drink like a fish, to

To  drink  a  great  deal,  usually  meaning  alcoholic beverages. The  simile  comes  from  the  fish’s  breathing  apparatus,  which causes it to be openmouthed much of the time, so that it looks as if it were constantly  drinking.  The  expression  is  quite  old,  appearing  in  print  in the  mid-seventeenth  century,  and  has  outlived  drinking  like  frogs,  like elephants, and like knights templar, as well as the medieval proverb, to drink like a pope. The newer synonym to drink under the table calls up an image of inebriated persons rolling under the table.