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.     

Synergistic effect of sodium selenite and Pediococcus acidilactici on growth,intestinal bacterial counts,selenium bioavailability,hepatic enzymes and non‐specific immune response in rainbow trout (Oncorhynchus mykiss)

Lactic acid bacteria (LAB) have a crucial role in inorganic selenium metabolism as well as their known desirable effects on fish. In this study, the synergistic effects of dietary sodium selenite and Pediococcus acidilactici on growth performance, intestinal bacterial counts, selenium bioavailability, hepatic antioxidant enzyme thioredoxin reductase activity and hepatic glycolytic enzyme activity that is hexokinase, phosphofructokinase and pyruvate kinase, and non‐specific immune response such as serum lysozyme and complements C₃, C₄ and ACH₅₀ activity in rainbow trout (Oncorhynchus mykiss) were investigated. Thus, a 3 × 3 factorial design experiment was conducted with nine purified diets including three levels of sodium selenite (0, 1 and 2 mg/kg) and three levels of P. acidilactici (0, 7 and 9 log CFU/g). After 8 weeks of feeding, weight gain and specific growth rate were increased by increasing dietary sodium selenite and P. acidilactici levels compared to control (p < .05), whereas feed conversion ratio and condition factor was decreased by increasing dietary sodium selenite and P. acidilactici amounts in comparison with control (p < .05). Survival rate was not significantly affected among the experimental treatments (p > .05). Total cultivable bacterial populations after 4 and 8 weeks of the feeding trial were not significantly different among the dietary treatments, while LAB levels were higher in P. acidilactici‐fed groups than in control and selenium‐fed groups (p < .05). Selenocysteine, methylselenocysteine and selenomethionine levels in the intestine of rainbow trout were increased by increasing the sodium selenite and P. acidilactici levels (p < .05), and selenocysteine was found the most selenium species in the trout intestine. The quantity of total selenium in the whole body, intestine, blood, liver and muscle of rainbow trout were increased by increasing the amounts of sodium selenite and P. acidilactici compared to control (p < .05). Hepatic thioredoxin reductase and hexokinase activity were increased by increasing dietary selenium and P. acidilactici levels in comparison to control (p < .05), whereas phosphofructokinase and pyruvate kinase activity in the liver of rainbow trout were not significantly different between the dietary treatments. Serum lysozyme, complements C₃, C₄ and ACH₅₀ activity were enhanced by increasing dietary selenium and P. acidilactici levels compared to control (p < .05). The most synergistic effects of dietary supplements on growth and metabolism of rainbow trout were obtained at 2 mg/kg sodium selenite and 7 log CFU/g P. acidilactici. The findings revealed the synergistic effect of dietary selenium and P. acidilactici on growth and metabolism in rainbow trout (O. mykiss).     

Aqualase®, a yeast‐based in‐feed probiotic,modulates intestinal microbiota,immunity and growth of rainbow trout Oncorhynchus mykiss

Yeast probiotics have great promise, yet they received little attention in fish. This study investigated the influence of Aqualase^®, a yeast‐based commercial probiotic composed of Saccharomyces cerevisiae and Saccharomyces elipsoedas, on health and performance of rainbow trout (Oncorhynchus mykiss). Probiotics were incorporated in the diets at three different inclusion levels (1%, 1.5% and 2%) and administered to the fish for a period of 8 weeks. After the feeding trial, intestinal total viable aerobic bacterial count was significantly higher in fish group that received 2% in‐feed probiotics. In addition, a significant increase in at least 11% in intestinal lactic acid bacteria population was observed in all probiotic‐fed groups. Total protein level and lysozyme activity in skin mucus were significantly elevated following probiotic feeding. Inhibitory potential of skin mucus against fish pathogens was significantly enhanced by at least 50% in probiotic‐fed groups. Humoral and cellular immune parameters were influenced by probiotic feeding and the effects were dependent on inclusion level. Digestive physiology was affected by in‐feed probiotics through improvement of intestinal enzyme activities. All growth performance parameters were significantly improved following probiotic administration specifically at inclusion rate 1.5% and above. Taken together, the results revealed that Aqualase^® is a promising yeast‐based probiotic for rainbow trout with the capability of modulating the intestinal microbiota, immunity and growth.     

Evaluation of dietary natural mineral materials as an antibiotic replacer on growth performance,non‐specific immune responses and disease resistance in rainbow trout,Oncorhynchus mykiss

We evaluated the effects of some dietary natural mineral materials as an antibiotic replacer based on growth performance, non‐specific immune responses and disease resistance in juvenile and subadult rainbow trout, Oncorhynchus mykiss. First experiment, juvenile rainbow trout averaging 2.7 ± 0.02 g (mean ± SD) were fed one of the six experimental diets; a basal commercial diet as a control (CON), CON with oxytetracycline (OTC), with yellow loess (YL), with Macsumsuk^® (MS), with Song‐Gang^® stone (SG) and with barley stone (BS) at 0.4% of each diet. At the end of 8‐week feeding trial, weight gain (WG), specific growth rate (SGR), feed efficiency (FE) and protein efficiency ratio (PER) of fish fed YL diet were significantly higher than those of fish fed CON diet. Non‐specific immune responses such as superoxide dismutase (SOD), myeloperoxidase (MPO), lysozyme (LYS) activity and oxidative radical production of fish fed YL diet were higher than those of fish fed CON diet. At the end of 15 days of challenge test with Aeromonas salmonicida, average cumulative survival rate of fish fed YL diet was significantly higher than that of fish fed BS and CON diets. However, there were no significant differences among fish fed YL, SG and OTC diets. Second experiment, subadult rainbow trout averaging 261.5 ± 3.5 g (mean ± SD) were fed one of the four experimental diets for 22 weeks: CON, and CON with OTC, YL or SG at 0.4% of each diet. At the end of feeding, growth performance of fish fed SG and YL diets was significantly higher than that of fish fed CON diet. Non‐specific immune responses in terms of SOD, MPO, LYS and NBT of fish fed SG and YL diets were significantly higher than those of fish fed CON diet. However, there were no significant differences among the fish fed YL, SG and OTC diets. The results indicate that dietary yellow loess or Song‐gang^® stone at 0.4% of diet could replace oxytetracycline in juvenile and subadult rainbow trout.     

Dietary supplementation of probiotics and influence on feed efficiency,growth parameters and reproductive performance in female rainbow trout (Oncorhynchus mykiss) broodstock

The aim of this study was to determine the effects of dietary probiotics on reproductive performance, growth, haematological and biochemical parameters of female rainbow trout broodstock. A total of 60 broodstocks with an average initial weight of 2,267.4 ± 54.9 g were divided into four groups and three replicates in raceway ponds. Fish were fed with diets containing 0 (control), 1 × 10⁹ (P1), 2 × 10⁹ (P2) and 4 × 10⁹ (P3) CFU probiotic per kg diet twice a day for 8 weeks before spawning season. Results revealed that higher levels of dietary probiotics (P3) enhanced protein efficiency ratio and decreased feed conversion ratio (p < .05). There were no significant differences in haematological and other growth parameters among different treatments. According to the results, probiotic‐fed treatments had the lowest levels of cholesterol (237.7 ± 4.3 mg/dl) and the highest levels of total protein (11.3 ± 0.3 g/dl) and albumin (6.9 ± 0.3 g/dl), so that differences were found between P3 and control groups in all cases (p < .05). Based on the observations from reproductive parameters, the highest egg diameter, working and relative fecundities, fertilization and hatching rates, eyed eggs survival and alevins survival rates up to the absorption of the yolk sac were observed in P3 treatment (p < .05). Moreover, eyeing, hatching and yolk sac absorbing stages in P3 treatment were earlier than those in other treatments (p < .05). The results of present study demonstrated that probiotic supplementation improved reproductive performance and some growth and biochemical parameters in female rainbow trout broodstock and the best performance was observed in fish fed 4 × 10⁹ CFU probiotic per kg diet. Due to an increase in egg production and egg size in probiotic‐fed treatments, this feed additive can be used as a suitable ingredient to increase high‐quality egg production in rainbow trout breeders.     

Effects of Bacillus subtilis Strains on Growth,Immune Parameters,and Streptococcus iniae Susceptibility in Nile Tilapia,Oreochromis niloticus

This study was conducted to evaluate the effects of probiotic‐amended diets fed to juvenile Nile tilapia, Oreochromis niloticus, on growth and susceptibility to Streptococcus iniae infection. Fish (average weight 16.5 ± 0.2 g) were fed five diets formulated with Bacillus subtilis strains SB3086, SB3295, SB3615, or AP193 either individually or in combination of strains SB3086 and SB3615 at a targeted concentration of approximately 4 × 10⁷ colony‐forming units (CFU)/g of feed or with a basal control diet with no additives for 21 d. After the 21‐d growth trial, no significant difference in growth performance was observed with any probiotic‐amended diet. Results from serum bactericidal activity showed a significant difference between treatments and the control (P = 0.0002), except for the SB3295‐amended diet (P = 0.9020). Lysozyme activity was also significantly different in fish fed probiotic diets from those fed control diet (P = 0.0001). After 21 d of feeding, fish were challenged with S. iniae by intraperitoneal injection at a dosage of 8 × 10⁶ CFU per fish. Results from the challenge also showed a significant difference between treatments and control (P = 0.0001). Overall, fish fed with strain SB3615 showed the lowest percent mortality (44.0 ± 7.2%) and those fed the control diet showed the highest mortality (77.3 ± 7.0%). The combined feeding with strains SB3086 and SB3615 did not result in any significant difference in reducing mortality because of S. iniae infection in juvenile Nile tilapia when compared with the individual probiotic treatments.     

Evaluation of Experimental and Practical Diets for Bluegill Lepomis macrochirus and Hybrid Bluegill L. cyanellus × L. macrochirus

Two experiments were conducted to identify appropriate experimental and practical diets for bluegill Lepomis macrochirus and hybrid bluegill L. cyanellus × L. macrochirus reared in aquaria. In the first study, four experimental diets and five commercial diets were evaluated in juvenile hybrid bluegill initially weighing 4.8 g/fish. The experimental diets contained casein (CAS), casein + gelatin (CAWGEL), casein + L‐arginine‐HCI (CAS/ARG), or casein + gelatin + crystalline amino acids (CAS/AA) as sources of crude protein. The commercial diets included three diets formulated to meet the nutritional requirements of rainbow trout Oncorhynchus mykiss and two diets formulated to meet the nutritional requirements of channel catfish Ictalurus punctatus. Each diet was fed twice daily at a rate of 4% of body weigh/d to triplicate groups of fish. At the end of the 8‐wk feeding trial, weight gain was significantly higher in fish fed the best commercial rainbow trout diets (205–217%) compared to fish fed diets formulated for channel catfish (87–104%). Weight gain and feed efficiency (FE) of fish fed the experimental diets (5346% and 0.19–0.32, respectively) were significantly lower than those of fish fed the commercial rainbow trout diets (143–217% and 0.49–0.64, respectively). In the second experiment, the same dietary treatments were fed for 8 wk to juvenile bluegill initially weighing 3.7 g/fish. Each diet was fed twice daily at a rate of 4% of body weight/d to triplicate groups of fish. Weight gain was significantly higher in fish fed commercial trout diets (291–402%) compared to fish fed diets formulated for channel catfish (164–191%). Weight gain and FE of fish fed CAS/ARG were significantly higher than those of fish fed the commercial catfish diets, but significantly lower than those of fish fed the best commercial trout diets. Results of this study indicate that commercial rainbow trout diets are preferable to commercial channel catfish diets for culture of bluegill and hybrid bluegill. More research is needed to identify appropriate experimental diets for this group of fishes.     

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.     

Dietary yeast culture supplementation improves initial rearing of McConaughy strain rainbow trout

The addition of a yeast culture food supplement (DVAqua from Diamond V. Mills, Cedar Rapids, IA, USA) was evaluated during feeding of McConaughy strain rainbow trout Oncorhynchus mykiss. Two trials were run consecutively, starting with initial feeding, and were replicated over 2 years. The yeast culture was added to commercial trout starter at levels of 0.125 and 0.25 g kg^?1. The number of rainbow trout that died during the first 4 weeks of rearing was significantly reduced in the tanks receiving either of the yeast culture‐supplemented diets compared with the tanks receiving a control starter diet. Ending tank weights and gain were significantly and consistently greater in the tanks fed the 0.25 g kg^?1 yeast culture diet. Individual fish weights were also significantly heavier in the fish‐fed yeast culture containing diets in each year of the study at the end of 27 days. In the trials from 4 to 8 weeks postinitial feeding, mortality rates were significantly less only in the tanks receiving 0.25 g kg^?1 yeast culture supplementation. Individual fish lengths and weights at the end of the second trial were significantly greater in the tanks receiving either level of yeast culture compared with the control diet only in 1 year. Total tank weights and feed conversion were not significantly different between any of the treatments. The inclusion of DVAqua yeast culture provided significant increases in trout survival and growth through the first 4 weeks of feeding, with continued benefits for the next 4 weeks.     

Partial replacement of soybean meal with Methylobacterium extorquens single‐cell protein in feeds for rainbow trout (Oncorhynchus mykiss Walbaum)

A feeding trial was conducted with juvenile rainbow trout (15–16 g initial weight) to assess the effects of including single‐cell protein (SCP) produced from Methylobacterium extorquens in trout feeds. Three isonitrogenous and isoenergetic diets were produced: a control diet and two experimental diets containing 5% or 10% bacterial protein meal replacing soybean meal. Triplicate tanks, each containing 35 fish, were fed each diet to apparent satiation in a constant‐temperature (15°C), flow‐through tank system for 12 weeks. No statistically significant differences in final fish weight or other fish growth parameters were observed. Similarly, feed efficiency parameters showed no significant differences among groups. Nutrient retention indices (protein, fat, energy) were relatively high and similar among fish in each dietary treatment group, as were whole body proximate compositions. Fish survival was high, with a small but statistically significant increase for the 10% SCP diet. Overall, results demonstrate that SCP from M. extorquens is a safe and effective alternative protein for rainbow trout diets at the low inclusion levels tested. Slightly lower weight gain in fish fed the 10% SCP diet was largely due to lower feed intake, suggesting that adding palatability‐enhancing ingredients to feeds may allow higher levels of M. extorquens SCP to be used without compromising fish growth.     

Probiotic applications for rainbow trout (Oncorhynchus mykiss Walbaum) I. Effects on growth performance,feed utilization,intestinal microbiota and related health criteria

The effect of dietary probiotics (Bacillus subtilis, Bacillus licheniformis and Enterococcus faecium) used singularly and synergistically on the growth performance, intestinal microbiota and health status of rainbow trout (Oncorhynchus mykiss Walbaum) were assessed after 10 weeks feeding on supplemented diets. No significant improvements of weight gain or specific growth rate were observed in the probiotic fed groups. However, a significant improvement of feed conversion ratio was observed in the group fed E. faecium. High levels of probiotic species were observed in the posterior gastrointestinal tract as transient digesta‐associated populations and potentially resident mucosal populations. Bacillus subtilis and B. licheniformis levels accounted for 36% of the total culturable microbial population adhered to the mucosa and 62% in the digesta. E. faecium levels accounted for 45% of the mucosal population and 89% of the population in the digesta. An increase of serum lysozyme activity was observed in the fish fed diets containing the Bacillus probionts and elevated leukocyte levels were observed in fish fed diets containing Bacillus + E. faecium synergistically. The results of the current study demonstrate potential for B. subtilis, B. licheniformis and E. faecium to improve feed utilization, modulate intestinal microbiota and the health status 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.     

Partial or total replacement of fishmeal by solvent-extracted cottonseed meal in diets for juvenile rainbow trout (Oncorhynchus mykiss)

The effect of solvent‐extracted cottonseed meal (SCSM) as a partial or total replacement of fishmeal was studied in juvenile rainbow trout (Oncorhynchus mykiss). Six experimental diets SCSM0, SCSM25, SCSM50, SCSM75, SCSM75A and SCSMT, containing a gradient of SCSM 0, 152, 305, 465, 460 and 610 g kg^?1 to replace 0, 112.5, 225, 337.5, 337.5 and 450 g kg^?1 fishmeal protein were fed to triplicate groups (initial body weight of 39.2 ± 0.1 g) for 8 weeks. The diet SCSM75A was supplemented with lysine and methionine, to be similar to SCSM0 for juvenile rainbow trout. Faeces were colleted after 4 weeks of normal feeding for apparent digestibility coefficients (ADC) of dry matter, crude protein and gross energy determination. Total replacement of fishmeal adversely affected growth performance. Fish fed with diet SCSMT had significantly (P < 0.05) lower weight gain, specific growth ratio, feed conversion efficiency (FCE) and protein efficiency ratio than fish fed with other diets. The FCE of SCSM75 and SCSM75A were significantly lower (P < 0.05) than those of fish fed with SCSM0 diets. The ADC of the dry matter of SCSM75 and SCSMT were significantly lower than the SCSM0 diet, and the ADC of crude protein and the energy of SCSMT were the lowest (P < 0.05). The ADC of threonine, proline, alanine, valine, isoleucine, leucine, lysine and methionine of fish fed with diet SCSMT were lower. Lysine and methionine supplement positively affected the ADC of SCS75A diet. There were no significant differences in the fish body composition. It is shown that SCSM can be utilized in the juvenile rainbow trout diet up to 305 g kg^?1, to replace about 50% of fishmeal protein in this experiment.     

Probiotic applications for rainbow trout (Oncorhynchus mykiss Walbaum) II. Effects on growth performance,feed utilization,intestinal microbiota and related health criteria postantibiotic treatment

The effect of dietary probiotics (Bacillus subtilis, Bacillus licheniformis and Enterococcus faecium) was assessed on rainbow trout (Oncorhynchus mykiss Walbaum) previously treated with oxolinic acid. After feeding on supplemented diets for 10 weeks growth performance, feed utilization, gastrointestinal colonization and health status were assessed. B. subtilis + B. licheniformis fed fish displayed a significant improvement of feed conversation ration (FCR), specific growth rate (SGR) and protein efficiency ratio (PER). High levels of probiotic species were observed in the posterior gastrointestinal tract as transient digesta associated populations and potentially resident mucosal populations. Levels of Bacillus spp. reached log 3.74 CFU g^?1 on the mucosal epithelium and log 7.41 CFU g^?1 in the digesta of fish fed diets supplemented with B. subtilis and B. licheniformis. Enterococci levels reached log 2.84 CFU g^?1 on the mucosa and log 7.78 CFU g^?1 in the digesta of fish fed E. faecium supplemented diets. Feeding trout the Bacillus probionts alone or synergistically with E. faecium resulted in elevated leucocyte levels. The results of the current study demonstrate a potential role of probiotics for stabilizing/reinforcing the gastrointestinal microbiota after antibiotic treatment. This could reinvigorate the intestinal defensive barrier mechanism and provide protection against secondary potential pathogens.     

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.     

Evaluation of dietary yellow loess as an antibiotic replacer on growth,immune responses,serological characteristics and disease resistance in rainbow trout,Oncorhynchus mykiss

A 12 weeks of feeding trial was conducted to evaluate the effects of different levels of dietary yellow loess as an antibiotic (oxytetracycline) replacer in rainbow trout, Oncorhynchus mykiss. Five experimental diets were formulated to contain no antibiotics or yellow loess (control/CON), three graded levels of yellow loess 5 (YL₅), 10 (YL₁₀) and 20 g YL kg^?1 diet (YL₂₀) and oxytetracycline at 5 g OTC kg^?1 diet. Forty‐five fish averaging 39.4 ± 1.6 g (mean ± SD) were randomly distributed in to 15 aquaria. Triplicate groups of fish were fed one of the experimental diets at 1.5 ~ 1.9% of wet body weight per day. At the end of the feeding trial, average weight gain (WG) and specific growth rate (SGR) from fish fed CON diet were significantly lower than those from fish fed YL₁₀, YL₂₀ or OTC diets (P < 0.05). Lysozyme activity from fish fed YL₂₀ was detected to be significantly higher than that from fish fed CON diet (P < 0.05). While, superoxide dismutase (SOD) activity from fish fed YL₁₀ and YL₂₀ was recorded to be significantly higher than that from fish fed CON diet (P < 0.05). Fourteen days of challenge test with bacteria A. salmonicida showed significantly lower survival rate for CON than those of fish fed other experimental diets. Therefore, these results indicated that dietary yellow loess at 10–20 g kg^?1 could be a promising alternative of oxytetracycline in rainbow trout.     

Probiotic bacteria <Emphasis Type="Italic">Lactobacillus rhamnosus</Emphasis> influences the blood profile in rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis> (Walbaum)

This paper reports the effect of feeding probiotic diets on blood profiles in rainbow trout. Two experiments were performed: in the first, fish of average weight 75 g were offered either a commercial feed or the same incorporated with 10⁹ CFU g⁻¹ of lactic acid bacteria Lactobacillus rhamnosus for 30 days; in the second study performed for a similar duration, fish of average weight 126 g were offered formulated diets that either contained the same bacteria in heat-killed or freeze-dried form (nearly 10¹¹ CFU g⁻¹), or the basal diet without the bacteria. Blood samples were collected at different times after commencement of probiotic feeding to determine the total cholesterol, triglyceride contents, the plasma alkaline phosphatase activity, plasma protein and hematocrit value. The plasma cholesterol significantly increased upon probiotic feeding in the first experiment. A significant elevation (P < 0.05) of plasma cholesterol and triglyceride and alkaline phosphatase activity level was found in the freeze-dried probiotic fed groups at 20 and 30 days postfeeding. This was concomitant with the increased plasma protein and hematocrit values in FD group at 20 and 30 days. Likewise, the heat-killed probiotic fed group registered significantly high values of triglycerides, alkaline phosphatase activity, and plasma protein compared to the control diet fed groups after 20 days of feeding. Thus, alterations in the blood profiles could serve as supplementary information when examining the benefits of probiotics for fish.     

Transfer of PCDDs and PCDFs into the edible parts of farmed rainbow trout, Oncorhynchus mykiss (Walbaum), via feed

This study was carried out to quantify the transfer of polychlorinated dibenzo‐p‐dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) from commercial fish feed into the edible part of rainbow trout (Oncorhynchus mykiss, Walbaum) under normal rearing conditions. Trout were fed with high‐energy feed for salmon (fat content 26–30%) over a period of 19 months. The average weight of the fish increased from 10 g to more than 2092 g, reaching a size of up to 51‐cm length (Tl). Considerable amounts of PCDDs and PCDFs were transferred from the fish feed into the tissue of the trout. Dioxin concentrations increased during the time of feeding from 0.054 up to 0.914 ng WHO‐PCDD/F‐TEQs kg^?1 wet weight and from 4.991 to 15.815 ng WHO‐PCDD/F‐TEQs kg^?1 fat. A correlation was found between the dioxin concentration of the feed and the resulting concentration in the fat of the muscle tissue. The data allow the establishment of transfer rates from a high‐energy diet to farmed rainbow trout.     

Antioxidant‐related parameters,digestive enzyme activity and intestinal morphology in rainbow trout (Oncorhynchus mykiss) fry fed graded levels of red seaweed,Gracilaria pygmaea

This study was conducted to investigate the effects of dietary red seaweed, Gracilaria pygmaea level on growth, antioxidant‐related parameters, digestive enzyme activity and intestinal morphology of rainbow trout (Oncorhynchus mykiss) fry. Five isocaloric and isonitrogenous diets were formulated to contain four G. pygmaea levels (30 (GL‐30), 60 (GL‐60), 90 (GL‐90) and 120 g/kg (GL‐120)), and a control diet was used, without inclusion of seaweed. Results of the feeding trial indicated that final body (FBW: 2.8–3.5 g) and specific growth rate (SGR: 4.8–5.2) were significantly improved when 60 g/kg G. pygmaea was supplemented in the diets. However, there was a significant reduction (p < .05) of final body weight (FBW) and specific growth rate (SGR) in fish fed 120 g/kg G. pygmaea. Protease activity was significantly lower in fish fed GL‐120 diet when compared to GL‐30 or control (p < .05). Lipase was significantly affected by dietary seaweed regardless its level of supplementation (p < .05). The inclusion of the Gracilaria in the diet led to evident changes in the fish antioxidant status with significant reduction of superoxide dismutase, glutathione peroxidase activity and lipid peroxidation products. The histological study demonstrated that all groups of fish displayed normal morphology of anterior intestine and pyloric caeca. Villi absorptive area in the anterior intestine of treatment groups GL‐90 and GL‐120 significantly decreased (p < .05). Overall, the results obtained in this study indicate that dietary G. pygmaea supplementation up to 90 g/kg improves growth performance in rainbow trout fry without compromising antioxidant responses and digestive function.     

Dietary probiotic supplementation in juvenile rainbow trout (Oncorhynchus mykiss) reared under cage culture production: effects on growth,fish welfare,flesh quality and intestinal microbiota

This study was conducted to evaluate the effects of dietary probiotic supplementation on growth performance, fish welfare, sensory evaluation, freshness during ice storage and changes in intestinal microbiota of rainbow trout (Oncorhynchus mykiss). The 9‐week feeding trial was conducted in cages under commercial conditions during the winter season, when water temperature decreased from 14°C to 7°C. Fish were fed either a diet without probiotic supplementation (control) or with 0.2% (2 × 10⁹ CFU kg^?1 diet) of multi‐strain probiotic bacteria (Bacillus sp., Pediococcus sp., Enterococcus sp., Lactobacillus sp.). Fish weight was recorded at 0, 2, 4, 6 and 9 weeks. Growth performance was not affected by dietary probiotic supplementation. Alternative complement activity (ACH50) was significantly higher in fish fed the diet with probiotic (58.4 ± 3.7 units mL^?1) than in the control group (46.9 ± 3.1 units mL^?1) (P = 0.03). Several biochemical markers were altered by the dietary treatment. 7‐ethoxyresorufin‐O‐deethylase (EROD) (P < 0.01), glutathione S‐transferase (GST) (P < 0.001), glutathione peroxidase (GPx) (P < 0.05) increased and lipid peroxidation (LP) (P < 0.01) decreased with dietary probiotic supplementation. Flesh quality and shelf‐life of fish stored on ice was not affected by dietary probiotic supplementation. Probiotic supplementation had a limited effect on the intestinal microbiota. Signal strength of the observed operational taxonomic units (OTUs) differed between the control and treatment samples and could indicate variations in the abundance of certain OTUs. Microbiota adhering to the intestinal mucus varied between sampling points, indicating that changes were associated with water temperature.