The studies in Danio rerio testis were performed during the 8 weeks between the first and second spawning. The testes were dissected from the animals and fixed after successive weeks. Semithin epon sections were analysed using stereological methods to assess the relative volumes of cysts containing successive stages of spermatogenesis. During the first three weeks the cysts with spermatogonia B have the highest relative volumes. At the 2nd week the first cysts with spermatocytes appear. At the 4th week the first cysts containing early spermatids are formed. During the 4th, 5th and the 6th weeks of the gonad cycle cysts containing spermatocytes I are the most numerous but one can also see volumes of cysts filled with late spermatids and sperm cells growing. In the 7th week of the cycle the volumes of cysts containing early spermatids as well as those containing late spermatids are very large. Many cysts have released completely formed sperm cells into the tubule lumen. In the 8th week of the gonad cycle the testis tubules are filled with sperm cells. In many places the tubule walls break off and join to make vast chambers filled with sperm. Therefore, the germinal epithelium of the D. rerio testis at this stage turns into a "discontinuous" type.