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.
1 The science of atomic radiation, atomic change and nuclear fission was developed from 1895 to 1945, much of it in the last six of those years.  Over 1939-45, most development was focused on the atomic bomb.
Becquerel had discovered radioactivity. Becquerel used an apparatus similar to that displayed below to show that the radiation he discovered could not be x-rays. X-rays are neutral and cannot be bent in a magnetic field. The new radiation was bent by the magnetic field so that the radiation must be charged and different than x-rays.