Effect of dietary lipid level on muscle composition in Atlantic salmon Salmo salar

This study was conducted to determine the effects of feeding increasing lipid concentrations (310, 380 and 470 g kg^–1 lipid on dry weight) in diets based mainly on herring byproducts to Atlantic salmon Salmo salar . The diets were isonitrogenous, varying in dietary lipid content at the expense dietary starch. Average fish weight increased from 1.2 kg in April to 2.2–2.7 kg at the end of the feeding trial in September. Significantly greater growth was found in fish fed either the 380 g kg⁻¹ or the 470 g kg⁻¹ lipid diets compared with the 310 g kg⁻¹ lipid diet. Muscle lipid content increased in all dietary groups on a wet weight basis from 7.7 ± 1.4% to 12 ± 3% in salmon fed the 310 g kg⁻¹ lipid diet, and to 16 ± 2% in salmon fed the 380 g kg⁻¹ and 470 g kg⁻¹ lipid diets. In fish of similar weight there was a positive correlation between dietary lipid and muscle lipid concentrations. Low concentrations of muscle glycogen were detected in fish fed each of the diets, while muscle vitamin E concentrations slowly decreased as muscle lipid increased. Muscle fatty acid composition reflected dietary fatty acid profiles, containing similar percentages of total saturated, monoenic and n-3 fatty acids (20:5n-3 and 22:6n-3) in fish from all dietary treatment groups. However, a higher ratio of n-3/n-6 was found in muscle from fish fed the 470 g kg⁻¹ lipid diet compared with the other two groups. Blood chemistry values varied somewhat, but all values were within normal ranges for Atlantic salmon of these sizes.     

Effects of dietary protein to metabolizable energy ratios and total protein concentrations on the performance of yellow perch Perca flavescens

Juvenile yellow perch Perca flavescens were fed semipurified diets with varying protein to metabolizable energy ratios (PME, g protein MJ⁻¹ metabolizable energy) and nutrient densities in three experiments to determine recommended dietary protein and energy concentrations. Experiment 1 fish (18.6 g) were fed diets containing 450 g crude protein kg⁻¹ dry diet and 14.5–18.8 MJ ME kg⁻¹ dry diet for 10 weeks. No differences were found in the growth of experiment 1 fish fed the different diets. Experiment 2 fish (21.9 g) were fed diets containing 15.7 MJ ME kg⁻¹ dry diet and 210–420 g crude protein kg⁻¹ dry diet for 8 weeks. Fish fed the diet containing 340 g kg⁻¹ protein (diet PME = 22) exhibited the greatest weight gain. Experiment 3 fish (27.1 g) were fed diets with a PME of 22 and varying nutrient density (yielding 205–380 g crude protein kg⁻¹ dry diet) for 8 weeks. No differences were found in the growth of experiment 3 fish. Yellow perch fed the semipurified diets exhibited increased liver fat content, liver size and degree of liver discoloration compared with fish fed a commercial fish meal-based diet. Liver changes may have resulted from high dietary carbohydrate levels. We conclude that a protein level of 210–270 g kg⁻¹ dry diet is suitable for juvenile yellow perch provided that the dietary amino acid profile and carbohydrate content are appropriate for yellow perch.     

Quantitative dietary threonine requirement of juvenile Pacific white shrimp, Litopenaeus vannamei (Boone) reared in low-salinity water

An 8-week feeding trial was conducted to determine the threonine requirement of juvenile Pacific white shrimp Litopenaeus vannamei (Boone) in low-salinity water (0.50–1.50 g L⁻¹). Diets 1–6 were formulated to contain 360 g kg⁻¹ crude protein with fish meal, wheat gluten and pre-coated crystalline amino acids with six graded levels of l -threonine (9.9–19.0 g kg⁻¹ dry diet). Diet 7, which was served as a reference, contained only intact proteins (fish meal and wheat gluten). Each diet was randomly assigned to triplicate groups of 30 shrimps (0.48±0.01 g), each four times daily. Shrimps fed the reference diet had similar growth performance and feed utilization efficiency compared with shrimps fed the diets containing 13.3 g kg⁻¹ or higher threonine. Maximum specific growth rate (SGR) and protein efficiency ratio were obtained at 14.6 g kg⁻¹ dietary threonine, and increasing threonine beyond this level did not result in a better performance. Body compositions, triacyglycerol and total protein concentrations in haemolymph were significantly affected by the threonine level; however, the threonine contents in muscle, aspartate aminotransferase and alanine aminotransferase activities in haemolymph were not influenced by the dietary threonine levels. Broken-line regression analysis on SGR indicated that optimal dietary threonine requirement for L. vannamei was 13.6 g kg⁻¹ dry diet (37.8 g kg⁻¹ dietary protein).     

Growth, haematological parameters and tissue lipid peroxidation of soft-shelled turtles, Pelodiscus sinensis, fed diets supplemented with different levels of ferrous sulphate

Soft-shelled turtles, Pelodiscus sinensis , with an average weight of 5.55 g, were fed diets supplemented with eight levels of ferrous sulphate for 8 weeks. The analysed iron content ranged from 50.8 to 482.9 mg kg⁻¹. Growth rate of turtles fed the control diet with no iron supplementation was the lowest among all dietary groups. Haematological parameters including red blood cell, haemoglobin, haematocrit, mean corpuscular volume, mean corpuscular haemoglobin and mean corpuscular haemoglobin concentration of the turtles fed the control diet were also significantly ( P  < 0.05) lower relative to the other groups. Thus, dietary iron at 50.8 mg kg⁻¹ (no supplemented iron) was deemed deficient for growth and ineffective at preventing anaemia in juvenile soft-shelled turtle. Whereas, a supplementation of 50 mg kg⁻¹ ferrous sulphate (a total dietary iron of 91.8 mg kg⁻¹) was enough to normalize the haematological values of soft-shelled turtles to the level similar to other iron supplement-fed groups. Within the tested dietary iron range, liver iron content curve-linearly ( r ² = 0.99) increased with increasing dietary iron level. Furthermore, thiobarbituric acid-reactive substances in liver tissues of the turtles have also increased when liver iron content increased. The dietary iron requirement of soft-shelled turtle is 120–198 mg kg⁻¹ when ferrous sulphate is used as the source of iron.     

Effects of digestible protein levels in isonitrogenous diets on growth performance and tissue composition of juvenile Atractoscion nobilis

A study was undertaken to estimate the effects of isonitrogenous diets (ca. 604 g kg⁻¹ crude protein) containing formaldehyde-treated (FT) fish meal and graded levels of digestible protein (DP) (541, 491, 372, 347 and 247 g kg⁻¹) on growth performance and tissue composition of juveniles white seabass. Five diets were formulated to contain increasing levels of FT fish meal (from 0 to 384 g kg⁻¹) and decreasing levels of non-treated fish meal (from 480 to 96 g kg⁻¹). Each dietary treatment was fed in triplicate to apparent satiation to groups of 25 fish for 50 days. Significantly higher growth performance and feed conversion ratio were obtained in fish-fed diets containing 491 or 541 g kg⁻¹ DP, compared with all other treatments. Apparent digestibility coefficient of protein in the diets was not significantly affected by the inclusion of treated fish meal in the diets. Estimation of protein requirements using a broken-line regression analysis indicated that maximum weight gain would be obtained with a diet containing 503 ± 23 g kg⁻¹ DP. The results from this study suggest that a single-diet formulation using protein treated with formaldehyde as filler might be useful to estimate the requirement of DP for fish.     

Growth and haematology of pacu, Piaractus mesopotamicus, fed diets with varying protein to energy ratio

Haematopoiesis and blood cells' functions can be influenced by dietary concentration of nutrients. This paper studied the effects of dietary protein:energy ratio on the growth and haematology of pacu, Piaractus mesopotamicus . Fingerling pacu (15.5±0.4 g) were fed twice a day for 10 weeks until apparent saciety with diets containing 220, 260, 300, 340 or 380 g kg⁻¹ crude protein (CP) and 10.88, 11.72, 12.55, 13.39, 14.22 MJ kg⁻¹ digestible energy (DE) in a totally randomized experimental design, 5 × 5 factorial scheme ( n =3). Weight gain and specific growth rate were affected ( P <0.05) by protein level only. Protein efficiency ratio decreased ( P <0.05) with increasing dietary protein at all levels of dietary energy. Daily feed intake decreased ( P <0.05) with increasing dietary energy. Mean corpuscular haemoglobin concentration was affected ( P <0.05) by DE and interaction between dietary CP and DE. Total plasma protein increased ( P <0.05) with dietary protein and energy levels. Plasma glucose decreased ( P <0.05) with increasing dietary protein. The CP requirement and optimum protein:energy ratio for weight gain of pacu fingerlings, determined using broken-line model, were 271 g kg⁻¹ and 22.18 g CP MJ⁻¹ DE respectively. All dietary CP and DE levels studied did not pose damages to fish health.     

The influence of dietary phospholipid level on the performances of juvenile amberjack, Seriola dumerili, fed non-fishmeal diets

The objective of the present study was to investigate the effect of dietary phospholipid (PL) level on growth and feed intake of juvenile amberjack ( Seriola dumerili ) fed non-fishmeal (non-FM) diet containing alternative protein sources; soybean protein isolate, tuna muscle by-product powder and krill meal. Three non-FM diets were prepared to contain three levels (14, 37 and 54 g kg⁻¹ dry diet) of PL (soybean lecithin acetone insoluble, 886 g kg⁻¹) and growth performance was monitored in a 30-day growth trial by using 2.6 g of fish. The results indicated that final body weight, weight gain and feed intake significantly increased with increasing dietary PL level. At the highest dietary PL level (54 g kg⁻¹ dry diet), the fish consumed 14.8% and 10.2% as much feed as those fish fed diets containing 14 g kg⁻¹ dry diet and 37 g kg⁻¹ dry diet PL, respectively. An increasing tendency with increasing dietary PL level on feed efficiency was observed. In conclusion, the present study demonstrated that dietary PL supplementation could increase feed intake, and improve the growth of juvenile S. dumerili fed non-FM diets. Therefore, purified PL might be a good candidate to stimulate the growth of fish through enhancing the feed intake when they are fed diets containing alternative protein sources.     

Effect of fermentation on the nutritive value of sesame seed meal in the diets for rohu, Labeo rohita (Hamilton), fingerlings

Six isonitrogenous (350 g kg⁻¹ crude protein) and isoenergetic (17573 kJ kg⁻¹) experimental diets incorporating raw and fermented sesame ( Seasamum indicum ) seed meal at 200, 300, and 400 g kg⁻¹ into a fishmeal based diet were fed to rohu Labeo rohita fingerlings for 60 days and the growth performance and feed utilization efficiency of the fish was studied. The antinutritional factor phytic acid, from raw sesame seed meal, could be reduced below detection limit by fermentation with lactic acid bacteria ( Lactobacillus acidophilus ). Fermentation of the oilseed meal resulted in reduction of the tannin content from 20 to 10 g kg⁻¹. In terms of growth response, feed conversion ratio and protein efficiency ratio, a diet containing 400 g kg⁻¹ fermented sesame seed meal resulted in a significantly ( P  < 0.01) best fish performance. In general, growth and feed utilization efficiencies of fish fed fermented sesame seed meal diets were superior to those fed raw oilseed meal diets. Apparent protein digestibility (APD) values decreased with increasing levels of raw oilseed meal. APD was, however, significantly ( P  < 0.01) higher at all levels of incorporation of fermented sesame seed meal, while diets containing raw oilseed meal resulted in poor protein and lipid digestibility. Carcass protein and lipid contents of fish fed fermented sesame seed meal diets increased with increasing level of incorporation, being highest with 400 g kg⁻¹ fermented oilseed meal-containing diet. The results showed that sesame seed meal may be incorporated in carp diets up to 200 g kg⁻¹ and 400 g kg⁻¹ in raw and treated (fermented) forms respectively.     

Effects of dietary phosphorus level on non-faecal phosphorus excretion from yellowtail (Seriola quinqueradiata Temminck & Schlegel) fed purified and practical diets

Non-faecal phosphorus (P) was determined for large yellowtail to estimate a minimum available P requirement (Experiment  1) and to justify inorganic P supplementation in a fish meal-based diet (Experiment 2). In Experiment 1, purified diets with incremental P concentrations were fed to yellowtail (mean weight 917 g) at a feeding rate of 1.5% of body weight. The peaks of non-faecal P excretion appeared 5–6 h after feeding in fish fed more than 4.5 g available P kg⁻¹ dry diet. Broken-line analysis indicated that the minimum available P requirement was 4.4 g kg⁻¹ dry diet. In Experiment 2, a purified diet (PR) containing 6.5 g available P kg⁻¹ and a fish meal-based diet with (F1) and without (F0) additional phosphorus were fed to yellowtail (mean weight 1.1 kg) at 1.5% (PR) and 2% (F0 and F1) feeding rates respectively. There was no significant difference in P excretion between fish fed the F0 (5.5 g soluble P kg⁻¹ dry diet) and the PR diet. However, significantly higher (34.5%) amounts of non-faecal P excretions (7.4 g soluble P kg⁻¹ dry diet) were found in fish fed F1 compared with the F0 diet. This suggested that there was an excess of dietary P in the F1 diet and that supplementation is not needed in fish meal-based diets for large yellowtail.     

Supplemental citric acid and particle size of fish bone-meal influence the availability of minerals in rainbow trout Oncorhynchus mykiss (Walbaum)

Juvenile rainbow trout Oncorhynchus mykiss (Walbaum) were fed six low-phosphorus (P) diets supplemented with two different sizes of ground fish bone-meals (fine, 68 μm or less; coarse, 250–425 μm) and a coarse bone-meal diet containing four levels of citric acid (0, 4, 8 or 16 g kg⁻¹ diet) to investigate the effects of pH and bone particle size on P bioavailability. The basal diet provided 3.4 g P   kg⁻¹ and bone-meal increased P contents to 5.4–6.0 g P   kg⁻¹. Coarse bone-meal diets supplemented with 0, 4, 8 or 16 g kg⁻¹ of citric acid had pH values of 6.0, 5.7, 5.4 and 5.0, respectively. Weight gain and whole-body water, protein and lipid contents were not influenced by bone-meal supplementation. Supplementing the basal diet with both coarse and fine bone-meal significantly increased whole-body ash content. Fish fed no bone-meal were hypophosphataemic compared with fish fed with either fine or coarse bone-meals. Phosphorus in fine bone-meal had higher availability than P in coarse bone-meal. Bone-meal supplementation significantly decreased whole-body manganese content from 8.9 μg g⁻¹ in fish fed no bone-meal to 2.3 and 4.5 μg g⁻¹ in fish fed with fine and coarse bone-meals, respectively. The concentration of magnesium increased but zinc concentration was not affected by bone-meal supplements. Citric acid increased whole-body ash content but the influence of citric acid on the body P content was not significant ( P  = 0.07). Dietary acidification by citric acid significantly increased whole-body iron in a linear fashion. The bioavailability of dietary P can be improved by fine grinding the bone in fish meals.     

Effects of processing on physical characteristics of diets with distinct levels of carbohydrates and lipids: the outcomes on the growth of pacu (Piaractus mesopotamicus)

The use efficiency and feed conversion of extruded and pelletized diets were compared. Eight isoproteic diets (220 g kg⁻¹ digestible protein) were assayed for 90 days in a 2 × 2 × 2 multifactorial design with two carbohydrate levels (400 and 500 g kg⁻¹), two lipids levels (40 and 80 g kg⁻¹) and two diet processing (pelletization and extrusion) with three repetitions. The growth of Piaractus mesopotamicus fed with these diets and the quality control indices of diets were gauged. The density of extruded diets was lower as carbohydrate level was 400 g kg⁻¹ and lipid 40 g kg⁻¹. The interaction carbohydrate and diet processing presented higher leaching value for low carbohydrate level in extruded diet. Fish fed with extruded diets presented the best feed conversion and protein efficiency ratio. When high levels of carbohydrate and lipid are combined, the weight gain is impaired. The interaction between diet processing diet and lipid levels resulted in the best fish performance when pelletized diets with 40 g kg⁻¹ lipid or extruded diets with 80 g kg⁻¹ lipid were considered. The protein efficiency ratio increased with the increment of carbohydrates in the pelletized diets. The fish show low tolerance to lipids and a preference for carbohydrate when the lipid productive values are taken into account.     

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.     

Effects of the probiotic, Lactobacillus acidophilus, on the growth performance, haematology parameters and immunoglobulin concentration in African Catfish (Clarias gariepinus, Burchell 1822) fingerling

This experiment was carried out to evaluate the effects of the probiotic, Lactobacillus acidophilus , on the growth performance, haematology parameters and immunoglobulin concentration in African catfish Clarias gariepinus fingerling. Two experimental diets were formulated to contain 35 g kg⁻¹ crude protein and 10 g kg⁻¹ lipids accordingly and fed three times daily for 12 weeks to 25 C. gariepinus fingerlings per fibreglass tank in 12 replicates each. The control diet was prepared with no probiotic supplementation whereas the second diet was prepared supplemented with a probiotic, L. acidophilus , containing about 3.01 × 10⁷ colonies/g of diet. The results show that growth performance [specific growth rate (SGR) and relative growth rate (RGR)], nutrient utilization [protein efficiency ratio (PER) and feed conversion ratio (FCR)] and survival were significantly ( P <0.05) higher in fish maintained on the probiotic-supplemented diet compared with those on the control diet. Haematology parameters (packed cell volume, haemoglobin, erythrocyte sedimentation rate, red blood cell and white blood cell, total serum protein, Ca²⁺, Mg²⁺, Cl⁻, glucose and cholesterol) and total immunoglobulin concentrations were also significantly better in fish fed the probiotic-supplemented diet than in the control. Although the water quality parameters monitored were better in the fish fed the probiotic-supplemented diet than in the control, the parameters were not significantly different ( P >0.05). From the results of this experiment, we conclude that L. acidophilus can be used as a probiotic agent in African catfish culture, to enhance fish health, survival and better feed efficiency and growth performance.     

Carbohydrate level in the diet of silver barb, Puntius gonionotus (Bleeker) fingerlings: effect on growth, nutrient utilization and whole body composition

Five iso-nitrogenous (300 g crude protein kg⁻¹ diet) semi-purified diets with graded levels of carbohydrate at 220 (D-1), 260 (D-2), 300 (D-3), 340 (D-4) and 380 (D-5) g kg⁻¹ diet were fed ad libitum to Puntius gonionotus fingerlings (average weight 0.59±0.01 g) in triplicate groups (20 fish replicate⁻¹) for a period of 90 days to determine the effect of the dietary carbohydrate level on the growth, nutrient utilization, digestibility, gut enzyme activity and whole-body composition of fish. 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. The maximum weight gain, specific growth rate, protein efficiency ratio, RNA:DNA ratio, whole-body protein content, protease activity, protein and energy digestibility and minimum feed conversion ratio (FCR) were found in the D-2 group fed with 260 g carbohydrate kg⁻¹ diet. The highest protein and energy retention was also recorded in the same group. However, from the second-order polynomial regression analysis, the maximum growth and nutrient utilization of P. gonionotus fingerlings was 291.3–298.3 g carbohydrate kg⁻¹ diet at a dietary protein level of 300 g kg⁻¹ with a protein/energy (P/E) ratio of 20.58 −20.75 g protein MJ⁻¹.     

Effect of dietary lysine and methionine supplementation on growth, nutrient utilization, carcass compositions and haemato-biochemical status in Indian Major Carp, Rohu (Labeo rohita H.) fed soy protein-based diet

An 8-week feeding trial was conducted in flow through system to examine the effects of dietary supplementation of lysine and methionine on growth, nutrient utilization, haemato-biochemical status and carcass compositions in Indian major carp, rohu, Labeo rohita fingerlings (average weight 6.32 ± 0.06 g). Four experimental soy protein-based diets D ₀ (without lysine or methionine supplementation), D ₁ (lysine supplementation alone), D ₂ (methionine supplementation alone) and D₃ (both lysine and methionine supplementation) were fed to triplicate groups. l -Lysine and dl -methionine were added to the diets containing 550 g kg⁻¹ soybean meals at 4 and 7 g kg⁻¹ of dry diet respectively. Significant higher weight gain, specific growth rate (SGR), protein efficiency ratio (PER), dry matter retention, nitrogen retention, total ash retention, whole carcass protein, haemoglobin concentration, haematocrit value, total erythrocytic count, total leucocytic count, plasma glucose and plasma total protein and lower FCR, per cent lipid retention and whole body moisture content were observed in fish fed soya protein-based diet supplemented with both lysine and methionine than that of fish of other dietary groups at the end of 8 weeks feeding trial. Although fish fed diet supplemented with either methionine or lysine did not show any significant differences of growth performances, feed utilization, carcass composition and haemato-biochemical status, fish of both of these dietary groups showed significantly better growth performances, feed utilization, carcass composition and haemato-biochemical status than that of fish fed diet without lysine and methionine supplementation.     

Use of full-fat winged bean Psophocarpus tetragonolobus seed meal as a protein feedstuff in fish-meal free diets for African catfish Clarias gariepinus

Mature winged bean Psophocarpus tetragonolobus seeds were quick-cooked and the full-fat meal derived was used to completely replace menhaden fish meal as a dietary protein source for the African catfish Clarias gariepinus . Five dry practical diets (400 g crude protein kg⁻¹ and 17.5 kJ gross energy g⁻¹ dry diet) containing menhaden fish meal (diet 1) or winged bean meal with or without graded levels of supplemental L -methionine (diets 2, 3, 4 and 5; 0, 5, 10 and 15 g kg⁻¹, respectively) were fed to catfish fingerlings (5.8  +  1.2 g) for 70 days. Weight gain, growth rate, feed conversion and protein utilization by catfish fed a winged bean meal diet without L -methionine supplementation (diet 2) was inferior ( P  > 0.05) to that in catfish fed the other diets, where performance differed nonsignificantly. Carcass protein of catfish was lower ( P  < 0.05) while liver protein was higher ( P  < 0.05) in catfish fed the winged bean meal diet without methionine supplementation. Results suggest that winged bean meal cannot replace fish meal as a protein source in catfish diets except with a minimum supplementation with 5 g L -methionine kg⁻¹ diet.     

Urea in feeds for sea water farmed Atlantic salmon: effect on growth, carcass quality and outbreaks of winter ulcer

The main objective of the present study was to evaluate whether dietary supplementation of urea might reduce the incidence of winter ulcer in sea water-farmed Atlantic salmon. Salmon destined to be S0 smolt were fed with a urea-supplemented diet (0 or 20 g kg⁻¹ urea) over an 8-week period prior to sea water transfer and were then fed supplemented diet (0, 5, 10 or 20 g kg⁻¹ urea) during the first and second winters in the sea. During the first winter positive relationships between dietary urea and plasma urea and between plasma urea and plasma osmolality were observed. Further, plasma osmolality displayed a negative relationship to mortality. Of the salmon that died during the first winter in the sea 90% had one or more skin ulcers. Both during the first and second winter there were fewer salmon with ulcer among fish fed with the diets supplemented with urea. Salmon fed with 20 g kg⁻¹ urea tended to have higher percentage water in the muscle. Mortality and incidence of salmon with ulcer seemed to relate to plasma osmolality amongst fish fed on diets that differed in levels of urea supplementation, suggesting that an osmotic imbalance may contribute to the development of winter ulcer in farmed salmon. Salmon fed with 20 g kg⁻¹ urea showed significantly greater body weight during the second winter in sea. Fish killed without prior starvation had significantly higher level of muscle urea in the 20 g kg⁻¹ urea group compared with fish fed with the unsupplemented diet. However, a 13-day starvation period reduced urea content in the muscle to the level of the control. No effects of dietary urea supplementation on the sensory quality of market size Atlantic salmon were observed.     

Optimum dietary soybean meal level for maximizing growth and nutrient utilization of on-growing gilthead sea bream (Sparus aurata)

Six isonitrogenous [450 g kg⁻¹ crude protein (CP)] and isoenergetic diets (23 kJ g⁻¹) with six levels of defatted soybean meal inclusion (0, 132, 263, 395, 526 and 658 g kg⁻¹) in substitution of fish meal were evaluated in gilthead sea bream of 242 g initial weight for 134 days. Fish fed diets S0, S13, S26 and S39 had a similar live weight (422, 422, 438 and 422 g, respectively) but fish fed diets S53 and S66 obtained the lowest final weight (385 and 333g, respectively), and similar results were presented in specific growth rate (SGR). Fish fed diets S53 and S66 also obtained the highest feed conversion ratio (FCR). Quadratic multiple regression equations were developed for SGR and FCR which were closely related to dietary soybean level. The optimum dietary soybean levels were 205 g kg⁻¹ for maximum SGR and 10 g kg⁻¹ for minimum FCR. Sensorial differences were appreciated by judges between fish fed S0 and S39 soybean level, but after a re-feeding period of 28 days with diet S0, these differences disappeared.     

The dietary protein requirement of a bagrid catfish, Mystus nemurus (Cuvier & Valenciennes), determined using semipurified diets of varying protein level

Triplicate groups of Mystus nemurus (Cuvier & Valenciennes) were fed isoenergetic semipurified diets containing seven dietary protein levels from 200 to 500 g kg^–1 diet for 10 weeks. Dietary protein was supplied by graded amounts of a protein mixture (tuna muscle meal:casein:gelatine) at a fixed ratio of 50:37.5:12.5. Mystus nemurus fingerlings of initial weight 7.6 ± 0.2 g were fed close to apparent satiation at 2.5% of their body weight per day in two equal feedings. Growth performance and feed utilization efficiency increased linearly with dietary protein level from 202 to 410 g kg^–1 diet and declined with protein levels of 471 g kg^–1 diet or above. Protein efficiency ratio and apparent net protein utilization started to decline when the fish were fed with dietary protein levels exceeding 471 g kg^–1 diet. Fish fed with lower protein diets (202–295 g kg^–1 diet) had significantly ( P  < 0.05) higher carcass lipid content compared with fish fed with higher protein diets. Carcass lipid contents were inversely related to moisture content. Dietary protein did not significantly affect fish carcass protein and ash content. Using two-slope broken-line analysis, the dietary protein requirement for M. nemurus based on percentage weight gain was estimated to be 440 g kg^–1 diet with a protein to energy ratio of 20 mg protein kJ^–1 gross energy. This level of protein in the diet is recommended for maximum growth of M. nemurus fingerlings weighing between 7 and 18 g under the experimental conditions used in this study.     

A dietary energy level of 14.6 MJ kg−1 and protein-to-energy ratio of 20.2 g MJ−1 results in best growth performance and nutrient accretion in silver barb Puntius gonionotus fingerlings

Five iso-nitrogenous (300 g protein kg⁻¹ diet) and iso-lipidic (80 g kg⁻¹ diet) semi-purified experimental diets with variable energy levels of 10.5 (D-1), 12.5 (D-2), 14.6 (D-3), 16.7 (D-4) and 18.8 (D-5) MJ kg⁻¹ diets were fed to Puntius gonionotus fingerlings (average weight 1.79 ± 0.02 g) in triplicate groups (15 healthy fishes per replicate) for a period of 90 days to assess the optimum dietary energy level and protein-to-energy ratio (P/E). 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. Maximum specific growth rate, protein efficiency ratio, protein productive value, RNA : DNA ratio, whole body protein content, digestive enzyme activity and minimum feed conversion ratio was found in fish-fed diet D-3 with 14.6 MJ kg⁻¹ energy level. There were no improvements in all these parameters with the further rise in dietary energy level. Hence, it may be concluded that the optimum dietary gross energy level for maximum growth and nutrient utilization of silver barb is 14.6 MJ kg⁻¹ diet with a resultant P/E ratio of 20.2 g protein MJ⁻¹ diet, when the dietary protein and lipid are maintained at optimum requirement levels of 300 and 80 g kg⁻¹ diet, respectively, for this species.