The influence of feeding diets containing wheat gluten supplemented with dipeptides or free amino acids on structure and development of the skeletal muscle of carp (Cyprinus carpio)

A 28-day feeding trial was conducted to evaluate the influence of feeding diets containing plant protein wheat gluten supplemented with dipeptides or free amino acids on structure and development of the skeletal muscles of carp (Cyprinus carpio). Common carp fingerlings (1 month old) having an of average weight of 0.07 ± 0.02 g and total length of 17.79 ± 1.79 mm were fed three formulated diets—wheat gluten protein-based diets supplemented with Lys–Gly dipeptide (PP), free lysine and glycine (AA), control diet without lysine supplemented (CON)—and two other diets: restrictive diet—frozen zooplankton (Z) and commercial diet Aglo Norse (AN). After 28 days of experimental feeding, statistically significant higher survival was observed among fish fed AN and Z diets (99.5 ± 1.0 %; P ≤ 0.05). The feeding AN diet has had also a positive influence on weight and growth rate as well as on development and growth of skeletal muscles. Furthermore, carps fed AN diet had the largest area of red and white muscle as compared with the other feeding groups, and the differences were statistically significant (P ≤ 0.05). The increase in the number of proliferating cells (proliferating cell nuclear antigen) was observed on the last day of the experiment among carps fed PP, AA and CON. Moreover, fish fed PP significantly had the greatest number of MyoD- and myogenin-positive nucleus (P ≤ 0.05). Among the experimental diets based on wheat gluten, a positive impact on structure and development of muscles has been observed in carps fed PP diet.     

Rearing of pike-perch larvae using formulated diets – first success with starter feeds

The present study evaluated the performance of two commercial diets: AgloNorse (AN) and BioKyowa (BK), and two experimental, formulated diets based on casein (C) or casein plus casein hydrolysates (CH) in rearing of pike‐perch larvae (Sander lucioperca L.). All fish were 5 day old and control group was fed live Artemia nauplii. Fish were sampled periodically for histological comparison of morphological changes in the digestive tracts. Survival of fish fed Artemia nauplii, BK and AN was similar: 54.4%, 50.8% and 52.4%, respectively, while the fish fed formulated diets C and CH showed considerably lower survival: 28.4% and 21.6% respectively. After 5 weeks of rearing, the average body mass of fish ranged from 212±32 mg in Artemia fed group to 53.8±6.8 mg in C diet fed group. A considerable vacuolization of supranuclear zone in enterocytes of posterior intestine was observed in the larvae fed commercial diets. No anomalies in liver development were found. Hepatocytes of fish fed BK diet showed larger glycogen storage areas, compared with those occupied by lipids. The highest zymogen accumulation of pancreatic cytoplasm was observed in fish fed Artemia. In fish fed C and CH diets, anomalies in digestive system development were indicated by lower and less numerous intestinal folds, smaller hepatocytes, retarded development of gastric glands, and in CH group – also local fatty degeneration of liver.     

Effects of various diet formulations (experimental and commercial) on the morphology of the liver and intestine of rainbow trout (Oncorhynchus mykiss) juveniles

The aim of the present study was to evaluate the effects of three formulated diets: wheat gluten protein‐based diets supplemented with Lys–Gly dipeptide (PP) or free lisine and glycine (AA), and a control diet without lysine supplementation (CON), two commercial starters: Aller Futura (AF), Aglo Norse (AN) and frozen Chironomidae larvae (CH) for on the growth and digestive system development of rainbow trout. The experiment lasted 28 days and survival at the end of the experiment was the highest in the group fed AF (87.9±4.2%) and the lowest in the group fed the CON diet (74.0±4.3%). Fish fed the CON diet showed a significantly lower crude protein content, and the AA group had a significantly higher lipid level (P≤0.05) in body carcass compared with the other groups. The highest density of intestinal goblet cells (P≤0.05) was observed in fish fed the CON diet, while the lowest density was seen in the distal intestine in the AF group. The hepatocyte cytoplasm of all fish stored more glycogen than lipids. These results indicate that wheat gluten protein‐based diets supplemented with dipeptide Lys–Gly (PP) or free lysine and glycine (AA) supported growth, protein efficiency rate and intestine epithelium homeostasis. On the other hand, fish fed CON (lysine‐deficient diet) showed lower survival and growth rate, and disturbances of intestine epithelium homeostasis, probably as a result of lysine deficiency.     

Structure and function of the small intestine of the tilapia Oreochromis niloticus×Oreochromis aureus (Teleostei, Cichlidae)

This study examined the microscopic structure of the small intestine and digestion and absorption in the hybrid tilapia, Oreochromis niloticus×Oreochromis aureus. The small intestine was lined on the luminal face with villi, which were narrower and more dense in the proximal small intestine and became wider and sparser distally. The columnar epithelial cells lining the villi were predominantly enterocytes containing a brush border, interspersed with mucus containing goblet cells approximately every 4–6 cells. These mucus‐secreting cells contained both acid and basic mucins and increased in density in the distal and the terminal sections of the intestine. Proliferation of enterocytes was observed in the intervillus areas and lower third of the villus. Fish were fed diets of either fish meal or fish meal–wheat to which chromic oxide had been added as a non‐absorbed reference standard. Activity of the pancreatic enzymes, lipase, trypsin and amylase were determined along the small intestine relative to the non‐absorbed marker. Activity of these pancreatic enzymes was maximal in the proximal segments and decreased distally. Changes in the activity patterns of trypsin and amylase were observed with the different diets in the proximal small intestine. Net secretion of both N and fatty acids was found in the hepatic loop and absorption commenced distally decreasing in rate with distance from the pylorus. The pattern of N absorption in the proximal small intestine changed with the different diets. The structure and function of the small intestine of the tilapian omnivore thus are generally similar to mammals and digestion and absorption adapt with diet.     

Morphometric evaluation of changes in the digestive tract of rainbow trout (Oncorhynchus mykiss) due to fish meal replacement with soy protein concentrate

Effects of the complete replacement of fish meal (FM) by soy protein concentrate (SPC) in high-energy diets (23 MJ kg^− 1 gross energy) on intestinal and liver histology were investigated in rainbow trout (Oncorhynchus mykiss). We developed a novel morphometric method to quantify the changes at the macro- and micromorphology level. Fish were acclimatized to the diet for 90 d and were then fed 1.0 g kg BW^− 1 d^− 1 once per day for 14 d before 10 fish per diet were randomly sampled, 6 h after their last meal. Fold height, epithelium length, stroma proportion of the proximal and distal intestines were not affected by the diet. No significant diet effect was detected on the features of the valve in the distal intestine. Fold height was linked to epithelium length in the proximal and distal intestines and this relationship was not modified by FM replacement. Enterocyte height and width were lower in SPC-fed fish in the distal intestine, but in the proximal intestine their morphology was not affected by the diet. There was no diet effect on the number of cells infiltered between the enterocytes in the proximal and distal intestines. The enterocyte nucleus was closer to the apex in the proximal and distal intestines in SPC-fed fish, but the features of the nucleus were not affected by the diet. The mean hepatocyte volume was on an average 36% lower in SPC-fed fish and was positively correlated to the hepatosomatic index for fish fed this diet only. In conclusion, SPC used in the present study did not either cause inflammatory reaction of the gut nor affected the epithelium surface. We suggest that the modifications due to SPC are linked to variations in the metabolic status of the enterocyte.     

Lipid digestibility and ultrastructural changes in the enterocytes of Arctic char (Salvelinus alpinus L.) fed linseed oil and soybean lecithin

Arctic char (Salvelinus alpinus L.) were fed two isocaloric diets supplemented with 15% linseed oil or soybean lecithin, and subsequently analysed for ultrastructural changes in various intestinal segments (pyloric caeca region, midgut and hindgut) as well as apparent digestibility coefficients (ADC) of the diets. The ADC of dry matter, lipid and individual fatty acids were always highest in fish fed the soybean lecithin diet. In hindgut for example, ADC of lipid and dry matter were 94 and 96%, respectively, in fish fed the soybean lecithin diet compared to 85 and 94% in fish fed linseed oil.There were major ultrastructural differences in the enterocytes between fish fed the two experimental diets. In char fed the linseed oil diet there were substantial accumulations of lipid droplets in the enterocytes from the pyloric caeca and midgut but not in hindgut. These accumulations were not observed in fish fed the soybean lecithin diet. In some cases, deposition of fat in the enterocytes was so great that it resulted in epithelial damage with lipid droplets and cell debris appearing in the intestinal lumen. These changes are likely to be pathological and may lead to intestinal malfunction and represent a major infection route to pathogenic bacteria. On the basis of these results it is suggested that endogenous phospholipid synthesis is insufficient to maintain lipoprotein synthesis in Arctic char when fed diets containing high levels of polyunsaturated fatty acid of total lipid, and that phospholipids should be supplied with such diets.     

Ultrastructure of the anterior intestinal epithelia of the orange-spotted grouper Epinephelus coioides larvae under different feeding regimes

Enterocytes of the anterior to midsection of the intestine in grouper Epinephelus coioides larvae were compared among different treatments: unfed to the point-of-no-return (PNR), fed natural food only, and co-fed natural food and artificial diet. On day 3, the nutritional condition of unfed grouper larvae regressed with its reduced enterocyte heights which were further degraded on day 4, the PNR, when all the enterocytes were in advanced stages of apoptosis. The apoptosis appeared to be internally directed via the mitochondria. Among day 3 fed larvae, enterocyte heights of those fed artificial diet did not differ from those fed natural food only. Dietary phospholipid deficiency was indicated in larvae co-fed artificial diet on day 3 with an unusually large chylomicron opening into the inter-enterocyte space, and on days 6 and 33 by intestinal steatosis. On day 19, scant to absent lipid droplets in enterocytes of larvae disclosed heightened nutritional requirement preparatory to metamorphosis. As observed in unfed day 3 and premetamorphic day 19 E. coioides, larvae undergoing critical periods and starvation during development employ apoptosis to dispose of degenerated enterocytes that are phagocytosed by adjacent healthy enterocytes without causing inflammatory distress. Upon metamorphosis, grouper larval gut develops better immunity fitness with eosinophilic granule cells observed in the intestinal epithelia of day 33 larvae. Future studies on grouper larval nutrition may consider the appropriate dietary phospholipid levels and larval competence to biosynthesize highly unsaturated fatty acid from linoleic acid vis-à-vis the use of plant ingredients in artificial diet formulations. In vivo challenge tests may validate appropriate dietary nutrient supplementation and lead to better feed formulation, matching the varying energetic demands and digestive capacities of developing E. coioides larvae.     

Effects of Dietary Binders on Survival and Growth Performance of Postlarval Tongue Sole, Cynoglossus semilaevis (Günther)

A 30‐d feeding experiment was conducted in tanks to investigate the effects of four different binders (2% in microdiet) on the survival, growth performance, and specific activity of digestive enzymes in tongue sole, Cynoglossus semilaevis Günther, postlarvae (24 d after hatching, with initial average wet weight of 22.4 ± 6.65 mg [mean ± SD]). Five approximately isonitrogenous and isoenergetic microbound diets were formulated with carrageenan (Car), sodium carboxymethylcellulose (CMS), sodium alginate (SA), and gelatin (Gel) as binders, and a diet with no special binder as a control. A commercial diet (RQ Com., manufactured by Marubeni Nisshin Feed Co., Ltd., Chita, Japan) was used as another tested diet, and Artemia nauplii was used as live prey control. The results showed that the survival of the fish fed SA diet (31.3%) was significantly higher than that of fish fed CMS (21.8%), Car (10.8%), and control (21.8%) diets (P < 0.05), but significantly lower than that of the fish fed the live prey (54.5%) diet (P < 0.05). The results of growth followed the similar pattern as that of survival, although there were no significant differences in specific growth rate (SGR) among fish fed SA, CMS, Gel, the control, and RQ diets (7.2, 6.8, 7.0, 6.9, and 7.3% per day; P > 0.05). However, fish fed Car diet had a significantly lower SGR (5.9% per day) than fish fed other diets. Percentages of secreted amylase in fish fed artificial diets were not significantly different, but fish fed artificial diets had significantly higher (P < 0.05) secreted amylase than live prey group. Percentage of secreted trypsin in fish fed SA diet (54.9%) was relatively higher compared with other binders, and not significantly different from RQ Com. and live prey treatments. However, trypsin in fish fed Car diets (29.3%) was significantly lower than in other groups. Specific activities of alkaline phosphatase (AP) in the intestine and AP and leucine aminopeptidase N in brush border membranes in fish fed SA diet (264.6, 1882.8, and 187.2 mU/mg protein) were relatively higher compared with other binders. These results indicate that SA is one of suitable binders compared with carrageenan, CMS, and gelatin in microdiet of postlarval tongue sole.     

Effect of diets containing a purified soybean trypsin inhibitor on growth performance,digestive proteases and intestinal histology in juvenile sea bream (Sparus aurata L.)

Juvenile sea bream were fed on diets containing 0.0, 2.0 or 4.0 g kg^?1 of a soybean trypsin inhibitor (SBTI) for 30 days. The growth performance, total protease activity and intestinal histology were studied after 0, 15 and 30 days of dietary treatment. No significant differences were found in the weight gain, specific growth rate (SGR) and feed conversion rate in fish fed on inhibitor‐supplemented diets when compared with those fed on an inhibitor‐free diet. Only the SGR at day 15 decreased significantly with protease inhibitor inclusion, although this effect was not observed at day 30. In relation to proteolytic activity at day 15, the total protease activity in the distal intestine decreased in fish fed on inhibitor‐supplemented diets. Zymograms of these extracts showed that the SBTI reduced the intensity of some proteolytic fractions in the distal intestine. A noticeable reduction in the protease activity of the intestinal content in fish fed on the highest level of soybean inhibitor (4.0 g kg^?1) was also observed. However, at day 30, the inhibition effect on these active bands was not detected, and the total protease activity was similar to that in fish fed on an inhibitor‐free diet. Histological examination revealed no perceptible differences in the intestinal structure between any of the diet groups. In addition, all fish were maintained under experimentation for 10 more days and fed on an inhibitor‐free diet to determine whether the possible effects caused by the protease inhibitor could be reverted. The administration of SBTI‐supplemented diets did not affect sea bream growth performance or intestine histology after 30 days, and only a decrease in the total alkaline protease activity was found at day 15.     

Supplementation of Protein Hydrolysates to a Low‐fishmeal Diet Improves Growth and Health Status of Juvenile Olive Flounder,Paralichthys olivaceus

An 11‐wk feeding trial was conducted to evaluate three different protein hydrolysates as feed ingredients in high‐plant‐protein diets for juvenile olive flounder. Five experimental diets were fed to juvenile olive flounder to examine the effect of three different protein hydrolysates on growth performance, innate immunity, and disease resistance against bacterial infection. A basal fishmeal (FM)‐based diet was regarded as a high‐FM diet (HFM) and a diet containing soy protein concentrate (SPC) as a substitute for 50% FM protein was considered as a low‐FM diet (LFM). Three other diets contained three different sources of protein hydrolysates, including shrimp, tilapia, and krill hydrolysates (designated as SH, TH, and KH), replacing 12% of FM protein. All diets were formulated to be isonitrogenous and isocaloric. Triplicate groups of fish (15.1 ± 0.1 g) were handfed one of the diets to apparent satiation twice daily for 11 wk and subsequently challenged against Edwardsiella tarda. Growth performance and feed utilization of fish fed hydrolysate‐supplemented diets were significantly improved compared to those of fish fed the LFM diet. Dietary inclusion of the protein hydrolysates significantly enhanced apparent digestibility of dry matter and protein of the diets. In the proximal intestine, histological alterations were observed in the fish fed the LFM diet. The fish fed the hydrolysate diets showed significantly longer mucosal fold and enterocytes and greater number of goblet cells compared to fish fed the LFM diet. Respiratory burst activity was significantly higher in fish fed the TH and KH diets than fish fed the LFM diet. Significantly higher immunoglobulin levels were found in fish fed SH and KH diets compared to those of fish fed the LFM diet. Dietary inclusion of the protein hydrolysates in SPC‐based diets exhibited the highest lysozyme activity. Significantly higher superoxide activity was observed in groups of fish fed the KH diet. Fish offered the protein hydrolysates were more resistant to bacterial infection caused by E. tarda. The results of this study suggest that the tested protein hydrolysates can be used as potential dietary supplements to improve growth performance and health status of juvenile olive flounder when they were fed a LFM diet.     

Influence of dietary soy protein and peptide products on bile acid status and distal intestinal morphology of rainbow trout Oncorhynchus mykiss

To investigate the influence of dietary soy protein size on the bile acid status and the distal intestinal morphology in rainbow trout Oncorhynchus mykiss, diets based on soybean meal (SBM), soy protein isolate (SPI) and 4 soy peptide products having different molecular sizes were fed to trout (initial BW, 19?g) for 10?weeks. A diet based on fish meal (Cont) and a diet including the smallest-peptide and low-saponin product (Hi-Nute AM) and supplemented with soya saponin (AMS) were also fed. In fish fed diets SBM and SPI, the gallbladder was atrophied, the proportion of biliary cholyltaurine decreased, and highly vacuolated epithelial cells of mucosal folds and proliferation of connective tissues in the submucosa of the distal intestine were observed. These parameters tended to improve in fish fed soy peptide diets and especially those of fish fed diet AM were similar to fish fed diet Cont. Although the gallbladder of fish fed diet AMS was smaller than fish fed the unsupplemented diet AM, no morphological abnormalities were observed in the distal intestine. These results suggest that soy proteins/peptides with relatively large sizes and with soya saponin affect the bile acid status and distal intestinal morphology of rainbow trout.     

Digestibility of diets containing different soybean meals in Atlantic cod (Gadus morhua); comparison of collection methods and mapping of digestibility in different sections of the gastrointestinal tract

The purpose of the experiment was to evaluate effects of partial replacement of fish meal with soybean meal on digestibility in Atlantic cod and effects of biotechnological processing of soybean meal. Other objectives were to find out if apparent digestibility in cod was affected by age, temperature and/or faecal sampling methods, and to map digestion and absorption patterns along the intestinal tract for different age classes and diets. A control diet with fish meal as the main protein source (FM), a diet with 24% of crude protein from conventional extracted soybean meal (SBM), and a diet with 24% of crude protein from a bioprocessed soybean meal (BP-SBM) were used. Yttrium oxide was added as an inert marker for digestibility determination. The diets were fed to duplicate groups of 534 g (1-year-old) and 1750 g (2-year-old) cod in seawater. Faeces were stripped from the distal-most section (distal chamber) of the intestine after 48 and 84 days of feeding. In addition, intestinal contents were removed by dissection after 84 days. The dissected intestine was divided into 5 sections and contents were analysed separately. Dietary soy did not alter the viscosity of the digesta. The replacement of fish meal protein with soybean protein reduced the apparent digestibility of crude protein, fat, energy and almost all amino acids, independent of type of soybean meal processing. Larger fish had higher digestibility of starch, ash and several amino acids than smaller fish. A temperature decrease from 9.1 °C at feeding day 48 to 6.8 °C at day 84 resulted in lower digestibility of starch, ash and several amino acids. Absorption of amino acids was quantitatively terminated in the distal part of the mid intestine when feeding the soy-containing diets, but continued into the distal chamber when feeding the FM diet. Absorption of fat was completed in the proximal part of the mid intestine when feeding the soy-containing diets, but continued into the middle part of the mid intestine when feeding the FM diet. Soy did not affect absorption pattern of starch along the intestinal tract. Faecal sampling by dissection resulted in higher apparent digestibility of macronutrients than stripping in the 2-year-old cod, and higher apparent digestibility of protein in the 1-year olds.     

Proteolytic enzyme activity of juvenile Asian sea bass, Lates calcarifer (Bloch), is increased with protein intake

The effect of high dietary protein intake on proteolytic enzyme activity of feeding juvenile Asian sea bass, Lates calcarifer (Bloch) was studied. Ninety fish [mean body weight ± standard error (SE) 304.62 ± 34.84 g] were randomly assigned to two dietary treatments, each with three replicates. In treatment 1, fish were fed by‐catch (Thunnus albacares) and in treatment 2, a formulated diet containing 50% protein. Proteolytic enzyme activity was determined in pyloric caecae and intestine at day 0, 7, 15, and 30. Initial proteolytic enzyme activity in sea bass ranged from 174 to 232 azocasein units (U^AC.) per mg of protein. After 7 days there was no significant difference in proteolytic enzyme activity of fish fed the two diets. However, a marked increase was observed in fish fed the formulated diet at day 15. After 30 days, the proteolytic enzyme activity in fish fed the formulated diet was threefold higher than that in fish fed the by‐catch diet. Fish fed the formulated diet had significantly higher total protein intake at day 7 than did fish fed by‐catch. Thereafter, a twofold weekly increase in the total protein intake was observed in both fish fed the by‐catch and formulated diets until day 30. These results suggest that a high dietary protein intake induces increased proteolytic enzyme activity in Asian sea bass.     

Replacement of Herring Fish Meal by Soybean Flour in Practical Diets for Red Tilapia,Oreochromis niloticus × O. mossambicus,Grown in Concrete Tanks

ABSTRACT

A feeding experiment was conducted for 100 days to evaluate the suitability of soybean flour (SBF) as a partial or complete substitute for the protein supplied by herring fish meal (HFM) in diets for growth of red tilapia, Oreochromis niloticus ×O. mossambicus, fingerlings (mean weight of 0.65 g/fish) grown outdoors in concrete tanks. Five isonitrogenous and isocaloric diets containing 35% crude protein and 3.36 kcal of digestible energy (DE)/g of diet were formulated in which SBF replaced 0%, 25%, 50%, 75% and 100% of the protein supplied by HFM. Results demonstrated that SBF has good potential as a substitute protein source for up to 75% of the protein supplied by HFM (diet 4) in red tilapia diets with no significant (P>0.05) adverse effects on growth, feed efficiency, body composition, and apparent digestibility of protein compared to the HFM-based control diet. The highest growth performance and best economic efficiency of fish weight gain were obtained with fish fed diet contained 50% of the protein from HFM and the other 50% from SBF. Fish fed this diet had the highest weight gain (11.95 g/fish), percent increase in weight (1838%) and growth rate (0.120 g/day) among fish fed all the other test diets. The lowest feed efficiency and growth performances were shown in the fish fed diet containing SBF as a complete substitute for protein supplied by HFM. Fish fed this diet had the lowest weight gain (4.70 g/fish), percent increase in weight (723%) and growth rate (0.047 g/day) among fish fed all the other test diets. Survival of fish was not statistically different (P>0.05) among all treatments. The apparent protein digestibility values showed wide variation between diets, ranging from 70.13% to 82.12% and the values were remarkably high in fish fed SBF-based diets. At the conclusion of the study, substituting HFM-protein with SBF-protein in diets for red tilapia did not affect the final fish protein, ash and moisture contents, but lipid content was significantly higher (P <0.05) in fish fed diets in which SBF substituted for 50% or more of the protein supplied by HFM. Hematological characteristics of red tilapia were examined at the end of the study and the results showed that all the blood parameter values were within normal values for fish. Economic analysis of diets suggested the possibility of using SBF as an alternative source of protein in red tilapia diets.     

Nutritional regulation of intestine morphology in larval cyprinid fish, silver bream (Vimba vimba)

The present study includes the evaluation of morphological changes in the digestive tract of larval, stomachless fish silver bream ( Vimba vimba ) fed with various diets – live Artemia nauplii, commercial feed Aglo Norse (NOR) and semi-purified formulated diets: casein–gelatin (CG), dipeptide-protein (50P), dipeptide (100P), no-arginine dipeptide diet (100Pw/oArg) and a free amino acid (FAA) mixture diet. The supranuclear area of enterocytes in the posterior intestine contained enlarged absorptive vacuoles in the FAA, 100P and 100Pw/oArg groups, compared with the remaining groups. Hepatocytes' cytoplasm in fish fed with FAA, 100P and 100Pw/oArg contained mainly glycogen, and no lipid vacuoles were found. Fish fed with 100Pw/oArg showed the lowest hepatocyte surface areas while in those fed with 50P, the largest nuclei diameters were observed. Fish fed with Artemia , NOR and CG diets showed significantly ( P <0.05) higher number of proliferating cells compared with the remaining groups. Chromogranin A staining showed endocrine-immunoreactive cells (CgA-IR) in the taste buds in the oral cavity and in the enterocytes' supranuclear areas of the anterior and posterior intestine. We conclude that the growth rate and histological examination of the digestive tract in the 50P group of silver bream showed no nutritional deficiency.     

Supplemental effect of bile salts to soybean meal-based diet on growth and feed utilization of rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>

A feeding experiment was conducted to evaluate the supplemental effect of bile salts to a defatted soybean meal-based non-fish meal diet for rainbow trout Oncorhynchus mykiss. A fish meal-based diet (FM) and two non-fish meal diets with and without bovine bile salts (SC+B and SC, respectively) were fed to fish (13 g initial weight) for 10 weeks. Fish fed diet SC showed inferior growth and feed efficiency, while bile salt supplementation improved the parameters to the same levels as fish fed diet FM. Crude fat and starch digestibility of diet SC-fed fish decreased after the 10-week feeding trial compared to the data obtained with fish that had no experience of the diet. Total biliary bile salt content and intestinal maltase activity of fish fed diet SC were the lowest among treatments, while these parameters were improved by bile salt supplementation. Morphological changes occurred in the distal intestine and liver of the diet SC group, although the histological features of fish fed diet SC+B were similar to those of fish fed diet FM. These results suggest that bile salt supplementation to a soybean meal-based diet improves the nutrient utilization by normalizing digestive processes in rainbow trout.     

Dietary organic acids blend alone or in combination with an essential oil on the survival,growth, gut/liver structure and de hemato‐immunological in Nile tilapia Oreochromis niloticus

This study evaluated the effects of dietary supplementation of organic acids blend (OAB) alone or in combination with essential oil, Lippia origanoides (OAE) for Nile tilapia fed supplemented diets for 30 days. Fish (1.1 ± 0.04 g) were fed control (Control), or OAB 0.5% or OAB 0.5% + essential oil 0.125% (OAE) respectively. At the end of the experiment, samples were collected for de hemato‐immunological, histological analysis of the intestine and liver, as well as microbiology of the intestine. The pH of the diets supplemented with OAB and OAE reduced 0.92 and 0.19 respectively. The growth and FCR were unaffected by the treatments, but survival was significantly higher in the OAB treatment. Fish fed the OAB diet showed reduced concentration of total heterotrophic bacteria and Pseudomonas sp. in the intestine. Increased glucose in fish fed OAB and high number of circulating monocytes in fish fed OAE diet were observed. The anterior intestine of fish fed OAE diet showed larger number of goblet cells and increased villi height. The diet supplemented with OAB, mainly, improved the intestinal health and survival of tilapia juveniles and can be used in juvenile production.     

Nutritional and environmental regulation of the synthesis of highly unsaturated fatty acids and of fatty-acid oxidation in Atlantic salmon (Salmo salar L.) enterocytes and hepatocytes

The objective of this work was to determine whether highly unsaturated fatty acid (HUFA) synthesis and fatty-acid oxidation in Atlantic salmon (Salmo salar L.) intestine was under environmental and/or seasonal regulation. Triplicate groups of salmon were grown through a full two-year cycle on two diets containing either fish oil (FO) or a diet with 75% of the FO replaced by a vegetable oil (VO) blend containing rapeseed, palm, and linseed oils. At key points in the life cycle fatty acyl desaturation/elongation (HUFA synthesis) and oxidation activity were determined in enterocytes and hepatocytes using [1−¹⁴C]18:3n−3 as substrate. As observed previously, HUFA synthesis in hepatocytes reached a peak at seawater transfer and declined thereafter, with activity consistently greater in fish fed the VO diet. In fish fed FO, HUFA synthesis in enterocytes in the freshwater stage was at a level similar to that in hepatocytes. HUFA synthesis in enterocytes increased rapidly after seawater transfer, however, and remained high for some months after transfer before decreasing to levels that were again similar to those observed in hepatocytes. Enterocyte synthesis of HUFA was usually higher in fish fed the VO diet than in those fed the FO diet. Oxidation of [1−¹⁴C]18:3n−3 in hepatocytes from fish fed FO tended to decrease during the freshwater phase but then increased steeply, peaking just after transfer before decreasing during the remaining seawater phase. At the peak in oxidation activity around seawater transfer, activity was significantly lower in fish fed VO than in fish fed FO. In enterocytes, oxidation of [1−¹⁴C]18:3 in fish fed FO reached a peak in activity just before seawater transfer. In fish fed VO, except for high activity at nine months the pattern was similar to that obtained in enterocytes from fish fed FO, with high activity around seawater transfer and declining activity in seawater. In conclusion, fatty acid metabolism in intestinal cells seemed to be under dual nutritional and environmental or seasonal regulation. Temporal patterns of oxidation of fatty acids were usually similar in the two cell types, but HUFA synthesis in enterocytes peaked over the summer seawater phase rather than at transfer, as with hepatocytes, suggesting the possibility of different regulatory cues.     

Effect of an alcohol extract from a defatted soybean meal supplemented with a casein-based semi-purified diet on the biliary bile status and intestinal conditions in rainbow trout Oncorhynchus mykiss (Walbaum)

A feeding experiment was conducted to examine the effect of a supplemental ethanol extract from a defatted soybean meal on the biliary bile status and intestinal conditions of rainbow trout Oncorhynchus mykiss . A semi-purified control diet based on casein (Cont) and three diets supplemented with the extract (ES), bovine bile salts (BS) and their combination (ESBS) were fed to trout (10 g) for 6 weeks. The growth, feed efficiency ratio, fat digestibility and gallbladder- and hepato-somatic indices of fish fed diet ES decreased. Compared with this group, these parameters were improved in fish fed diet ESBS. The total biliary bile salt content was the lowest in fish fed diet ES and this group had a high proportion of chenodeoxycholyltaurine. The inclusion of the bile salts to diet ES (diet ESBS) increased the total biliary bile salt content. A similar trend was observed in the bile salt concentration of intestinal digesta. Although morphological changes occurred in epithelial cells of the distal intestine of fish fed diet ES, the histological features of fish fed diet ESBS were similar to those of fish fed diet Cont. These results indicate that alcohol-soluble substances of soybean meal cause physiological changes in the biliary bile and intestine of rainbow trout.     

Effects of exogenous non-starch polysaccharide-degrading enzymes in diets containing <Emphasis Type="Italic">Gracilaria lemaneiformis</Emphasis> on white-spotted snapper <Emphasis Type="Italic">Lutjanus stellatus</Emphasis> Akazaki

A feeding experiment was conducted to investigate the effects of exogenous non-starch polysaccharide (NSP)-degrading enzymes in diets containing Gracilaria lemaneiformis (GL) on growth performance and digestive enzyme activities of white-spotted snapper Lutjanus stellatus Akazaki (initial mass 8.0 ± 0.1 g). A basal diet (D0) containing a mixed protein source (fish meal, soybean meal and GL meal) was used as the control. Two diets supplemented with 0.5 g (D1) and 1 g (D2) exogenous NSP-degrading enzymes per kilogram of diet were formulated. Each diet was assigned to triplicate groups of fish in a total of nine floating sea cages (270 fish, 30 fish per cage). After a 60-day feeding trail, significantly higher weight gain, specific growth ratio and feed efficiency ratio were observed in fish fed D2 diet compared to those of control (P < 0.05). Body lipid, moisture and ash contents were not significantly affected by NSP-degrading enzyme supplementation, but significantly higher protein content was noticed in fish fed D2 diet compared to that of control (P < 0.05). The amylase activity in the stomach and intestine was significantly higher in fish fed D2 diet (P < 0.05), but no significant differences were observed in pepsin and lipase activities in the stomach or trypsin and lipase activities in the intestine between all treatments. The results suggested that addition of 1 g kg^?1 NSP-degrading enzymes in diet could efficiently improve seaweed feed utilization and growth performance of white-spotted snapper fish.