Basics of aquarium fish breeding.
To produce young fish that are truly typical of their species (regardless of whether it is a natural form for this species or some new, artificially created one), it is important to select for breeding only healthy individuals with characteristics typical of the given species or form. Do not use fish that are too small or too large, deformed, or have color deviations. It is better to pair unrelated fish to avoid inbreeding, which after several generations can lead to overall deterioration and deviation from the typical appearance.
If you are breeding a species with numerous selective forms (well-known examples include the guppy Poecilia reticulata and the angelfish Pterophillum scalare), then purchase representatives of only one specific form. The fact is that if you buy individuals of several forms, they will most likely crossbreed, as they still belong to the same species. As a result, they will produce a batch of fry that do not match the appearance of either parent.
When preparing fish for reproduction, it is important to choose the right pair. In some cases, selecting males is key; in others, females. If there is a choice, young, brightly colored, and normally developed fish are selected. When breeding certain species, a problem sometimes arises with aggressive males beating the female. In this case, the female should be chosen larger than the male. When selecting breeders, special attention should be paid to their age. In various fish species, the ability to reproduce occurs at different ages. Some species breed only at a young age, while others retain this ability throughout their lives.
Preparation of the male and female for spawning should begin 2-3 weeks before spawning. In some cases, females and males should be separated, but sometimes this is not necessary at all, especially regarding livebearing fish. Feeding plays an important role in preparing breeders, and during this period it should be especially diverse and nutritious. The feeding regime should be intensified 7-10 days before spawning, and the fish should be fed live food, although plant foods occupy a special place for certain species. If fish are kept in inappropriate conditions, this improper pre-spawning care can negatively affect the offspring and sometimes prevent spawning altogether.
Sometimes not a single pair is placed in the spawning tank, but, for example, one female and two males, so the sex ratio should correspond to the characteristics of the given species. Under good maintenance conditions, fish spawn year-round, but this should not be abused, as frequent spawning exhausts the female.
To create the necessary conditions for spawning, you need to choose the right spawning tank itself. Most of the time, the size of the spawning tank and the water level in it affect breeding success, but some species can breed in containers of any size. The size of the spawning tank depends on the size of the fish and their temperament.
The spawning method and the required spawning tank depend on the fish species. It is undesirable to set up a spawning tank in new aquariums. The spawning tank is equipped according to the breeding characteristics of the fish. Egg-scattering fish often lay eggs in a separate aquarium with a minimum of decorations. Usually, a pair or a small group of fish is placed in such an aquarium. Livebearing fish mate and give birth to fry without paying much attention to their surroundings.
For fish that care for their eggs and offspring, you will have to reasonably reproduce their natural environment, and sometimes even allocate a separate aquarium for the breeders for a long period. In many cases, most of the aquarium is planted with fine-leaved plants and Java moss. A smaller part of the aquarium is left open. For fish that glue their eggs to plant leaves, broad-leaved plants are used as a substrate.
Most fish species that spawn in the water column and near the surface do not need a bottom substrate. For cannibalistic fish that usually scatter eggs haphazardly and do not need any special substrate, a fine-mesh plastic grid is laid on the bottom of the spawning tank. The fish spawn above the grid, and the eggs fall through the mesh and remain safe. For those fish species that lay eggs on the bottom surface of the aquarium, various stones, tubes, flower pots, and other underwater landscape elements can stimulate spawning.
In livebearing fish, the newborn fry will most likely be eaten immediately by their tank neighbors or even their own mother. To prevent this, a special container is usually used. The pregnant female is placed in this container. After birth, the fry have the opportunity to escape from the mother by swimming through small holes in the container. The spawning tank should be free of snails, crustaceans, and cyclops.
Seasonally breeding fish in nature usually experience a series of events that combine to lead to physical and psychological readiness for spawning. Among these phenomena may be changes in temperature and water chemistry, food supplies, and sometimes photoperiod and light intensity. Temperature and lighting conditions play a significant role in the reproduction process. It is necessary to ensure that there are no sharp temperature fluctuations in the spawning tank, as this negatively affects spawning and egg development.
Lighting requirements vary for different species: some require bright light, while others require moderate brightness. For species requiring bright light, increasing daylight hours promotes the maturation of reproductive products and stimulates spawning. Some species require water aeration, while others prefer standing water. Important factors include pH and dH values, which should be as close as possible to those in natural habitats. To accelerate or stimulate spawning, fresh, soft water is added daily in small portions for 5-6 days. Fish are usually introduced to the spawning tank in the evening, as spawning typically occurs early in the morning over 2-6 hours. Partners are placed in the spawning tank simultaneously.
Preserving eggs requires special conditions: • Ensure the water contains the required amount of oxygen; • Shaded spawning tank while maintaining the necessary temperature; • Water acidity and hardness. To prevent the risk of fungal or bacterial infection, you need to change a small amount of water and carefully remove unfertilized eggs using a fine pipette (fertilized eggs are always round and transparent, while unfertilized ones are white and become covered with fungus).
Eggs of different species develop at different rates. The development period ranges from 20 hours to 10 days or more. An inexperienced aquarist often does not notice newly hatched transparent fry and may accidentally pour them out with the water. The larvae of most egg-scattering fish are completely helpless. The fry look like hair-thin threads with a round yolk sac from which the fry receive their first nourishment. When the larvae are in the stage where they hang on plants and glass or wriggle at the bottom of the aquarium, they do not need to be fed. Larvae should not be offered food until they begin to swim freely. At this time, it is best to culture infusoria.
Having absorbed the contents of the yolk sac, the larvae begin to swim. When the larvae begin to swim more actively, feeding must begin. Most fry in aquariums die from starvation or overfeeding. It is crucial not to miss the transition period of larvae to independent feeding, as starving the fry even for a few hours can lead to their death. Fry are fed frequently, but in small portions. When the fry begin to grow actively, they need to be well-fed. Growing fry should be timely transferred to larger foods, but for this, slower-growing fry must be sorted out. Upon reaching maturity, the appetite of the fry decreases slightly.
It must be kept in mind that after obtaining numerous offspring, our task is to preserve them. From what has been said, it follows that offspring should not be kept in cramped aquariums. Aquarium size and water quality are of great importance for the normal development of fry. Overcrowding can lead to poor hygiene, low water quality, and stress.
Rearing larvae and fry. Rearing aquarium.
Spawning methods of killifish. Subgroup “Divers”. Egg-hanging species. 
