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The morphological and functional development of the digestive system in meagre ( Argyrosomus regius, Asso, 1801) was described by means of histological and enzymatic approaches in order to provide insight into the digestive physiology of the species at early life stages of development and evaluate whether the acquisition of digestive capacities matched the morphological development of digestive organs. For this purpose, A. regius were reared from hatching to the juvenile stage at 18 °C using a standard feeding sequence of enriched rotifers (2–15 days posthatching, dph), Artemia metanauplii (14–51 dph) and microdiet (35–51 dph). Histological and enzymatic analyses indicated that A. regius larvae had at the onset of exogenous feeding (2 dph, 3.2 ± 0.1 mm in standard length, SL) a well differentiated exocrine pancreas, and bile salt-activated lipase and alkaline proteases being the main pancreatic enzymes involved in food digestion. Ontogenic changes in pancreatic enzymes occurred between 3.2 and 3.9 mm in SL, coinciding with the resorption of the oil globule and the complete transition to exogenous feeding, and between 4.2 and 5.8 mm in SL (20–25 dph). Regarding acid digestion, pepsin was not detected in A. regius until 6.0 and 6.8 mm in SL (31 dph), coinciding with notochord flexion and the progressive decrease in the activity of alkaline protease and leucine-alanine peptidase (intestinal cytosolic enzyme) activities, indicating a shift in the mode of digestion. The detection of pepsin activity in A. regius occurred after the appearance of the first gastric glands (4.6 and 5.8 mm SL). Thus, authors need to be cautious when extracting conclusions about the beginning of acid digestion and the onset of weaning of larvae just using histological data, since it has been shown that morphology does not match functionality with regards to the stomach. The comparison of present results with other studies conducted in this species using different rearing conditions ( e.g. mesocosm technique, larval density, water temperature, feeding sequence) indicated that the functional development of the digestive system in A. regius assessed by the activity of alkaline and acid proteases is a well-conserved process that generally occurs within a range of body size regardless of larval age and rearing conditions. Thus, authors recommend using morphometric and/or morphological variables ( e.g. length, developmental stage) together with the age of larvae expressed in days after hatching for comparative purposes among different studies. Statement of relevance The morphological and functional development of the digestive system in meagre ( Argyrosomus regius ) was described by means of histological and enzymatic approaches in order to provide insight into the digestive physiology of the species at early life stages of development. Combining histological and enzymatic analytical procedures we evidenced that stomach's functionality did not match its morphological organization, since pepsin activity was not detected until some days after the appearance of the first gastric glands. This indicates that authors need to be cautious when extracting conclusions about the beginning of acid digestion and the onset of weaning of larvae just using histological data. [ABSTRACT FROM AUTHOR]

Trypsin is an important serine protease that is considered to be involved in digestion of protein in teleost fish. Nevertheless, studies on trypsin/trypsinogen in fish embryos are very limited. In this study, the trypsinogen of turbot ( Scophthalmus maximus ) ( tTG ) was identified and the expression patterns and activity of trypsinogen/trypsin were investigated. The results showed that the tTG mRNA was evenly distributed in the oocytes and was also expressed along the yolk periphery in early embryos. At later embryo stages and 1 days after hatching (dph), the tTG mRNA concentrated at the alimentary tract and head. Quantitative expression analysis showed that the tTG transcripts decreased after fertilization until the gastrula stage, then increased with the embryo and larvae development. This result was also confirmed by the specific activity analysis of trypsin and in-situ-hybridization (ISH). All of the results indicated that tTG in early embryo stages was maternally derived and expressed by itself after gastrula stages. Additionally, location of tTG mRNA in embryos and larvae was investigated; we considered that trypsin may have multiple functions during the embryo development process. Based on our results regarding trypsinogen in embryos and early development, we concluded that the trypsin/trypsinogen in turbot embryos was inherited from a maternal source and we suggested that trypsin in early development has multiple functions in the process of development. [ABSTRACT FROM AUTHOR]

This study was undertaken to address a lack of understanding of the early developmental stages of the tropical elasmobranch whitespotted bamboo shark,Chiloscyllium plagiosum, to assist with advancement of its aquaculture. It is the first report of the histological and ultrastructural characteristics of its developing digestive tract. The study was carried out from hatching to 60 days after hatching (DAH). Embryos for this study were maintained in the laboratory. Histological investigations yielded the following data. At hatching, the gut of an embryo consisted of an undifferentiated straight tube that lay over the yolk sac. The digestive tract was differentiated into buccopharynx, esophagus, stomach, and intestine by 8 DAH. During the preflexion phase (within 16 DAH), the mucous cells of the esophagus were differentiated. Gastric glands were present at 60 DAH, indicating the transition from the embryonic to the juvenile stage and the acquisition of an adult mode of digestion. The lumen of the intestine appeared on 6 DAH; the intestinal valve appeared and divided the intestine into anterior and posterior sections on 20 DAH. The liver and the pancreas were formed on 8 DAH. The yolk sac was partially depleted by 80 DAH. In terms of ultrastructure, on 30 DAH, the anterior section of the esophagus was lined by a stratified epithelium, whereas the posterior section was lined by simple tall columnar epithelial cells. Goblet cells and oxynticopeptic cells were found in the stomach. The pancreatic acinar cells were strongly elongated and of two types: one with a pale and the other with a more opaque cytoplasm. [ABSTRACT FROM AUTHOR]

In this work, histological and histochemical features of the larval digestive system of Argentine anchovy Engraulis anchoita were described. Structural changes during ontogenetic development were also characterized, and comparisons between the beginning and the end of larval development were made. Histological sections of larvae were subjected to histochemical and routine histological techniques to localize and differentiate glycoproteins ( GPs). Both at an early and a late larval stage, the oesophageal goblet cells reacted more intensely than those of the rest of the digestive tract, and only the oesophagus exhibited metachromasia with toluidine blue techniques at different pHs, thus revealing diverse GPs at different concentrations. The GPs histochemical composition in the intestine varied with the developmental stage and the intestinal zone. The absence of goblet cells characterized the foregut; however, they started differentiation at an advanced stage in the midgut. These cells could be detected in the hindgut both at the beginning and at the end of development. The attached glands showed a varied glycoprotein composition. The digestive tract of E. anchoita presented a high level of complexity, related to the multiple functions of mucus in the digestive tract, such as lubrication, protection, antimicrobial function and ionic and osmotic regulation. [ABSTRACT FROM AUTHOR]