Fish are vertebrate animals, that is, they all have a vertebral column or âspineâ. There are two main groups of fish, bony fish (Teleosts) and cartilaginous fish (Elasmobranchs). As the common names imply, the skeletons of teleosts are made of bone while the elasmobranchs have cartilaginous skeletons.
Villard found a third type of radiation from pitchblende: gamma rays, which were much the same as X-rays. Then in 1896 Pierre and Marie Curie gave the name 'radioactivity' to this phenomenon, and in 1898 isolated polonium and radium from the pitchblende.
1 Nuclear energy was first discovered accidentally by French physicist Henri Becquerel in 1896, when he found that photographic plates stored in the dark near uranium were blackened like X-ray plates, which had been just recently discovered at the time. Nuclear energy is energy that is released either by splitting atomic nuclei or by forcing the nuclei of atoms together. 2  Nuclear energy comes from mass-to-energy conversions that occur in the splitting of atoms. 3  Albert Einsteinâs famous mathematical formula E = mc 2 explains this.