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...

Effects of the ratio of dietary fatty acids, namely n‐3 (mainly long chain polyunsaturated – LC‐PUFA) to n‐6 PUFA on the fecundity of Macrobrachium amazonicum were evaluated. In T1, the diet had equal and low levels of dietary n‐3 and n‐6 fatty acids (6 mg g−1). In T2, the concentration of n‐3 (6 mg g−1) was a half of the concentration of the n‐6 (12 mg g−1), and in T3, the diet had equal and high concentrations of n‐3 and n‐6 (12 mg g−1). Females with ovaries in stages I, III and V were collected. Higher gonadosomatic index (GSI) (6.89%) was observed in females in ovarian stage V than at other ovarian stages; however, the hepatosomatic index (HIS) showed high values in all females with ovaries in the stage III. A ratio of 1:2 n‐3:n‐6 fatty acids increased the GSI of mature females and the number of eggs spawned. Raising the level of both n‐3 and n‐6 fatty acids from ~0.6% to ~1.2% of the diet did not produce any effect on the GSI or on fecundity, suggesting that the ratio is more important than the absolute value of these two families of fatty acids.

The Amazon River prawn Macrobrachium amazonicum is endemic to tropical South America and is being intensively exploited by artisanal fisheries in Brazil. Limited information is available about the nutritional requirements of M. amazonicum, although the production of this species is now technically feasible. The digestive process in this species is still unclear and investigation into the digestive cells of its hepatopancreatic epithelium is required. Thus, the hepatopancreas from 15 specimens were fixed in Karnovsky Solution and processed for Transmission Electron Microscopy. Our results indicate that E cells are located at the distal portion of the hepatopancreatic tubule and are involved in mitotic activity. The cylindrical R cells are sparse and are only found in the proximal portion of the hepatopancreatic tubule. According to its ultrastructural characteristics, this cell is involved in pinocytosis. M cells are generally found near the R cells. The F cells are scattered throughout the length of the hepatopancreatic tubules, and B cells are observed mainly in the proximal and middle regions. F cells and B cells are likely related to, respectively, the synthesis of enzymes and the intracelular digestion. R-and M cells are probably related to material storage. Thus, these findings provide basic information on the cell types that perform protein digestion in M. amazonicum, and will be useful in further nutritional research. The identification and characterization of digestive cells is an important step towards understanding the digestive mechanisms.