“Testis morphology in two atherinomorph fishes with different fertilization modalities.”

F. LO NOSTRO; F. MEIJIDE; H. GRIER; G. REY VAZQUEZ; M. C. MAGGESE; G. GUERRERO

Manaos, Brasil

Congreso; 81th Annual Meeting American Society of Ichthyologist and Herpetologits (ASIH-AES).; 2003

The testes of Odontesthes bonariensis and Cnesterodon decemmaculatus, two atherinomorph freshwater species from Argentina, are examined. O. bonariensis (Order Atheriniformes) is an externally fertilizing, oviparous silverside. C. decemmaculatus (Order Cyprinodontiformes) is viviparous, fertilization being internal. Although these species possess different fertilization modalities, they share the same basic testis morphology. The testes are unfused, paired organs running laterally along the body wall on either side of the gut. Primary spermatogonia are restricted to the distal termini of the testicular lobules just beneath the tunica albuginea, thus conforming to the typical atherinomorph testis type. In restricted testes, there is a maturational progression of germ cell stages towards the efferent ducts. Unlike the unrestricted testis type, a lobular lumen never develops. The only lumina present are those of spermatocysts, which do not qualify to the definition of germinal epithelium. Then, males never develop a germinal epithelium; rather the germ tissue is epithelioid. In O. bonariensis, mature sperm are released into the efferent ducts, which empty into a single longitudinal main duct in each testis. C. decemmaculatus package sperm in the form of unencapsulated sperm bundles or spermatozeugmata. Spermatozeugmata appear to be formed before spermiation within the lobules. Unlike other cyprinodontiform fishes, each spermatocyst releases a single, large spermatozeugma. PAS+ testicular secretions help mantain the integrity of the sperm packets once they reach the efferent and main testis ducts.