Influence of certain soybean antinutritional factors supplemented to a casein-based semipurified diet on intestinal and liver morphology in fingerling rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>

To investigate the cause of morphological changes occurring in the liver and intestine of rainbow trout Oncorhynchus mykiss fed defatted soybean meal (SBM)-based non-fish meal diets, morphological observations were conducted on fish fed casein-based semipurified diets supplemented with soybean antinutritional factors (soya saponin, soya isoflavone, soya lectin, oligosaccharide, Ca-phytate and their mixture). Hepatocytes and the epithelial cells in the hepatic ducts were not atrophied in any of the treatments. Lack of microvilli and pinocytotic vacuoles, and fatty degeneration of the epithelial cells were observed in the distal intestine of fish fed diets containing soya saponin. The proliferation of connective tissue in the mucosal folds and submucosa was shown in the distal intestine of fish fed the diet containing all substances including lectin. These results suggest that both saponin and lectin are the responsible factors in SBM for the occurrence of morphological changes of the distal intestine in rainbow trout fed SBM-based diets.     

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.     

Supplemental effect of cholyltaurine and soybean lecithin to a soybean meal-based fish meal-free diet on hepatic and intestinal morphology of rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>

The supplemental effects of cholyltaurine and soybean lecithin to a defatted soybean meal (SBM)-based fish meal-free diet on the hepatic and intestinal morphology of rainbow trout Oncorhynchus mykiss were investigated. A fish meal-based diet (FM), three fish meal-free diets supplemented either with soybean lecithin (SL), bovine gall powder (BG) or cholyltaurine (C-tau) and an unsupplemented fish meal-free diet (NFM), were given to fish (−11 g) for 10 weeks. The growth was the lowest in fish fed diet NFM, intermediate in fish fed diet SL and the highest in fish fed diet FM, BG and C-tau. Hepatocytes of fish fed diet NFM were atrophied, and the distal intestine of these fish showed abnormal features: disintegrated microvilli and fatty degeneration in epithelial cells and increased amount of connective tissue in the submucosa. Hepatic and intestinal histological features in fish fed diets SL, BG and C-tau were similar to those in fish fed diet FM. These results indicate that soybean lecithin, bovine bile salts and cholyltaurine have similar effects on normalizing the hepatic and intestinal morphologies of rainbow trout fed the SBM-based diet, although growth promotion effect was limited in the soybean lecithin.     

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.     

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.     

The potential of soya oil industry products as oil alternatives in rainbow trout (Oncorhynchus mykiss) diet

This study investigated the effects of different soya oil products on growth, nutrient digestibility, and fatty acid composition of muscle in rainbow trout. The products’ ingredients were soap stock, fat powder, crude oil, and refined soya oil as a control. Four experimental diets were formulated by addition of 12 % of each of the four ingredients to a basal diet. Replacement of refined soya oil by the soya oil products did not influence growth performance until 8 weeks (P > 0.05). This replacement, however, reduced fat digestibility in rainbow trout (83.7 vs. 73.3–79.8 %; P < 0.05). Dietary inclusions of fat powder and crude oil led to larger values of protein digestibility than those of refined soya oil and soap stock (P < 0.05). The compositions of saturated and monounsaturated fatty acids of the muscle were similar, but linoleic acid concentration (LA, 18: 2n-6) increased in fish muscle fed refined soya oil compared to the other diets (37 vs. 30–31 %; P < 0.05). Arachidonic acid (ArA, 20: 4n-6) concentration was higher (P < 0.05) in fish fed both fat powder and soap stock than those fed the other diets. In conclusion, refined soya oil can be replaced by soya oil products in rainbow trout diet with no negative impacts on the growth. However, fish fed on diet containing refined soya oil had higher concentration of LA and lower density of ArA. It appears that rainbow trout is capable of digesting soya oil products though the digestibility rate reduced slightly with an increase in saturated fatty acid content.     

Partial substitution of fish meal and full-fat soya bean meal with wheat gluten and influence of lysine supplementation in diets for rainbow trout, Oncorhynchus mykiss (Walbaum)

A 65-day study was undertaken to evaluate the utilization of lysine-supplemented wheat gluten meal as a protein source for rainbow trout, Oncorhynchus mykiss (Walbaum). The performance of the trout fed wheat gluten was compared to that of trout where protein was principally supplied using fish meal and full-fat soyabean meal. Six isonitrogenous diets (approximately 45% crude protein) were formulated. Thus, the reference diet (FS) was based on fish meal and full-fat soya bean meal while a further five diets were formulated with a mixture of wheat gluten and wheat middlings used to isonitrogenously replace approximately 75% and 57% of the full-fat soya and fish meal respectively. Crystalline l -lysine representing 0.00%, 0.29%, 0.58%, 0.87% and 1.16% of the complete diet was then added to the wheat-gluten-based diets. Optimal performance in terms of weight gain and apparent net protein utilization was achieved by the fish fed a wheat-gluten-based diet supplemented with lysine (0.58%) yielding a digestible lysine level of 1.9% of the complete feed. Within the range of supplements provided, lysine digestibility was high. However, at the highest levels of supplemental lysine the relationship between uptake and supplement level was not linear. Additionally, arginine digestibility was not affected by the level of lysine supplementation. However, amongst the wheat-gluten-based diets, optimal performance was associated with a lysine: arginine ratio of 1.1: 1. Despite a lysine: arginine ratio of approximately 1.1: 1, the overall performance of the fish fed the fish-meal-soya-based reference diet was poorer than expected. The results are discussed with respect to optimal patterns of gross and digestible amino acids, lysine-arginine antagonism and the possible relationship between antinutritional factors and the poor performance of the fish fed the fish-meal-soya-based reference diet.     

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.     

Optimization of the supplemental essential amino acids to a fish meal-free diet based on fermented soybean meal for rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>

To minimize the supplemental essential amino acids (EAAs) to a fish meal-free diet for rainbow trout Oncorhynchus mykiss, four types of fish meal-free diets and a control fish meal-based diet were fed to triplicate groups of trout (initial BW, 16 g) for 10 weeks. Two fish meal-free diets based on a fermented and an unfermented soybean meal were unsupplemented with EAAs (diet FSBM and SBM), and two fish meal-free diets based on the fermented soybean meal were supplemented with a combination of lysine and methionine (diet F + ML) and all EAAs (diet F + All), the EAA contents of which were lower than those of the control diet (diet FM). Although physiological conditions such as the biliary bile acid status and morphological features of fish fed diet FSBM were improved and similar to those of fish fed diet FM, the growth performance was not significantly different (P > 0.05) from fish fed diet SBM. The growth performances and whole body protein contents of fish fed F + ML and F + All diets were similarly improved compared to fish fed diet FSBM. These findings indicate that supplementation of lysine and methionine to a fermented soybean meal-based fish meal-free diet is enough to maximize the amino acid utilization of the diet.     

Urea and trimethylamine oxide in diets for seawater farmed rainbow trout: effect on fat belching,skin vesicle,winter ulcer and quality grading

Three experiments were conducted in order to evaluate the effects of urea and trimethylamine oxide (TMAO) supplementation in diets for seawater‐farmed rainbow trout Oncorhynchus mykiss. In all experiments, commercial extruded feed was used as basal control diet, whereas experimental diets were the basal diet supplemented with either 10 g kg^–1 TMAO, 10 g kg^–1 urea or 10 g kg^–1 TMAO and 10 g kg^–1 urea. The experiments were conducted both in research units and in a commercial fish farm. Quality was evaluated in three different commercial slaughterhouses, sorting the rainbow trout into superior, ordinary or processing grade. Significantly more TMAO was observed in muscle of rainbow trout given dietary supplementation of TMAO. However, the levels were low compared with levels in marine fish in general. Trimethylamine (TMA) was not found. No increase in muscle urea content was observed in trout fed urea in the diet. Significantly reduced fat belching, seen as reduced number of fat droplets surfacing in the net pen, was observed in groups given TMAO‐supplemented feeds. At least twice as many rainbow trout with skin vesicles were observed in the control group as in the group fed urea‐supplemented diet. In addition, skin vesicles developed into open sores in the winter only in rainbow trout fed control diet. In a large‐scale trial, quality grading of almost 200 000 market‐sized rainbow trout showed significantly more (88 vs. 83%) trout of superior grade in the group fed dietary urea compared with fish fed control diet. The main reason for downgrading from superior to ordinary and processing grade was skin lesions, supporting the observations made in the experimental units.     

Effects of biotechnologically processed soybean meals in a nonfishmeal diet on growth performance, bile acid status, and morphological condition of the distal intestine and liver of rainbow trout Oncorhynchus mykiss

This study evaluated four commercially available biotechnologically processed soybean meals (SBMs) that were included as the primary protein sources in a nonfishmeal diet for juvenile rainbow trout Oncorhynchus mykiss. The processed SBMs were Afcep SBM fermented with mixed bacteria predominantly Bacillus spp., DaBomb SBM fermented with Lactobacillus acidophilus, PepSoyGen SBM fermented with Aspergillus oryzae and Bacillus subtilis, and HP300 SBM treated enzymatically. Fishmeal (FM) and common heat-treated and hulled SBM were used in the reference diets. Sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (PAGE) analysis revealed that the protein components of Afcep SBM appeared to have relatively small molecular sizes compared with the other SBM products. After a 10-week feeding trial, growth of fish fed the common SBM diet was depressed, and abnormal liver and distal intestinal morphologies and bile acid characteristics were observed. The Afcep SBM diet showed approximated growth performance and comparable physiological conditions relative to the FM diet, while only limited improvements were observed in fish fed the other processed SBMs. These findings suggest that Afcep SBM, with its smaller molecular mass proteins, is the most promising processed SBM in nonfishmeal diets for rainbow trout.     

Heat Shock Protein Regulation in Rainbow Trout,Oncorhynchus mykiss,is Altered by Dietary Soybean Meal Inclusion and Anti‐Phopholipase A2 Antibody

Heat shock proteins (Hsps) can promote integrity of damaged intestinal epithelial tissues. The aim of this study was to determine the effects of a commercially available anti‐phospholipase A₂ antibody on growth, feed efficiency, Hsp expression, and intestinal health of rainbow trout fed diets containing high levels of soybean meal (SBM). Six practical‐type diets (45% protein; 15% fat) were formulated to contain 0, 17.5, or 35% SBM with and without antibody. Each diet was fed to three replicate tanks of fish (20 fish/tank; initial weight 21 g) for 9 wk. RNA was isolated from liver and intestinal tissues (n = 3/tank) to detect alterations in Hsp 27, Hsp 70, and Hsp 90 expression. Fish fed a diet containing 35% SBM had decreased growth and intestinal damage. Hsp 27 and Hsp 90 mRNA was elevated in fish fed 35% SBM. Fish fed 35% SBM with antibody had lower Hsp 90 mRNA expression than fish without antibody. These data indicate that feeding rainbow trout high levels of SBM alters the expression of some Hsps and anti‐phospholipase A₂ antibody supplementation does not normalize growth or prevent distal enteritis in fish fed 35% SBM.     

Effects of Microbial Phytase Supplementation in Corn Distiller's Dried Grain with Solubles on Nutrient Digestibility and Growth Performance of Rainbow Trout,Oncorhynchus mykiss

Abstract

Two experiments were conducted to evaluate the effects of microbial phytase in corn distiller's dried grain with solubles (DDGS) on apparent digestibility coefficients (ADCs) and growth performance of rainbow trout, Oncorhynchus mykiss. In experiment 1, DDGS was supplemented with phytase at 0,300,600,900, and 1200 FTU/kg diet. A total of 180 fish (129.1±9.3 g) were stocked into six 140-L tanks with 30 fish/tank. Fish were assigned randomly to a reference diet and each of the 5 diets containing DDGS. Yttrium oxide was used as an inert marker. Results showed that ADCs in DDGS supplemented with different dosages of phytase were: dry matter, 49.1-58.6%; crude fat, 78.9-88.9%; crude protein, 80.0-91.9%; gross energy, 50.5-66.6%; minerals, -7.3-99.7%; and amino acids: 73.9 to 96.8%. In experiment 2, abasal diet containing 15% DDGS supplemented with lysine and methionine was used to determine if trace mineral supplemental levels in rainbow trout diets could be reduced if microbial phytase was supplemented. Six diets were made with trace mineral premix supplementation at 0.1, 0.08, 0.06, 0.04, 0.02, and 0%. Phytase was not supplemented in the basal diet, but supplemented at 500 FTU/kg diet in all other diets. Ten-week results showed that there were no significant differences in fish weight gain, feed conversion ratio, and survival (P < 0.05). There were no significant differences in fish body composition and apparent nutrient retention among fish fed all diets, except that fish fed a diet without trace mineral supplementation had the lowest zinc level and the highest manganese retention. Results indicated that phytase was effective in releasing most of minerals, and that trace mineral supplementation level could be reduced when phytase was used in rainbow trout diets.     

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.     

Influence of multiple amino acid supplementation on the performance of rainbow trout, Oncorhynchus mykiss (Walbaum), fed soya based diets

Using rainbow trout, Oncorhynchus mykiss (Walbaum), of approximately 50 g, a 63 day feeding trial was undertaken to evaluate the efficacy of individual and multiple amino acid supplements in diets where soyabean meal was used as the principle protein source. Iso-nitrogenous diets (45% crude protein) were formulated where the control diet (F) contained fishmeal as the reference protein and a solvent extracted soyabean meal (S) replaced approximately 66% of this protein source. The soyabean containing diets were then supplemented with crystalline amino acids thus; methionine only, dual supplemented with two methionine and lysine levels and finally, a supplement comprising methionine, lysine, tryptophan, threonine, arginine and histidine. The results showed that soyabean meal (SBM) was inferior to the reference protein when SBM was used to replace 66% of the fishmeal and that no significant restoration in growth, feed efficiency and apparent net protein utilization was obtained by either methionine only or dual methionine and lysine supplementation. However, by comparison with the fish fed the unsupplemented, single and dual supplemented diets, multiple amino acid incorporation was associated with significantly improved percentage weight gain, specific growth rate and marginal improvements in apparent net protein utilization. However, performance was not equal to that of the fish fed the fishmeal based control diet. The results are discussed with respect to the level of each of the essential amino acids (EAA) as a proportion of the total EAAs (A/E index) of test diets by reference to the whole body tissue amino acid profile of rainbow trout.     

Effects of diets containing a bacterial protein meal on growth and feed utilisation in rainbow trout (Oncorhynchus mykiss)

Triplicate groups of rainbow trout with initial weight 361 g were fed either a fish meal based control diet or diets containing 9, 18 or 27% bacterial protein meal (BPM) or 9% of an autolysate (AU) of the BPM. No significant treatment effects were found on specific growth rates (SGR), feed intake, feed efficiency ratio (FER), or retention of nitrogen, amino acids or energy. The apparent digestibility coefficients (ADC) of nitrogen, energy and most indispensable amino acids decreased when BPM was included in the diet. The ADC of lipid, sum of amino acids, arginine, lysine, threonine and most of the dispensable amino acids were reduced at 27% BPM inclusion compared to the control, 9% and 18% BPM diets. None of the ADC estimated was different in the 9% AU diet compared to the 9% BPM diet. The loss of nitrogen and energy in faeces per kg gain increased as the dietary BPM or AU levels increased, and the energy used for activity and maintenance was higher in fish fed the 27% BPM diet than in fish fed the other diets (P < 0.05). There were no significant differences in the urea concentrations in plasma, liver and muscle, whereas the uric acid level in plasma was elevated in trout fed the 27% BPM diet. Histological evaluation of tissue from the stomach, pyloric caeca, mid-intestine and distal intestine did not reveal any diet-related morphological changes.In conclusion, no significant differences in growth and feed efficiency were found in the rainbow trout fed diets containing up to 27% BPM, and the AU did not increase fish performance compared to the BPM. Based on the data from this study, at levels up to 27% dietary inclusion, BPM is a good replacement for fish meal in diets for rainbow trout.     

Granulomatous enteritis in rainbow trout (Oncorhynchus mykiss) associated with soya bean meal regardless of water dissolved oxygen level

This study investigated morphological changes associated with soya bean meal‐induced enteritis (SBMIE) in distal intestine (DI) of rainbow trout (Oncorhynchus mykiss) fed a soya bean meal (SBM)‐based diet and exposed to normoxia or hypoxia created by optimal and low water flow rates, respectively. A 28‐day adaption period was followed by a 42‐day challenge period where 600 fish were subjected to dietary challenge and/or hypoxia. Twelve tanks each containing 50 juvenile trout were assigned randomly in triplicate to each treatment. Histopathological and immunohistochemical evaluation revealed pathological features that have not previously been described in association with SBMIE. Vacuolar degeneration of epithelial cells mainly at the base of mucosal folds, epithelial cysts, epithelial dysplasia, necrosis, shedding of necrotic cells, and granulomatous inflammation including infiltration of enlarged, sometimes finely vacuolated or “foamy” macrophages, multinucleated giant cells and increased proliferation of fibroblasts were observed. Acid‐fast bacteria were not detected in enlarged macrophages; however, these cells contained AB‐PAS‐ and sometimes cytokeratin‐positive material, which was interpreted to be of epithelial/goblet cell origin. Hypoxia did not affect the morphological changes in DI. These results suggest that SBM was associated with a granulomatous form of enteritis in DI of rainbow trout regardless of water oxygen level.     

Tributyrin‐supplemented high‐soya bean meal diets of juvenile black sea bream,Acanthopagrus schlegelii: Study on growth performance and intestinal morphology and structure

An 8‐week growth trial was conducted to evaluate the effects of different levels of tributyrin supplementation in a high‐soya bean meal diet on juvenile black sea bream (11.30 ± 0.16 g). The positive control (PC) diet contained 45% fishmeal and 20% soya bean meal, while the negative control (NC) contained 12% fishmeal and 45% soya bean meal. Graded levels of tributyrin were added to the NC diet at 0.05% (TB 0.05), 0.1% (TB 0.1), 0.2% (TB 0.2), 0.4% (TB 0.4) and 0.8% (TB 0.8). Ultimately, the fish fed the PC diet had a higher weight gain and specific growth rate than the fish fed other diets. The fish fed the NC diet had the lowest growth, and TB 0.05–TB 0.2 diets increased growth performance while TB 0.4–TB 0.8 diets caused reduction in growth. Dietary tributyrin supplementation improved protease activity and enhanced antioxidant capacity. Compared with the fish fed the NC diet, the fish fed the tributyrin‐supplemented diets had improved gut morphology and structure, and the results were similar to those of the fish fed the PC diet. Furthermore, the analysis of the dose response with second‐order polynomial regression indicated that the optimum tributyrin supplementation for juvenile black sea bream is 2.24 g/kg in the 45% soya bean meal diet.     

Assessment of the effects of vegetative and lyophilized Pediococcus acidilactici on growth,feed utilization,intestinal colonization and health parameters of rainbow trout (Oncorhynchus mykiss Walbaum)

A study was conducted to assess the probiotic effect of different dietary forms of Pediococcus acidilactici on rainbow trout (Oncorhynchus mykiss Walbaum). Growth performance, feed utilization, intestinal colonization and basic health status were investigated after a 10 week feeding trial. Fish were fed either vegetative (Veg) or lyophilized (Lyo) cells incorporated into a basal diet at either 10⁷ (Lo) or 10⁸ (Hi) CFU g^?1. P. acidilactici temporarily colonized the digestive tract (as both epithelium associated and transient populations) in all probiotic groups during supplemented feeding. Scanning electron microscopy confirmed the presence of localized colonization of P. acidilactici‐like cells between intestinal folds of the probiotic fed fish. Compared to the control group, no significant improvements in growth performance, feed utilization or carcass composition were observed in the probiotic fed fish (P > 0.05). However, a significant reduction of condition factor (K) was evident in fish fed the lyophilized diets. Increased leucocyte levels were observed in fish fed the low level vegetative P. acidilactici supplemented diet yet leucocyte types were not affected. The study demonstrates some potential for the application of P. acidilactici with rainbow trout but further research is required to optimize applications.     

Effect of Oyster Mushroom,Pleurotus ostreatus,Extract on Hemato‐Immunological Parameters of Rainbow Trout,Oncorhynchus mykiss

The current study investigated the effects of oyster mushroom Pleurotus ostreatus, extract on immunological and hematological parameters of rainbow trout, Oncorhynchus mykiss. The fish were fed diets containing 0 (control), 1, and 2% supplementation of the oyster mushroom extract for 6 wk. Blood samples were collected weekly for the first 6 weeks. After 6 wk of feeding, the fish were challenged with Lactococcus garvieae and mortality was recorded. The results of this study showed that feeding rainbow trout an oyster mushroom extract–supplemented diet stimulated phagocytic activity of phagocytic cells, lysozyme activity, and myeloperoxidase activity in serum, but it did not significantly affect the total serum immunoglobulin level. At the same time, a significant increase was found in the number of neutrophils, monocytes, and total white blood cells. Fish fed the diet supplemented with oyster mushroom extract showed reduced mortalities following L. garvieae infection compared with controls. These results show that supplementation of fish diets with oyster mushroom extract at 1 and 2% concentrations significantly imrpoves hematological parameters and modulates the immune response against L. garvieae in rainbow trout.