Effects Of Dietary Lipid Levels Research Articles

Dietary Lipid Utilization by White Sea Bream (Diplodus sargus) Juveniles

Abstract.— A 8‐wk trial was performed with white sea bream, Diplodus sargus, juveniles (17.3 g initial weight) to evaluate the effect of dietary lipid levels on growth performance and whole‐body composition. Six experimental diets were formulated to be isoproteic (45% protein) and to contain from 9 to 24% dietary lipid levels (dry matter basis). Fish meal and fish oil were used as the main protein and lipid sources, respectively. At the end of the trial, there were no significant differences (P > 0.05) among groups in fish performance or in whole‐body composition. From the results of this trial, it is concluded that, within the range of values tested, increasing dietary lipid levels above 9% has no advantage as it does not promote growth or spare protein for growth purposes.

Optimal dietary lipid level for large yellow croaker (Pseudosciaena crocea) larvae

A 30-day feeding experiment was conducted in blue tanks (70 × 50 × 60 cm, water volume 180 L) to determine the effects of dietary lipid levels on the survival, growth and body composition of large yellow croaker (Pseudosciaena crocea) larvae (12 days after hatchery, with initial average weight 1.93 ± 0.11 mg). Five practical microdiets, containing 83 g kg−1 (Diet 1), 126 g kg−1 (Diet 2), 164 g kg−1 (Diet 3), 204 g kg−1 (Diet 4) and 248 g kg−1 lipid (Diet 5), were formulated. Live feeds (Artemia sinicia nauplii and live copepods) were used as the control diet (Diet 6). Each diet was randomly assigned to triplicate groups of tanks, and each tank was stocked with 3500 larvae. During the experiment, water temperature was maintained at 23(±1) °C, pH 8.0 (±0.2) and salinity 25 (±2) g L−1. The results showed that dietary lipid significantly influenced the survival and growth of large yellow croaker larvae. Survival increased with the increase of dietary lipid from 83 to 164 g kg−1, and then decreased. The survival of larvae fed the diet with 83 g kg−1 lipid (16.1%) was significantly lower than that of larvae fed other diets. However, the survival in larvae fed the diet with 16.4 g kg−1 lipid was the highest compared with other artificial microdiets. Specific growth rate (SGR) significantly increased with increasing dietary lipid level from 83 to 164 g kg−1 (P < 0.05), and then decreased. The SGR in larvae fed the diet with 164 g kg−1 lipid (10.0% per day) was comparable with 204 g kg−1 lipid (9.6% per day), but were significantly higher than other microdiets (P < 0.05). On the basis of survival and SGR, the optimum dietary lipid level was estimated to be 172 and 177 g kg−1 of diet using second-order polynomial regression analysis respectively.

Effect of dietary lipid level on growth performance, feed utilization and digestive enzyme of juvenile ivory shell, Babylonia areolate

A growth trial was conducted to evaluate the effects of dietary lipid levels on growth performance, feed utilization, carcass composition and digestive enzymes of juvenile ivory shell. Six isonitrogenous and isoenergetic experimental diets (43% crude protein and 15.46 kJ/g diet) using Pollack fish oil as the lipid source, were formulated to contain six lipid levels (1.83, 3.83, 5.91,7.80, 9.76 and 11.73% dry diet, respectively). Triplicate groups of 50 shells (average weight 160.50±1.20 mg) were stocked in 120-l tanks and fed to apparent satiation twice daily for 10 weeks. The results showed that growth performance and feed utilization were significantly affected by dietary lipid levels (P<0.05). Maximum weight gain, mean protein gain and specific growth rate occurred at 5.91% dietary lipid level (P<0.05), soft body to shell ratios were not significantly difference above 3.83% dietary lipid level, and there were no significant differences (P<0.05) in survival of ivory shell fed the experimental diets. There were significant difference in protein, lipid, moisture and ash content in soft body (P<0.05). Lipid content in soft body positively correlated with dietary lipid level, however, protein and ash content in soft body significantly decreased with the increase in dietary lipid level. Pepsin activity in soft body significantly increased with dietary lipid level increasing from 1.83 to 7.80%, and trypsin-like enzyme activity significantly increased with increase in dietary lipid level from 1.83 to 5.91%. However, lipase activity in soft body increased with an increase in dietary lipid level, but amylase activity was not significantly affected by the dietary lipid level. The results of this trial indicated that dietary lipid levels above 7.80% dry matter did not improve growth performance or feed utilization of juvenile ivory shell. Quadratic regression analysis of mean protein gain against dietary lipid level indicated that the optimal dietary lipid requirement for maximum mean protein gain of juvenile ivory shell is about 6.54% of dry diet.

Effect of Dietary Lipid Level and Protein Energy Ratio on Growth and Body Composition of Largemouth Bass Micropterus salmoides

A feeding trial was conducted in aquaria with juvenile largemouth bass Micropterus salmoides to examine the effects of increasing dietary lipid levels on growth and body composition. Feed-trained largemouth bass fingerlings were graded to a similar size (16.3 ± 2.4 g) and randomly stocked into 15 113.6-L glass aquaria at 25 fish/aquarium. Fingerlings were fed twice daily to apparent satiation with one of five isonitrogenous extruded experimental diets based on practical ingredients. Diets contained approximately 40% crude protein and either 0, 5, 10, 15, or 20% added lipid. Due to background lipids in the ingredients, this equated to total lipid levels of 7, 10, 16, 20, and 23%, respectively. These diets had protein to energy ratios of 137, 120, 106, 95, and 86 mg/kcal, respectively. There were three replicate aquaria per dietary treatment. After 12 wk, there were no statistically significant differences (P > 0.05) in average weight (g), specific growth rate (% body weight/d), survival (%), or protein efficiency ratio (PER, %) among fish fed the five diets, which averaged 79.3 ± 5.6, 1.9 ± 0.1, 99.5 ± 1.5, and 2.11 ± 0.19, respectively. Juvenile largemouth bass fed diets containing 15 and 20% added lipid had significantly lower (P± 0.05) feed conversion ratios (FCR) (1.1 ± 0.0 and 1.1 ± 0. 1, respectively) than fish fed diets containing 0, 5, and 10% added lipid (1.4 ± 0.1, 1.3 ± 0. 1, and 1.3 ± 0.2, respectively). Proximate analysis of whole body samples indicated a significantly higher (P ± 0.05) lipid content in fish fed 15 and 20% added lipid compared to fish fed lower lipid levels. While FCR was lowest in fish fed the 15 and 20% added lipid diets, increased whole body lipid deposition may indicate that these levels are above optimal levels for juvenile largemouth bass. It appears that 7–16% total dietary lipid (P/E:137–106 mg/kcal) is sufficient to support efficient growth without impacting body composition in juvenile largemouth bass when fed a diet containing 40% crude protein.

Effects of dietary lipid level on growth, survival and body composition of Brazilian codling (Urophycis brasiliensis Kaup, 1858)

El objetivo del presente trabajo es determinar la influencia de los niveles de lipidos en dietas formuladas sobre el crecimiento, supervivencia, indice hepatosomatico (HSI) y composicion proximal del musculo e higado de la brotola. Se fabricaron tres dietas diferentes (40% proteina cruda) con 3%, 6% y 10% de aceite de pescado, obteniendo un 5%, 8% y 11% de lipidos crudos, respectivamente. La tasa diaria de alimentacion fue del 3%. Al finalizar el experimento a los 40 dias, los animales fueron pesados y se tomaron muestras de tejido muscular y hepatico. La mayor tasa de crecimiento en peso se obtuvo en el grupo alimentado con los niveles mas bajos de lipidos. Se observaron diferencias significativas (P<0,05) en crecimiento, supervivencia e indice hepatosomatico entre los grupos. En los animales alimentados con altos niveles de lipidos se encontraron higados de mayor tamano y color mas palido. El contenido de proteina cruda, lipidos y humedad del tejido hepatico en este grupo fue significativamente diferente (P<0,05) al compararlo con los otros dos tratamientos; siendo el contenido de proteina en musculo significativamente menor (P<0,05). No se encontraron diferencias significativas (P<0,05) al comparar entre tratamientos los contenidos de cenizas en ambos organos y en los niveles de lipidos y humedad en musculo. Se concluye que los niveles mas adecuados de lipidos en la formulacion de dietas para la brotola podrian estar en torno al 5%

Effects of dietary lipid level on growth and lipid utilization by juvenile Atlantic halibut ( Hippoglossus hippoglossus, L.)

A study was conducted to determine the efficiency of lipid utilization by juvenile Atlantic halibut ( Hippoglossus hippoglossus, L.). Triplicate groups of fish (average weight, 33.0 ± 0.3 g) were fed four isonitrogenous (56% crude protein, DM-basis) experimental diets containing 14, 18, 22 and 25% lipid for 13 weeks. The effects of dietary lipid levels on growth, feed utilization, body composition, nutrient and energy retention, tissue lipid accumulation and fatty acid composition were determined. Growth and feed conversion ratio were not affected by an increase in dietary lipid intake. Whole body lipid content increased from 24.9 ±0.8% to 31.6 ± 0.6%, reflecting the increase in dietary lipid level. Nitrogen and energy retention values did not show significant differences among treatments. Despite a large individual variability in liver lipid content, the liver of fish fed the 22% lipid diet showed significantly higher values (18.9 ± 3.7%) than fish fed 14 and 18% lipid (13.1 ± 1.3% and 12.9 ± 2.5%, respectively). Muscle lipid content was not significantly affected by an increase in dietary lipid content. The dietary fatty acid profile was reflected in both liver and muscle tissue. Higher eicosapentaenoic (EPA) and lower linoleic acid concentration in liver were observed with increasing fish oil levels. It appears that halibut juveniles can tolerate up to 25% dietary lipid; however, there are no beneficial effects in terms of growth and macronutrient retention beyond 14% dietary lipid level.

The effect of dietary lipid level and composition on growth, survival, and development of the digestive system of larval sneep, Chondrostoma nasus (L.)

Background. Rearing larval fish under laboratory conditions requires the use of appropriate artificial diets that fully replace natural food. Up till now, no starter has been developed for cyprinid rheophilic fish larvae, and these fish are therefore fed diets developed for other fish species. The present study was undertaken to evaluate the effects of diets of different protein-, lipid-, and fatty acid compositions on growth, survival, and changes in the digestive system during larval development of sneep (nase), Chondrostoma nasus (L.), from hatching until the juvenile stage. Material and methods. From day 4 until day 21 post-hatch, sneep larvae were fed, Artemia nauplii and three starters: Nutra AB 3.0 (NU), Perla plus (PP), and Perla larva proactive (PL). Each experimental treatment was run in triplicate. On day 21 of the experiment, samples of fish were taken for size measurement, histological and morphometrical examination, and fatty acid analyses. Results. The fish fed Artemia exhibited the highest growth rate and survival. Among the groups fed artificial diets, the highest survival and growth were observed in NU group, while PL group showed the worst results (P < 0.05). Comparison of the fatty acid composition in the diets and fish bodies revealed that the levels of n-3 PUFA were considerably higher in the bodies of fish fed starters than in the diets themselves, while concentrations of n-6 PUFA in the PP and PL groups were lower in fish than in diets. The NU diet showed the highest n-3 : n-6 ratio (5.54), while PP had the lowest. The highest MUFA : PUFA ratio occurred in Artemia nauplii and the lowest in the PP diet. Histological observations revealed the presence of supranuclear lipid vacuoles in the enterocytes of the middle intestine section of Artemia-fed larvae. No such vacuoles were found in fish fed artificial diets. Morphological changes in the livers of fish fed various diets involved hepatocyte size and cytoplasm area containing glycogen and lipids. Conclusions. Among the artificial diets, Nutra was the most appropriate for rearing sneep larvae. The results revealed that sneep larvae are capable of elongating and desaturating linolenic- and linoleic acids into longerchain fatty acids.

Effect of dietary lipid level on growth performance, lipid deposition, hepatic lipogenesis in juvenile cobia ( Rachycentron canadum)

A study was undertaken to evaluate the effect of the dietary lipid level on growth, feed utilization, lipid deposition and lipid metabolism by cobia juveniles. Three isonitrogenous diets containing 47% crude protein with increasing dietary lipid levels 5%, 15% and 25% (DM, dry matter) were fed to satiety to triplicate groups of 20 fish (7.71 g) for 6 weeks. At the end of the feeding trial, fish fed diets containing 5% and 15% lipid showed a higher growth than those fish fed with 25% lipid. Though daily feed intake (DFI) decreased with increasing dietary lipid, there was no significant difference in daily energy intake (DEI) among treatments. As dietary lipid level increased, energy retention (EI), daily energy gain (DEG), daily lipid intake (DLI), daily lipid gain (DLG), viscerosomatic index (VSI), intraperitoneal fat ratio (IPF) and body lipid content increased dramatically and the 25% group had the highest values. Hepatosomatic index (HSI) and muscle lipid content were higher at 25% lipid group than 5% lipid group, but no significant different was found between 15% and 25% lipid group. Activities of G6PD and ME were reduced with increasing lipid intake, but activities of IDH and 6PGDH did not change among groups. In conclusion, high dietary lipid levels above 15% produced little practical benefit because of higher fat accretion in cobia.

Effect of dietary lipid level on growth performance, feed utilization and body composition of grouper Epinephelus coioides juveniles fed isonitrogenous diets in floating netcages

An experiment was conducted to determine the effect of dietary lipid levels on growth performance and body composition of grouper Epinephelus coioides juveniles cultured in floating netcages (1.5 m × 1 m × 1.5 m). Six isonitrogenous diets (53% dietary protein) with increasing dietary lipid concentration (5.16, 7.38, 9.73, 12.36, 14.13, 16.04% of dry material, DM) were fed to satiation to triplicate groups of 20 fish (mean weight: 10.9 ± 0.1 g) for 56 days. Dietary energy levels were 300, 322, 340, 371, 382, 400 kcal/100 g DM, respectively. Fish fed the 9L diet had the highest weight gain (WG) and specific growth rate (SGR), but they were not significantly different from that of fish fed the 7L or 12L diet (p > 0.05). FI varied inversely with dietary lipid levels. The poorest FCR and the lowest PER were observed in fish fed the 5L diet but these parameters showed no significant differences (p > 0.05) for fish fed the dietary lipid level ranging from 9 to 16%. Nitrogen intake decreased with dietary lipid levels. Fish fed the 7L diet showed the highest N gain, which was not markedly different from that of fish fed the 9L and 12L diets (p > 0.05). N retention was significantly lower in fish fed the 5L diet than in the other groups. Lipid intake and lipid gain increased with dietary lipid levels. Lipid retention (%) of the 7L diet was lowest but showed no significant differences among other treatments (p > 0.05). Proximate composition of fish body was significantly affected by dietary lipid level (p 0.05). Condition factor (CF), hepatosomatic index (HSI) and viscerosomatic index (VSI) increased with increasing dietary lipid level. Based on second-order polynomial regression analysis of WG against dietary lipid level, a breakpoint of 10.0% was indicated to be the optimal dietary lipid concentration for maximum growth for grouper Epinephelus coioides juveniles cultured in floating netcages.

Effect of dietary lipid level on growth, feed utilization and body composition by juvenile grass carp (Ctenopharyngodon idella)

A study was undertaken to determine the effect of dietary lipid level on growth, feed efficiency and body chemical composition of juvenile grass carp. Seven isonitrogenous diets (400 g kg(-1) crude protein) containing seven dietary lipid level (0, 20, 40, 60, 80, 100 and 120 g kg(-1) dry matter) were fed to triplicate groups of 40 fish with initial weight 6.52 g, for 70 days. No obvious and assured essential fatty acid deficiency symptom appeared in fish fed the lipid-free diet. Excess dietary lipid level (100 and 120 g kg(-1)) resulted in decreased feed intake. The best growth performance and feed utilization was observed in fish fed 20-40 g kg(-1) dietary lipid. The fish fed a lipid-free diet had the lowest protein efficiency and protein retention. Growth performance and feed utilization increased with the increasing dietary lipid levels up to 40 g kg(-1) dietary lipid. Higher dietary level (above 40 g kg(-1)) made growth performance and feed utilization decrease and no protein sparing effect was observed. Lipid retention decreased as dietary lipid level increased. Mesenteric fat index (MFI) increased, hepatosomatic index (HSI) decreased with dietary lipid level. The increased MFI and simultaneous decrease lipid retention can be explained by differences in growth. The effect of dietary lipid levels on the chemical composition of tissues was significant only for whole body and muscle. The excess lipid content of liver in all groups was regarded as a slight symptom of fatty liver, which was partly identified by microscopic structural study and lower plasma lipid indexes, comparing to the initial plasma data. In conclusion, grass carp is a fish with low energy requirement and excess dietary lipid level should be avoided.

Performance, carcass composition and nutrient utilization of surubim Pseudoplatystoma coruscans (Agassiz) fed diets with varying carbohydrate and lipid levels

Five isonitrogenous diets formulated to contain 470 g kg(-1) of crude protein, five different levels of crude lipids (190, 210, 230, 250 and 270 g kg(-1)), five different levels of carbohydrates (178, 155, 158, 125 and 110 g kg(-1)) and gross energy (21.2, 21.6, 22.4, 22.8 and 23.2 MJ kg(-1)) were used to investigate the effect of dietary lipid levels on performance and carcass composition of the surubim, Pseudoplatystoma coruscans (Agassiz). Triplicate groups of 11 fish with an average individual body weight of 5.1 +/- 0.2 g were randomly assigned to 15 net cages and fed each test diet twice a day to apparent satiation for 64 days. At the end of the trial there were no significant differences in feed consumption or fish performance. No differences (P > 0.05) were observed in the lipid content of fish carcass and liver. On the contrary, visceral lipid increased (P 0.05) by the dietary lipid and carbohydrate levels. The results of this trial suggest that increasing dietary lipid levels from 190 to 270 g kg(-1) did not improve growth performance or protein sparing and caused an undesirable increase in the visceral lipid content of surubim fingerlings.

Interacting effects of dietary lipid level and temperature on growth, body composition and fatty acid profile of rohu, Labeo rohita (Hamilton)

Three isonitrogenous (320 g kg−1 crude protein, casein and gelatine) semi-purified diets with 80 (L8), 130 (L13) and 180 (L18) g kg−1 lipid (sunflower oil at increasing levels and cod liver oil fixed at 50 g kg−1) at three digestible energy levels (12 096, 13 986 and 15 876 kJ kg−1 dry weight) and were tested, in triplicate, on rohu fingerlings (3.2 ± 0.08 g) at two different temperatures (21 and 32 °C). Fish were fed to apparent satiation, twice daily, at 09.00 and 15.00 h, 7 days a week for 56 days. Maximum growth was obtained at a lipid level of 80 g kg−1 (L8) at 21 °C (439.37%) and 130 g kg−1 (L13) at 32 °C (481.8%). In general growth rate was higher at 32 °C than at 21 °C at all lipid levels. Tissue monounsaturated fatty acid (MUFA) contents decreased with increasing lipid level at 32 °C, but the reverse occurred at 21 °C. At 21 °C, Polyunsaturated fatty acid (PUFA) level increased significantly (P > 0.05) over initial values, but was affected insignificantly by dietary lipid level. At 32 °C, fish fed diet L13 had more n-3 fatty acid (FA) in liver and muscle than the other two dietary groups while at 21 °C, both liver and muscle FA profiles exhibited significant change (P > 0.05) in n-3 and n-6 FA content which corresponded to variation in percent addition of dietary lipid. However, n-3/n-6 ratio was higher for fish fed diet L13 at 32 °C and diet L8 at 21 °C and may be correlated with fish growth.

Effect of Dietary Lipid Level on Growth Performance of Splittail at 18°C

AbstractA 12‐week feeding trial was conducted to study the effect of dietary lipid level on growth performance of juvenile Sacramento splittail Pogonichthys macrolepidotus at 18°C. We selected this temperature to simulate their natural habitats, although an earlier study showed that their optimum temperature was 22–26°C. Six isonitrogenous and isoenergetic purified diets were formulated to contain 2–12% lipid in 2% increments, and dietary lipid was an equal mix of corn oil and cod liver oil. Fish with an average initial body weigh of 9.0 ± 0.2 g (mean ± SE, n = 24) were kept in a 24‐tank, flow‐through system with 15 fish per tank, and each diet was randomly assigned to four replicate tanks of fish. Fish were fed 3.0% of their body weight per day by automatic feeders, which dispensed a small amount of feed every few minutes in daylight hours. Body weight and feed efficiency increased significantly with increasing dietary lipid level up to 8%. Fish fed the diet containing 8% lipid showed significantly higher body weight increase and feed efficiency than those fed the diets containing less than 6% lipid. Dietary lipid level did not affect the hepatosomatic index, condition factor, and intraperitoneal fat ratio. Whole‐body moisture was significantly lower but lipid was higher in fish fed the diet containing 8% lipid than in those fed the diets containing less than 6% lipid. Histological analysis revealed a higher prevalence of hepatocellular fatty vacuolation in fish fed the diet containing 12% lipid. Based on a broken‐line analysis, a dietary lipid level of 8.4% is recommended for juvenile splittail reared at 18°C.

Comparative study on the effect of dietary lipid level on growth and feed utilization for gibel carp (Carassius auratus gibelio) and Chinese longsnout catfish (Leiocassis longirostris Gunther)

An 8-week growth trial investigated the effect of dietary lipid level on growth performance of a carnivorous fish, Chinese longsnout catfish (Leiocassis longirostris Gunther) and an omnivorous fish, gibel carp (Carassius auratus gibelio). For each species, seven isonitrogenous semi-purified diets (455 g kg(-1) crude protein for Chinese longsnout catfish and 385 g kg(-1) crude protein for gibel carp) were formulated to contain 30, 60, 90, 120, 150, 180 or 210 g kg(-1) lipid. For Chinese longsnout catfish, feed intake (FI) decreased with increasing dietary lipid and there was no significant difference in feed intake from 90 to 210 g kg(-1) lipid. Specific growth rate (SGR) increased with dietary lipid level (P < 0.05) and the 150 and 180 g kg(-1) groups were the best. Feed conversion efficiency (FCE), protein retention efficiency (PRE) and energy retention efficiency (ERE) were higher at 180 g kg(-1) lipid. For gibel carp, FI decreased with increased dietary lipid and 180 and 210 g kg(-1) lipid groups showed lower values. SGR increased with dietary lipid level and the 150 and 180 g kg(-1) were the best. FCE was higher at 180 g kg(-1) lipid level. PRE increased with dietary lipid level and there was no significant difference in groups from 120 to 210 g kg(-1) dietary lipid. ERE increased with increasing dietary lipid level, and groups fed 120, 150 and 180 g kg(-1) lipid showed the highest values. In Chinese longsnout catfish, increase in dietary lipid level, resulted in increased carcass dry matter, crude protein, crude lipid and gross energy. In gibel carp, dry matter, crude protein, and crude lipid increased with dietary lipid level. Based on regression between SGR and dietary lipid, dietary lipid requirements for Chinese longsnout catfish and gibel carp were 142.6 and 140.5 g kg(-1), respectively.

Effect of dietary lipid level on fatty acid β-oxidation and lipid composition in various tissues of haddock, Melanogrammus aeglefinus L.

Haddock ( Melanogrammus aeglefinus) is a gadoid fish species that deposits dietary lipid mainly in the liver. The fatty acid (FA) β-oxidation activity of various tissues was evaluated in juvenile haddock fed graded levels of lipid. The catabolism of a radiolabelled FA, [1- 14C]palmitoyl-CoA, through peroxisomal and mitochondrial β-oxidation was determined in the liver, red and white muscle of juvenile haddock fed 12, 18 and 24% lipid in the diet. There was no significant increase in the mitochondrial or peroxisomal β-oxidation activity in the tissues tested as the dietary lipid level increased from 12 to 24%. Peroxisomes accounted for 100% of the β-oxidation observed in the liver, whereas mitochondrial β-oxidation dominated in the red (91%) and white muscle (97%) of juvenile haddock. Of the tissues tested, red muscle possessed the highest specific activity for β-oxidation expressed on a per mg protein or per g wet weight basis. However, white muscle, which forms over 50% of the body mass in gadoid fish was the most important tissue in juvenile haddock for overall FA catabolism. The total lipid and FA composition of these tissues were also determined. This study confirmed that the liver was the major lipid storage organ in haddock. The hepatosomatic index (HSI; 10.0–15.2%) and lipid (73.8–79.3% wet wt.) in the liver increased significantly as dietary lipid was increased from 12 to 24% lipid. There was no significant increase in the lipid composition of the white muscle (0.8% wet wt.), red muscle (1.9% wet wt.) or heart (2.5% wet wt.).

Effects of dietary lipid level and source on growth and proximate composition of juvenile redclaw (Cherax quadricarinatus) reared under semi-intensive culture conditions

Abstract The influence of dietary lipid level on growth, survival, and proximate composition of juvenile redclaw crayfish was evaluated during a 12-week growth trial utilizing semi-intensive culture conditions. Four diets were formulated to be isoenergetic (17.58 kJ g −1 ) and isonitrogenous (30% crude protein). Three of the diets were designed to contain 4.2% (L4), 8.2% (L8) and 12.3% (L12) lipid in a 1:1 ratio of corn oil/fish oil. A fourth diet was formulated to contain 8.7% (LC8) lipid, with corn oil as lipid supplement. A fifth treatment (UF) was included in which the redclaw were not fed in order to estimate the contribution of primary production. Juvenile redclaw (4.08±0.2 g initial weights) were stocked at a density of 10 per tank in 15, 2.5-m 3 fiberglass tanks with three replicates per treatment. The trial was conducted in an outdoor flow-through water system. The redclaw in the unfed treatment gained 8.3 g whereas redclaw that received a prepared ration gained an average of 31.9 g. Hence, in this experiment natural productivity contributed about 26% of the weight gain of the redclaw maintained in outdoor tanks. Among the fed treatments, there were no significant differences in survival, final weight, growth, or feed utilization. The hepatosomatic index (HI) generally increased with lipid level and was influenced by the sex of the redclaw. Results indicated that in similar culture conditions, diets containing 4% lipid are sufficient for redclaw growth and survival when natural food is present.

Effects of dietary lipid level and vegetable oil on fatty acid metabolism in Atlantic salmon (Salmo salar L.) over the whole production cycle

Changes in fatty acid metabolism in Atlantic salmon (Salmo salar) induced by vegetable oil (VO) replacement of fish oil (FO) and high dietary oil in aquaculture diets can have negative impacts on the nutritional quality of the product for the human consumer, including altered flesh fatty acid composition and lipid content. A dietary trial was designed to investigate the twin problems of FO replacement and high energy diets in salmon throughout the entire production cycle. Salmon were grown from first feeding to around 2 kg on diets in which FO was completely replaced by a 1:1 blend of linseed and rapeseed oils at low (14–17%) and high (25–35%) dietary oil levels. This paper reports specifically on the influence of diet on various aspects of fatty acid metabolism. Fatty acid compositions of liver, intestinal tissue and gill were altered by the diets with increased proportions of C18 polyunsaturated fatty acids and decreased proportions of n-3 highly unsaturated fatty acids (HUFA) in fish fed VO compared to fish fed FO. HUFA synthesis in hepatocytes and enterocytes was significantly higher in fish fed VO, whereas β-oxidation was unaltered by either dietary oil content or type. Over the entire production cycle, HUFA synthesis in hepatocytes showed a decreasing trend with age interrupted by a large peak in activity at seawater transfer. Gill cell prostaglandin (PG) production showed a possible seasonal trend, with peak activities in winter and low activities in summer and at seawater transfer. PG production in seawater was lower in fish fed the high oil diets with the lowest PG production generally observed in fish fed high VO. The changes in fatty acid metabolism induced by high dietary oil and VO replacement contribute to altered flesh lipid content and fatty acid compositions, and so merit continued investigation to minimize any negative impacts that sustainable, environmentally-friendly and cost-effective aquaculture diets could have in the future. Abbreviations: FO - fish oil; HUFA - highly unsaturated fatty acids acids (carbon chain length ≥C 20 with ≥3 double bonds); LO - linseed oil; RO - rapeseed oil; VO - vegetable oil.

Effect of high-oil corn or added corn oil on ruminal biohydrogenation of fatty acids and conjugated linoleic acid formation in beef steers fed finishing diets.

Three Angus steers (410 kg) cannulated in the proximal duodenum were used in a replicated 3 x 3 Latin square to evaluate the effects of dietary lipid level and oil source on ruminal biohydrogenation and conjugated linoleic acid (CLA) outflow. Dietary treatments included: 1) typical corn (TC; 79.2% typical corn), 2) high-oil corn (HOC; 79.2% high-oil corn), and 3) the TC diet with corn oil added to supply an amount of lipid equal to the HOC diet (OIL; 76.9% TC + 2.4% corn oil). Duodenal samples were collected for 4 d following 10-d diet adaptation periods. Data were analyzed with animal, square, period, and treatment in the model and planned, nonorthogonal contrasts were used to test the effects of dietary lipid content (TC vs HOC and OIL) and oil source (HOC vs OIL) on ruminal biohydrogenation. Intake and duodenal flow of total long-chain fatty acids were increased (P < 0.05) by over 63% for diets containing more lipid regardless of oil source. Apparent ruminal dry matter and long chain fatty acid digestibilities were not altered (P > 0.05) by dietary lipid level or oil source. Ruminal biohydrogenation of total and individual 18-carbon unsaturated fatty acids was greater (P < 0.05) for diets with higher lipid content. Biohydrogenation of oleic acid was greater (P < 0.05) for HOC than OIL, but biohydrogenation of linoleic acid was lower (P < 0.05) for HOC than OIL. Duodenal flows of palmitic, stearic, oleic, linoleic, and arachidic acids were more than 30% greater (P < 0.05) for diets containing more lipid. Flow of all trans-octadecenoic acids was greater (P < 0.05) for diets containing more lipid. Corn oil addition increased (P < 0.05) the flow of trans-10 octadecenoic acid and the trans-10, cis-12 isomer of CLA by threefold compared to feeding high-oil corn. Feeding high-oil corn or adding corn oil to typical corn rations increased intake, biohydrogenation, and duodenal flow of unsaturated long-chain fatty acids. Compared with high-oil corn diets, addition of corn oil increased duodenal flow of trans-10, trans-12 and cis-12 isomers of octadecenoic acid and the trans-10, cis-12 isomer of CLA. The amount of cis-9, trans-11 isomer of conjugated linoleic acid flowing to the duodenum was less than 260 mg/d, a value over 20 times lower than flow of trans-11 vaccenic acid indicating the importance of tissue desaturation for enhanced conjugated linoleic acid content of beef.

Effects of dietary phosphorus and lipid levels on utilization and excretion of phosphorus and nitrogen by rainbow trout (Oncorhynchus mykiss ). 2. Production-scale study

In a 8-week production-scale experiment at a commercial trout farm, the effects of dietary lipid level and phosphorus level on phosphorus (P) and nitrogen (N) utilization of rainbow trout (initial mean weight 99 g) were assessed. A low-phosphorus, high-lipid experimental diet (457 g protein, 315 g lipid, 9.1 g P kg–1 dry diet) was compared with a commonly used commercial diet (484 g protein, 173 g lipid, 13.6 g P kg–1 dry diet). P and N budgets were constructed using data from the production-scale experiment and digestibility data for the two diets. In addition, orthophosphate and ammonia-N waste were measured in effluent over one 24-h period. Relative to the commercial diet, the experimental diet resulted in significantly increased feed efficiency ratio, N retention and P retention, and substantially reduced dissolved, solid and total P waste (g kg–1 dry feed). Although N retention resulting from the experimental diet was higher, this was attributable to higher N (protein) digestibility of the experimental diet. Solid N waste (g kg–1 dry feed) resulting from the experimental diet was substantially lower, but dissolved N waste (g kg–1 dry feed) was not significantly different relative to the commercial diet. Mean effluent orthophosphate production (mg day–1 kg–1 fish) of fish fed the experimental diet was substantially lower than that of fish fed the commercial diet (P < 0.05), but effluent ammonia-N production (mg day–1 kg–1 fish) was not significantly affected by dietary treatment.

Effect of dietary lipid level on nutritional performance of the surubim, Pseudoplatystoma coruscans

Four diets were formulated to contain a constant protein level (46%) and four different lipid levels (6%, 10%, 14% and 18%). The diets were fed to surubim, a Brazilian native carnivorous freshwater fish. Gross energy of the diets were 4440, 4650, 4840, and 5140 (kcal/kg). Surubim fingerlings (average weight: 2.72 g/fish) were randomly assigned to treatments and fed the test diets twice a day to apparent satiation for 62 days. The study was conducted in triplicate with 13 fish distributed in 60-l net-cages set up in 1000-l plastic tanks (three cages per tank), equipped with a flow through freshwater system and water temperature of 27±1 °C. The diet with 6% lipid gave the poorest performance, while fish fed the highest lipid level showed the best nutritional performance. Feed conversion ratio and daily feed consumption showed a marked decrease ( P<0.05) in inverse proportion to lipid level in the diet. Proximate composition of fish whole body was markedly affected ( P<0.05) by dietary lipid, particularly in relation to moisture and crude lipid. Visceral lipid content and nutrient retention also increased in direct proportion to the dietary lipid level ( P<0.05). Results of the present study indicate that soybean lipid is well metabolized by this species, serving as a source of energy and promoting excellent growth.