[Histology of reproductive cycle of tropical gar Atractosteus tropicus females (Lepisosteiformes: Lepisosteidae) in Tabasco, Mexico].

In Southeast Mexico, A. tropicus is a species with great ecological, economic, cultural and aquaculture value, however wild populations have diminished due to diverse anthropological causes. The objective of this study was to characterize the reproductive cycle of A. tropicus, with a description of complete gonad structure and the changes in germinal and somatic elements during oogenesis, for better management and use of this species. Six sexually mature females (N=72) were captured monthly with drag nets during one year cycle (October 2003-October 2004) in wild populations of Pomposu lagoon, municipality of Jalpa de Mendez, Tabasco, Mexico. Females were sacrificed by decapitation and the ovaries were processed by standard histological methods; the diameter of 10-20 oocytes taken at random was determined in different stages of development. Gonadosmatic index (GSI), gonadal volume (gV) and follicule diameter (fD) were determined monthly. Among results we could determine eight oogenesis developmental stages: I: chromatin nucleolus stage, II: early perinucleolus stage, III: mid perinucleolus stage, IV: advanced perinucleolus stage, V: early vitellogenesis stage, VI: mid vitellogenesis stage, VII) advanced vitellogenesis stage and VIII: final maturation stage. The reproductive cycle could be divided in four phases: 1: proliferative phase, II: initial maturation phase, III: late maturation phase, IV: regressing phase. Analysis of the data obtained from the IGS, gV and fD values, oogenesis stages and reproductive phases, indicate that in December previtellogenesis phase restarts, from March through July yolk deposition (vitellogenesis) occurs, and from August to November the maximum reproductive activity takes place. Contrasting this pattern with local environmental factors such as temperature and precipitation, we suggested that these may serve as an environmental activator in the development of oogenesis and spawning of this species.