How breeding happens
Theodoxus fluviatilis has separate sexes. After mating, the female attaches egg capsules to hard substrates (stones, snail shells, etc.), which are often mistaken for individual eggs. However, each contains approximately 25–75 eggs. Only 1 egg develops in each capsule. The other eggs in the capsule serve as food for the juvenile. Larval development takes place inside the egg capsule. After approximately 4 to 8 weeks (depending on temperature), a fully developed juvenile measuring approximately 0.5 to 1 mm hatches from it.