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The geological hypothesis of a marine origin of the Nicaraguan depression and its lakes was until the fifties of the present century exclusively based upon the occurrence of marine species (shark, sawfish and tarpon) in Lake Nicaragua. A recent view, however, is that the fault was never connected with the sea and that the lakes were filled by rain only.
In view of the fact that there seems to be no agreement among geologists about the geological history of the Nicaraguan depression, an attempt is made to contribute to the discussion by evaluating the fish faunal elements of the fault.
The nature, composition and evolution of Central American inlandwater fish are discussed in relation to the various geohistorical views about the formation of the Isthmian link of Southern Middle America.