﻿Eigenma/rm: Fishes of Panama 



13 



Awaous transandeanus and taiasica. Four other species from the 

 Atrato, Tuyra, and Chepo reach the Pacific slope west of the 

 Chagres, but as far as is known did not reach the Chagres. They 

 are Curimatus magdalence, Astyanax fasciatus, Ctenolucinus beani, 

 and Thoracocharax maculatus. 



A glance at the detailed list given below will show that a number 

 of species find their farthest north in the Chepo basin. Others 

 have not succeeded in passing north of the Tuyra, as if their 

 line of migration had been stopped at one or another of these 

 rivers. 



It is a remarkable fact that while 12 of the 23 species of 

 strictly fresh-water families, the Characidse, Siluridse, Loricar- 

 iidse, Gymnotidse, and Cichlidse have crossed the divide at Pan- 

 ama, only Sicydium salvini of the 15 species of the marine and 

 lowland Gobiidse is identical on the two sides. It would seem 

 that the marine or lowland forms have been separated long 

 enough to become specifically distinct on the two sides and that 

 the intrusion and intermigration of the strictly fresh-water 

 species has been more recent. The isthmus may have been a 

 barrier to the intermigration of marine forms long before it 

 became suitable for colonization by fresh-water species which 

 have not been long enough in the area to become altogether 

 distinct on the two sides. It is also quite probable that a certain 

 amount of intermigration from river to river is still taking place. 



There is a very great probability that all of the immigrants 

 of the Chagres from the south except the Atlantic slope Eleotridince, 

 (Gobiidse) followed the route Atrato, Tuyra, Chepo (Grande?), 

 Chagres, altho this involved two crossings of the continental divide. 

 Only the partly marine Eleotridinse came by way of the ocean, 

 and possibly Hyphessobrycon panamensis. 



It appears that the ocean served to a very small extent as a 

 highway for the migration of fresh-water fishes, even for such a 

 short distance as that between the Atrato and Chagres. 8 It is 

 a separate question whether the ocean with its high tides and the 

 long tidal areas of the Tuyra and Chepo facilitated the migration 

 from the Tuyra to the Chepo and Rio Grande. 



8 This conclusion is re-enforced by the fact that aside from members of the Gobiidse 

 the only fresh- water fish that got from the Tuyra to the San Juan or the reverse without 

 getting into the intermediate Atrato is Astyanax ruberrimus, which also went as far 

 south as the Rio Patia. 



