EFFECTS OF TEMPERATURE AND PHOTOPERIOD ON THE GAMBUSIA-AFFINIS HOLBROOKI TESTIS DURING SPERMATOGENESIS PERIOD

Adult male Gambusia affinis were collected at the beginning of the spe rmatogenesis period and placed into four groups which were subjected i n the laboratory to the following experimental conditions of temperatu re and photoperiod for two months: Group I: 18 C and 16L:8D; group II: 18 C and 8D:16L; group III: 8 C and 16L:8D; and group IV: 8 C and 8L: 16D. At the end of the experiment, their testes were studied by histol ogic quantitative methods and compared with those of initial and final field controls. Initial controls showed complete spermatogenesis. Fin al controls and group I testes had complete spermatogenesis with fewer spermatocytes and round spermatids and more elongated spermatids and spermatozoa than the initial controls. The testes of group II fish wer e similar to those of the initial controls except for an increased vol ume of primary spermatocytes. Testes in groups III and IV were similar to those of the initial controls except for increased volumes of prim ary and secondary spermatogonia. These results suggest that mild tempe ratures are necessary and sufficient for spermatocyte formation. Mild temperatures are also necessary, but not sufficient, for meiosis and s permiogenesis, because these processes also require long photoperiods.