Permanent germinal epithelium and reproductive cycle of tropical gar Atractosteus tropicus males (Lepisosteiformes: Lepisosteidae), Tabasco, Mexico

Abstract

Tropical gar A. tropicus plays an important ecological role, as a regulator of other fish stocks, in the water bodies of Mexico but their wild populations are being reduced. One conservation alternative is breeding which requires the study of germ and somatic structures of testis to characterize the reproductive cycle, basic knowledge required to create exploitation and conservation models. Three sexually mature males were captured on a monthly basis (N=24), in wild populations of Pomposu lagoon, municipality of Jalpa de Mendez (18°19'59" N - 93°01'12" W), Tabasco, Mexico. The capture technique was trawl net; they were transported live to the Tropical Aquaculture Laboratory, DACBiol, UJAT. Males were sacrificed by decapitation; testis fragments from all of the specimens collected were processes using a routine histological procedure, that consisted of dehydration for ascending etanol series, xylol, and inclusion in paraffin, with a sliding microtome 7µm thick cuts, and were dyed with hematoxylin-eosin (HE). The diameter of 20 seminiferous tubules (Tse), height of germinal epithelium (Egl), gonadosomatic index (GSI) and gonad volume (Gv) were determined on a monthly basis, as well as the gonadosomatic index GSI=PG/PT(100) and the gonad volume vG=4/3 pa2.b. Morpho-physiological characteristics of the testis show that it consists of a network of tubules anastomosed with non-restricted cystic spermatogenesis, and a permanent germinal epithelium. As far as we are concerned, this is the first time that this type of epithelium is reported in Holostei (Lepisosteiformes: Lepisosteidae). Five reproductive classes were identified: Class I Recrudescence, Class II Early Maturation, Class III Intermediate Maturation, Class IV Advanced Maturation, Class V Regression, that when contrasted with the monthly value of the "GSI, GV, Tse" sexual indicators it shows a variation pattern: January-February shows low values with empty testis, with discontinuous germinal epithelium in regeneration; in March spermiogenesis increased and spermatogenesis decreased. Generally speaking, these variations show that at a population level they do not mature synchronously, but with an annual seasonal reproductive cycle with spermatogenesis throughout the year, where temperature and precipitation seem to play an important role as a factor that stimulates reproductive activity and therefore spermiation.