Answer:
京 KYOU, KEI - capital
青 SEI, ao(i) - blue
章 SHOU - chapter, badge, mark
利 RI, ki(ku) - interest, take effect
系 KEI - system, group
They all take the "fish" radical (魚 GYO, sakana, uo - fish) to become other characters,
but in fact only one of the words they become is actually a fish!
鯨 GEI, kujira - whale
鯖 saba - mackerel
鱆 SHOU , tako - octopus
鯏 asari, ugui - clam
鯀 KON - a historical figure in China