Interaction of fish and plants in the aquarium.
Stem plants are usually planted in bunches – 5-6 lush twigs to form sufficiently dense protective green zones. Separately planted (with the same quantity) stem plants are not suitable for this purpose – they will only intertwine near the water surface. Equally unsuitable are sprawling wide-leaved and hard-leaved plants, even if there are dozens of them. Usually, they form too loose thickets, unlikely to create protective areas of dense growths where fish could hide in case of danger, calm down, and rest. Such small groves are necessary as a refuge for weak individuals and fry.
Many fish need bushes with thin feathery or broad leaves as a substrate for caviar or as shelter. Labyrinth fish like to build their saliva-cemented nests on floating plants. Shoaling fish with light signals require a shaded location in the back of a densely planted aquarium.
Territorial fish often use large plants as visual landmarks when dividing spheres of influence or simply define them as their property. In such a situation, there should be at least as many bushes as there are breeding pairs formed in the tank. Otherwise, conflicts are inevitable.
For many fish, underwater thickets are an essential attribute used in reproduction. Some use aquatic flora as a substrate for spawning, while others simply spawn in the thick of the aquarium garden. During schooling spawning in a general aquarium, it is usually not the number of plants that matters, but the very fact of their presence, as well as the suitability of the hydrophyte’s texture for the upcoming event. Spawning pairs rush over the thickets or dive into their depths, peacefully replacing one another and not disputing the rights of their relatives. Overgrown plants that prevent the free movement of fish should be removed from the aquarium in a timely manner. The required number of plants for these purposes is determined depending on the ecological characteristics of the fish, their species, and individual traits. Take care of the availability of the required amount of working “material” in advance.
Cichlids of the Mbuna group feed mainly on algae abundantly covering underwater rock formations, as well as aquatic organisms living in or near this underwater carpet. In other words, fish feed mainly on plant food, that is, plants. As a result, all plants planted directly into the substrate will be dug up with damaged roots. Many large cichlids, although they do not eat plant food, also destroy plants. When the spawning period begins, the male and female begin to transform the aquarium landscape to their own taste, which completely does not coincide with the taste of the aquarium owner. In addition to massive soil digging, aquatic plants are ruthlessly uprooted, branches are broken and crumbled, and leaves are torn off. There are even herbivorous cichlids. For example, the American triangle cichlid (Uaru) has over 80% plant food in its diet.
The diet of many species of cichlids (especially “Africans”) must include plant food, and there is a high probability that the fish will simply eat most of the plants in the aquarium. Therefore, one either has to abandon a number of plants or remove the “undisciplined fish”. But in certain situations, vegetarians and aquatic plants can coexist quite satisfactorily. The main thing here is to maintain parity; a compromise is possible when plant food is not the basis of the diet for fish, but only a desired dessert. Then the damage to the underwater garden is insignificant, and it is usually possible to form thickets whose biomass growth more than compensates for what the fish ate.
If fish dig up roots heavily, it is best to place plants in pots or leave them floating. If fish dig the substrate (Cyprinids), plants with thin feathery leaves should be avoided because they easily get dirty. Cichlids and harlequin barbs, as well as a number of other fish species that do not neglect tender greens, cannot be placed in the same aquarium with delicate plants (Cabomba) unless, of course, you are going to provide them with such expensive food.
Many species (*Vesicularia dubyana*, *Microsorum pteropus*, *Ceratopteris thalictroides*, *Myriophyllum*, *Limnophila*, etc.) are excellent spawning substrates. In turn, floating *Riccia*, *Azolla*, *Salvinia*, *Pistia*, *Najas* are reliable refuges for fry and weakened fish. *Ceratophyllum*, spring mosses are natural, highly efficient filters that precipitate suspended mechanical particles on the surface of their leaves. *Chara*, *Potamogeton*, *Elodea canadensis* actively absorb calcium from the water, significantly reducing its hardness. Certain algae (*Chlorella*, *Phaeocystis*) secrete antibiotic substances harmful to pathogenic bacteria.
How to distinguish land plants from aquatic plants.
How to relate the quantity and type of plants to the quantity and species of fish? 
