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To develop specific recommendations on the feeding strategies for farmed lumpfish, four duplicate groups (n = 70; N = 280) of lumpfish with a mean ± SD start weight of 30.4 ± 5.3 g were distributed among eight sea cages (5 × 5 × 5 m) each stocked with 220 one year old Atlantic salmon with a mean (± SD) weight of 1485.9 ± 213.2 g. The fish were fed either pelleted feed at 3% BW−1 or with feed blocks at 1.5%, 2% and 3% BW−1 respectively for 66 days. There were clear differences in growth performance between the four treatment groups with lumpfish fed with pelleted feed attaining the highest weight gain. There were only minor histopathological changes observed between the dietary treatments with mainly mild focal and multifocal inflammation observed in sampled tissues. There were no significant differences in liver vacuolisation between the dietary groups and baseline samples with most of the livers evaluated appeared to be vacuolized within what is regarded as normal range for all four treatment groups. Only minor differences in welfare score between the four treatment groups were found. The incidence of cataracts varied between the treatment groups and was correlated to differences observed in growth between the four groups. Lumpfish fed once daily from automatic feeders with pelleted feed had the highest incidence and severity of cataracts. This study suggests that feeding lumpfish with moderate amounts of feed blocks (≤ 2% BW−1) may be advantageous for maintaining slow growth and good welfare in salmon cages, and this should be further tested in large scale studies in commercial salmon farms. • We assessed growth, cataract development, welfare score and gut histopathology in lumpfish fed either pelleted feed or with feed blocks. • Lumpfish fed with pelleted feed attaining the highest weight gain. • Lumpfish fed with pelleted feed had the highest incidence and severity of cataracts. • Only minor histopathological changes observed between the dietary treatments. • Feeding lumpfish with moderate amounts of feed blocks (≤ 2% B−1) in salmon cages is recommended. [ABSTRACT FROM AUTHOR]

Abstract Three duplicate groups of individually tagged lumpfish (mean initial weight: 22.3 ± 2.5 g) were fed either daily (7DW); four days per week (4DW) or three days per week (3DW) at a feeding rate of 2% body weight day−1 for a period of 126 days. There were significant differences in growth rates between the groups with the 7DW fish having the highest growth rates. Cataract prevalence was 53% lower in the 3DW group compared to the 7DW group. Histological examination showed that in some individuals in all three groups there was moderate expansion of the lamina propria in the mid and hind gut regions of the intestine with tissue most likely to represent fibrous tissue with scattered leucocytes. The severity of inflammation appeared to increase the more frequent the fish were fed with the 7DW fish having the highest inflammation score in these tissues. Feeding fish daily also resulted in higher levels of liver vacuolisation and chronic inflammation of the lamina propria in the mid and hind gut region of the intestines. Results from the present study show that restricted feeding regimes can be used to control growth and improve gut and eye health in lumpfish. Highlights • We assessed growth, cataract development and gut histopathology in lumpfish feed 7, 4 and 3 days per week (DW). • Growth and cataract prevalence was lowest in the 3DW group. • Liver vacuolisation and chronic inflammation in the gut was higher in the 7DW group. [ABSTRACT FROM AUTHOR]

Changing trends in fish feed formulation, with progressively higher inclusion levels of plant ingredients, are invariably introducing more fibre despite the fact that this component cannot be utilized by most fish. The effects of increasing insoluble dietary fibre level on growth, nutrient utilisation, blood parameters and gut health in European sea bass ( Dicentrarchus labrax L.) were studied over a period of 117 days. Moreover, investigation on digesta transit time through gastrointestinal evacuation pattern and digesta characteristics (moisture of digesta) were studied. Five isoproteic diets were formulated to contain increasing insoluble fibre levels, neutral detergent fibre, NDF (7.2, 8.9, 11.5, 13.1 and 15.5%) derived by the inclusion of sunflower hulls and soybean hulls. No significant differences due to fibre inclusion levels were observed in final body weight, specific growth rate, feed intake, feed conversion rate, protein and lipid efficiency. No significant differences in serum total protein, glucose, triglycerides, alkaline phosphatase and inorganic phosphorous were found. All the histological sections showed normal intestinal architecture, and inflammatory and/or degenerative changes were not present in any histological section from all subjects examined. The investigation into gastrointestinal evacuation pattern revealed no significant differences between treatments, however higher dietary fibre levels seem to increase the time required to empty the stomach while the time required to empty 90% of the hindgut content was similar in all the treatments: around 46–47 h. No differences were found between diets in the moisture content of digesta along the digestive tracts. We can conclude that the different insoluble fibre levels tested in this trial have no effects on overall performances and feed efficiency in European sea bass. Results from blood biochemistry profile and histology confirm good nutritional and health status of fish under all feeding treatments. The inclusion of fibre had no influence on digesta transit time. In formulation of feed for the on-growing of European sea bass insoluble fibre derived from sunflower hulls and soybean hulls can be included at a level of up to 15.5%. [ABSTRACT FROM AUTHOR]

The present study evaluated the effects of magnesium (Mg) on growth, antioxidant capacity, intestinal morphology and ammonia nitrogen resistance in juvenile oriental river prawn, Macrobrachium nipponense. Six semipurified diets (crude protein 401.1 g kg−1 diet; crude lipid 88.7 g kg−1 diet) containing Mg levels of 1.1, 1.4, 1.6, 2.1, 2.8 or 4.5 g kg−1 were formulated. A total of 1080 healthy juvenile prawns (0.151 ± 0.003 g) were randomly stocked into eighteen 300 L tanks (100 × 80 × 60 cm), each tank with 60 prawns. Each experimental diet was fed to prawns in triplicate twice daily (08:00 and 17:00) for eight weeks. After the feeding trial, 20 prawns from each tank were challenged with 37 mg/L ammonia nitrogen for 96 h, and the hemolymph, hepatopancreas and muscle of the rest of the prawns were collected. Final biomass was higher in prawns fed diets containing 1.6 and 2.1 g Mg kg−1 compared with those fed the diet with 1.1 g kg−1. Higher alkaline phosphatase (ALP) activity was obtained in the serum of prawns fed the 2.1 and 2.8 g Mg kg−1 diets. The highest activities of hepatopancreas superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and total antioxidant capacity (T-AOC) were observed in prawns fed 1.6–2.8 g Mg kg−1 of feed, and the lowest hepatopancreas malondialdehyde (MDA) concentrations and serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities were found in these treatment groups. Similarly, the prawns fed diets with 1.6 and 2.1 g Mg kg−1 had significantly lower MDA concentrations and cumulative mortality and higher antioxidant enzyme activities after ammonia nitrogen exposure. The intestinal epithelial cells were closely attached to the membrane in prawns fed the 2.1 g Mg kg−1 diet, but they were partly detached in those fed the 1.1 and 4.5 g Mg kg−1 diets. The minimum dietary Mg supplementations of juvenile M. nipponense were determined to be 1.6, 1.9, 2.0 and 2.2 g kg−1 feed, respectively, using broken-line regression analysis based on the final biomass, SOD, ALT and ALP. • Optimal dietary magnesium (Mg) enhanced antioxidant capacity and health of juvenile Macrobrachium nipponense. • After ammonia stress, prawns fed on 1.6 and 2.1 g Mg kg−1 had lower cumulative mortality and higher antioxidant capacity. • Dietary supplementation of 1.6–2.2 g Mg kg−1 feed is recommended to promote the growth and well-being of juvenile prawns. [ABSTRACT FROM AUTHOR]

Abstract: A trial on turbot (Psetta maxima) juveniles was undertaken to evaluate the effect of replacing dietary fishmeal (FM) with a complementary mixture of plant proteins (PP) consisting of soybean meal (SBM), wheat gluten meal (WGM) and corn gluten meal (CGM). Four practical diets were formulated to progressively replace 25% (PP25), 39% (PP39), 52% (PP52) and 66% (PP66) of FM protein. Forty animals per tank (initial weight 24.2±4.4g) were randomly distributed into twelve 450-liter square tanks connected to a closed recirculation system (temperature 18±1°C). The diets were tested in triplicate for 77days. Final weight ranged from 126.6g (PP25) to 99.5g (PP66). Voluntary feed intake of group PP66 (55.5gfish−1) was significantly lower than in PP25. Specific growth rate in fish fed diet PP25 (2.14% day−1) was significantly higher than those found both in PP52 (2.01% day−1) and PP66 (1.82% day−1) groups. Feed conversion ratio (FCR) in groups PP25 and PP39 (0.66–0.67) was lower in comparison with those of the other groups (FCR 0.70–0.74). None of the diets affected whole-body composition and hepatosomatic index. Condition factor significantly decreased with increasing dietary PP (2.06, 2.02, 1.97 and 1.91) whereas a significant increase in viscerosomatic index was observed in fish fed PP52 and PP66 (6.70–6.95) in comparison with the other two groups (6.31–6.21). Reduced protein retention was found in groups fed diet PP52 and PP66, with protein efficiency ratio (PER) ranging from 2.71 to 2.63 and gross protein efficiency (GPE) from 40.3 to 40.0, in comparison with the other two groups (PER 2.83 and GPE 45.5–45.8), even though apparent digestibility coefficients were not reduced. Ammonia excretion, (g total ammonia nitrogen 100gproteinintake−1), was significantly higher for group PP25 (3.41) than group PP52 (2.61). Gut histology examined in four different sites of intestine (pyloric caeca, proximal, intermediate and distal intestine) revealed no noticeable differences among fish of the various diet groups. In conclusion, substitution of a mixture of SBM, WGM and CGM for up to 52% of FM protein did not reduce feed intake, and at 39% substitution, turbot maintained optimal growth rate and nutrient utilization. Worsened FCR of fish fed diets containing higher plant protein levels was not associated with a reduced digestibility of ingredients or alterations of gut histology. [Copyright &y& Elsevier]

Abstract: Two experiments were conducted in order to investigate the effect of dietary mannan oligosaccharides (MOS) on gilthead sea bream (Sparus aurata). Experiment I was designed to assess the effect of dietary MOS (0%, 0.2% and 0.4%) on fish fed diets containing fishmeal (FM) as the only protein source. Experiment II was designed to assess the effect of MOS (0% and 0.4%) on fish fed soybean meal (SBM) as a partial replacement of FM (SBM inclusion 31% of diet). After 9weeks feeding on the experimental diets growth parameters, body composition, liver and intestinal histology and intestinal microbial diversity were assessed. The results showed that mean final weight, specific growth rate (SGR), feed conversion ratio (FCR) and protein efficiency ratio (PER) remained unaffected by MOS supplementation of fish fed FM or SBM diets. However, compared to the control group (FM0), condition factor (K) and hepatosomatic index (HSI) were significantly lower in fish fed 0.2% MOS (FM02) and 0.4% MOS (FM04), respectively. These parameters were unaffected in SBM-fed fish. Body proximate composition remained unaffected by MOS supplementation in fish fed either FM or SBM diets (P >0.05). Histological evaluation revealed that MOS had no effect on glycogen deposition in liver and no effect on gross villi morphology in the anterior intestine in either Experiment I or II. However, relative to the control groups (FM0) dietary MOS appeared to improve gross morphological absorptive surface area in the posterior intestine in Experiment I. Electron microscopy revealed that dietary MOS had a pronounced effect at the ultrastructural level in both experiments, as microvilli density and length were elevated in both intestinal regions in fish fed both the FM and SBM based diets. No significant histological differences were found between respective FM0 and SBM0 groups. DGGE analysis revealed that both SBM and MOS affected the intestinal microbial species richness and diversity. However, the effect of dietary MOS on the gastrointestinal microbiota was more pronounced in FM-based diets (Experiment I) as was reflected by increased species richness and diversity and reduced similarity between microbial profiles of the different FM groups. The effect of MOS in Experiment II on SBM-fed fish was marginal, as species richness and diversity remained unaffected and similarity between microbial profiles of the SBM groups and replicates remained high (i.e. >80%). Dietary SBM exerted a greater effect on gut microbiota than dietary MOS. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Fatty acid ethyl esters (FAEE) are a potential alternative to fish oil as a source of polyunsaturated fatty acids in fish feeds. This investigation examined the growth performance, lipid composition, and intestinal and liver histology of rainbow trout (Oncorhynchus mykiss) fed experimental starter diets with graded levels of FAEE and fish oil. Five experimental diets were formulated with 20% total lipid content and 0%, 25%, 50%, 75%, and 100% replacement of Alaskan Pollock oil with FAEE oil, and they were formulated with analogous fatty acid levels. The five diets used defatted fish meal as the primary protein source, and a sixth diet was included that used full-fat fish meal and extracted fish oil. Triplicate groups of rainbow trout (144 ± 20 mg initial weight) were fed experimental diets for 62 days on a restricted feeding regime (4–5.5% biomass/day). The group fed the full-fat fish meal diet had faster growth and a lower feed conversion ratio than the defatted fish meal diet groups after 31 and 62 days of feeding. The growth rate and feed conversion ratios of fish were significantly different between the FAEE-containing diet groups in the first 31 days of feeding, but were not significant from 32 to 62 days of feeding. Fatty acid analysis showed similarity between the fatty acid profiles in experimental diets and in fish muscle and liver tissues at the end of the experiment (all groups mean weight ~3.6 g/fish). Satiation feed intake for a single day was measured at 31 days of feeding, and feed intake was higher in the 100% FAEE diet than the control (8.3 ± 1.1% vs 6.4 ± 0.3% daily satiation ratio). This result suggests that FAEE has a positive effect on voluntary feed intake. Histological analysis of posterior intestine enterocytes and hepatocytes showed a significant reduction in lipid vacuole size in the 100% FAEE group, relative to the defatted and full-fat fish meal control groups. These results suggest that rainbow trout had utilized diet with ≥50% FAEE less efficiently in the first feeding phase, likely due to reduced fatty acid absorption, but that these trends were diminished as fish grew to a larger size. • Test diets were created using Alaskan pollock oil and/or fatty acid ethyl ester (FAEE) oil with analogous fatty acid levels. • Voluntary feeding was greater in the 100% FAEE diet than the control diet (8.3 ± 1.1% vs 6.4 ± 0.3% daily satiation ratio). • Liver and posterior intestine histology results suggest that FAEE oil is not absorbed as efficiently as Alaskan pollock oil. • Up to 25% of fish oil can be replaced with FAEE oil in trout starter feeds without significantly effecting growth rates. [ABSTRACT FROM AUTHOR]