Р380
КАК РЫБА В ВОДЕ быть0, чувствовать себя (где, в чём, с кем)
coll (как +
NPInvaradv or
subj-compl with copula (
subj:
humanfixed WO (to be, feel) totally at ease (in the specified surroundings, with the specified area of knowledge, in s.o. 's company etc): (be) in one's element
(be (feel)) right at home(be (feel)) as much at home as a fish in water(feel) perfectly comfortable.