In I got It!
A Stop in Babylonia
According to our Sages, when the People of Israel were expelled from the Holy Land and scattered in Babylonia, hundreds of animal species followed them there, all animals returned as well, except for one kind of fish which will return after the arrival of the Messiah.
According to our Sages, when the People of Israel were expelled from the Holy Land to Babylonia, seven hundred species of kosher fish, eight hundred species of kosher grasshoppers and an unidentified number of birds followed them to the Diaspora.
After seventy years, when the People of Israel returned to their land to rebuild the Temple, almost all animals returned with them through an underground canal that passed under the land of Babylonia (today's Iraq) and to the Land of Israel.
Almost all animals – except for one sort of fish. That species of fish was called 'Shibota - and it is mentioned in the Talmud as the fish that Rava, a Sage, would prepare for the Sabbath.
"Said Rabi Chanina Bariah DeRabi Avahu: "Seven hundred species of kosher fish and eight hundred species of kosher grasshoppers and countless numbers of birds – they all followed the Children of Israel into the Diaspora and returned with them, except for the fish that is called 'Shibota".
(Jerusalem Talmud)