A histological and morphometric study was conducted to evaluate the seasonal testicular variations in the adult Japanese quail (Coturnix coturnix japonica) in Bangladesh. The weight of birds and testes, volume, length, circumference, seminiferous tubule diameter, circumference and height of germinal epithelium of testes were measured. Sections of testes obtained from studied birds were stained with H&E and images were taken by J software. Weight and volume of paired testes of quails significantly heavier (P<0.05) in long day period of summer and rainy season (March – September) than the short day period of autumn and winter (October – February). Seasons had no significant effect on live weight gain of quails. The weight and diameter of testes or height of the germinal epithelium of the seminiferous tubule were positively correlated (r= 0.84; r= 0.88). Spermatogenic activity was pronounced during summer and rainy season than that of autumn and winter (P<0.05).

KEY WORDS: Japanese quail; Morphometry; Testis; Season; Day length; Temperature.