Aspects of the Physiological Ecology of Species of Gambusia from Belize, Central America

Aspects of the physiological ecology of three species of Gambusia from Belize, Central America were investigated through field observations and experimental analyses. These species, mainland Gambusia yucatana (slender-bodied), marine G. yucatana, G. sexradiata and G. luma, have different distributions within Belize. Direct transfer and salinity selection tests indicate mainland G. yucatana (slenderbodied) and marine G. yucatana tolerate changes in salinity to a greater extent than do G. luma or G. sexradiata. Ecological distributions indicate mainland G. yucatana (slender-bodied) and marine G. yucatana occur more frequently along northern coastal areas and offshore localities, whereas G. luma and G. sexradiata occur usually at inland localities away from the influence of the sea. Determination of plasma osmotic concentrations indicates that mainland G. yucatana (slender-bodied) and marine G. yucatana have a greater ability than either G. luma or G. sexradiata to quickly adjust to elevated salinities. These features may contribute to habitat selection. T HIS study is concerned with three species of poeciliids in Gambusia. Species of Gambusia inhabit fresh, brackish and marine environments along the Atlantic drainage from the eastern and southern United States southward in Middle America to northern Colombia, and in the Greater Antilles east to Hispaniola and the Bahamas (Rosen and Bailey, 1963). Four species of Gambusia occur in Belize, Central America. Gambusia sexradiata has its center of abundance in the northern portion, usually at inland localities away from the influence of the sea. Gambusia luma has its center of abundance in the southern portion where it is usually the only species of Gambusia present, but it is broadly sympatric with G. sexradiata in large rivers in the north. Gambusia nicaraguensis appears to be restricted to offshore localities in 34%o seawater or at river mouths with high salinity in the southern portion of Belize. Since