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Summary

In the Neotropical cichlid Cichla kelberi the spermiogenesis appears to be of the cystic type and is characterized by gradual chromatin condensation in juxtaposed clusters, nuclear rotation (with the flagellum perpendicularly to the nucleus), and consequent nuclear fossa formation. Besides, there is cytoplasma migration to the nuclear base while eliminating the cytoplasmic residual mass. The heads of the spermatozoa are round, with approximately 1.87 μm in diameter; the nucleus has clusters juxtaposed of condensed chromatin. The nuclear fossa in single arc shape is moderate and slightly eccentric to the nuclear base. The midpiece is short and presents a cytoplasmic sheath, which dilated in its extremes. The mitochondria are spherical or slightly elongated. The flagellum presents the classical axoneme 9 + 2 and one pair of fins. The Type I C. kelberi spermatozoon has its flagellum perpendicularly positioned in relation to the nucleus base. The presence of only one flagellum characterize it as the basic spermatozoon in teleost, known as single anacrosomal aquasperm spermatozoon. Besides the patterns of previously cited characteristics between its representatives, the cytoplasmic sheath and flagellum fins presence can be consider as characteristics of the Cichla genus.