World trends for a home breeding of exotic freshwater and marine fishes did not miss Poland. There are almost all species of aquarium fishes available in Polish pet shops, but there is not enough information about threat given to customers. In some fish, there are masses of one-cell glands, mainly serous, in the proximity of the spines. In others, those one-cell glands may be grouped in larger aggregates of cells called venom glands, that may form organs resembling multicellular glands of terrestrial animals. They are usually located around the spines or hard rays of the fins. Even if covered with a connective tissue sheath, the aggregates of the venom cells do not have any common outlet; they are not, therefore, proper multicellular glands. The venom glands of the catfish are covered with a thin sheath and they release their contents when the fin ray is pressed. Spines are derived from fin rays. When the spine penetrates the body of its prey, it presses its base against the cells, squashes them and squeezes the venomous contents into the wound. Catfish, lionfish and stonefish have the venom glands producing secretion which could be dangerous. The eels and morays blood is also dangerous, as well as slime of reduced squamae. Poison information centers noted several cases of fishes' stings in Poland.