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Abstract Rey Vázquez, G., Da Cuña, R.H., Meijide, F.J., and Guerrero, G.A. 2012. Spermatogenesis and changes in testicular structure during the reproductive cycle in Cichlasoma dimerus (Teleostei, Perciformes). —Acta
Zoologica (Stockholm) 93: 338–350. The present study aimed at analyzing spermatogenesis and the changes occurring in the testis throughout the reproductive cycle in the South American perciform fish Cichlasoma dimerus. Testes were studied using light and electron
microscopy techniques. This species has an unrestricted lobular testis composed of two compartments: germinal, containing Sertoli and germ cells, exhibiting a cystic mode of spermatogenesis; and interstitial, composed of Leydig cells and connective tissue elements. Spermatozoa belong to the
anacrosomal type I aquasperm and possess two flagella, this being the first report of an externally fertilizing cichlid exhibiting biflagellate sperm. Under laboratory conditions, C. dimerus proved to be a multiple spawner throughout the year, with a season of higher reproductive
activity extending from September to March, during which fish spawned on average every 29.4 days. Changes in the germinal epithelium and the germ cell stages present allowed the description of five reproductive classes: regressed, early, mid‐, and late maturation, and regression.
During the high reproductive season, each cycle went through the first four classes. The regressed class overlapped with the late maturation class, because sperm was being released while spermatogonia were proliferating. The regression class occurred solely in sexually inactive males during
the period of low reproductive activity.
Laboratorio de Embriología Animal, Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires C1428EHA, Argentina