Influence of low temperature on structure and dynamics of spermatogenesis during culture of Oreochromis niloticus

Understanding the influence of different temperature conditions on the spermatogenesis is important for improvement of the fish aquaculture. This study evaluated the influence of low temperature on structural and quantitative dynamics of the spermatogenesis in Oreochromis niloticus. Adult males were cultivated with room temperature water (20.28-22.46 degrees C) and testes were collected for histological, ultrastructural and morphometric analyses. This species has unrestricted lobular testis with cystic spermatogenesis and type I spermiogenesis that results in a single anacrosomal aquasperm. Seminiferous lobules and spermatogenic cells had a radial arrangement toward the spermatic duct. Superior and central portions of testes had a greater lobular area than the inferior portion in all samplings. Spermatogonia (9.3%) were distributed in the inferior portion of testes, spermatocytes (25.3%) and spermatids (34.4%) in the central portion, while spermatozoids (39.4%) and secretory cells (4.6%) in the superior portion. Throughout the study, correlation between water temperature and lobular area characteristics was significant only in the inferior portion of testes (r(2) = 0.95), although the lobular area in the other testicular portions increased when the water temperature increased by 2 degrees C. Correlation between the water temperature and spermatogenic cells was significant for undifferentiated spermatogonia (r(2) = 0.54) and number of spermatids (r(2) =0.67). It is concluded that low cultivation temperatures may positively influence the generation of primary spermatogonia in the inferior periphery of O. niloticus testes. In addition, males maintain reservoirs of germ cells at low temperatures and the radial zonation of spermatogenesis has an important role in the renewal and production of germ cells. (C) 2016 Elsevier B.V. All rights reserved.