The gonad morphology and gametogenesis of Lophiosilurus alexandri Steindachner, 1877 from Santo Antônio river (Minas Gerais, Brazil) were studied through anatomical and histological techniques. Examination of the testis revealed that they were paired, fringed organs with two distinct regions: cranial spermatogenic and caudal spermatogenic and secretory. The cranial region represents ca. 60% of the mature/maturing testis, containing 41 to 73 fringes, while the caudal portion represents ca. 40% and contains 44 to 68 fringes. At the cranial portion the length of the fringes was 3.70 ± 1.70 mm and in the caudal portion was 0.20 ± 0.10 mm. The spermatogenesis was cystic, synchronic, and occurred throughout the whole extension of the seminiferous tubules. The ovaries were saculiforms, paired organs, which present ovigerous lamellae containing cells of the oogenic lineage. The oocytes were classified into four developmental stages according to their cytological characteristics and the characteristics of the cell layers that surround them.

Lophiosilurus alexandri reproduces in captivity, has a high commercial value in Brazil and carries great potential for aquaculture. Research was carried out on L. alexandri larvae from days 1 to 30 post-hatch (DPH). Based on descriptions in the literature four developmental stages were observed using anatomic, histological and statistical techniques to provide useful data for the taxonomy, aquaculture and conservation of this species. In the yolk sac stage (1-2 DPH) the larvae presented myomeres (pre 17-23 and post anal 25-32) evident along the body, open mouth, the beginning of eye pigmentation and intestine with simple prismatic epithelium. The preflexion stage (3-4 DPH) was characterized by onset of body pigmentation and appearance of the pectoral fin bud. The oesophagus, stomach and intestine presented a folded mucosa. The flexion stage (5-7 DPH) was characterized by a flexion of the notochord, the chondrogenesis of the neural arches, formation of the dorsal and anal fins (11 rays) and appearance of the pelvic fin bud. In the postflexion stage (8-30 DPH) the formation of pelvic fin rays (6 rays) occurred along with the development of three different stomach regions. Except for the variables related to the yolk sac, all other studied variables presented significant differences between developmental stages.

The reproduction of Astyanax scabripinnis captured bimonthly in the Cristais small stream (20 o 00¢03¢S and 43 o 56¢46¢W), in the Das Velhas River basin, was studied using gross anatomical and histological techniques. Standard length of females (56 ± 8 mm) was longer than males (49 ± 6 mm). The diameter of the nucleus of the primary spermatogonia was 7.5 ± 0.9 lm and of the spermatozoon head 1.8 ± 0.4 lm. For the females, the oogonia nuclei measured 10.2 ± 2.2 lm and the vitellogenic oocyte nuclei measured 675.0 ± 66.7 lm. The following stages of the reproductive cycle were established: developing, mature, partially spent ⁄ spawned and completely spent ⁄ spawned. Maximum number of males (61.3%) and females (58.2%) at the mature stage was observed during November ⁄ December. The gonadosomatic index of males and females was highest during the mature stage (2.4 ± 0.6; 7.5 ± 1.3, respectively) and decreased in subsequent stages. In females, the hepatosomatic index was highest during the developing stage (2.8 ± 0.3), and slightly decreased in the following stages. The highest stomach repletion index found for males was observed during the partially spent stage (2.0 ± 1.2), while for the females, this index varied discretely between the reproductive stages. The highest values of FultonÕs condition factor were registered during the mature stage in both sexes (2.9 ± 0.4 for males; 3.0 ± 0.3 for females). The continuous reproductive period and the presence of partially spawned females during the entire sampling period indicated that the species has fractional spawning.

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The aim of the present study was to characterize the relationships that occur between morphometric variables of larvae of Lophiosilurus alexandri Steindachner, 1876 through their allometric growth analysis. Total length, head length and body height were correlated with standard length, head height and body height, as well as eye diameter and head height with head length. The results revealed allometric positive relation during the initial development, where the b coefficient varied between 1.10 and 2.81. The variable pre-anal distance in relation to the standard length and the snout length in relation to the head length revealed an allometric negative relation, where the b coefficient was 0.85 and 0.94, respectively.