on; on top; upon; first (of two parts); previous or last (week etc); upper; higher; above; previous; to climb; to go into; above; to go up; to attend (class or university); third tone of putonghua[cedict]
我
wǒㄨㄛˇ
I; me; my[cedict]
是
shìㄕˋ
is; are; am; yes; to be[cedict]
如鱼得水
rú yú dé shuǐㄖㄨˊ ㄩˊ ㄉㄜˊ ㄕㄨㄟˇ
like a fish back in water (成语 saw); glad to be back in one's proper surroundings[cedict]