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Carbohydrate utilization by fish varies with feeding habits and feed processing. Extruded aquafeeds have increased digestibility of carbohydrate sources resulting from the cooking and gelatinization of this nutrient, making it readily available for all aquatic species. This study aimed at determining the effects of extrusion cooking of feeds in the digestibility of different dietary carbohydrate sources for dourado. Isonitrogenous and isoenergetic diets (530 g kg−1 crude protein and 20.80 MJ kg−1 gross energy) containing either corn, toasted cassava flour, wheat flour, broken rice, cassava starch, or corn starch, in extruded or pelletized form and added of chromic oxide as inert marker, were fed to groups of juvenile dourado (73.97 ± 12.0 g; n = 40) stocked in 500-L polyethylene tanks. Extrusion cooking improved the digestibility of energy and/or starch of corn, cassava starch, wheat flour, rice and corn starch ( P < 0.05), but did not affect digestibility of toasted cassava flour ( P > 0.05). It is thus fair to infer that dourado, despite being a carnivorous species, is properly fit to digest wheat flour, rice and corn starch in natural form. [ABSTRACT FROM AUTHOR]

The aim of this study was to determine the impact of diets with different plant protein ingredients on proximate composition, tissue metabolites and tissue fatty acid composition, as well as hepatic and intestinal histological modifications in Senegalese sole ( Solea senegalensis). Fish (21.5 ± 2.8 g body weight) were fed six isonitrogenous and isoenergetic diets during 11 weeks. A control diet containing fish meal as the main protein source was compared with five experimental diets replacing 30% fish meal protein by different plant protein sources: soybean meal ( SBM), soybean protein concentrate ( SPC), soybean protein isolate ( SPI), wheat gluten meal ( WGM) or pea protein concentrate ( PPC). The inclusion of different plant protein did not significantly affect growth and proximate composition of fish. The hepatosomatic index was not significantly different to the control group; however, utilization of WGM significantly increased hepatocyte size. Plasma protein values and muscle triglycerides were influenced by the inclusion of SBM and WGM in the diets respectively. Feeding fish on SBM, WGM and PPC diets significantly enhanced n-6 fatty acid levels in muscle, particularly linoleic acid. None of the plant protein ingredient used in the diets decreased arachidonic, eicosapentaenoic as well as docosahexaenoic acid values in liver and muscle. Overall, histological studies did not reveal the existence of any intestinal alterations induced by the inclusion of different plant proteins. Despite moderate changes produced by SBM, SPC and WGM, inclusion of dietary plant protein ingredients has no major impact on growth, tissue and blood biochemistry, fatty acid profile and gut integrity of Senegalese sole juveniles. [ABSTRACT FROM AUTHOR]

This study investigates the effects of gradual or abrupt changes in rearing salinity on food transit time and digestive enzymes activity of Caspian kutum (Rutilus kutum) larvae. The larvae (532 ± 0.05 mg) were supplied and randomly allocated into 12 tanks at a density of 45 fish per tank. Experimental treatments were fresh water (salinity 0) [FW] as control, exposure to salinity 5 [T1], and gradual transfer to salinity 10 in two steps of first to 5 h, then and after 12 h to a salinity of 10 [T2], and abrupt change (direct transfer to a salinity of 10 [T3]). Results showed at 8 h after start of feeding that the larvae intestine was filled with food pellets except in treatment T1. Enzyme activity responded to salinity change as follows: the highest trypsin, amylase, and chymotrypsin activities were observed in T1; however, these were not significantly different to treatment T3 (P > 0.05). Trypsin activity peaks in the FW and T2 groups occurred 8 h after feeding, and in T3 and T1 groups 5 h after feeding. Peak chymotrypsin and alkaline phosphatase activity was observed 5 and 8 h after feeding in all experiments, respectively. The highest a amylase activity in FW and T2 groups occurred 5 h after feeding, while in T3 and T1 these peaks were observed 8 h after feeding. These results indicate that salinity had some noticeable effects on the activities of digestive enzymes after feeding. [ABSTRACT FROM AUTHOR]

A 90-day feeding trial was conducted to determine the effects of dietary organic selenium ( OS) supplementation on immune responses, total selenium accumulation in various tissues and the digestive system health of marron Cherax cainii. A group of marron (initial weight 3.65 ± 0.05 g) were fed 0.2 g kg−1 of Sel-Plex® as a source of OS and were compared to a control group of marron that were not fed OS. After 90 days of feeding OS, total haemocyte counts ( THC) and the percentages of granular and semigranular cells in marron were significantly higher than in marron fed a control diet. However, dietary OS did not affect the proportion of hyaline cells. The marron fed OS had significantly lower bacteraemia and longer neutral red retention times than the control group. Total selenium levels in the haemolymph, hepatopancreas and muscle tissues of the OS-fed marron group were significantly higher ( P < 0.05) than in control diet group. The highest total soluble selenium levels were found in the muscle tissues of OS-fed marron on the final day of the feeding trial. Amylase and protease activity, soluble protein, and numbers of microvilli were significantly higher ( P < 0.05) in marron fed OS. These findings demonstrate the benefits of including 0.2 g kg−1 OS in marron diet to enhance immune parameters, increase total selenium accumulation in muscle and improve marron digestive system health. [ABSTRACT FROM AUTHOR]

The effect of burbot weight ( BW) and length ( TL) on the efficiency of weaning under controlled conditions was investigated. Growth, survival rate, cannibalism and histological analysis of digestive tract were examined. The experiment lasted 49 days (40-89 days post hatch [ DPH]). The fish ( BW 0.12 g; TL 14.1 mm) were divided into four groups: a control group ( C) exclusively fed Artemia sp. nauplii and groups F40, F47 and F54 that were weaned to dry feed on 40, 47 and 54 DPH, respectively. The highest survival rate was observed in groups C (78%) and F54 (58%). In group F54, similar TL (53.8 mm) and higher BW (1.36 g) at the end of experiment, in comparison with group C (43.9 mm, 0.84 g for TL and BW, respectively), were obtained. At the end of the experiment, the length of enterocytes in groups C and F54 was at a similar level (over 23 μm), whereas in group F47 was significantly lower (approximately 20 μm; P < 0.05). This study for the first time presents successful weaning of the burbot. The data indicate that live food should be offered until the fish reach 25 mm and 0.20 g. [ABSTRACT FROM AUTHOR]

In bay snook ( Petenia splendida) larvae the histological development of the digestive system and swim bladder, and their relative timing of differentiation were studied from hatching to 45 days post-hatch (dph) at 29°C. Newly hatched larvae showed a simple digestive tract, which appeared as a straight undifferentiated tube lined by a single layer of columnar epithelial cells (future enterocytes). The anatomical and histological differentiation of the digestive tract and accessory glands was a very intense, asynchronous process, proceeding from the distal to the anterior part. The intestine was the first region to differentiate (9 days post-hatch - dph, 6.5 mm SL), and the oesophagus the last (21 dph, 8.4 mm SL). At the onset of feeding, the digestive system was organized into different functional and histologically differentiated sections, such as the buccopharynx, oesophagus, glandular stomach, and anterior and posterior intestine. This organization resembled that of the juveniles, with the exception of pharyngeal teeth and buccopharyngeal as well as oesophageal goblet cells, which proliferated later during the mixed feeding period. Histological observations revealed that bay snook larvae retained endogenous yolk reserves until 24 dph (8.9 ± 0.4 mm SL), which might be helpful for weaning this species onto a compound diet. The important lipidic accumulation observed in the intestinal mucosa, liver, and pancreas in fish fed a compound trout diet indicated that although fish were able to digest and absorb lipids, the diet formulation did not fit the nutritional requirements of early juveniles of this species. The ontogeny of the digestive system followed the same general pattern as in most cichlid species described to date. However, we detected species-specific differences in the timing of differentiation that were related to their reproductive guild. According to the histological results, some recommendations regarding the intensive culture of this species are also provided. [ABSTRACT FROM AUTHOR]

Five iso-nitrogenous (300 g crude protein kg−1 diet) semi-purified diets with graded levels of carbohydrate at 220 (D-1), 260 (D-2), 300 (D-3), 340 (D-4) and 380 (D-5) g kg−1 diet were fed ad libitum to Puntius gonionotus fingerlings (average weight 0.59±0.01 g) in triplicate groups (20 fish replicate−1) for a period of 90 days to determine the effect of the dietary carbohydrate level on the growth, nutrient utilization, digestibility, gut enzyme activity and whole-body composition of fish. Fifteen flow-through cement tanks of 100 L capacity with a flow rate of 0.5 L min−1 were used for rearing the fish. The maximum weight gain, specific growth rate, protein efficiency ratio, RNA:DNA ratio, whole-body protein content, protease activity, protein and energy digestibility and minimum feed conversion ratio (FCR) were found in the D-2 group fed with 260 g carbohydrate kg−1 diet. The highest protein and energy retention was also recorded in the same group. However, from the second-order polynomial regression analysis, the maximum growth and nutrient utilization of P. gonionotus fingerlings was 291.3–298.3 g carbohydrate kg−1 diet at a dietary protein level of 300 g kg−1 with a protein/energy (P/E) ratio of 20.58 −20.75 g protein MJ−1. [ABSTRACT FROM AUTHOR]

A 60-day feeding trial was carried out with juvenile Jian carp ( Cyprinus carpio var. Jian) to study the effects of myo-inositol (MI) on the growth, digestive enzyme and intestinal microbial population. Diets with seven levels of inositol (163.5, 232.7, 384.2, 535.8, 687.3, 838.8 and 990.3 mg MI kg−1 diet) were fed to Jian carp (initial weight 22.28±0.07 g). Per cent weight gain (PWG) was improved with increasing inositol levels up to 535.8 mg MI kg−1 diet ( P<0.05), and plateaued ( P>0.05). The protein production value, lipid production value and ash production value were increased with increasing dietary inositol levels up to 384.2, 838.8 and 838.8 mg MI kg−1 diet respectively ( P<0.05). Although intestinal protein content and trypsin activity were not affected by inositol levels ( P>0.05), chymotrypsin, lipase and amylase activities in intestine were the lowest for fish fed the MI-unsupplemented diet ( P<0.05). Alkaline phosphatase, Na+, K+-ATPase, γ-glutamyl transpeptidase and creatinkinase activities in the intestine were increased with an increase in the inositol levels up to 384.2–687.3 mg MI kg−1 diet ( P<0.05). Intestinal Aeromonas hydrophila and Escherichia coli decreased with an increase in the levels of dietary inositol up to 232.7 and 687.3 mg MI kg−1 diet respectively ( P<0.05), while Lactobacillus in the intestine increased with an increase in inositol levels up to 990.3 mg MI kg−1 diet ( P<0.05). In conclusion, inositol improved growth, digestive capacity and intestinal microbial population of juvenile Jian carp, and the dietary inositol requirement for PWG of juvenile Jian carp is 518.0 mg MI kg−1 diet. [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]

An experiment was conducted to evaluate the effects of dietary composition on apparent digestibility coefficients of protein, fat and carbohydrate of gilthead sea bream. In addition α-amylase and proteolytic activities were measured in the digestive tract of fish, held at 20±1°C. Six experimental diets were formulated containing approximately 40%, 45% and 50% protein, 11% and 21% fat and a starch level which fluctuated from 14% to 36%. Fish having an average weight of 100–130 g were used, fed at 1.5% of their body weight daily, and digestibility was measured using an indirect method. Enzyme activities were measured in the digestive tract of fish, fed diets containing a combination of 40%, 50% protein with 11%, 21% fat at 0.5, 5, 10, 24 h after a single meal. Starch digestibility was reduced with its level in the diet. It also negatively affected fat digestibility as well as protein digestibility, the last only at the high fat level. Dietary fat level had a negative effect on starch and protein digestibility. Fat affected also strongly α-amylase levels in the digestive tract, while its effect on protease activity was of smaller magnitude. These results indicate that digestive enzyme activities and nutrient digestibility values are affected by dietary composition, carbohydrates and fat indicating the strongest effect. [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]

The apparent digestibility of both raw and treated (16 h soaked in water) deoiled salseed (Shorea robusta) meal by Labeo rohita (Hamilton) fingerlings was evaluated at 20, 30, 40, 50 and 60% levels of incorporation for each, using fish meal based feed as the reference diet. The tannin content from salseed meal could be reduced from 3.4% (in raw salseed meal) to 1.1, 0.9, 0.8 and 0.7% by soaking in water at room temperature for 30 min, 1 h, 2h and 16 h, respectively. The digestibility of dry matter, protein, lipid and ash declined with increasing levels of inclusion of raw and soaked salseed meal. The diets containing soaked salseed meal resulted in better digestibility of nutrients at all levels of inclusion as compared to those obtained with diets that incorporate raw salseed meal. The results indicate that deoiled salseed meal can be incorporated upto a level of 30% in processed (16 h soaking in water) condition by reducing tannin. [ABSTRACT FROM AUTHOR]