp 2-3 centimeters in size, it is difficult to see and localize the genital openings.
In Macrobrachium, males and females are usually easiest to distinguish by the first pair of limbs with claws, which are larger in males. As a rule, sexually mature individuals also differ significantly in total body size. Fan shrimp males have a larger first pair of walking legs, while females show an expansion of the carapace in the abdominal area, facilitating egg-bearing.
Mating occurs shortly after the female molts, before she deposits eggs onto her abdomen. Mating can only happen after the female’s molt, only then are the new female cuticles soft and flexible, allowing fertilization to take place. As soon as the female moves away from the discarded carapace, she begins to secrete pheromones to attract males. As noted, in the male, the anterior pleopods are transformed into a special organ – the gonopod.
Having found a female by scent who is molting before mating, he uses the gonopod to attach spermatophores (sacs with sexual fluid) near her genital opening. A young male up to 8-10 mm in size can fertilize five females, while large individuals (15-20 mm) only one. The interval between mating and egg-laying is from a few days to two weeks.
The egg-laying process itself is very difficult to see, as the female chooses the safest and most hidden places for this. This happens as follows. At the bottom of the aquarium, the female lies on her side and curves her abdomen so that a space is formed between it and the breast surface, where the eggs end up. At the same time, a secretion is released that dissolves the membranes of the spermatophores. The released spermatozoa fertilize the eggs, which remain hanging on the pleopods until the larvae hatch. At this time, she hides in a shelter.
The fecundity of most ornamental decapods significantly depends on the size of the female. The larger and, accordingly, older she is, the more eggs she is able to carry. Another important factor influencing decapod reproduction is tank overcrowding: all the neighbors’ energy is spent on maintaining their living space, and there is no energy left for reproduction. So if a hundred shrimp live in the aquarium, you shouldn’t be surprised that at one fine moment they will stop breeding. Moreover, excessive crowding increases the risk of the emergence and rapid spread of diseases.
For young mothers, a clutch of 10-15 eggs is the norm. Older ones are able to handle a heavier load – 1.5-2 times more. And it also happens that under the tail of a mother (especially a young one), you can barely count 3-4 eggs.
Eggs remain attached for a long time: at a temperature of 18-21°C – 50 days, at 26°C and above – 20 days. A larva hatches from the egg – a zoea, which strongly differs from adults both in structure and lifestyle. The zoea has stalked eyes, well-developed maxillipeds that serve as swimming organs. The posterior thoracic and abdominal legs are not yet developed. The zoea is followed by the mysis stage, when abdominal limbs develop, and the next stage is the decapodita. Larvae grow very quickly and molt frequently. The lifespan of the larva depends on the water temperature – from 10 to 30 days. After passing through subsequent stages, when pleopods become the organs of movement, the larvae begin to move head-first.
Larvae hatched from eggs differ greatly from adults. Most of them die from predators or due to adverse conditions. If the aquarist manages to “raise” and feed 25-30% of the juveniles, this is already a success. When bred in an aquarium, only single specimens survive to adulthood.
Mass mortality of larvae occurs mainly for two reasons: first – due to the lack of the necessary amount of full-value food, and second – due to oxygen deficiency during the decay of uneaten food residues. In an aquarium, feeding with dust consisting mainly of nauplii and rotifers, as well as aquarium snails cut into small pieces (pond snail, Physa, etc.), gives good results. 20-30 minutes after feeding, all uneaten food should be removed from the aquarium. Water aeration is mandatory for larvae.
During the breeding period, shrimp are best placed in a separate spawning aquarium where the female can safely raise her offspring. In a community aquarium, they will be eaten by fish and other shrimp. Females with eggs should be moved to a separate aquarium or all-glass container (jar) with a volume of 5 to 40 liters (depending on the size of the specimen). The water in the spawning tank must be fresh, clean, oxygen-rich, with a temperature of 22-26°C. But even in a separate tank, no more than 25% of the larvae can be raised to adulthood.
Shrimp juveniles are very delicate creatures that can die from water pollution, temperature drops, or changes in chemical composition. First, you must make sure they won’t get sucked into the filter. To do this, use a fine-pored sponge or place a fine sieve around the filter. Another danger for juveniles is water pollution. Small shrimp are very sensitive to water quality, especially during the first two weeks of life.
It is necessary to perform small regular water changes and check its quality as often as possible. As for food, adolescents have enough of what naturally exists in your long-established aquarium. Without your intervention, they will find microorganisms, plant debris, food waste, etc. However, you can offer them optimal nutrition by occasionally giving specialized products for shrimp.
By the way, in some aquariums densely planted with plants, shrimp breed wonderfully despite the presence of fish. First of all, you should use Java moss, Riccia, Monosolenium, Cladophora, in the clusters of which microorganisms that serve as food for young decapods willingly settle and actively multiply. The main thing is that they have plenty of shelters and hiding places. And in swimming speed, shrimp are not inferior to many aquarium fish.
When choosing shrimp for your aquarium, you have to reckon with the possibility of undesirable crossbreeding. There is the problem of “hybrid shrimp”, when fry are bred from two different species. It is no secret that there are many “hybrids” that result from crossbreeding two different species of shrimp kept in an aquarium. Creating hybrid shrimp sounds great, but in reality, it is nothing more than ugly, dirty, mixed-color shrimp. In essence, this is a kind of “mutt” in the shrimp world.
Shrimp do not reproduce like other organisms where two species can intersect and combine the best characteristics. You cannot take a Snowball shrimp and cross it with a Red Cherry to create a “Pink Shrimp”. This primarily applies to selective variations, in which “inbreeding” usually produces offspring with a “dirty”, dull, and unattractive coloration, and the wild dominant form breaks through.
Crossbreeding is possible only when meaningful and aimed at improving coloration. Selective breeding is the only way to create colorful forms. Selection, where you take the color and characteristics of wild shrimp as a basis and breed specific colors that you would like to have. If you keep shrimp together that can interbreed, then the money spent on acquiring purebred aquatic organisms is wasted, and gray-brown-crimson forms will appear in the aquarium. On top of that, quite often shrimp of one species come under a false name, and it happens that externally similar shrimp can belong to different species.
Some shrimp (for example, representatives of the genus Macrobrachium) are relatively easy to breed in captivity. External sexual characteristics in these animals usually manifest themselves in size 
. Males are generally smaller, but armed with more impressive claws. Ideally, an aquarium population should consist of one male and several females. The concentration of several males in a small area will inevitably lead to fights for the right to control the territory and harem. But in a spacious aquarium with many shelters, several males can peacefully coexist: after brief clashes, they will strictly delineate spheres of influence. True, even in this situation, there should be more females.
Males of crayfish and long-clawed shrimp tightly grasp their partners with claws and lay them on their backs on the substrate. This may be preceded by hours-long mating rituals during which partners, bringing themselves into a state of readiness for mating, rhythmically touch each other with antennae. The spermatophore is attached directly near the female’s genital opening. Fertilization occurs at the moment when the eggs leave her body and pass through the spermatophore on their way to the pleopods. So-called threads-cords serve to fix them on the abdominal legs and secure the eggs to each other.
For another 10-14 days, the female carries the eggs between her swimming legs. At the same time, she not only provides protection for the offspring, but also creates an optimal environment by actively ventilating the clutch with her abdominal limbs. If you want to try to save the offspring, the “egg-bearer” will have to be moved to a separate container. In the community aquarium, the tiny larvae that emerge will be instantly destroyed by the fish or other shrimp living there.
Amano shrimp and filter feeders cannot reproduce in the aquarium, like many other large shrimp. One of the features of filter feeders, as well as Amano shrimp (Caridina multidentata), is that they do not reproduce in completely fresh water. While their offspring go through the larval stage, they need brackish water for a successful transition to the next stage of development. Their larvae are capable of developing exclusively in salt water.
The principle of shrimp selection. Why does shrimp degeneration occur?
