Marine Fishes of Panama as Related to the Canal

Recent papers by Eskinazi, compared to studies made on the Texas and Louisiana coasts 35 to 45 years ago and on the south Atlantic coast 15 years ago, show remarkable similarities of the estuarine fishes of northeastern Brazil and the northern Gulf of Mexico. Forty-five of 48 families of the two areas are in common and about 35% of the species are in common. On the west coast even greater correspondence might be expected between fishes of Peru and southern California, were it not for the restriction of tropical fishes by the Humboldt and California currents. When the lithospheric plate under North America pulled away from Pangaea, strong swimmers and pelagic fishes maintained connections. Thus, the marine fishes have had strong connections for the last 70 million years. Further, the Pacific and Atlantic faunas were connected until the mid-Pliocene when Isthmus America became continuous about 5.7 million years ago. Marine euryhaline fishes are much more abundant than their freshwater counterparts. Thus large numbers of marine fishes are found in the fresh waters of Panama. One hundred thirty-seven (1 37) marine fishes have been found there and 57 species have taken up more or less permanent residence. No freshwater fish have taken up residence in the seas of Panama. The freshwater fishes of Central America came from the south and their movement has been very slow. Isthmus America was a ridged mountainous area with short, small rivers and small basins. The estuaries were small or nonexistent. Thus, one avenue for spread of fishes from fresh water was generally nonexistent. There are 32 river basins in Panama and fish have little access from one to the other. So the river basins have an insular aspect. The Canal runs through only three river basins. There are generally no problems to the passage of freshwater fishes in the Canal but they are stopped by even low salinity and, if back pumping becomes necessary to maintain the lakes used in the operation of the locks, most freshwater fishes will not traverse the Canal. Thus, it may be said that there is little chance of transfer of freshwater fishes from one coast to the other. However, the tarpon has already crossed the isthmus and eight other species, including blennies, gobies and pipefishes, have made the passage according to ichthyological collectors. Actually only four fishes are indubitable crossers. Back pumping will increase the potentiality a great deal but no foreign process of gene flow or heredity other than what is present all over the world today and which was present when the Pacifi'c and Atlantic were connected, is to be expected. Thus a sea level canal would present a new situation but nothing that could be antibiological or deadly. COMMINGLING OF FISHES BETWEEN NORTH AND SOUTH AMERICA The zoogeography of marine and freshwater fishes are quite different affairs, and nowhere is this shown more clearly than in a comparison of the coastal fishes populations of northern South America and southern North America with parallel comparisons of the freshwater fishes of the same regions. The question is touched upon here because it relates to the composition of the fishes of Panama.