No abstract

SUMMARY:In decapod crustaceans, the digestive gland is concerned with the digestion, absorption of nutrients, the storage of reserves and excretion. The metabolism and the histological and histochemical changes of the hepatopancreas are observed in response to physiological demands as moult, reproduction, digestive process. Thus the hepatopancreas structure should be recognized to provide important morphological information to future studies involving the nutrition requirements of freshwater prawn culture. In this study, second-generation Macrobrachium amazonicum produced from wild broodstock collected in the state of Pará in Brazil were used. Thirty adult male and female M. amazonicum were selected and randomly transferred to five experimental units for macroscopic and microscopic studies. The hepatopancreas of M. amazonicum is a large, yellowish-brown, compact organ, which occupies much of the cephalothoracic cavity. It has right and left halves that are enclosed together in a laminar connective tissue capsule, and at the same time they are separated by an interstitial connective tissue. The two halves are thereby called the right and left hepatopancreatic lobes. The principal tubule gives rise to four secondary tubules at each hepatopancreatic lobe. The morphological and functional unit consists of a blind-ended hepatopancreatic tubule, considered in the present study as the hepatopancreatic lobule. Each hepatopancreatic tubule can be subdivided into distal, medial and proximal zones. The hepatopancreatic tubule is lined by a pseudostratified epithelium that consists of five different cell types, which include the E-cell (embryonic), F-cell (fibrillar), B-cell (blister-like), R-cell (resorptive) and M-cell (midgut or basal). It is important to emphasize that the function of each cell type in the hepatopancreas during the digestive cycle is not yet established for decapods.KEY WORDS: Hepatopancreas; Morphology; Decapoda; Macrobrachium amazonicum. INTRODUCCIÓNDecapod crustaceans have a digestive gland associated to the midgut. It has received different names from which hepatopancreas is the most accepted (Van Weel, 1974). The hepatopancreas is concerned with the digestion, absorption of nutrients, storage of reserves and excretion (Johnston et al., 1998;Sousa & Petriella, 2000). It is also involved in the synthesis of digestive enzymes (Icely & Nott, 1992). In general, the organ occupies much of the cephalothoracic cavity and is connected to the pyloric stomach by two primary ducts. Each duct branches into many hepatopancreatic tubules, which comprise the hepatopancreas (Johnston et al.; Souza & Petriella). Each hepatopancreatic tubule consists of different cell types, which include the E-cell (embryonic), R-cell (resorptive), F-cell (fibrillar), B-cell (blisterlike) and M-cell (midget or basal) (Gibson & Barker;Al-Mohanna & Nott, 1987Caceci et al., 1988;Icely & Nott). The different cellular types have specific roles in the cyclical digestive process (Hirsch & Jacobs, 1992;Gibson & Barker;Sousa & Petriella). Th...

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.

Veríssimo-Silveira R., Gusmão-Pompiani P., Vicentini C. A., Quagio-Grassiotto I. 2006. Spermiogenesis and spermatozoa ultrastructure in Salminus and Brycon , two primitive genera in Characidae (Teleostei: Ostariophysi: Characiformes).-Acta Zoologica (Stockholm) 87 : 305-313In Salminus , spermiogenesis is cystic and gives origin to a type I aquasperm. Spermatid differentiation is characterized by chromatin condensed into thick fibres, nuclear rotation, nuclear fossa formation, cytoplasmic channel formation, mitochondrial fusion producing long and ramified mitochondria, and the presence of several membranous concentric rings around the plasma membrane that encircles the cytoplasmic channel. In Salminus and Brycon , spermatozoa are very similar. They exhibit a spherical nucleus and chromatin condensed into fibre clusters, and a deep nuclear fossa. They show a long midpiece with few elongate mitochondria at the initial region and a cytoplasmic channel completely encircled by one or two membranous concentric rings. The flagellar axis is perpendicular to the nucleus and exhibits the classic axoneme (9 + 2). The very strong similarity observed between Salminus and Brycon spermatozoa supports the hypothesis that these subfamilies are likely to have a monophyletic origin. Fig. 1-Spermiogenesis in Salminus brasiliensis. -A-D. Young spermatids, longitudinal sections. -E, F. Centriolar complex, longitudinal sections. -G-I. Transverse section of the midpiece showing the several membranous concentric rings. -J. Midpiece, transverse section. -K, L. Late spermatids, longitudinal sections. Scale bars: A = 0.70 µm; B = 0.60 µm; C and J = 0.35 µm; D and L = 0.50 µm; E, F, H and I = 0.25 µm; G = 0.30 µm; K = 0.40 µm. Abbreviations: arrow = membranous concentric rings; arrowhead = cytoplasm-surrounded flagellar initial portion; asterisk = cytoplasmic channel; a = axoneme; b = basal body; c = centriolar complex; f = nuclear fossa; m = mitochondria; n = nucleus; pc = proximal centriole. Ultrastructure of the gametic cells in fish • Veríssimo-Silveira et al. Acta Zoologica (Stockholm) 87 : 305-313 ( October 2006)

The ultrastructure of the epididymal duct of the dog is described in this paper. The epididymis was divided into three morphofunctional segments: initial, middle and terminal. The cellular population of the lining epithelium is formed from principal, apical, basal and clear cells. The peritubular stroma and the tubular interstitium surrounding the epithelium are also described. The outcome is compared to the description made in other species of mammals.

Fifteen male mosquito fish (Gambusia affinis holbrooki) were collected in 1989 on the 15th of each month to perform a quantitative histologic study of the annual testicular cycle including a calculation of the gonadosomatic index, testicular volume, and the total volume per testis occupied by each germ cell type. The cycle comprises two periods: spermatogenesis and quiescence. The spermatogenic period begins in April with the development of primary spermatogonia into secondary spermatogonia, spermatocytes and round spermatids. In May, the first spermatogenic wave is completed and the testicular volume begins to increase up to June when the maximum testicular volume and gonadosomatic index are reached. Germ cell proliferation with successive spermatogenetic waves continues until August. In September germ cell proliferation ceases and neither secondary spermatogonia nor spermatocytes are observed. However, spermiogenesis continues until October. In November, spermiogenesis has stopped and the testis enters the quiescent period up to April. During this period only primary spermatogonia and spermatozoa are present in the testis. In addition, a few spermatids whose spermiogenesis was arrested in November are observed. Testicular release of spermatozoa is continuous during the entire spermatogenesis period. The spermatozoa formed at the end of this period (September‐October) remain in the testis during the quiescent period and are released at the beginning of the next spermatogenesis period in April. Developed Leydig cells appear all year long in the testicular interstitium, mainly around both efferent ducts and the testicular tubule sections showing S4 spermatids.

This work presents the structure and ultrastructure of the interrenal gland and chromaffin cells, as well as the morphology of the head kidney of Brycon cephalus. The head kidney is composed of fused bilateral lobes located anterior to the swim bladder and ventrolateral to the spinal column. The parenchyma revealed lympho-haematopoietic tissue, melano-macrophage centres, interrenal gland and chromaffin cells. The interrenal gland consisted of cords or strands of cells grouped around the posterior cardinal vein and their branches. Chromaffin cells are found in small groups, closely associated with the interrenal gland and/or under the endothelium of the posterior cardinal vein. So far, the ultrastructural analysis has revealed only one interrenal cell type which contained abundant smooth endoplasmic reticulum and numerous mitochondria with tubulo-vesicular cristae, characteristic of steroid-producing cells. Two types of chromaffin cells were observed. The first type was characterized by the presence of vesicles with round, strongly electron-dense granules, which were eccentrically located. Such cells were interpreted as noradrenaline cells. Meanwhile, cells which contained smaller vesicles and electron-lucent granules, with a small halo separating the granule from the vesicular limiting membrane, were identified as adrenaline cells.

The morphological characteristics of the ventricular myocardium and of coronary vascularization were studied in three freshwater teleost species, Piaractus mesopotamicus, Colossoma macropomum and Clarias gariepinus (African catfish), by correlating their ventricular shapes and swimming habits. In Piaractus mesopotamicus and Colossoma macropomum, species with highly active swimming habits, the cardiac ventricle showed a pyramidal shape and a richly vascularized myocardium consisting of an outer compact layer and inner spongy layer. In Clarias gariepinus, a less active species, we observed a saccular ventricle with a mixed myocardium and coronary arteries, in contrast to the ventricular structure of other species described in the literature.