What kind of fish can be kept together
Compatibility (or incompatibility) of fish species should be considered before they are put together. The main criterion is habitat similarity. Few people decide to launch marine and freshwater species into one aquarium, but much more often fish from brackish ponds are transplanted into fresh water. Many errors occur due to incorrect determination of water hardness and acid-base balance of various freshwater biotopes. Fish live well in captivity, if they create conditions as close as possible to the natural. The water temperature requirements should be similar. Some species got into aquariums from fast rivers, others from calm water bodies, which means that they cannot exist under the same conditions. Some fish prefer rocky bottom, others. thickets of plants or open spaces; some require bright light, others. twilight. All this must be considered when you create a suitable environment for your pets.
Size and temperament
The size and temperament of the fish are very important characteristics. Although not all fish are predators, in nature, usually larger ones eat smaller ones. If you are planting exclusively herbivorous species, make sure that even the smallest inhabitants of your aquarium are large enough not to become victims of others, and you need to pay attention to this in the future when the fish grow.
Some species jealously guard their territory, using a certain part of the aquarium as a storeroom or nest (feeding and reproductive areas, respectively). Such fish are usually aggressive to the representatives of their own, and often other species. Sometimes they can be kept together. if they are compatible in temperament and size, but it is better to plant them in a separate aquarium.
Think of the stern. Do you want to start fish that require a varied diet, for which you will have to cook food for them every day? Will there be enough food for fish that slowly consume it if they are put in the same tank with agile, food-hungry species? If it does not prove to be fatal, then will not fast, large fish burden the life of small and fearful ones? All these questions need to find answers.
Do not make hasty conclusions, looking at the incompletely populated aquarium of the seller, which contains incompatible species. The behavior of fish depends on the relative density of the population, the number of plants planted and the age of the fish (often sell immature individuals). Give them plenty of space, where there is certainly a reason for fighting, let them grow up, and the situation may change radically.