Liver samples of Oreochromis niloticus cultivated in floating net cages were fixed for histological and ultrastructural studies with the objective of describing the hepatic parenchymal structure and the intrahepatic exocrine pancreatic tissue. Anatomically, the liver showed only two hepatic lobes. Histological analysis demonstrated that the hepatocytes were spread out as anastomotic cords, arranged in two cellular layers and surrounded by sinusoids. The intrahepatic exocrine pancreatic tissue exhibited an acinar arrangement and was diffused in the hepatic parenchyma. Structural analysis showed that the hepatocytes had a rounded nucleus and a rough endoplasmic reticulum with a parallel disposition to the nuclear membrane. The exocrine pancreatic cells showed secretion granules at the apical portion and the rough endoplasmic reticulum was concentrically distributed.

The aim of this study was to characterize the embryonic development of Zungaro jahu, a fresh water teleostei commonly known as 'jaú'. Samples were collected at pre-determined times from oocyte release to larval hatching and analysed under light microscopy, transmission electron microscopy and scanning electron microscopy. At the first collection times, the oocytes and eggs were spherical and yellowish, with an evident micropyle. Embryo development took place at 29.4 ± 1.5°C and was divided into seven stages: zygote, cleavage, morula, blastula, gastrula, organogenesis, and hatching. The differentiation of the animal and vegetative poles occured during the zygote stage, at 10 min post-fertilization (mpf), leading to the development of the egg cell at 15 mpf. From 20 to 75 mpf, successive cleavages resulted in the formation of 2, 4, 8, 16, 32 and 64 blastomeres. The morula stage was observed between 90 and 105 mpf, and the blastula and gastrula stage at 120 and 180 mpf; respectively. The end of the gastrula stage was characterized by the presence of the yolk plug at 360 mpf. Organogenesis followed, with differentiation of the cephalic and caudal regions, elongation of the embryo by the cephalo-caudal axis, and somitogenesis. Hatching occurred at 780 mpf, with mean larval total length of 3.79 ± 0.11 mm.

The Zungaro jahu is an important large catfish of the order Siluriformes that is in danger of extinction due to habitat destruction. Studies on its biology are scarce and the majority relates only to nutrition or parasitology. In order to provide greater information on its morphology and aid husbandry and larviculture studies, the aim of this study was to characterize larval development in Z. jahu from hatching to total yolk absorption. Samples were collected at pre-established times, processed, stained, and analyzed under stereomicroscopy, light microscopy, and scanning electron microscopy. Total yolk absorption was observed by 60 hours post-hatching (hph) at 28.75 ± 0.59°C. The newly hatched larvae showed slightly pigmented body, the outline of the digestive tract, evident eyes, and the first swimming movements. Mouth opening took place at 12 hph and the connection between the oral cavity and the rudimentary intestine was observed at 24 hph. Were analyzed the main larval organs and systems: digestive organs, heart, gill arches, sensory system, thyroid, kidney, and swim bladder. As the larvae grew, these organs became more mature and functional. The development of the sensory and feeding structures was observed at the start of larval development, and thus before depletion of endogenous energy reserves, the strategy for this species is to increase its chances of survival in the environment.

ABSTRACT. Livers of thirty specimens of Astyanax altiparanae obtained from a commercial fish farm were subjected to light and transmission electron microscopy, in order to describe the hepatic parenchyma and the intrahepatic exocrine pancreatic tissue. Anatomically, the liver showed only three hepatic lobes. Histological analysis demonstrated that the hepatocytes were spread out as anastomotic cords, arranged in two cellular layers and surrounded by sinusoids. The intrahepatic exocrine pancreatic tissue exhibited an acinar arrangement and was diffused in the hepatic parenchyma. Ultrastructural analysis showed that the hepatocytes had a rounded nucleus and a rough endoplasmatic reticulum, with a parallel disposition to the nuclear membrane. The exocrine pancreatic cells showed secretion granules at the apical portion, and the rough endosplasmatic reticulum was concentrically distributed.Key words: liver histology, hepatocyte ultrastructure, exocrine pancreas, teleost.RESUMO. Histologia e ultraestrutura do fígado de Astyanax altiparanae Garutti e Britski, 2000 (Teleostei, Characidae). Fígados de 30 exemplares de Astyanax altiparanae, obtidos de pesqueiros, foram submetidos à microscopia de luz e à microscopia eletrônica de transmissão para descrição do parênquima hepático e do tecido pancreático exócrino intrahepático. Anatomicamente, o fígado apresenta somente três lobos hepáticos. A análise histológica demonstra que os hepatócitos se encontram arranjados na forma de cordões anastomosados, dispostos em duas camadas celulares, sendo que estes estão cercados por sinusóides. O tecido pancreático exócrino intra-hepático apresenta arranjo acinar difuso pelo parênquima hepático. A análise ultraestrutural demonstra que os hepatócitos possuem um núcleo arredondado e retículo endoplasmático rugoso, com disposição paralela à membrana nuclear. As células pancreáticas exócrinas apresentam grânulos de secreção na porção apical e retículo endoplasmático rugoso com distribuição concêntrica.Palavras-chave: histologia hepática, ultraestrutura hepática, pâncreas exócrino, teleósteo.