Dietary effects of poly‐β‐hydroxybutyrate on the growth performance,digestive enzyme activity,body composition,mineral uptake and bacterial challenge of rainbow trout fry (Oncorhynchus mykiss)

This study investigated the effects of diet supplementation with poly‐β‐hydroxybutyrate (PHB) on growth performance, digestive enzyme activity, lipid metabolism, mineral uptake and bacterial challenge of the rainbow trout fry (initial weight: 111.3 ± 13.7 mg) during a 6‐week experimental period. In the experimental set‐up, the commercial diet of rainbow trout fry was replaced with 0.5%, 1% and 2% PHB. The results of our work showed that the replacing of diets with PHB in experimental treatments decreases the weight of rainbow trout fry during the first 2 weeks before significantly increasing final weight at the end of the 6‐week period. PHB also improved digestive enzyme activity in experimental treatments. The highest total protease, pepsin activity and pancreatic enzyme secretion were observed with the 0.5% PHB treatment. A higher concentration of Na and K was observed in the whole body of the fry fed on 1% and 2% PHB‐supplemented diets. Enhanced survival rates occurred in all groups of fry after bath exposure to Yersinia ruckeri compared to rates in those fed the control diet. Our results suggest that the diet supplemented with PHB may improve growth performance, digestive enzyme activity and the functioning of the immune system. These positive effects could be considered for new applications in aquaculture.     

In vitro selection of a synbiotic and in vivo evaluation on intestinal microbiota,performance and physiological response of rainbow trout (Oncorhynchus mykiss) fingerlings

The aim of this study was to determine the best synbiotic combination (based on growth and short chain fatty acids production) between Pediococcus acidilactici and five prebiotics in vitro, inulin, fructooligosaccharide (FOS), xylooligosaccharide (XOS), galactooligosaccharide (GOS), isomaltooligosaccharide (IMO). The best in vitro growth under aerobic and anaerobic culture condition was observed in the treatment, P. acidilactici + GOS. Furthermore, the study of short chain fatty acids (SCFA) production at the end of exponential growth phase revealed that the major SCFA produced was propionic acid in all synbiotic treatments except for the P. acidilactici + GOS treatment where butyric acid production was significantly higher compared with the other treatments. Based on the results of in vitro studies, P. acidilactici + GOS that were selected as synbiotic and rainbow trout fingerlings (15.04 ± 0.52 g) were fed on diet supplemented with the selected synbiotic. After 8 weeks of feeding, growth performance, intestinal microbiota and physiological responses were evaluated. Growth performance was significantly improved by synbiotic feeding. No significant differences of haematological parameters were revealed between the different treatments. Level of presumptive autochthonous lactic acid bacteria was elevated, while total autochthonous bacterial level remained unaffected. These results showed that P. acidilactici + GOS can be considered as an efficient synbiotic for rainbow trout.     

Immunostimulatory effects of dietary poly‐β‐hydroxybutyrate in European sea bass postlarvae

The stable production of high‐quality fry in marine aquaculture is still hampered by unpredictable mortality caused by infectious diseases during larval rearing. Consequently, the development of new biocontrol agents is crucial for a viable aquaculture industry. The bacterial energy storage compound poly‐β‐hydroxybutyrate (PHB) has been shown to exhibit beneficial properties on aquatic organisms such as enhanced survival, growth, disease resistance and a controlling effect on the gastrointestinal microbiota. However, the effect of PHB on the developing immune system of fish larvae has so far not been investigated. In this study, the effect of feeding PHB‐enriched Artemia nauplii on survival, growth and immune response in European sea bass (Dicentrarchus labrax) postlarvae was examined. Amorphous PHB was administered to 28‐day‐old sea bass postlarvae over a period of 10 days. The survival and growth performance were monitored, and the expression of 29 genes involved in immunity, growth, metabolism and stress‐response was measured. While the expression of the insulin‐like growth factor 1 (igf1), an indicator of relative growth, was upregulated in response to feeding PHB, the larval survival and growth performance remained unaffected. After 10 days of PHB treatment, the expression of the antimicrobial peptides dicentracin (dic) and hepcidin (hep) as well as mhc class IIa and mhc class IIb was elevated in the PHB fed postlarvae. This indicates that PHB is capable of stimulating the immune system of fish early life stages, which may be the cause of the increased resistance to diseases and robustness observed in previous studies.     

A comparative molecular study of the presence of “Candidatus arthromitus” in the digestive system of rainbow trout,Oncorhynchus mykiss (Walbaum), healthy and affected with rainbow trout gastroenteritis

Observations were made using histopathological techniques in conjunction with a nested polymerase chain reaction (PCR) protocol for the specific detection of “Candidatus arthromitus” on DNA extracted from wax‐embedded tissues and fresh digestive contents of rainbow trout. Samples positive for “Candidatus arthromitus” DNA included fish with rainbow trout gastroenteritis (RTGE), clinically normal cohabiting fish, and apparently healthy controls from RTGE positive and RTGE negative sites. The results obtained from the PCR were confirmed by nucleotide sequencing. “Candidatus arthromitus” DNA was found in distal intestine as well as in sections of pyloric caeca, suggesting that both these locations are appropriate for molecular detection of “Candidatus arthromitus” DNA in trout. Furthermore, rainbow trout fry distal intestinal samples from two different hatcheries where RTGE had not been reported were also positive. Differences in “Candidatus arthromitus” DNA detection between paraffin wax‐embedded and fresh digestive content samples from the same fish suggested that it may be predominantly epithelium‐associated in healthy trout. Parallel histopathological observations indicated that pyloric caeca are the preferred site for visualizing segmented filamentous bacteria (SFB) in trout with RTGE. The results of this study showed that the presence of SFB was not invariably associated with clinical disease and that more information is required to understand the role of these organisms.     

Effects of low‐level dietary microalgae supplementation on the distal intestinal microbiome of farmed rainbow trout Oncorhynchus mykiss (Walbaum)

In this study, high throughput 16S rRNA sequencing was used to investigate the effect of a novel whole‐cell dietary microalgae meal (Schizochytrium limacinum), on the distal intestinal microbiome of farmed rainbow trout, Oncorhynchus mykiss. Heterotrophic microalgae are rich in omega 3 polyunsaturated fatty acids, can be produced sustainably and have been shown to have beneficial effects on host health. After a 15‐week trial period, microbial community profiles were compared between the distal intestinal contents of fish fed either a control diet or a treatment diet that partially replaced fish oil with microalgae meal, at a substitution level of 5%. The results of this research showed that the microbial communities of both fish populations were composed of similar microbial taxa, however, the treatment group fed the microalgae supplement possessed a greater level of microbial diversity than those in the control group. A limited number of bacterial taxa were discriminatory between diets and were significantly elevated in the treatment group, notably operational taxonomic units (OTUs) assigned to the genera Streptococcus, Leuconostoc, Lactobacillus, Lactococcus and Weissella. However, the overall structure of the intestinal microbiome between control and treatment groups was not found to be significantly different. The treatment group displayed a heavier mean weight and condition factor at the end of the trial period. The results of this study suggest that the tested microalgae meal can be used as a replacement for a proportion of fish oil in aquafeeds, with minor changes to the intestinal microbiome of farmed rainbow trout, and positive effects on growth.     

Haemato‐immunological and serum biochemical parameters,intestinal histomorphology and growth performance of rainbow trout (Oncorhynchus mykiss) fed dietary fermentable fibre (Vitacel®)

The aim of this study was to investigate the effects of dietary fermentable fibre (Vitacel^®) on haemato‐immunological and serum biochemical parameters, intestinal histomorphology, growth performance and proximate body composition of rainbow trout (Oncorhynchus mykiss). One hundred and twenty fish (81.65 ± 1.49 g) were fed diets containing 0 and 10 g kg^?1 fermentable fibre (Vitacel^®) for 50 days. At the end of feeding trial, growth performance parameters were significantly improved in fermentable fibre (Vitacel^®)‐fed fish. Although feeding on fermentable fibre (Vitacel^®)‐supplemented diet had no remarkable effect on haematological parameters (RBC, Htc and Hb) (P > 0.05), white blood cell (WBC) count and monocyte level were significantly affected (P = 0.040 and P = 0.020, respectively). In case of serum biochemical parameters, a significant increase and decrease were observed in serum total protein (P = 0.040) and cholesterol level (P = 0.000), respectively. Also, lysozyme level was significantly increased following administration of Vitacel^® in diet (P = 0.006). Histomorphological evaluations revealed that villus length (P = 0.004) and tunica muscularis thickness (P = 0.000) were significantly higher in fermentable fibre (Vitacel^®)‐fed fish. These results indicate that fermentable fibre can be considered as a dietary supplement for improving the health status and performance of rainbow trout.     

Comparative effects of dietary l‐carnitine supplementation on diploid and triploid rainbow trout (Oncorhynchus mykiss)

This study compared the effects of dietary l ‐carnitine and ploidy on growth performances and fatty acid content in rainbow trout (Oncorhynchus mykiss). Fish [initial body weight (BW) = 30 g] reared under high density (50 kg biomass m^?3) were hand‐fed in triplicate (3 tanks treatment^?1, 34 fish tank^?1) twice a day, with three nutritionally identical diets containing 15, 200 or 530 mg l ‐carnitine kg^?1 of diet. No significant growth differences were observed over a 56‐day grow‐out period, during which BWs increased threefold. Growth performances and survival were not significantly affected by either ploidy or dietary l ‐carnitine content, although daily growth index showed an increasing trend (2.52–2.65% day^?1) with increasing dietary l ‐carnitine. Body l ‐carnitine content increased significantly with dietary l ‐carnitine content. Diploid fish had higher plasma ammonia (716–725 μmol L^?1) and osmolality (297–303 mOsm) levels than triploid trout (523–649 μmol L^?1 and 285–291 mOsm, respectively). l ‐carnitine, ploidy and their interaction showed to affect significantly the concentration of several fatty acids. Palmitoleic (16:1), oleic (18:1) and erucic (22:1) acids showed lower concentrations, while the eicosadienoic (20:2n‐6) and arachidonic (20:4n‐6) acids were elevated in liver of triploid fish. Eicosapentaenoic acid (22:5n‐3) was significantly higher in fish fed 200 mg than in fish fed 15 mg l ‐carnitine.     

Effect of dietary Ergosan on growth performance, digestive enzymes, intestinal histology, hematological parameters and body composition of rainbow trout (Oncorhynchus mykiss)

Present study examined the effects of Ergosan on growth performance, digestive enzyme activities, hematological parameters and gastrointestinal structure of rainbow trout. Rainbow trout (mean weight 100–110 g) were fed basal diet (control) and diet treated with Aquavac Ergosan (5 g kg^?1 of diet) for 50 days. Results of this study showed that Ergosan supplementation significantly increased weight gain (94.27 g vs. 65.04 g), specific growth rate (4.09 vs. 3.10) and feed intake (136.85 g vs. 111.22 g) and decreased feed conversion ratio (1.43 vs. 2.03) compared to control (P < 0.05). Lipase activity and leukocyte and erythrocyte count also increased in juvenile fish fed Ergosan-treated diet compared to control (P < 0.05). Light microscopy demonstrated that both groups of fish displayed normal morphology of proximal intestine and pyloric caeca. In Ergosan-treated group, higher percentage of goblet cell was shown in proximal intestine and pyloric caeca. Present study suggests that Ergosan effectively promotes growth performance, lipase activity and gastrointestinal structure in rainbow trout.     

Siberian sturgeon (Acipenser baerii) larvae fed Artemia nauplii enriched with poly‐β‐hydroxybutyrate (PHB): effect on growth performance,body composition,digestive enzymes,gut microbial community,gut histology and stress tests

The effects of feeding Artemia nauplii enriched with or without poly‐β‐hydroxybutyrate (PHB) and/or highly unsaturated fatty acids (HUFA) on Siberian sturgeon (Acipenser baerii) larvae were investigated. Feeding larvae with PHB‐enriched nauplii (PHB, PHB + HUFA) decreased the growth performance of the larvae. PHB affected the body composition by increasing the lipid content of the whole body and decreasing total saturated, monoenoic, n3, n6 and decosahexanoeic acid (DHA) in the larvae, indicating that the PHB addition affected lipid metabolism. A high activity of pepsin was observed in the digestive extracts of PHB treatments (PHB, PHB + HUFA), while PHB suppressed amylase activity in the intestine of the larvae. Based on molecular analysis, PHB changed the microbial community in the distal intestine of the larvae. The highest counts of goblet cells were observed in the HUFA‐containing treatments (HUFA, PHB + HUFA), indicating that HUFA addition may improve the mucosal barrier defence system. The overall quality of the larvae was evaluated by exposing them to different salinities and ammonia stress levels. PHB decreased survival rates in these challenges. Our results show that optimal PHB doses for bio‐encapsulation into Artemia remain to be determined for further application at the earliest larval stages of sturgeon.     

Quantitative expression (Walbaum) of immunological factors in rainbow trout, Oncorhynchus mykiss (Walbaum), after infection with either Flavobacterium psychrophilum, Aeromonas salmonicida, or infectious haematopoietic necrosis virus

To further enhance our understanding of immunological gene expression in rainbow trout, Oncorhynchus mykiss, after infection with naturally occurring pathogens, a series of probes and primers were developed for the quantification of immune factors. Separate groups of specific-pathogen-free rainbow trout were infected with either Flavobacterium psychrophilum, Aeromonas salmonicida or infectious haematopoietic necrosis virus (IHNV). Three different concentrations of each pathogen were used and samples from infected and mock-infected fish were taken at either 1 or 5 days after infection. Ten fish were sampled at each time point for individual sections of liver, spleen and head kidney. Organ specimens from five of the fish were used to re-isolate and quantify the pathogen at the time the samples were taken. Total RNA was extracted from the organs of the remaining five animals. Using real-time polymerase chain reaction with fluorescent-labelled probes, the RNA from these organs was examined for the level of expression of the following immunological factors; an interferon related protein (MX-1), interleukin-8 (IL-8), the cytotoxic T-cell marker CD-8 and complement factor C3 (C3). They were also measured for the level of beta-actin, which was used as a standardization control for cellular RNA expression. Infection with IHNV produced the greatest change in expression level for all the immunological related factors examined in this study. IHNV elicited the best dose response profile, which was typically seen at 5-days post-infection for MX-1, C3, IL-8 and CD-8. Infection with A. salmonicida and F. psychrophilum showed elevated, but variable expression levels for several of the genes tested.     

Immunomodulation of rainbow trout (Oncorhynchus mykiss) fry by bath exposure to a β‐glucan from Euglena gracilis

Early developmental stages of fish mostly depend on innate immune factors for their protection. Augmenting these factors by application of different immunostimulatory substances may be beneficial for rearing and survival of the early life stages of fish. Bath administration of stimulants leads to a uniform exposure of fish independent of feed intake and reduces the individual handling. The present study demonstrates the immunostimulatory effect of β‐glucan (bath exposure) in rainbow trout fry at different dosages and exposure time. Rainbow trout fry (avg. wt. 770 mg; 87 days post hatch) were exposed to three different concentrations of β‐glucan (10, 100 and 1000 μg mL^?1) by bath exposure for 1 and 24 h. Expression of immune related genes from pooled internal organ samples of individual fish were analysed using a real time qPCR assay. Expression of complement factors (C3 and factor B) and acute phase proteins (hepcidin, precerebellin and transferrin) was significantly up‐regulated after 24 h bath stimulation with β‐glucan (100 μg mL^?1). These innate immune factors may play a vital role in clearance of pathogens. The expression of most of genes showed both a dose‐ and time‐dependent response. A medium dose (100 μg mL^?1) induced a significant increase in expression of complement factors and acute phase proteins mainly at 24 h exposure, whereas the highest dose of β‐glucan (1000 μg mL^?1) down‐regulated the expression of most of the studied genes. The result from the present study indicates that β‐glucan bath exposure could be applied for enhancing the innate immune factors even in fry.     

Effect of dietary inclusion of lysozyme on growth performance and plasma biochemical parameters of rainbow trout (Oncorhynchus mykiss)

This study was conducted to evaluate the effect of dietary lysozyme supplementation on growth performance and plasma biochemical parameters of rainbow trout (Oncorhynchus mykiss). Graded levels of lysozyme [0 (control), 150, 300, 450 and 600 mg kg^?1 diet] were fed to fish (initial average weight 7.76 g) for 10 weeks. Dietary lysozyme supplementation regardless of inclusion level generally improved the growth, feed utilization and nutrient retention, but significant differences were mainly observed between the 450 or 600 mg kg^?1 lysozyme group and the control group. Lysozyme supplementation generally decreased the plasma aspartate aminotransferase and alanine aminotransferase (ALT) activities, but significant difference was only observed in the ALT activity between the 450 mg kg^?1 lysozyme group and the control group. In contrast, lysozyme supplementation generally increased the plasma alkaline phosphatase and lysozyme activities, but significant difference was only observed in the lysozyme activity between the 600 mg kg^?1 lysozyme group and the control group. Lysozyme supplementation generally increased the plasma antioxidant activities of enzymes (including superoxide dismutase, glutathione peroxidase and catalase) and total antioxidant capacity, but decreased the plasma malondialdehyde level. These results suggest that dietary 450–600 mg kg^?1 lysozyme inclusion may improve the growth and non‐specific immune response of rainbow trout.     

The effects of experimental anaemia on CO2 excretionin vitro in rainbow trout,Oncorhynchus mykiss

The effects of severe experimental anaemia on red blood cell HCO₃ ^– dehydrationin vitro were examined in rainbow trout,Oncorhynchus mykiss. After 5 days of anaemia (haematocrit=4.9±1.1%) induced by intraperitoneal injection of phenylhydrazine hydrochloride, fish displayed elevated arterial CO₂ tensions (anaemic PaCO₂=3.19±0.42 torrvs. control PaCO₂=1.35±0.17 torr) and a significant acidosis (anaemic pHa=7.73±0.04vs. control pHa=7.99±0.04). However, after 15–20 days of anaemia (hct=6.6±0.8%) induced by blood withdrawal, the arterial CO₂ tension was significantly lower than the control value, suggesting that physiological adjustments occurred within this time period to compensate for the lowered haematocrit. Compensation probably did not involve alterations in ventilation, which was unaffected by 5 days of anaemia (anaemic ;w=786±187 ml min^–1 kg^–1 vs. control ;w=945±175 min^–1 kg^–1), based on indirect Fick principle measurements.Potential adaptations to longer term anaemia at the level of the red blood cells were investigated using a radioisotopic HCO₃ ^– dehydration assay. Owing to the difference in haematocrits, the HCO₃ ^– dehydration rate for blood from anaemic fish was significantly lower than that for control fish following equilibration at the same CO₂ tension. This difference was eliminated when HCO₃ ^– dehydration rates were measured on blood samples adjusted to the same haematocrit, a result which implies that the intrinsic rate of CO₂ excretion at the level of the red blood cell was not up-regulated during anaemia. The difference was also eliminated by equilibrating the blood samples with CO₂ tensions appropriate for the group from which the sample was obtained,i.e., PCO₂=1.4 torr for control samples and PCO₂=3.2 torr for anaemic samples; each at the appropriate haematocrit. It is concluded that the elevated PaCO₂ helps to reset CO₂ excretion to the control level, but that some additional physiological adjustment occurs to lower the PaCO₂ after 15–20 days of anaemia.     

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.     

Effect of dietary bovine lactoferrin on growth,haematology and non‐specific immune response in rainbow trout (Oncorhynchus mykiss)

The aim of this study was to investigate the effect of dietary lactoferrin (Lf) on growth, haematology and non‐specific immune response of rainbow trout Oncorhynchus mykiss (Walbaum). Fish were fed an experimental diet containing 0 (as control), 50, 100, 200 and 400 mg Lf kg^?1 diet twice daily for 8 weeks and sampled at 2, 4, 6 (immune function and growth), and 8 weeks (immune function, haematology and growth). Statistical analyses revealed no significant effects of dietary Lf on growth performance (specific growth rate, weight gain, feed conversion ratio, feed intake and condition factor) or haematological parameters (red and white blood cell count, haemoglobin, haematocrit, serum iron and total iron binding capacity [TIBC]). Among the serum non‐specific immune parameters, lysozyme activity increased significantly in fish fed 100, 200, or 400 mg Lf kg^?1 feed for 8 weeks, whereas haemolytic complement activity increased in fish fed 100 and 400 mg Lf kg^?1 diet after 6 weeks. The antiprotease activity increased in groups fed 100, 200 or 400 mg Lf kg^?1 diet after 8 weeks. However, no significant effect was observed on serum peroxidase level. It can be concluded that feeding of rainbow trout on the diet supplemented with 100 mg kg^?1 or higher for 8 weeks enhances the non‐specific immune response.     

Effects of dietary Persian oak (Quercus brantii var. persica) fruit extract on survival,growth performance,haematological and immunological parameters in rainbow trout,Oncorhynchus mykiss,fingerlings

The aim of study was to evaluate the effects of jaft (internal layer of oak fruit) extract on growth, haematological and immunological parameters in rainbow trout fingerlings. A total of 360 fish (average weight 6.25 g, total length 7.75 cm) were randomly distributed in 12 fibreglass tanks (stocking density: 1.04 g L^?1) with flow rate of 8 L min^?1. The ethanolic extraction of jaft was taken, and, then, a basal diet was supplemented with 0 (control), 0.5, 1 and 2 g kg^?1 to formulate four experimental diets. After 8 weeks, blood sampling was performed for haematological and immunological parameters. While immunological parameters such as IgM and lysozyme showed their lowest level in control group, their highest amounts appeared in 2 g kg^?1 group. C3, C4 and alternative complement activity increased in fish fed 2 g kg^?1 extract compared to control (P ? 0.05). Haematological parameters such as white blood cell, red blood cell, haemoglobin and haematocrit were enhanced in experimental groups (P ? 0.05). Survival and growth indices did not show significant changes in experimental treatments (P ? 0.05). Results indicated feeding rainbow trout with Persian oak extract at 0.5, 1.0 and 2.0 g kg^?1 levels significantly enhance the immunological parameters.     

Effects of supplemental dietary l‐carnitine and ractopamine on the performance of juvenile rainbow trout,Oncorhynchus mykiss

This study was carried out to investigate a possible protein‐sparing action of l ‐carnitine and ractopamine in rainbow trout, Oncorhynchus mykiss. An 8‐week feeding trial was carried out to evaluate the effects of supplementation of three levels of l ‐carnitine (0, 1 and 2 g kg^?1) and two levels of ractopamine (0 and 10 mg kg^?1) on growth performance, fillet fatty acid compositions and blood biochemical parameters in a 3 × 2 factorial experimental design. Ractopamine and 1 g kg^?1 carnitine improved the specific growth rate (1.03% and 1.05% day^?1), feed conversion ratio (FCR, 1.3 and 1.29), protein efficiency ratio (PER, 1.88 and 1.85) of fish and crude protein (73.5 and 73.8) content of fish fillet. l ‐carnitine and ractopamine increased the levels of albumin, total protein and globulin in the serum of fish. Apart from eicosapentaenoic acid and docosahexaenoic acid, other fatty acids of fish fillet were increased by ractopamine, while total saturated fatty acids were almost intact. However, the total n‐3 poly unsaturated fatty acids were reduced by l ‐carnitine supplementation (P<0.05). The present study showed that 1 g kg^?1l ‐carnitine and 10 mg kg^?1 ractopamine each can improve the performance of rainbow trout and their combination in diet could enhance the protein level and change the fatty acids profile in fillet muscle.     

Dietary β‐glucan modulate haematological parameters,cytokines and gene expression in TLR and ERK pathways of rainbow trout (Oncorhynchus mykiss) during infection by Aeromonas salmonicida

To explore the role of β‐glucan (0, 0.05%, 0.1% and 0.2%) in resisting bacteria, rainbow trout (Oncorhynchus mykiss) was challenged with Aeromonas salmonicida after 42‐day β‐glucan administration, and then sampled at 0, 2, 4 and 6 days post infection (dpi). The data showed that 0.2% β‐glucan reduced the accumulated mortality rates compared with the ICG (infected control group) (p < .05). The white blood cells, red blood cells and haemoglobin were higher in the 0.2% β‐glucan group (BG) than the ICG (p < .05). 0.1% and 0.2% β‐glucan elevated serum total antioxidative capability and glutathione activity but alleviated the increase of serum alkaline phosphatase activity and glucose concentration (p < .05) during infection. Serum TNF‐α, IL‐1β, IL‐8 and IgM in three BGs elevated remarkably on 6 dpi compared with the ICG (p < .05). Expression of tnf, il1b and cxcl8 of the head kidney in the 0.1% and 0.2% BGs was higher than the ICG on 4 dpi while ighm expression in the 0.2% BG was higher than in the ICG on 2 and 6 dpi (p < .05). 0.1% and 0.2% β‐glucan increased the expression of tlr5m, tlr5s, tmek and myd88 in the spleen after infection (p < .05). Similarly, 0.2% β‐glucan up‐regulated the expression of tmek, myd88, oncmyk‐dab and c3 in head kidney (p < .05). Overall, 0.2% dietary β‐glucan effectively decreased accumulated mortality rate by modulating the biochemistry process, cytokines, and activating TLR and ERK signalling pathways during A. salmonicida infection.     

Effect of soybean oil and soybean lecithin on intestinal lipid composition and lipid droplet accumulation of rainbow trout, Oncorhynchus mykiss Walbaum

Rainbow trout (Oncorhynchus mykiss Walbaum) were fed purified diets containing fish oil for six weeks and then soybean lecithin or soybean oil for 25 days. The gastrointestinal tract segments, stomach, midgut and hindgut were then sampled for lipid and fatty acid composition and electron microscopy. Membrane lipid class composition was fairly similar in all three segments of trout fed fish oil. Hindgut contained slightly more phosphatidylserine than stomach and midgut, while midgut contained more phosphatidylcholine and less lysophospatidylcholine/sphingomyelin. Feeding soybean products appeared to marginally decrease free cholesterol. The fatty acid compositions of the main lipid classes showed significant regional differences. In control fish, stomach had higher levels of arachidonic acid (20:4n-6) and n-6 polyunsaturated fatty acids than midgut and hindgut, and lower content of docosahexaenoic acid (22:6n-3) and n-3 polyunsaturated fatty acids. Midgut phosphatidylethanolamine also had higher levels of saturated fatty acids and less n-3 polyunsaturated fatty acids than the other tissues. Feeding soybean products decreased the n-3/n-6 ratio mainly due to increases in linoleic (18:2n-6) and 20:4n-6 and decreases in 22:6n-3 and eicosapentaenoic acid (20:5n-3). Phosphatidylcholine and to a lesser extent phosphatidylethanolamine adapted more readily to dietary changes by major increases in 18:2n-6 and C₂₀₋₂₂ n-6 polyunsaturated fatty acids. The composition of phosphatidyl-serine and -inositol appeared to be under more strict metabolic control. Linoleic acid hardly increased at all while the increase in other n-6 polyunsaturated fatty acids was less pronounced than for the other lipid classes. Regardless of lipid class, stomach resisted dietary changes more strongly than midgut and hindgut. Increases in n-6 polyunsaturated fatty acids were minor as were the loss of n-3 polyunsaturated fatty acids. The dead-end product 20:2n-6 accumulated to a higher degree in hindgut phosphatidyl-ethanolamine and -coline compared to midgut and stomach, suggesting that the activity of Δ₆ desaturation is higher in the anterior part of the intestine where most of the lipid is absorbed. Feeding soybean oil caused massive accumulation of free lipid droplets in midgut enterocytes while little lipid droplets were observed in trout fed fish oil or soybean lecithin. Since both soybean products influenced intestinal composition to the same degree, altered fatty acid profiles in membranes is not responsible for the observed lipid accumulation. This supports previous observations in Arctic charr (Salvelinus alpinus L.), suggesting that fish may require exogenous phospholipids in order to sustain a sufficient rate of lipoprotein synthesis. This revised version was published online in July 2006 with corrections to the Cover Date.     

Anaesthetic efficacy and biochemical effects of 1,8‐cineole in rainbow trout (Oncorhynchus mykiss,Walbaum, 1792)

The aim of the present study was to investigate the anaesthetic efficacy and biochemical effects of 1,8‐cineole (cineole) in rainbow trout (Oncorhynchus mykiss). The fish were exposed to 200, 300, 400, 500, 600 and 800 μl/L cineole and time of induction of anaesthesia and recovery from anaesthesia were recorded. Thereafter, the fish haematological and biochemical responses to anaesthesia with different concentrations of cineole were studies. Moreover, the haematological and biochemical response of fish anaesthetized for 300 s with either cineole (283 μl/L) or eugenol (25 μl/L) were compared. Cineole at the concentrations of 200–800 μl/L induced stages 2, 3 and 4 anaesthesia within 109‐29.3, 226‐59 and 418‐117 s respectively. Increase in anaesthesia induction time led to higher stress responses and enzymes’ activity characterized by elevation in red blood cell (RBC), white blood cell (WBC), blood haematocrit and haemoglobin, and plasma cortisol, glucose and lactate levels, and aspartate aminotransferase (AST), alkaline phosphatase (ALP), lactate dehydrogenase and creatine phosphokinase (CPK) activities. However, cineole concentrations had no significant effects on plasma alanine aminotransferase (ALT) activity and ions levels. Comparison of cineole with eugenol showed that cineole showed less change in blood RBC and plasma AST, ALP, CPK, cortisol and glucose levels compared to eugenol. In conclusion, cineole is efficient to anaesthetize trout at concentrations of 200–800 μl/L. Increase in cineole concentration shortens anaesthesia induction time, stress response and probably tissue damage. The concentrations of 600–800 μl/L cineol is recommended for rapid sampling as it causes the least stress and enzymatic responses. The present results suggest that cineole causes slightly lower side effects in trout compared to eugenol.