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Assessing the activity of digestive enzymes is a common procedure in many biological, physiological and nutritional studies. After reviewing the available literature on fish digestive tract maturation and enzymatic activity (pancreatic and intestinal enzymes) published between 1994 and 2017, authors detected some possible methodological and/or interpretative inconsistencies in this kind of studies, and concluded that special attention should be paid on: i ) the time of conservation of frozen samples prior their analysis, ii ) the proper purification of the brush border of enterocytes by a double centrifugation step (Crane et al., 1979) when authors want to evaluate the activity of intestinal brush border enzymes in order to avoid the overestimation, particularly of alkaline phosphatase (AP), because it is present in other tissues; iii ) the use of the proper reaction conditions at the normal range of values in terms of ions, temperature and intestinal alkalinity for the species of interest, and AP unit calculation. The implementation of these recommendations will promote the standardization of actual analytical procedures, as well as improve the reliability of comparative studies between different fish species or rearing procedures. [ABSTRACT FROM AUTHOR]

An understanding of the development of the digestive system of marine fish larvae is of critical importance in determining optimal feeding regimes for their culture. The present study provides information on the histomorphological development of the digestive system of clown fish, Amphiprion percula, larvae during the first month of life. Before hatching, clownfish larvae possess an alimentary tract, liver and pancreas with absorptive and digestive capabilities. The yolk sac is completely consumed within 5–7 days at 25 °C. Clownfish larvae readily accept rotifers after hatching and a complete dietary shift from rotifer to Artemia can be accomplished at 10 days after hatch (DAH). Gastric glands in the stomach first develop 11 DAH and proliferate by 15 DAH. Both non-staining vacuoles (NSV) and supranuclear inclusion vesicles (SIV) appear at 11 DAH in the midgut and hindgut respectively. Pinocytosis and extracellular digestion coexist for about 2 weeks after hatching. While SIV disappeared completely at 25 DAH, NSV continued to be a prominent feature of the midgut during the first month. [ABSTRACT FROM AUTHOR]

Summary The occurrence of runt sturgeons is not an unusual event in rearing Acipenser transmontanus . The aim of this study was to describe morphological and histochemical features of the alimentary canal in both feeding and runt fish in order to identify specific structural changes that characterize the differences resulting from the nutritional status of the fish. Compared to feeding fish, runt fish showed: (i) a lack of lobuli of adipose tissue in the tunica propria-submucosa of their oesophagus; (ii) an increased thickness of the intestine near the spiral valve, due to the presence of several large lymphatic follicles within the tunica propria-submucosa; (iii) a reduced height of the intestinal folds; and (iv) a lesser immunohistochemical reactivity of the intestinal mucous cells towards a macrophage antiserum. The results tentatively suggest that a reduced defensive mucosal effectiveness occurs in runt specimens and this may be either linked to specific environmental stressors or to responses caused by pre-exposure to so far undetected disease agents, which requires further studies. [ABSTRACT FROM AUTHOR]

Summary This study was aimed at investigating the anatomy and luminal surfaces of the entire gut of Acipenser naccarii , through optic and transmission and scanning electron microscopy (TEM and SEM). Two-year-old individuals as well as larval and post-larval developmental stages were studied. The results confirm the gross morphology found in the entire genus Acipenser . The presence of numerous ciliated cells in the gastric and intestinal parts of the alimentary canal and a spiral valve show ancient features in these fish. From an aquaculture perspective, observations on the ontogenesis of the digestive system suggest that feeding should start as soon as the connection between oesophagus and stomach is established. Our observations indicate that A. naccarii reach this functional threshold not before the eighth day post-hatching (larval rearing temperature: 21°C). [ABSTRACT FROM AUTHOR]