Digestibility of Calanus finmarchicus wax esters in Atlantic salmon (Salmo salar) freshwater presmolts and seawater postsmolts maintained at constant water temperature

Calanoid copepods are a rich source of marine lipid for potential use in aquafeeds. Copepod oil is primarily composed of wax esters (WE) and there are concerns over the efficiency of wax ester, versus triacylglycerol (TAG), digestion and utilization in fish. As smoltification represents a period of major physiological adaptation, the present study examined the digestibility of a high WE diet ( Calanus oil; 48% WE, 26% TAG), compared with a TAG diet (fish oil; 58% TAG), in Atlantic salmon freshwater presmolts and seawater postsmolts, of similar age (9 months) and weight (112 g and 141 g initial, respectively), over a 98-day period at constant temperature. Fish grew significantly better, and possessed lower feed conversion ratios (FCR), in seawater than freshwater. However, total lipid apparent digestibility coefficient (ADC) values were significantly lower in seawater fish, as were total fasted bile volumes. Dietary Calanus oil also had a significant effect, reducing growth and lipid ADC values in both freshwater and seawater groups. Postsmolts fed dietary Calanus oil had the poorest lipid ADC values and analysis of faecal lipid class composition revealed that 33% of the remaining lipid was WE and 32% fatty alcohols. Dietary prevalent 22:1n-11 and 20:1n-9 fatty alcohols were particularly poorly utilized. A decrease in primary bile acid, taurocholate, concentration was observed in the bile of dietary Calanus oil groups which could be related to the lower cholesterol content of the diet. The dietary WE : TAG ratio is discussed in relation to life stage and biliary intestinal adaptation to the seawater environment postsmoltification.     

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.     

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 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.     

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).     

Atlantic salmon, Salmo salar, utilizes wax ester-rich oil from Calanus finmarchicus effectively

Against a background of decreasing availability of fish oils for use in aquaculture, the present study was undertaken to examine whether a wax ester-rich oil derived from the calanoid copepod Calanus finmarchicus, could be used effectively by Atlantic salmon when supplied in their diet. Individually tagged Atlantic salmon of initial weight around 500 g were divided into replicate tanks of two dietary groups and fed either a fish oil supplemented diet, or an experimental diet coated with Calanus oil. Wax esters accounted for 37.5% of the lipids in the Calanus oil diet but were absent from the fish oil diet in which triacylglycerols (TAG) were the major lipid class. Over the feeding period (140 days) the salmon fed fish oil displayed a greater increase in length, but there was no significant difference between the two groups in weight gained. The specific growth rates (0.75) and the feed conversion ratio of fish fed the two diets were similar throughout the study. No differences were observed in the apparent digestibility coefficients (ADC) of fish fed Calanus oil or fish oil. The ADC of fatty acids decreased with chain length and increased with unsaturation. Long-chain alcohol utilization showed a similar tendency although there was a notable difference in that saturated long-chain alcohols were utilized better than the comparable fatty acid homologue. In fecal lipid of fish fed Calanus oil, the content of 16:0 alcohol decreased in both the free long-chain alcohol and wax ester fractions, while the corresponding fatty acid increased in the feces of both dietary groups of fish. In contrast, the proportion of the 22:1n−11 alcohol increased in both fecal wax esters and free long-chain alcohol fractions whereas 22:1n−11 fatty acid displayed no accumulation. The observed patterns of fatty acid and long-chain alcohol compositions in fecal lipid compared to those of the initial dietary lipid are consistent with the digestive lipases of salmon preferentially hydrolyzing esters containing polyunsaturated fatty acid (PUFA) moieties. The wax esters of Calanus oil contained substantial amounts of the n−3 PUFA, 20:5n−3 and 22:6n−3, that were effectively deposited in muscle and liver tissues. No major differences were seen in either lipid content/lipid classes or in gross fatty acid composition of these tissues between the two dietary groups. It is concluded that that Atlantic salmon in seawater can effectively utilize diets in which a major lipid component is derived from zooplankton rich in wax ester without any detrimental change in growth or body lipid composition. This finding gives support to the use of lipid from zooplankton from high latitudes as an alternative or as a supplement to fish oil and a provider of long-chain n−3 PUFA in diets for use in salmon aquaculture.     

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.     

Triacylglycerol-, wax ester- and sterol ester-hydrolases in midgut of Atlantic salmon (Salmo salar)

Bile salt‐dependent lipase (BSDL) is assumed to be the predominant lipid hydrolase in fish digestive tracts where it hydrolyses dietary triacylglycerols (TAG), sterol esters (SE) and wax esters (WE). BSDL is known to hydrolyse TAG at much faster rates than SE and WE in both fish and mammals. An assay for BSDL has previously been developed for rainbow trout (Oncorhynchus mykiss). However, this setup may not be valid in other fish species. Accordingly, the present study aimed at optimizing previous assays in rainbow trout for use on intestinal luminal contents of Atlantic salmon (Salmo salar L.). Crude intestinal extracts from midgut were desalted before the assay and concentrated bile salts supplemented. In general, the rank order for the degree of hydrolysis in Atlantic salmon was TAG > WE > SE. The optimal assay conditions were determined as being 100 μg protein, 125 μm lipid substrate and 20 mM bile salt (taurocholate) during the 4 h of incubation. Atlantic salmon and rainbow trout of 1500 g showed similar lipolytic activity, while salmon smolts of 300 g showed a significantly lower activity. Furthermore, the inhibition of intestinal lipase activities, especially triacylglycerol hydrolase and sterol ester hydrolase, observed in trout intestinal extracts at bile salt concentrations around 10 mm , was not observed in salmon. This could indicate that the activities in these two salmonids may display different enzyme biochemistry.     

Effect of Dietary Lipids on Macrophage Function,Stress Susceptibility and Disease Esistance in Atlantic Salmon (<Emphasis Type="Italic">Salmo salar</Emphasis>)

As the supply of marine fish oil is becoming a limiting factor in the production of Atlantic salmon (Salmo salar), new diets and alternative sources of energy are being tested. Plant oils are natural potential candidates to replace fish oil, but the different levels of essential polyunsaturated fatty acids may influence the health and growth of salmon. In this study, we have investigated the resistance to transport stress and bacterial infection, phagocytic activity in head kidney macrophages and eicosanoid metabolism in salmon fed three different diets. In high-energy fishmeal based diets, 50% and 100% of the supplementary fish oil (FO) was replaced with soybean oil (SO). The three dietary groups were fed for 950 day-degrees at 5 °C (27 weeks) and 12 °C (11 weeks) before challenging the fish with Aeromonas salmonicida, analyzing the lipid composition of head kidney and examining macrophage function in vivo and in vitro. Dietary fatty acids affected the lipid composition of the kidney. The level of eicosanoid precursor’s 20:4n-6 and 20:3n-6 were 3 and 7-fold higher in the 100% SO group compared with the FO group. The total fraction of n-3 lipids in kidney was 19% in the SO group, compared to 16% and 12% in the 50% or 100% SO groups, respectively. However, the production of leucotriene B₄ (LTB) and prostaglandin E₂ (PGE) immunoreactive materiel from exogenously added arachidonic acid in head kidney macrophages was only affected by the composite diet (increased) at 5 °C. In addition, the phagocytic activity of kidney macrophages in vivo and in vitro was not affected by diet. No effect of diet was observed on transport stress or susceptibility to a bacterial infection with Aeromonas salmonicida. Atlantic salmon therefore seems to tolerate a diet solely based on soybean oil as lipid source, without any detrimental effects on growth, health and immune functions.     

Digestive function and intestinal integrity in Atlantic salmon (Salmo salar) fed kernel meals and protein concentrates made from yellow or narrow-leafed lupins

This study assessed the effects of yellow lupin (Lupinus luteus) and narrow-leafed lupin (L. angustifolius) kernel meals and protein concentrates on the gastrointestinal integrity, capacity for digestive hydrolysis, and digestibility of nutrients in Atlantic salmon. A basal diet (FM) was made from fish meal, wheat, and fish oil. Six additional diets were formulated by replacing 30% of the FM diet with lupin kernel meal made from L. l. cv. Wodjil (LKM), L. a. cv. Belara (BKM), and L. a. cv. Myallie (MKM), lupin protein concentrates made from the same L. l. (LPC) and L. a. cv. M (MPC), or extracted soybean meal (SBM). All diets were extruded. Each diet was fed to three groups of 176 g salmon kept in 1 m² tanks with 5.6 °C saltwater for 3 weeks prior to sampling of blood, intestinal organs, digesta, and faeces. Inclusion of lupin meals in the diets resulted in harder and more condensed feed particles. Ulcer-like lesions were observed in the stomach of fish from all feeding groups, and this was worsened by lupin in the diet, but did not appear to be pellet hardness related. No consistent altered morphology was observed in the distal intestine (DI) of fish fed the FM and lupin diets, while the DI of fish fed SBM showed consistent and typical soybean meal-induced pathomorphological changes. Plasma cholesterol was higher when feeding MKM and LKM than when feeding FM, MPC, and LPC, with intermediate levels when feeding BKM and SBM. Feeding LKM and LPC resulted in a higher weight of the GIT when related to body weight. Trypsin activity and bile acid concentration were generally higher in digesta from the pyloric (PI) and mid (MI) intestine when feeding FM and lupin diets than when feeding SBM, while the opposite was seen for trypsin activity in digesta from DI. There were no effects of diet on leucine aminopeptidase (LAP) and maltase activity in PI and MI, but in DI the activity of these brush border enzymes were significantly lowered when feeding SBM. SBM in the diet resulted in watery faeces and lowered apparent digestibility of lipid, but this was not observed when feeding the lupin diets. To conclude, the tested lupin kernel meals and protein concentrates did not alter the intestinal function in Atlantic salmon when included at 30% of the diet. Dietary lupin was, however, involved in the worsening of ulcer-like gastric lesions.     

Effect of dietary carbohydrate level on growth performance,body composition,apparent digestibility coefficient and digestive enzyme activities of juvenile cobia,Rachycentron canadum L

A 9‐week feeding trial was conducted to investigate the effect of dietary carbohydrate level on the growth performance, body composition and apparent digestibility coefficient and digestive enzyme activities of juvenile cobia. Six isonitrogenous and isolipidic diets containing graded levels of starch (1.3%, 6.5%, 12.5%, 18.4%, 24.2% and 30.4%) were fed to juvenile cobia. Specific growth rate (SGR), feed efficiency ratio (FER) and protein efficiency ratio (PER) increased with increasing dietary starch up to 18.4% (P<0.05), and thereafter SGR declined but FER and PER remained nearly the same. Apparent digestibility coefficient of starch reduced significantly when dietary starch up to 30.4%. Fish fed the diets with starch from 18.4% to 30.4% showed higher amylase activities in intestinal tract than those fed diets containing starch 1.3% and 6.5% (P<0.05). Significantly higher whole‐body lipid contents were observed in fish fed the diets containing higher starch. Whole‐body moisture content was inversely correlated with whole‐body lipid content, while protein and ash showed no significant differences. Plasma glucose, hepatosomatic index, liver glycogen and liver lipid increased with an increasing dietary starch. Based on SGR and FER, the appropriate dietary starch supplementations of juvenile cobia were estimated to be 21.1% and 18.0 % of diet respectively.     

Optimal dietary lipid level of silver barb, Puntius gonionotus fingerlings in relation to growth, nutrient retention and digestibility, muscle nucleic acid content and digestive enzyme activity

Five iso-nitrogenous (300 g kg⁻¹ diet) purified diets with graded level of lipid at 40 (D-1), 60 (D-2), 80 (D-3), 100 (D-4) and 120 (D-5) g kg⁻¹ diet were fed to Puntius gonionotus fingerlings for 90 days to determine their dietary lipid requirement. Two hundred and twenty-five fingerlings (average weight 2.34 ± 0.03 g) were equally distributed in five treatments in triplicate groups with 15 fish per replicate. Fifteen flow-through cement tanks of 100 L capacity with a flow rate of 0.5 L min⁻¹ were used for rearing the fish. Specific growth rate (SGR), feed conversion ratio (FCR), nutrient digestibility, retention, digestive enzyme activity, RNA : DNA ratio and whole-body composition were considered as the response parameters with respect to dietary lipid levels. Maximum SGR and minimum FCR with highest RNA : DNA ratio, whole-body protein content and digestive enzyme activity was found in D-3 group fed with 80 g kg⁻¹ diet lipid. Nutrient digestibility was similar in all the groups irrespective of the dietary lipid level. Maximum protein and energy retention was recorded at 80 g kg⁻¹ dietary lipid fed group. However, from the second-order polynomial regression analysis, the maximum growth of P. gonionotus fingerlings was found at 96.9 g lipid kg⁻¹ diet.     

Comparison of effects of vegetable oils blended with southern hemisphere fish oil and decontaminated northern hemisphere fish oil on growth performance, composition and gene expression in Atlantic salmon (Salmo salar L.)

Replacement of fish oil with sustainable alternatives, such as vegetable oil, in aquaculture diets has to be achieved without compromising the nutritional quality, in terms of n-3 highly unsaturated fatty acid (HUFA) content, of the product. This may be possible if the level of replacement is not too high and oil blends are chosen carefully but, if high levels of fish oil are substituted, a fish oil finishing diet prior to harvest would be required to restore n-3HUFA. However, a decontaminated fish oil would be required to avoid increasing undesirable contaminants. Here we test the hypotheses that blending of rapeseed and soybean oils with southern hemisphere fish oil will have a low impact upon tissue n-3HUFA levels, and that decontamination of fish oil will have no major effect on the nutritional quality of fish oil as a feed ingredient for Atlantic salmon. Salmon (initial weight ~ 0.8 kg) were fed for 10 weeks with diets in which 60% of fish oil was replaced with blends of soybean, rapeseed and southern hemisphere fish oil (SVO) or 100% decontaminated northern fish oil (DFO) in comparison with a standard northern fish oil diet (FO). Decontamination of the oil was a two-step procedure that included treatment with activated carbon followed by thin film deodorisation. Growth performance and feed efficiency were unaffected by either the SVO or DFO diets despite these having lower gross nutrient and fatty acid digestibilities than the FO diet. There were also no effects on the gross composition of the fish. Liver and, to a lesser extent flesh, lipid levels were lower in fish fed the SVO blends, due to lower proportions of neutral lipids, specifically triacylglycerol. Tissue lipid levels were not affected in fish fed the DFO diet. Reflecting the diet, flesh eicosapentaenoic acid (EPA) and total n-3 fatty acids were higher, and 18:1n-9 lower, in fish fed DFO than FO, whereas there were no differences in liver fatty acid compositions. Flesh EPA levels were only slightly reduced from about 6% to 5% although docosahexaenoic acid (DHA) was reduced more severely from around 13% to about 7% in fish fed the SVO diets. In contrast, the liver fatty acid compositions showed higher levels of n-3 HUFA, with DHA only reduced from 21% to about 18% and EPA increased from under 8% to 9–10% in fish fed the SVO diets. The evidence suggested that increased liver EPA (and arachidonic acid) was not simply retention, but also conversion of dietary 18:3n-3 and 18:2n-6. Increased HUFA synthesis was supported by increased hepatic expression of fatty acyl desaturases in fish fed the SVO diets. Flesh n-3HUFA levels and desaturase expression was significantly higher in fish fed soybean oil than in fish fed rapeseed oil. In conclusion, partial replacement of fish oil with blends of vegetable oils and southern hemisphere fish oil had minimal impact on HUFA levels in liver, but a greater effect on flesh HUFA levels. Despite lower apparent digestibility, decontamination of fish oil did not significantly impact its nutritional quality for salmon.     

Growth, feed efficiency and slaughter quality of salmon, Salmo salar L., given feeds with different ratios of carbohydrate and protein

The effects of using increasing levels of carbohydrate to replace protein in diets for Atlantic salmon were studied in a long-term, semicommercial-scale experiment in sea cages, using wheat and corn starch as carbohydrate sources. The fish were fed extruded diets containing 24 g and 602 g kg^?1, 98 g and 521 g kg^?1, 165 g and 454 g kg^?1, 230 g and 384 g kg^?1 of carbohydrate and protein, respectively. The contents of lipid were kept constant at 280 g kg^?1. The experiment lasted for 9 months until the fish had reached about 4 kg. All groups showed good growth in the experimental period. Feed efficiency decreased and feed intake increased linearly with increased level of carbohydrate in the diet. Digestibility of dry matter and energy were seriously decreased with increased carbohydrate level in the diets. This was mainly due to decreased digestibility of carbohydrate, but also to decreased digestibility of lipid. The digestibility of protein or amino acids was not affected by diet. Higher levels of carbohydrate resulted in increased storage of energy as lipid in fillet and abdominal fat. Red coloration showed an optimum at 98 g kg^?1 carbohydrate in the diets. No differences in maturation were found between diets. Overall, based on feed efficiency, growth and slaughter quality, the optimum level of carbohydrate in the diet for Atlantic salmon in sea water is found to be approximately 100 g kg^?1 dry matter.     

Growth and feed utilization efficiencies of seawater Atlantic salmon, Salmo salar L., fed a diet containing supplementary enzymes

Abstract. Supplementary enzymes were added to a diet in order to increase its digestibility and improve the growth achieved by seawater Atlantic salmon, Salmo salar L. The supplementary enzymes were selected to hydrolyse proteins and carbohydrates. Three diets, with fishmeal as the only source of protein (C1), with fishmeal and soybean meal (C2) and diet C2 with supplementary enzymes (C3) were fed to seawater salmon (100g) for 12 weeks at nominal tank rations equivalent to 2·5% body weight per day. Consumption rates of individual fish were measured by radiography. The salmon fed C3 had higher rates of food consumption, significantly higher final weights and rates of growth and lower food conversion efficiencies and maintenance ration than those fed C2. Salmon fed C1 had similar food conversion efficiencies to the C3 fed fish. These results indicate that the addition of supplementary enzymes to diets containing soybean meal improves the growth and food conversion efficiency of salmon.     

Effects of fish oil and partial fish meal substitution with oilseed oils and meals on growth performance, nutrient utilization and health of the rainbow trout Oncorhynchus mykiss

A feeding trial was conducted to investigate the effects of the replacement of dietary fish meal and fish oil with oilseed meals (soybean or canola) and canola oil on growth, nutrient utilization, body composition, diet digestibility and hematological parameters of rainbow trout Oncorhynchus mykiss. Seven diets were used; the control diet (designated FM) contained fish meal and fish oil as the main protein and lipid sources. For the experimental diets, 40% of fish meal protein was substituted with soybean meal, canola meal or a soybean/canola meal mixture, and these diets (designated SM, CM and SCM, respectively) contained fish oil as the lipid source. Three additional diets (SM?+?CO, CM?+?CO and SCM?+?CO) were formulated with the same vegetable protein meals but with fish oil replaced by canola oil. Fish were fed twice daily to apparent satiation for 11?weeks. The growth of fish fed the CM?+?CO diet was significantly lower than that of fish fed the FM, SCM, SM?+?CO and SCM?+?CO diets. The feed conversion ratio (FCR) was significantly better in fish fed the FM and SCM?+?CO diets than in fish fed the CM and CM?+?CO diets. Furthermore, feed intake was significantly lower for fish fed the CM?+?CO diet than in fish fed the SCM diet, and lipid digestibility of the CM?+?CO diet was significantly lower than that of all other diets. No significant differences of body composition were observed. Circulating leukocyte levels, leukocyte ratios and serum lysozyme activity remained unaffected by dietary treatment. However, it was observed that fish fed the CM?+?CO diet displayed hematocrit levels significantly lower (P?<?0.05) than that of fish fed the other diets. The results indicate that when diets contain either fish oil or canola oil, canola meal and soybean meal can be incorporated into rainbow trout feeds at a combined 32% inclusion level (replacing 40% of fish meal protein) without inducing significant negative effects on growth, nutrient utilization or health.     

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, 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.     

The effect of dietary lipid and protein source on the swimming performance, recovery ability and oxygen consumption of Atlantic salmon (Salmo salar)

The effect of different dietary lipid sources on the athletic health of five groups of Atlantic salmon (Salmo salar) was tested by measuring oxygen consumption rates, prolonged swimming performance, and recovery from exhaustive exercise in a closed circuit respirometer. These groups of fish differed from each other in the source of the supplemental lipid in their diet. The control diet contained 100% anchovy oil, while in the test diets, poultry fat, de-gummed canola oil, or flaxseed oil were used to replace up to 75% fish oil. The composition of the industry diet was a 1:1 blend of anchovy oil and poultry fat, also 50% of the fishmeal protein in this diet was replaced with protein from poultry by-product meal. Despite major differences in dietary lipid and protein composition that altered the lipid composition of the fish, all of our treatment groups performed equally well with respect to their oxygen consumption, swimming performance and recovery ability. Since these swim tests integrated many physiological functions, and collectively represented a sensitive measure of the athletic health of the fish, we concluded that our alternative lipid and protein-based diets represented viable possibilities for salmon farming.