Digestive capacity, intestinal morphology, and microflora of 1-year and 2-year old Atlantic cod (Gadus morhua) fed standard or bioprocessed soybean meal

The objectives of this work were to evaluate how dietary soybean meal (SBM) or a soy meal made by bioprocessing the SBM (BPSBM) to remove anti-nutritional factors affected hydrolytic capacity, amino acid absorption, intestinal morphology, and microflora along the intestinal tract of Atlantic cod at two life stages. Three fish meal based standard cod diets were formulated to contain no soy (FM control), 25% SBM, or 22% BPSBM. Prior to sampling the diets were fed to duplicate groups of 0.5 kg (1-year old) and 1.7 kg (2-year old) cod for a period of 3 months, and the groups reached 0.9 and 2.5 kg, respectively. Digesta was then sampled from different intestinal sections for analyses of trypsin and amylase activity as well as absorption of amino acids, nitrogen, and sulphur. Gastrointestinal sections were sampled for measurements of relative weight (kg^− 1 body weight), and tissues from these sections were sampled for analyses of brush border enzyme (alkaline phosphatase (ALP), leucine aminopeptidase (LAP), and maltase) activity and histological examination. Microflora was sampled from both digesta and the intestinal wall. The SBM diet stimulated relative growth of all gastrointestinal sections except the distal intestine in both age classes. Relative growth of the pyloric intestine was also stimulated by BPSBM. The pyloric caeca and the upper mid intestine were found to be the major sites for enzymatic hydrolysis of protein and starch and for amino acid absorption. Dietary SBM and BPSBM did not alter the activity of trypsin and LAP, but the activity of these enzymes in the proximal intestine was affected by age, being higher in 1-year old than in 2-year old cod. The rate of amino acid, nitrogen, and sulphur absorption along the gastrointestinal tract was not affected by SBM, but was slowed by BPSBM. Dietary SBM or BPSBM did not alter the morphology of the intestinal mucosa in any sections of the cod intestine. The distal-most structure of the intestine, a compartment with inlet and outlet (anus) valves, showed very high microbial colonisation in the mucosal brush border. Inclusion of SBM in the diet changed the intestinal microflora, increasing the population level of transient bacteria in the pyloric and mid intestine, but reducing the population level of adherent bacteria throughout the intestine. To conclude, Atlantic cod appeared to have a robust and flexible digestive system able to adjust to high dietary levels of soy protein meals.     

Use of 16S rRNA gene sequencing analysis to characterize culturable intestinal bacteria in Atlantic salmon (Salmo salar) fed diets with cellulose or non-starch polysaccharides from soy

Duplicate groups of Atlantic salmon (Salmo salar L.), kept in seawater, were fed fish meal‐based cold‐pelleted diets. Diets with non‐starch polysaccharides (NSP), either cellulose, purified soybean NSP or extruded purified soybean NSP at a dietary level of 100 g kg^?1, were compared with a diet without supplemental NSP and a diet with soybean meal in a 28‐day feeding trial. Isolation and characterizations were limited to culturable bacteria and population levels of aerobic and facultative aerobic heterotrophic autochthonous (adherent) and allochthonous (transient) bacteria present in the mid and distal intestines of Atlantic salmon fed the five different diets estimated using traditional bacteriological techniques. The presence of an autochthonous microbiota was demonstrated using transmission electron microscopy. No significant effects of diet composition were observed on total population levels of culturable bacteria present in the digestive tract, but the study showed that the composition of the gut microbiota (autochthonous or allochthonous) was sensitive to dietary changes. A total of 752 culturable isolates from the intestines were characterized by biochemical and physiological properties. Of these, 188 isolates were further characterized by partial sequencing the 16S rRNA genes. Among these, 146 isolates belonged to 31 phylotypes that were >94% identical to previously described species. However, 42 isolates showed similarity <94% to species available at the National Center of Biotechnology Information. Several of the phylotypes identified in the present study have not been reported previously in the gastrointestinal (GI) tract of fish, including the Gram‐negative bacteria Gelidibacter salicanalis, Pseudoalteromonas elyakovii, Psychrobacter aquimaris, Psychrobacter cibarius, Psychrobacter fozii, Psychrobacter maritimus, Psychrobacter okhotskensis and Psychrobacter psychrophilus. Among the Gram‐positive bacteria identified were Arthrobacter bergeri, Arthrobacter psychrolactophilus, Arthrobacter rhombi, Bacillus pumilus, Bacillus subtilis, Exiguobacterium spp., Microbacterium oxydans, Planococcus maritimus, Sporosarcina ginsengisoli and several bacteria that have been described as unculturable previously. In addition, we identified Carnobacterium inhibens, a lactic acid bacterium that is not frequently isolated from the GI tract of fish. Psychrobacter cibarius was the dominant bacterial species and was isolated from the digestive tract of all fish investigated.     

Lactic acid bacteria vs. pathogens in the gastrointestinal tract of fish: a review

Intensive fish production worldwide has increased the risk of infectious diseases. However, before any infection can be established, pathogens must penetrate the primary barrier. In fish, the three major routes of infection are the skin, gills and gastrointestinal (GI) tract. The GI tract is essentially a muscular tube lined by a mucous membrane of columnar epithelial cells that exhibit a regional variation in structure and function. In the last two decades, our understanding of the endocytosis and translocation of bacteria across this mucosa, and the sorts of cell damage caused by pathogenic bacteria, has increased. Electron microscopy has made a valuable contribution to this knowledge. In the fish‐farming industry, severe economic losses are caused by furunculosis (agent, Aeromonas salmonicida spp. salmonicida) and vibriosis [agent, Vibrio (Listonella) anguillarum]. This article provides an overview of the GI tract of fish from an electron microscopical perspective focusing on cellular damage (specific attack on tight junctions and desmosomes) caused by pathogenic bacteria, and interactions between the ‘good’ intestinal bacteria [e.g. lactic acid bacteria (LAB)] and pathogens. Using different in vitro methods, several studies have demonstrated that co‐incubation of Atlantic salmon (Salmo salar L.) foregut (proximal intestine) with LAB and pathogens can have beneficial effects, the cell damage caused by the pathogens being prevented, to some extent, by the LAB. However, there is uncertainty over whether or not similar effects are observed in other species such as Atlantic cod (Gadus morhua L.). When discussing cellular damage in the GI tract of fish caused by pathogenic bacteria, several important questions arise including: (1) Do different pathogenic bacteria use different mechanisms to infect the gut? (2) Does the gradual development of the GI tract from larva to adult affect infection? (3) Are there different infection patterns between different fish species? The present article addresses these and other questions.     

Effects of soybean meal based diet on growth performance, gut histopathology and intestinal microbiota of juvenile rainbow trout (Oncorhynchus mykiss)

Effects of soybean meal (SBM) based diet on growth performance, histology of the intestinal epithelium and on the gut microbiota of juvenile rainbow trout (Oncorhynchus mykiss) were investigated on two trials lasting for 8 weeks (Trial I) and 18 weeks (Trial II). The microbiological characterization was done both with conventional plating techniques, biochemical profiling and length heterogeneity analysis of PCR amplified 16S rDNA (LH-PCR).Typical histological changes were found after 18 weeks of SBM feeding (Trial II). Mean height of simple foldings were significantly higher within the group fed with fish meal (FM) based diet. These changes were not, however, reflected in the appearance, behavior and weight gain of the fish, although the feed conversion rate (FCR) was higher, compared to fish fed with the traditional FM feed.In both SBM and FM groups the counts of cultivable intestinal bacteria dropped within the first 4 weeks of feeding (Trial I). Subsequently, the bacterial numbers increased in the FM group, but not in the SBM group by the 8th week of the trial. The LH-PCR data suggested also that diet-related qualitative changes in the microbiota had occurred (Trial II). The main identified bacteria were mainly representatives of the genera Aeromonas, Sphingomonas and Chryseomonas, and among the lactic acid bacteria, Lactococcus and Lactobacillus.Future research will be directed to the identification and eventual elimination the SBM-associated factors involved in the inflammatory responses and unfavorable FCR, in particular by modifying the intestinal microbiota.     

The inclusion of plant protein in cod diets, its effects on macronutrient digestibility, gut and liver histology and heat shock protein transcription

This paper reports on the use of plant protein in cod diets, and where corn gluten meal, soybean meal, a mixture of these, or a mixture of wheat gluten meal and soy protein concentrate, substituted fish meal in a regression design up to 440 g kg^?1 plant ingredients. Feeding lasted for a period of 20 weeks. High growth rates were obtained, and fish were able to maintain growth in all groups by increasing feed intake when plant proteins exerted high amounts of the protein fraction. This was confirmed by increased feed conversion ratio (FCR) values. The apparent digestibility measured by means of faecal stripping, showed high apparent digestibility coefficients (ADC) for fat, starch and protein. Small decreases in protein ADC and larger decreases in fat ADC were observed with high levels of plant protein ingredients. No histopathological changes were found, neither in liver nor in the different sections of the gastrointestinal (GI) tract, for any of the diet groups. Expression of stress genes (heat shock protein 70 and 90 (HSP70 and HSP90)) in liver showed no response to high levels of plant protein. Invasion of gut‐bacteria in the distal part of the GI tract was substantial, but independent of diet level of plant ingredients. Gut evacuation analysis showed that the time for a meal to pass through the stomach and the GI tract was more than 72 h, with no variation dependent on diet plant protein level. The major conclusion is that cod shows a high tolerance to the plant protein sources investigated in this experiment, and consequently that Atlantic cod safely can be fed diets holding up to 440 g kg^?1 of the present investigated plant protein ingredients without any adverse effects on intestinal or liver function. There seems to be no gain if feeding frequency exceeds more than one large meal every 24 h at 6–7°C.     

The effects of soybean, linseed and marine oils on aerobic gut microbiota of Arctic charr Salvelinus alpinus L. before and after challenge with Aeromonas salmonicida ssp. salmonicida

Populations of heterotrophic bacteria present in the hindgut region of Arctic charr Salvelinus alpinus L. fed dietary soybean, linseed and marine oils before challenge with Aeromonas salmonicida ssp. salmonicida and marine oil after challenge were estimated using the dilution plate technique. There were differences in bacterial composition between the rearing groups before and after challenge, as well as interindividual variations. For example, carnobacteria were only isolated from the hindgut region of fish fed soybean oil and linseed oil before challenge, whereas Carnobacterium spp. and Carnobacterium funditum‐like species were isolated from fish fed the same oils after challenge. Three non‐motile Aeromonas spp. were isolated from infected fish fed marine oil. One of these isolates was identified as identical to A. salmonicida ssp. salmonicida used in&the challenge test by microbial fingerprinting (amplified fragment length polymorphism). Electron microscopic examinations of hindgut regions demonstrated substantial numbers of bacterial cells associated with enterocytes, but bacterial colonization of the enterocyte surface varied between different rearing groups. The potential of bacteria found associated with the hindgut region to inhibit the fish pathogens A. salmonicida, Vibrio salmonicida and Vibrio anguillarum differed between rearing groups.     

Effect of intraperitoneal injection of immunostimulatory substances on allochthonous gut microbiota of Atlantic salmon (Salmo salar L.) determined using denaturing gradient gel electrophoresis

The allochthonous microbiota in the proximal and distal intestine was investigated in three groups of Atlantic salmon (Salmo salar L.) fed a commercial diet and intraperitoneally injected with (a) phosphate‐buffered saline (control), (b) lipopolysaccharide (LPS) from the fish pathogenic bacteria, Aeromonas salmonicida ssp. salmonicida, and (c) laminaran [β‐(1,3)‐d ‐glucan]. Denaturing gradient gel electrophoresis (DGGE) of the hyper variable V3 region was used to present the microbiota in different experimental groups. Sequencing and phylogenetic analysis of excised DGGE bands suggested that an intraperitoneal injection of LPS from A. salmonicida affects the allochthonous gut bacteria of Atlantic salmon to some extent, as Aeromonas enteropelogenes, Aeromonas veroni, Psychrobacter, Lactobacillus letvazi, Lactobacillus satsumensis, Pantoea, swine manure bacterium and several uncultured bacteria were unique for this group. On the other hand, the bacterial diversity of the allochthonous microbiota did not seem to be affected by injection of β‐(1,3)‐d ‐glucan. Sequences of this experimental group were most closely related to A. enteropelogenes, uncultured Escherichia and Lactobacillus aviarius ssp. aviarius.     

Growth and intestinal morphology in cobia (Rachycentron canadum) fed extruded diets with two types of soybean meal partly replacing fish meal

Juvenile cobias, Rachycentron canadum, were fed extruded diets containing toasted defatted soybean meal (SBM) or untoasted defatted SBM [white flakes (WF)] to study growth and feed conversion, and to study if SBM induces morphological changes in the gastrointestinal (GI) tract. Three diets were produced: a fish meal‐based control diet (FM diet) with 558 g FM kg^?1, and two diets with 335 g FM and either 285 g SBM kg^?1 (SBM diet) or 285 g WF kg^?1 (WF diet). The diets were extruded at approximately 120°C with 280 g kg^?1 moisture. Triplicate groups of cobias (mean weight: 25.9 g) were fed the diets during 6 weeks. Feed intake of the FM and SBM diets were not significantly different, whereas the cumulative feed intake of cobias fed the WF diet was lower (P < 0.05) than that of cobias fed the FM and SBM diets after the first 21‐day period. Specific growth rate and feed conversion ratio were not significantly different between cobias fed the FM and SBM diets, but significantly poorer results were obtained in cobias fed the WF diet. No morphological differences in the GI tract could be attributed to the diets, and cobias fed soy did not develop enteritis in the distal intestine.     

The acute stress response in fed and food deprived Atlantic cod, Gadus morhua L.

The aim of the present study was to evaluate the effect of stress and nutritional state (fed vs food deprived) on the generalized stress response and intestinal integrity in Atlantic cod (Gadus morhua L.). Cod in feeding or food deprived states were subjected to 15 min of acute stress (exhaustive exercise). Blood was collected at 9 intervals from before stress (t = 0), to t = 48 h post stress and analysed for blood haematocrit and haemoglobin, and plasma cortisol, lactate, glucose, osmolality, chloride, as well as the tissue damage indicators glutamate oxaloacetate transaminase, glutamate pyruvate transaminase and thiobarbituric acid reactive substances. Intestinal segments were prepared for histology with the same intervals, while assessment of intestinal integrity and microbiology was performed at t = 0, 4 and 48 h post stress.Subjecting cod to exhaustive stress initiated a standard stress response including increased blood Hct and plasma cortisol, glucose, chloride, osmolality and lactate. Food deprived fish did in general have reduced stress resistance compared to fed fish. For many parameters, cod returned slowly to basal levels. Cellular indicators of tissue damage and oxidative stress increased in a biphasic manner following stress. Stress did not affect gut histology but did transiently increase gut permeability. Furthermore, stress had no effect on the adherent bacterial population level in midgut, but did cause a small decrease in hindgut (non-significant) and hindgut chamber (p < 0.05). Isolates belonging to Carnobacterium were predominant but not affected by stress.In conclusion, food deprived cod are less resistant to stress than fed cod. The magnitude of the response is less than in salmonids, but the effects are persistent (including tissue damage indicators and oxidative stress) and may have negative long term consequences. The gut is relatively resistant to stress, there is however a transient increase in the intestinal permeability and alterations in microbiota that may indicate lower protection against invading pathogens.     

The ability of carnobacteria isolated from fish intestine to inhibit growth of fish pathogenic bacteria: a screening study

In the present study a microtitre plate assay was used to evaluate antagonistic activity of 157 intestinal bacteria belonging to Carnobacterium isolated from Arctic charr (Salvelinus alpinus L.), Atlantic salmon (Salmo salar L.) and wolf fish (Anarhichas lupus L.) against fish pathogenic bacteria. One hundred and forty‐nine strains isolated from Arctic charr fed; (a) different lipid levels and (b) different fatty acids were screened for their ability to inhibit growth of the fish pathogen Aeromonas salmonicida ssp. salmonicida strain AL 2020 (the causative agent of furunculosis). Carnobacterium maltaromaticum and Carnobacterium mobile isolated from fish fed a low‐lipid diet inhibited growth of the pathogen, while none of the Carnobacterium divergens isolated from fish fed the high‐lipid diet had this ability. When Arctic charr was fed different fatty acids, was the frequency of antibacterial ability of C. maltaromaticum highest in strains isolated from fish fed 4%α‐linolenic acid (18:3 n‐3) and lowest in strains isolated from fish fed 4% linoleic acid (18:2 n‐6). Extracellular growth inhibitory compounds harvested in exponential and stationary growth phase from eight carnobacteria strains isolated from three fish species were tested for their ability to inhibit growth of six fish pathogens [A. salmonicida, Vibrio splendidus strain VS11, Vibrio salmonicida strain LFI 315, Vibrio anguillarum strain LFI 317, Moritella (Vibrio) viscosa strain LFI 5000 and C. maltaromaticum (piscicola) CCUG 34645]. The highest antibacterial activity was found when cellular extracts of the producer isolate were harvested in stationary growth phase. Scanning electron microscopy (SEM) investigations of A. salmonicida showed that cell morphology was affected by the inhibitory substance produce by strain 8M851, a Carnobacterium inhibens‐like bacteria.     

Short‐term effects of dietary soybean meal and lactic acid bacteria on the intestinal morphology and microbiota of Atlantic salmon (Salmo salar)

The aim of this study was to evaluate the role of the intestinal microbiota in soybean meal enteritis. Three groups of Atlantic salmon (Salmo salar) were fed for 35 days with different diets: a control diet (CD) containing 510 g kg^?1 fishmeal, diet 1 (D1) containing 378 g kg^?1 of soybean meal and diet 2 (D2) containing D1 supplemented with two viable lactic acid bacteria (LAB). As expected, the fish fed with D1 showed clear signs of distal intestinal inflammation during the study compared with the fish fed CD. For the fish fed with D2, the addition of LAB diminished the inflammation at day 28, but did not abolish it. Microbiological analysis demonstrated that specific bacterial groups were not correlated with the development of enteritis, but were correlated with the three diets. Microbacterium, Pseudomonas, Lactococcus lactis sp. cremoris and Aeromonas VIa were correlated with the CD, Aeromonas VIb and Sporosarcina aquimarina were correlated with D1, and Alcaligenes, Acinetobacter, L. lactis sp. lactis and Carnobacterium maltaromaticum were correlated with D2. Shewanella was not affected by the diet and was present in all fish intestines. Our study suggests that LAB may modulate intestinal inflammation; however, the role of the microbiota in the aetiology of enteritis in fish still requires further study.     

Growth and nutrient utilization of Murray cod Maccullochella peelii peelii (Mitchell) fingerlings fed diets with varying levels of soybean meal and blood meal

Abstract The Australian native freshwater fish Murray cod, Maccullochella peelii pellii (Mitchell), currently supports a fledgling inland aquaculture industry, which is thought to have considerable growth potential. The aim of this study was to evaluate the suitability of two alternate protein sources [blood meal (BM) and defatted soybean meal (SBM)] as substitutes for fish meal at various levels of inclusion in diets for juvenile Murray cod. The growth performance of juvenile Murray cod in response to nine isonitrogenous and isocalorific diets (50% protein, 14% lipid, 20.2 kJ g^?1) consisting of a control diet in which protein was supplied from fish meal, and test diets in which the fish meal protein was substituted at levels of 8%, 16%, 24%, and 32% with BM or SBM was evaluated from a 70‐day growth experiment. The per cent apparent dry matter (% ADC_dm) and percentage protein digestibility (% ADC_p) of the test diets were also determined using Cr₂O₃ as a marker. Survival in all the SBM dietary treatments was high but that of fish on the BM dietary treatments was significantly (P < 0.05) lower than in all the other dietary treatments. Specific growth rate (% day^?1) of Murray cod fed SBM incorporated diets ranged from 1.63 ±  0.06 to 1.78 ±  0.10 and even at the highest level tested (32% of the dietary protein from SBM) was not significantly different (P > 0.05) from the fish fed the control diet (1.65 ±  0.09). Feed conversion ratios of the SBM dietary treatments ranged from 1.36 ±  0.08 to 1.45 ±  0.07. The protein efficiency ratios and protein conversion efficiencies of Murray cod in the soybean meal treatments were also good and for a majority of the SBM diets were better than those for the control diet. Per cent ADC_dm and ADC_p of the SBM diets tested ranged from 70.6 ±  1.46 to 72.3 ±  1.81% and 88.6 ±  0.57 to 90.3 ±  0.17%, respectively, and was not significantly different (P > 0.05) from the control diet (% ADC_dm 74.3 ±  1.63; % ADC_p 91.3 ±  0.55). The reasons for significantly poor survival and growth of Murray cod reared on BM incorporated diets, and relatively poor digestibility of these diets are discussed. The study shows that for Murray cod diets in which fish meal protein is substituted up to 32% performance or carcass composition is not compromised.     

The effect of dietary krill supplementation on epithelium-associated bacteria in the hindgut of Atlantic salmon (Salmo salar L.): a microbial and electron microscopical study

Atlantic salmon (Salmo salar L.) were fed fishmeal protein for 46 days, and 500 g kg⁻¹ of fishmeal protein substituted with meal from Northern krill (Meganyctiphanes norvegica). No differences were observed in weight gain, length gain, feed conversion or specific growth rate between the groups that could be attributed to dietary manipulation. The adherent microbiota in the hindgut of the two rearing groups were further investigated. By substituting fishmeal with krillmeal, the total viable counts of aerobic and facultative aerobic bacteria colonizing the hindgut of Atlantic salmon increased from 8.5 × 10⁴ to 2.2 × 10⁶. Furthermore, dietary krillmeal affected the adherent hindgut microbiota. The Gram‐positive bacteria Carnobacteria piscicola, Microbacterium oxydans, Microbacterium luteolum and Staphylococcus equorum spp. linens and the Gram‐negatives Psychrobacter spp. and Psychrobacter glacincola were not isolated from hindgut of fish fed the krill diet. On the other hand, Pseudomonas fulgida, Pseudomonas reactans and Stenotrophomonas maltophila were not isolated from the control group fed fishmeal. Acinetobacter lwoffi, which is not normally found in the fish gut, was isolated from both feeding groups. Transmission electron microscopy showed bacteria‐like profiles between the hindgut microvilli in both feeding groups indicating autochthonous microbiota. When fish were fed the krill diet, hindgut enterocytes were replete with numerous irregular vacuoles. These vacuoles were not observed in fish fed the fishmeal protein.     

Alternative dietary protein sources for Atlantic salmon (Salmo salar L.) effect on intestinal microbiota,intestinal and liver histology and growth

The present study has addressed the issue of dietary alterations on gut microbiota in fish by investigating modulation of the allochthonous and autochthonous bacterial gut community of Atlantic salmon following feeding with pea protein concentrate, soy protein concentrate, extracted sunflower, poultry by‐product and feather meal. The results revealed that total allochthonous and total autochthonous bacteria isolated from the distal intestine (DI) were affected by dietary modulations. Total autochthonous bacteria in proximal intestine remained unaffected. Corynebacteriaceae dominated the allochthonous bacteria and Lactobacillaceae dominated the autochthonous bacteria community in proximal and DI indicating that the most abundant groups are not shifted by alternative proteins. Some variations were observed between the bacterial communities as result of dietary manipulations. Alternative protein sources resulted in no severe signs of enteritis. Vacuolization of the liver was unaffected by diet. Furthermore, addition of plant materials significantly affected production of acetic acid. Weight of pyloric‐, proximal‐ and DI was influenced by diet, especially feather meal. Growth performance was significantly affected by inclusion of feather meal to the diet. In conclusion the results showed that pea protein concentrate and poultry by‐products are suitable protein replacements for Atlantic salmon and that soy protein concentrate is a potential candidate.     

The effect of dietary chitin on the autochthonous gut bacteria of Atlantic cod ( Gadus morhua L.)

In the present study the impact on autochthonous (adherent) bacteria in proximal intestine (PI) and distal intestine (DI) of Atlantic cod ( Gadus morhua L.) was evaluated following feeding of a control diet and a diet supplemented with 5% chitin. The autochthonous gut bacteria were investigated using denaturing gradient gel electrophoresis (DGGE). Analysis of the microbiota associated with PI and DI of Atlantic cod indicate that dietary chitin modulate the intestinal bacterial community. For example, band 25 ( Escherichia coli–like), band 14 ( Anaerorhabdus furcosa–like) and band 29 (uncultured bacterium–like) in PI were depressed by dietary chitin (P < 0.05). The number of bands (23.7 ± 5.4) in DI of fish fed chitin was marginally higher than the control fish (16.7 ± 2.1) (P = 0.065), and the relative abundances of band 6 (swine faecal bacterium–like) were marginally stimulated by dietary chitin (P = 0.095). Furthermore, the present study reports several novel sequences not previously reported in the gastrointestinal tract of Atlantic cod. Whether the dietary effect of chitin on gut bacterial community has any positive effect of fish health merits further investigations.     

Effects of butyrate glycerides supplementation in high soybean meal diet on growth performance,intestinal morphology and antioxidative status of juvenile black sea bream,Acanthopagrus schlegelii

This study aimed to investigate the effects of graded butyrate glyceride (BG) supplementation levels in high soybean meal diet on juvenile black sea bream. Three hundred and sixty fish were fed diets containing 199 g/kg fishmeal and 450 g/kg soybean meal, with increasing levels of BG at 0, 2, 4, 6, 8 or 16 g/kg for eight weeks. The growth performance of the fish increased with increasing dietary BG supplementation up to 6 g BG/kg, beyond which growth rate reduced significantly (p < .05). Dietary BG supplementation increased the intestinal protease activity, but had no significant (p > .05) effect on lipase and amylase activities. Fish fed the basal diet exhibited villus shortening with a decrease in the number of goblet cells and a reduction in absorptive and digestive epithelial surface, while fish fed ≥4 g BG/kg diets showed a well‐integrated gut, with large absorptive and digestive epithelial surface. Dietary BG supplementation also improved antioxidative capacity by increasing superoxide dismutase and glutathione peroxidase activities while decreasing malondialdehyde content. The inclusion of BG in high soybean meal diets can improve growth performance, maintain healthy gut morphology and enhance antioxidative capacity of black sea bream.     

豆粕替代鱼粉对牛蛙生长、体组成、消化酶活力及肝脏生化指标的影响

为减少牛蛙饲料鱼粉使用量以降低养殖成本,研究了豆粕替代饲料中不同比例的鱼粉对牛蛙的生长性能、体组成、肠道消化酶活力和肝脏生化指标的影响。用豆粕分别替代0%、20%、40%、60%、80%和100%的鱼粉配制出6种等氮等能的实验饲料,每组饲料设3重复,养殖牛蛙60 d。结果显示,豆粕替代鱼粉对牛蛙摄食率、成活率、肝体指数、脏体指数、蛙体水分和灰分含量、蛙腿肌肉组成以及肝脏丙二醛含量的影响不显著;豆粕100%替代鱼粉显著降低牛蛙增重率、特定生长率、饲料系数、蛋白质效率、蛋白质累积率;随豆粕替代鱼粉比例的提高,牛蛙的肥满度和后腿指数呈下降趋势,替代100%鱼粉显著降低牛蛙肥满度,替代60%鱼粉显著降低牛蛙后腿指数;替代80%鱼粉显著降低牛蛙全体粗蛋白的含量;牛蛙全体粗脂肪含量随替代鱼粉比例的提高呈上升的趋势,替代100%鱼粉组粗脂肪含量最高;随着替代比例的提高,牛蛙肠道蛋白酶的活力显著降低,而肠道淀粉酶和脂肪酶活力显著提高。豆粕替代鱼粉显著影响肝脏超氧化物歧化酶和过氧化氢酶活力,其中超氧化物歧化酶活力最低值出现在替代80%鱼粉组,过氧化氢酶活力最低值出现在替代100%鱼粉组。基于以上实验结果,建议牛蛙饲料中豆粕可替代鱼粉的比例为60%~80%。     

Effects of partial substitution of dietary fish meal by fermented soybean meal on growth performance,amino acid and biochemical parameters of juvenile black sea bream Acanthopagrus schlegeli

A feeding trial was conducted to evaluate the effect of replacing fish meal protein with fermented soybean meal (FSM) on the growth performance, feed utilization, amino acid profile, body composition, morphological parameters, activity of antioxidant and digestive enzymes of black sea bream (Acanthopagrus schlegeli) juvenile. Five isonitrogenic and isolipidic diets were prepared with levels of 0 (control), 80, 160, 240 and 320 g kg^?1 FSM. Triplicate groups (40 fish per tank) of juvenile black sea bream with initial weight of 1.17 ± 0.04 g were hand‐fed to visual satiation at three meals per day for 8 weeks. The fish fed diets containing different levels of FSM had no significant differences regarding survival and specific growth rate compared with control group. Feed and protein efficiency ratios of fish fed diet containing 320 g kg^?1 FSM were significantly lower than those of control group. Daily feed intake and daily protein intake of fish fed diet containing 240–320 g kg^?1 were significantly higher than those of control group. Hepatosomatic index and condition factor of fish were not affected by different dietary FSM level. Fish fed diets containing 240–320 g kg^?1 FSM had significantly higher visceral somatic index than control group. Whole body proximate and amino acid compositions of fish were not affected by dietary FSM level. The activity of digestive enzymes in the intestine was not affected by dietary FSM level. The activity of glutathione peroxidase in liver was significantly higher for fish fed the diet containing 160 g kg^?1 FSM compared with control group. This study showed that up to 40% fish meal in the diets of juvenile black sea bream could be replaced by fermented soybean meal with supplementation of methionine, lysine and taurine.     

Effect of dietary soybean meal associated with feeding time on the growth performance and intestinal microbiota composition of northern snakehead

A 63‐day growth trial was conducted with northern snakehead Channa argus to evaluate how rapidly its growth performance and how reproducibly its gut microbiota respond to different dietary protein sources. Four diets were formulated with different levels of soybean meal as a replacement for fishmeal (0%, 25%, 50% and 75%). Each diet was fed to three replicates of juvenile C. argus (30 juveniles per replicate, initial weight 8.65 ± 0.25 g) to produce groups G1, G2, G3 and G4 respectively. During this trial, survival rate, growth performance and intestinal microbiota composition were determined on days 9, 21 and 63. At day 9, there was no effect of the dietary soybean meal on the final weight (Wt), weight gain (WG) and specific growth rate (SGR) between the four groups (p > 0.05). However, at day 21 (p < 0.05), they were significantly lower in G4 fish than that in G1 and G2. The highest Wt, WG and SGR were found in G1 and G2 fish, the lowest growth was found in G4 fish at day 63 (p < 0.05). Furthermore, higher operational taxonomic units (OTUs) and alpha diversity were found in G4. With the dietary soybean level increased, the proportion of Firmicutes, Bacteroidetes and Verrucomicrobia, as well as some genera of bacteria (Carnobacterium, Cetobacterium, Planctomyces, Shewanella and Thermomonas) significantly increased in the G3 and G4 fish (p < 0.05). However, the OTUs, Chao index, and the proportion of Firmicutes and some genera (Acinetobacter, Bacillus and Geobacillus) in G4 fish were significantly higher at days 21 and 63 than that at day 9 (p < 0.05). Taken together, in response to dietary soybean meal levels, dynamic and significant changes in microbiota occurred, which then ultimately attained a new equilibrium.     

Effects of replacing fish meal and oil with plant resources in on‐growing diets for Atlantic cod Gadus morhua L

The present paper gives an overview on the use of plant protein and plant oils as replacers for fish meal and fish oil in diets for Atlantic cod Gadus morhua L. In focus are effects on growth, feed utilization, digestibility, gut health, muscle and liver uptake and retention of nutrients, and muscle quality. Plant oil can replace fish oil without affecting growth provided that the requirement of marine long chain (LC) n‐3 fatty acids is met, but the altered dietary fatty acid profile in diet will be reflected in both muscle and liver. This can reduce the value of cod liver as an oil source for cod liver oil production. For the fish itself, there are more challenges replacing fish meal than fish oil, due to the amount of fibre and antinutrients in plant protein meals. However, A. cod seems to tolerate a wide range of plant types and their inclusion levels provided that the amino acids requirements are met. It is our view that there is sufficient knowledge to be able to design an A. cod diet based on a mixture of plant and marine ingredients and be able to predict performance such as growth, feed utilization, digestibility, liver size and fish health in general.