Male reproductive system in Senegalese sole Solea senegalensis (Kaup): anatomy, histology and histochemistry.

Despite the fact that the Senegalese sole Solea senegalensis is a target species for the aquaculture industry in Spain and Portugal, very little is known about its gametogenesis and especially about testicular development. Therefore, the male reproductive system in adult S. senegalensis was described using a histological and histochemical approach. Mean gonadosomatic index was very low (0.094+/-0.004%) and suffered slight changes throughout the experimental period. In transverse sections, the testis presents a reniform structure with two main regions, a cortical one with seminiferous lobules where germ cells proliferate in spermatocysts (germ/Sertoli cells units), and a medullar one with spermatic ducts that collect and store the produced sperm. The germinal compartment is organized into branching lobules of the unrestricted spermatogonial type, although the majority of type A spermatogonia are located at the distal part of the lobules. Spermatogenesis seems to be semi-cystic, since spermatids are released into the lobule lumen, where they are transformed into spermatozoa. Proteins in general, especially those rich in arginine, and carboxylated mucosubstances/glyco-proteins increased from spermatogonia to spermatozoa. 3beta-Hydroxysteroid dehydrogenase enzymatic activity was exclusively observed in Leydig cells. The present study provides the first precise description of male reproductive apparatus in S. senegalensis.