THERMAL ECOLOGY OF 2 FRESH-WATER FISHES APHANIUS-DISPAR AND GAMBUSIA-AFFINIS FROM CENTRAL SAUDI-ARABIA

Temperature selection of two fresh water fishes Aphanius dispar (Ruppe l 1828) and Gambusia affinis Holbrooki (Girard 1859) was investigated in a thermal gradient. One animal at a time was studied in three tempe rature gradients extending from 6 to 40-degrees-C (Low range 6-21-degr ees-C; Medium range 13-31-degrees-C; High range 21-40-degrees-C). Most of A. dispar selected temperatures between 14-15-degrees-C in the low range, 19-22-degrees-C in the medium range and 26-32-degrees-C in the high range, while G. affinis selected temperatures between 13-20-degr ees-C in the low range; 22-30-degrees-C in the medium range and 22-32- degrees-C in the high range. The mean critical thermal maximum (C.T. M ax.) for A. dispar and G. affinis was 38.1-degrees-C and 38-degrees-C respectively. The mean critical thermal minimum (C.T. Min.) was 4.2-de grees-C and 4.4-degrees-C for A. dispar and G. affinis. Both species s howed a tolerance to high temperature, but the introduced species, G. affinis had a wider range and is better suited to adopt to the desert habitat, and hence could constitute a threat to the endemic species A. dispar.