Feeding Atlantic salmon Salmo salar L. soybean products: effects on disease resistance (furunculosis), and lysozyme and IgM levels in the intestinal mucosa

Two trials were initiated to investigate the consequences of including various soybean products in diets for Atlantic salmon Salmo salar L. on (1) mortality following infection by Aeromonas salmonicida ssp. salmonicida during a cohabitation challenge, and (2) the lysozyme and IgM content of the intestinal mucosa. Groups of salmon were fed control diets containing fishmeal as the sole protein source (Contr1 and Contr2, respectively), soy concentrate-containing diets (SoyConc1 and SoyConc2, respectively), or diets containing either solvent-extracted soybean meal (SoyMeal, trial 1) or soybean molasses (SoyMol, trial 2), an alcohol extract of soybean meal. Both SoyMeal and SoyMol caused enteritis-like changes in the distal intestine, which were not observed in fish fed the Contr1, Contr2, SoyConc1, or SoyConc2 diets. There were significant differences ( P  < 0.05) in mortality between feeding groups following the A.s. salmonicida challenge: these differences were greatest in fish fed SoyMeal (65.6%), least in fish fed SoyConc1 (60.5%), and intermediate in the fish fed the Contr1 diet (62.9%). The SoyMol diet caused significantly ( P  < 0.0001) increased levels of both lysozyme and IgM in the mid and distal intestinal mucosa. It is concluded that components of soybean meal and soybean molasses cause an inflammatory response in the distal intestine that may lead to increased susceptibility to furunculosis.     

The influence of environmental temperature on the apparent nutrient and fatty acid digestibility in Atlantic salmon (Salmo salar L.) fed finishing diets containing different blends of fish oil, rapeseed oil and palm oil

A 12‐week feeding trial was conducted to investigate the interactive effects between water temperature and diets supplemented with different blends of fish oil, rapeseed oil and crude palm oil (CPO) on the apparent nutrient and fatty acid digestibility in Atlantic salmon. Two isolipidic extruded diets with added fish oil fixed at 50% and CPO supplemented at 10% or 25% of total added oil, at the expense of rapeseed oil, were formulated and fed to groups of Atlantic salmon (about 3.4 kg) maintained in floating cages. There were no significant effects (P>0.05) of diet on growth, feed utilization efficiency, muscle total lipid or pigment concentrations. Fatty acid compositions of muscle and liver lipids were mostly not significantly different in salmon fed the two experimental diets but showed elevated concentrations of 18:1n‐9 and 18:2n‐6 compared with initial values. Decreasing water temperatures (11–6°C) did not significantly affect protein, lipid or energy apparent digestibilities of the diets with different oil blends. However, dry matter digestibility decreased significantly in fish fed the diet with CPO at 25% of added oil. Increasing dietary CPO levels and decreasing water temperature significantly reduced the apparent digestibility (AD) of saturated fatty acids. The AD of the saturates decreased with increasing chain length within each temperature regimen irrespective of CPO level fed to the fish. The AD of monoenes and polyunsaturated fatty acids was not affected by dietary CPO levels or water temperature. No significant interaction between diet and water temperature effects was detected on the AD of all nutrients and fatty acids. The results of this study showed that the inclusion of CPO up to about 10% (wt/wt) in Atlantic salmon feeds resulted in negligible differences in nutrient and fatty acid digestibility that did not affect growth performance of fish at the range of water temperatures generally encountered in the grow‐out phase.     

Effects of feed processing conditions and acid salts on nutrient digestibility and physical quality of soy‐based diets for Atlantic salmon (Salmo salar)

Two experiments were conducted to investigate effects of feed processing conditions and potassium diformate (KDF) supplementation on apparent digestibility of nutrients in Atlantic salmon (Salmo salar) and physical quality of extruded feed. In Exp. 1, diets with raw or expander pretreated full‐fat soybean meal (FFSBM) at 100 or 120 °C were extruded at 110 °C. Expander pretreatment significantly (P < 0.05) improved the digestibility of arginine, glutamine and tyrosine in Atlantic salmon. The higher digestibility of expander pretreated FFSBM was confirmed in mink (Mustela vison). In Exp. 2, diets with defatted soybean meal (SBM) were extruded at 110, 130 or 150 °C. The results showed that increasing extrusion temperatures significantly (P < 0.05) improved the digestibility of most major nutrients and amino acids in Atlantic salmon. In general, KDF supplementation to FFSBM and SBM diets did not affect digestibility of nutrients in Atlantic salmon or mink. Expander pretreatment and increasing extrusion temperatures increased pellet expansion, while KDF supplementation reduced pellet expansion.     

Alcohol-soluble components in soybeans cause morphological changes in the distal intestine of Atlantic salmon, Salmo salar L.

Standard soybean meal, heat treated to differing degrees and containing varying levels of soybean lectin and trypsin inhibitor, was used to study the effect of soybean-containing diets on the morphology of the distal intestine in Atlantic salmon, Salmo salar L. A reference diet based on fish meal and a fish meal diet mixed with an alcohol extract of soybean meal were used. The fish (145 g) were kept in 27 m³ net pens (200 fish per pen) in sea water with an average temperature of 11 °C for 12 weeks. Whereas a normal morphology of the distal intestine was seen in the fish fed the reference diet, all soybean diets caused alterations in the distal intestine irrespective of heat treatment. Similar changes were observed with the diet which had added alcohol solubles. It is concluded that alcohol-soluble components in the soybeans are responsible for the observed changes. It cannot be determined which of the soybean antinutrients is causing the alterations from the present study. Oligosaccharides and saponines are possible candidates. However, the possibility that unknown antinutrients are affecting the salmon intestine should not be overlooked.     

Nutrient digestibilities and gut function in Atlantic salmon (Salmo salar) fed diets with cellulose or non-starch polysaccharides from soy

Duplicate groups of Atlantic salmon (Salmo salar), kept in saltwater, were fed fish meal based cold-pelleted diets where graded levels of native or extruded non-starch polysaccharides (NSP) from soybeans replaced cellulose, at a total NSP level of 100 g kg^− 1 for 28 days. The study also included a diet where defatted soybean meal (SBM) constituted the NSP at a level of 100 g kg^− 1 and a reference diet without NSP supplementation.The SBM diet resulted in a significant reduction in faecal dry matter content, apparent digestibilities of starch and organic material, and growth, and an increased faecal output of several elements (K, Na, Zn), compared to all the other diets. Morphological changes were only seen in the intestine of the fish fed the SBM, i.e. the diets holding purified soy-NSP did not induce enteritis. When compared to the diet without NSP, cellulose addition increased faecal dry matter, while inclusion of native soy-NSP reduced it. Dry matter in faeces and apparent digestibility of crude protein decreased in a linear manner, while the digestibility of starch and faecal output of K and Na increased linearly when native soy-NSP replaced graded levels of cellulose from 0 to 100 g kg^− 1 feed. When diets with 75 or 100 g kg^− 1 of native NSP and extruded soy-NSP were compared, fish fed native soy-NSP had reduced faecal dry matter, higher digestibility of starch, and increased faecal output of Cu, Fe, and K. Dry matter in faeces and faecal output of Cu was lower for the highest inclusion level, while digestibility of starch and faecal output of Mn and K were higher.In conclusion, soy-NSP was inert compared to the fish meal reference, with respect to nutrient digestibilities and intestinal pathologies, but affected faecal mineral excretion in Atlantic salmon.     

Growth, feed efficiency, digestibility and nutrient distribution in Atlantic cod (Gadus morhua) fed two different fish meal qualities at three dietary levels of vegetable protein sources

Atlantic cod were fed six diets where the ratio of protein from fish meal to vegetable protein were varied from 91%, 67% to 46%, respectively. The experimental groups were performed in triplicate in a 20 week growth trial, increasing fish weight from about 167 g to 690 g. The vegetable protein sources constituted full-fat soybean meal and corn gluten meal at a fixed ratio of 1:2, and replaced either a high quality fish meal (DC_Mink 92.3%) or a lower quality fish meal (DC_Mink 85.6%) in the diet. All diets were extruded and balanced to be equal in gross energy, crude protein, lipid, carbohydrate, lysine and phosphorus. No difference in growth (SGR 1%) was observed comparing the two fish meal qualities. However, feed intake was significantly higher (9%) and feed efficiency lower (10%) for lower quality fish meal compared to high quality fish meal. Protein and amino acid digestibility was significantly reduced in the lower quality fish meal, while unaffected by vegetable protein inclusion for both fish meal qualities. Protein utilization as measured by protein efficiency ratio and net protein value was not affected by fish meal inclusion, except in the diet using lower quality fish meal and high vegetable protein inclusion. Lipid and energy digestibility was significantly reduced by vegetable protein inclusion for both fish meals. The lower fish meal quality increased lipid deposition in the liver and affected slaughter quality of cod by increasing HSI and dressing out percentage at low and intermediate substitution levels. Muscle composition showed small dietary changes except for arginine, while liver fatty acid composition clearly reflected fatty acid profile of full-fat soya in the diets. Corn gluten meal and full-fat soybean meal (2:1) can replace approximately 50% of dietary protein without affecting feed intake, growth, protein digestibility or slaughter quality of cod when exchanging high quality fish meal. For the lower quality fish meal diets some lower inclusion of vegetable protein sources seem to be acceptable.     

Growth, feed conversion and chemical composition of Atlantic salmon (Salmo salar L.) and Atlantic halibut (Hippoglossus hippoglossus L.) fed diets supplemented with krill or amphipods

The effects of partial replacement of fish meal (FM) with meal made from northern krill (Thysanoessa inermis), Antarctic krill (Euphausia superba) or Arctic amphipod (Themsto libellula) as protein source in the diets for Atlantic salmon (Salmo salar L.) and Atlantic halibut (Hippoglossus hippoglossus L.) on growth, feed conversion, macro‐nutrient utilization, muscle chemical composition and fish welfare were studied. Six experimental diets were prepared using a low‐temperature FM diet as control. The other diets included northern krill where 20, 40 or 60% of the dietary FM protein was replaced with protein from northern krill, and two diets where the FM protein was replaced with protein from Antarctic krill or Arctic amphipod at 40% protein replacement level. All diets were iso‐nitrogenous and iso‐caloric. Atlantic salmon grew from 410 g to approximately 1500 g during the 160 day experiment, and Atlantic halibut grew from 345 g to 500–600 g during the 150 day experiment. Inclusion of krill in the diets enhanced specific growth rate in salmon, especially during the first 100 days (P < 0.01), and in a dose–response manner in halibut for over the 150 day feeding period (P < 0.05). Feed conversion ratio did not differ between dietary treatments, and no difference was found in dry matter digestibility, protein digestibility and fish muscle composition. Good growth rates, blood parameters within normal ranges and low mortalities in all experimental treatments indicted that fish health was not affected either Atlantic salmon or Atlantic halibut fed the various zooplankton diets.     

Partial substitution of fishmeal with soybean meal products and derivatives in diets for the gilthead sea bream Sparus aurata (L.)

Two growth trials were conducted to evaluate the nutritional quality of several soybean products as constituents in diets for the gilthead sea bream, Sparus aurata (L.). In a preliminary experiment, the fish were fed six diets containing different levels of solvent extracted soybean meal as a replacement for white fishmeal at four substitution levels: 10, 20, 30 and 40% of the fishmeal protein component. The diets supported less growth as the inclusion of soybean meal increased. However, significant reductions in growth were apparent at the 30% substitution level. All growth parameters followed the same trend. In the second experiment, six diets with 35% of the total protein contributed from differently processed soybean meals were tested. The products included three industrial full-fat meals heat processed for different periods, a solvent extracted meal and a soya protein concentrate. Protein digestibility coefficients were measured for all the experimental diets. All growth parameters of the fish fed the underheated full-fat meal, solvent extracted meal and soya concentrate were significantly lower than the control group. Protein digestibility coefficients were similar with no statistical differences (P < 0.05).     

Net production of Atlantic salmon (FIFO,Fish in Fish out < 1) with dietary plant proteins and vegetable oils

Adult Atlantic salmon (Salmo salar; approximately 800 g start weight) were fed diets with a high replacement of fish meal (FM) with plant proteins (70% replacement), and either fish oil (FO) or 80% of the FO replaced by olive oil (OO), rapeseed oil (RO) or soybean oil (SO) during 28 weeks in triplicate. Varying the lipid source only gave non‐significant effects on growth and final weight. However, a significantly reduced feed intake was observed in the SO fed fish, and both feed utilization and lipid digestibility were significantly reduced in the FO fed fish. Limited levels of dietary 18:3n‐3, precursor to EPA and DHA, resulted in no net production of EPA and DHA despite increased mRNA expression of delta‐5‐desaturase and delta‐6‐desaturase in all vegetable oil fed fish. Net production of marine protein, but not of marine omega‐3 fatty acids, is thus possible in Atlantic salmon fed 80% dietary vegetable oil and 70% plant proteins resulting in an estimated net production of 1.3 kg Atlantic salmon protein from 1 kg of FM protein. Production of one 1 kg of Atlantic salmon on this diet required only 800 g of wild fish resources (Fish in ‐ Fish out < 1).     

Apparent digestibility of macro‐nutrients and phosphorus in plant‐derived ingredients for Atlantic salmon,Salmo salar and Arctic charr,Salvelinus alpinus

Alternative protein sources for aquafeeds need to be indentified in order to increase the efficiency of production. Many studies have examined terrestrial plant meals/protein concentrates as alternatives. Recently the focus has turned to aquatic protists and plants as well as by‐products from other industries, such as breweries. Atlantic salmon, Salmo salar, and Arctic charr, Salvelinus alpinus, were fed diets containing canola meal, soybean meal, corn gluten meal, soy protein concentrate, barley protein concentrate, and solar dried algae included at 30% of the test diet. Barley protein concentrate had the highest apparent protein digestibility values for both species (96.3% for Atlantic salmon and 85.1% for Arctic charr), followed by corn gluten meal. Algae had the highest organic matter digestibility value for arctic charr (80.1%) while corn gluten meal had the highest organic matter digestibility value for Atlantic salmon (88.4%). Algae had a high energy apparent digestibility coefficient (82.4 salmon, 82.7 charr) along with corn gluten meal (78.5 salmon, 82.7 charr) for both species. In general, Atlantic salmon had higher apparent digestibility coefficients compared to Arctic charr for most of the tested ingredients. Both corn gluten and barley protein concentrate appear good candidates as alternative protein sources with both species.     

Insect‐based diets high in lauric acid reduce liver lipids in freshwater Atlantic salmon

We evaluated the effect of a diet containing insect meal and insect oil on nutrient utilization, tissue fatty acid profile and lipid metabolism of freshwater Atlantic salmon (Salmo salar). Insect meal and insect oil from black soldier fly larvae (Hermetia illucens, L.; BSF), naturally high in lauric acid (12:0), were used to produce five experimental diets for an eight‐week feeding trial. 85% of the dietary protein was replaced by insect meal and/or all the vegetable oil was replaced by one of two types of insect oil. A typical industrial diet, with protein from fishmeal and soy protein concentrate (50:50) and lipids from fish oil and vegetable oil (33:66), was fed to a control group. The dietary BSF larvae did not modify feed intake or whole body lipid content. Despite the high content of saturated fatty acids in the insect‐based diets, the apparent digestibility coefficients of all fatty acids were high. There was a decrease in liver triacylglycerols of salmon fed the insect‐based diets compared to the fish fed the control diet. This is likely due to the rapid oxidation and low deposition of the medium‐chain fatty acid lauric acid.     

The effect of temperature and dietary fat level on tissue lipid composition in Atlantic salmon (Salmo salar) fed wax ester‐rich oil from Calanus finmarchicus

Copepod oil (CO) from the marine zooplankton, Calanus finmarchicus, is a potential alternative to fish oils (FOs) for inclusion in aquafeeds. The oil is composed mainly of wax esters (WE) containing high levels of saturated fatty acids (SFAs) and monounsaturated fatty alcohols that are poorly digested by fish at low temperatures. Consequently, tissue lipid compositions may be adversely affected in salmon‐fed CO at low temperatures. This study examined the lipid and FA compositions of muscle and liver of Atlantic salmon reared at two temperatures (3 and 12 °C) and fed diets containing either FO or CO, supplying 50% of dietary lipid as WE, at two fat levels (～330 g kg^?1, high; ～180 g kg^?1, low). Fish were acclimatized to rearing temperature for 1 month and then fed one of four diets: high‐fat fish oil (HFFO), high‐fat Calanus oil (HFCO), low‐fat fish oil (LFFO) and low‐fat Calanus oil (LFCO). The fish were grown to produce an approximate doubling of initial weight at harvest (220 days at 3 °C and 67 days at 12 °C), and lipid content, lipid class composition and FA composition of liver and muscle were determined. The differences in tissue lipid composition between dietary groups were relatively small. The majority of FA in triacylglycerols (TAG) in both tissues were monounsaturated, and their levels were generally higher at 3 °C than 12 °C. Polyunsaturated fatty acids (PUFA), particularly (n‐3) PUFA, predominated in the polar lipids, and their level was not significantly affected by temperature. The PUFA content of TAG was highest (～26%) in the muscle of fish fed the HFCO diet at both temperatures. Tissue levels of SFAs were lower in fish‐fed diets containing HFCO than those fed HFFO, LFFO or LFCO, particularly at 3 °C. The results are consistent with Atlantic salmon being able to incorporate both the FA and fatty alcohol components of WE into tissue lipids but, overall, the effects of environmental temperature on tissue lipids were more pronounced in fish fed the CO diets than FO diets.     

Apparent Digestibility Coefficients of Various Feed Ingredients for Grouper Epinephelus coioides

Apparent digestibility coefficients (ADC) of dry matter, crude protein, lipid, gross energy, amino acids, and fatty acids in white fish meal, brown fish meal, soybean meal, peanut meal, and yeast were determined for grouper Epinephelus coioides. Apparent digestibility was determined using a reference diet with 0.5% chromic oxide indicator and test diets that contained 70% reference diet and 30% of the feed ingredient being evaluated. The fish, averaging 12.0 g, were held in 250-L tanks at a density of 30 fish per tank. Feces were collected from three replicate groups-of fish. Apparent dry matter digestibility of ingredients was 78.85 ± 2.43, 79.11 ± 0.61, 69.85 ± 3.60, 73.67 ± 2.30 and 57.70 ± 4.69% for white fish meal, brown fish meal, soybean meal, peanut meal, and yeast, respectively. Apparent gross energy digestibility of ingredients was 93.27 ± 2.90, 89.48 ± 1.78, 70.52 ± 4.01, 73.13 ± 2.41 and 51.67 ± 2.01% for white fish meal, brown fish meal, soybean meal, peanut meal, and yeast, respectively. Apparent protein digestibility of ingredients was 89.82 ± 1.24, 87.34 ± 1.25, 83.97 ± 1.92, 80.79 ± 1.95, and 61.14 ± 0.54% for white fish meal, brown fish meal, soybean meal, peanut meal, and yeast, respectively. White fish meal and brown fish meal showed higher protein digestibility among ingredients tested (P ± 0.01). Lipid digestibility of ingredients was high (90.66-94.48%) and not significantly different except for yeast. Amino acid availability values for test ingredients were similar to values of protein digestibility. Amino acid availability values of white fish meal and brown fish meal were higher than other ingredients. Fatty acid availability values for test ingredients were similar to values of lipid digestibility. In general, the digestibility of most fatty acids was over 80% in all ingredients, except for 14:0 in yeast and 18:0 in peanut meal, PUFA + HUFA > MUFA > SFA. Longer-chain saturated fatty acids were less digestibility, except for 14:0, with digestibilities diminishing as fatty acid chain length increased. Apparent digestibility of dry matter, crude protein, lipid, gross energy, amino acids, and fatty acids in yeast was the lowest among the ingredients.     

The replacement of fish meal with Antarctic krill, Euphausia superba in diets for Atlantic salmon, Salmo salar

A total of six isoprotein and isolipid diets for Atlantic salmon, Salmo salar L., were prepared substituting from 0 to 100% of fish meal protein (0–68% of diet by dry weight) with meal from Antarctic krill (Euphausia superba). The feed produced from high inclusion levels of krill meal had lower ability to absorb lipid during vacuum coating than fish meal. Both amino acid and fatty acid compositions of the diets were fairly similar. The experiment commenced using salmon averaging 500 g and ended at a mean weight of 1500–1800 g (140 days of feeding). Moderate amounts of krill meal (20–60% of krill protein) in the diets increased growth during the first 71 days of feeding compared with the fish meal control, while no growth difference was observed during the last 69 days of feeding. This may, at least in parts, be explained by a feed‐attractant function of the krill meal. Muscle dry weight and lipid concentrations were unaffected by the diet. Feed conversion rate increased with high levels of krill meal in the diets (e.g. for the last period from 0.94 in the 0% diet to 1.26 in the 100% diet). This indicates that the fish were able to compensate by eating more to maintain growth. The apparent digestibility coefficients of dry matter and protein were not influenced by diet, but both faecal moisture and lipid had a tendency to increase at the highest inclusion level (all protein from krill meal). This may be related to chitin in the krill diet that is known to decrease lipid absorption and induce diarrhoea (increased water content in faeces). Chitin was not utilized to any major extent. Welfare parameters such as blood haemoglobin, red blood cell counts, plasma protein, cholesterol, triacylglycerols and glucose levels were unaffected by diets. Clinical indicators of cellular damage (alanine aminotransferase and aspartate aminotransferase) were similar indicating no diet‐induced tissue damage during the trial.     

Marine wax ester digestion in salmonid fish: a review

Alternative marine resources from lower trophic levels could partly cover the rapidly increasing needs for marine proteins and oils in the future. The North Atlantic calanoid copepod, Calanus finmarchicus, has a high level of lipids rich in n‐3 fatty acids. However, these animals have wax esters as the main lipid storage component rather than triacylglycerol (TAG). Although these esters are considered difficult to digest by many fish, is it well known that juvenile Atlantic salmon (Salmo salar) feed on zooplankton species. It is therefore possible that the capacity to utilize these lipids should be well developed in salmonids. Nonetheless, salmon hydrolyse wax esters slower than TAG and absorb fatty alcohols slower than fatty acids. However, salmon have several adaptations to digest diets rich in wax esters. These includes increased feed conversion, higher production of bile and higher activity of lipolytic enzymes in the midgut. Atlantic salmon has been shown to feed and grow on diets with a medium amount of wax esters (30% of the lipid) with results comparable to fish maintained on fish oil diets. Ingestion of higher level of wax esters (50% of the lipid) cause, however, poorer lipid digestibility and growth, so that optimal utilization of wax esters in Atlantic salmon is closer to 30% than 50% of the dietary lipid.     

The effect of low inclusion levels of Antarctic krill (Euphausia superba) meal on growth performance,apparent digestibility and slaughter quality of Atlantic salmon (Salmo salar)

Two trials with Atlantic salmon (Salmo salar) were conducted to evaluate the potential of krill meal to improve feed intake. In the first experiment, after transfer to sea water, salmon smolts were fed diets added 75 or 150 g kg^?1 Antarctic krill meal in substitution for fish meal for 13 weeks. The apparent digestibility coefficient for crude protein and the majority of the amino acids was significantly lower in the feeds added krill meal (around 83.5%) than in the control diet (84.9%), whereas the digestibility of crude lipids, dry matter and energy was not significantly different among the three diets. Krill meal addition resulted in higher feed intake, which led to higher growth rates and final body weights. In the second experiment, large salmon were fed a diet containing 100 g kg^?1 krill meal for 6 weeks before slaughter. Their feed intake and growth performance were assessed, and fillet and visceral fat contents were measured. Salmon fed the 100 g kg^?1 krill meal diet tended to eat more, resulting in significantly increased growth rates, when compared to control fish. Fish fed krill meal also had a significantly lower condition factor.     

Growth and health performance of African catfish Clarias gariepinus (Burchell 1822) juvenile fed with graded levels of biofloc meal

The objective of the study was to evaluate the utilization of biofloc meal as a feed ingredient in enhancing the growth and health status of African catfish (Clarias gariepinus) juvenile. The study consisted of two experiments, that is digestibility and growth experiments. The digestibility of two biofloc meals produced with two different carbon sources, that is tapioca and molasses, were assessed in the digestibility experiment. Whereas the effect of four dietary treatments with different levels of biofloc meal, that is 0%, 5%, 10% and 20%, on the fish growth performance, feed utilization, immuno‐haematological response, antioxidant status and robustness against environmental stress were evaluated in the growth experiment. The results showed that the digestibility of dry matter, protein, lipid and phosphorus of biofloc grown using molasses as the carbon source were remarkably higher than that grown using tapioca (p < 0.05). The inclusion of biofloc meal in the diets at 10% and 20% resulted in higher feed intake, fish growth and final biomass and protein efficiency ratio, and lower feed conversion ratio (p < 0.05). Furthermore, the red blood cells counts, phagocytic, lysozyme activities and antioxidative capacity were significantly enhanced in the fish provided with diet containing 20% biofloc meal (p < 0.05).The fish survival following salinity stress test was higher in the treatments with biofloc meal at 10% and 20% inclusion levels. In conclusion, dietary inclusion of biofloc meal could improve the growth performance and health status of African catfish juvenile and an inclusion level of 20% could be recommended.     

Dietary fat type affects lipid metabolism in Atlantic salmon (Salmo salar L.) and differentially regulates glucose transporter GLUT4 expression in muscle

An experiment was conducted to study dietary fat type (fish oil (FO) vs. vegetable oil) effect on lipid and glucose metabolism in post-smolt Atlantic salmon. Duplicate groups of salmon were fed one of eight diets in which the two fat sources FO (long chain n-3 fatty acids, FA) or linseed oil (LO) (short chain n-3 FA) were combined in a 2 × 4 factorial design with sunflower oil (SO) (rich in n-6 FA) at inclusion levels of 0, 25, 50 and 75% of total added fat. The effects of the diets on plasma metabolites, the activity of selected enzymes involved in lipid metabolism, biometric indices and muscle glucose transporter GLUT4 expression were determined after 12 weeks of feeding. Lower viscero-somatic indices (VSI) and fatty livers were observed in fish fed LO based diets. Increasing inclusion levels of SO affected plasma glucose concentration in fish fed FO based diets, and plasma triglycerides, which decreased in a linear and quadratic pattern in fish fed FO based diets, but increased linearly in fish fed LO based diets. Specific activity of liver carnitine palmitoyl transferase I (CPT I) and glucose-6-phosphate dehydrogenase (G6PD) and plasma nonesterified fatty acids (NEFA) concentration was higher in fish fed LO based diets. Two GLUT4 isoforms I and II have been described in muscle and proved to be differentially expressed related to dietary fatty acids. In summary, dietary fat type affects lipid metabolism in post-smolted Atlantic salmon. In addition, a possibility to interfere on glucose metabolism by means of dietary fat type is discussed.     

Digestibility of diets containing different soybean meals in Atlantic cod (Gadus morhua); comparison of collection methods and mapping of digestibility in different sections of the gastrointestinal tract

The purpose of the experiment was to evaluate effects of partial replacement of fish meal with soybean meal on digestibility in Atlantic cod and effects of biotechnological processing of soybean meal. Other objectives were to find out if apparent digestibility in cod was affected by age, temperature and/or faecal sampling methods, and to map digestion and absorption patterns along the intestinal tract for different age classes and diets. A control diet with fish meal as the main protein source (FM), a diet with 24% of crude protein from conventional extracted soybean meal (SBM), and a diet with 24% of crude protein from a bioprocessed soybean meal (BP-SBM) were used. Yttrium oxide was added as an inert marker for digestibility determination. The diets were fed to duplicate groups of 534 g (1-year-old) and 1750 g (2-year-old) cod in seawater. Faeces were stripped from the distal-most section (distal chamber) of the intestine after 48 and 84 days of feeding. In addition, intestinal contents were removed by dissection after 84 days. The dissected intestine was divided into 5 sections and contents were analysed separately. Dietary soy did not alter the viscosity of the digesta. The replacement of fish meal protein with soybean protein reduced the apparent digestibility of crude protein, fat, energy and almost all amino acids, independent of type of soybean meal processing. Larger fish had higher digestibility of starch, ash and several amino acids than smaller fish. A temperature decrease from 9.1 °C at feeding day 48 to 6.8 °C at day 84 resulted in lower digestibility of starch, ash and several amino acids. Absorption of amino acids was quantitatively terminated in the distal part of the mid intestine when feeding the soy-containing diets, but continued into the distal chamber when feeding the FM diet. Absorption of fat was completed in the proximal part of the mid intestine when feeding the soy-containing diets, but continued into the middle part of the mid intestine when feeding the FM diet. Soy did not affect absorption pattern of starch along the intestinal tract. Faecal sampling by dissection resulted in higher apparent digestibility of macronutrients than stripping in the 2-year-old cod, and higher apparent digestibility of protein in the 1-year olds.     

Atlantic salmon (Salmo salar) postsmolts adapt lipid digestion according to elevated dietary wax esters from Calanus finmarchicus

Wax esters (WE) in copepods constitute huge natural marine lipid resources, which can contribute as future lipid source in formulated diets in aquaculture, and thereby reduce the pressure on use of marine resources at higher trophic levels. The present study was undertaken to investigate factors affecting WE digestibility, including production of bile and lipases in Atlantic salmon fed diets containing high proportions of oil derived from copepods. Individually tagged postsmolt Atlantic salmon (initial weight 250 g) were distributed into three dietary groups in triplicate tanks and fed either a fish oil supplemented diet or diets where 50% or 100% of the fish oil was replaced with oil extracted from Calanus finmarchicus . WE accounted for 30.7% or 47.7% of the lipids in these latter diets, respectively. Over the 100 day feeding period, the salmon fed the fish oil diet displayed a significantly higher specific growth rate (SGR; 0.74) than fish fed the 100% Calanus oil diet (SGR; 0.67). The apparent digestibility coefficient of total lipid and total fatty acids was significantly higher in salmon fed the fish oil and the mixed diet compared to fish fed the pure Calanus oil diet. However, the fish appeared to enhance the lipid digestive capacity by increasing bile volume and the lipolytic activity. It is concluded that the digestion of WE in Atlantic salmon is poorer than for triacylglycerols. However, the digestive capacity is increased by elevating the bile content and lipase activity. At very high levels however, WE of lipid between 37.5% and 47.7%, are there no more compensation and WE utilisation decreases.