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.     

Effects of dietary protein and lipid level on growth and body composition of juvenile ayu (Plecoglossus altivelis) reared in seawater

A 3 (protein levels, 380, 460 and 520 g kg^–1 diet) × 2 (lipid levels, 65 and 140 g kg^–1 diet) factorial experiment with three replicates was conducted. Weight gain, feed efficiency and daily feed intake were not significantly affected by dietary protein level, but were by dietary lipid level. Weight gains of fish fed 65 g lipid kg^–1 diet were significantly, or slightly, higher than for 140 g lipid kg^–1 diet at all protein levels. Daily protein intake was significantly affected by both dietary protein and lipid levels ( P  < 0.002). Daily lipid intake was not significantly affected by dietary protein level, but was by dietary lipid level ( P  < 0.001). Protein efficiency ratio was significantly affected by dietary protein level ( P  < 0.02), but not by dietary lipid level. Protein efficiency ratio tended to improve with the decrease of dietary protein level at the same lipid level. Moisture, protein and lipid contents of whole fish were significantly affected by dietary lipid level ( P  < 0.01). Increased dietary lipid did not improve growth or feed efficiency, but increased body fat deposition. It was concluded that the optimum dietary protein and lipid level for growth of juvenile ayu may be 380 and 65 g kg^–1 diet, respectively, when fish were fed to satiety three times daily in seawater.     

The assessment of the chemical composition of fishmeal by near infrared reflectance spectroscopy

The use of near infrared reflectance spectroscopy (NIRS) was investigated as an alternative method for predicting moisture (M), oil, crude protein (CP), ash, salt as NaCl, total volatile nitrogen (TVN) and buffer capacity in fishmeal. The NIRS calibration models were developed using the modified partial least squares (MPLS) regression technique. One thousand and ten ( n =1010) fishmeal samples were used to predict chemical composition for quality control in the fishmeal industry. Equations were selected based on the lowest cross validation errors (SECV). The coefficient of determination in calibration ( R ²) and SECV were 0.93 and 3.9 g kg^–1 dry matter (DM); 0.85 and 5.7 g kg^–1 DM; 0.92 and 3.7 g kg^–1 DM; 0.91 and 4.7 g kg^–1 DM; 0.88 and 6.7 g kg^–1 DM; 0.94 and 1.8 g kg^–1 DM; for M, CP, oil, ash, TVN and NaCl, respectively. It was concluded that NIRS can be used as a method to monitor the quality of fishmeal under industrial conditions.     

Phosphorus and calcium requirements in the diet of the American cichlid Cichlasoma urophthalmus (Günther)

An experiment was carried out with Cichlasoma urophthalmus (Günther) juveniles to determine the phosphorus requirement and its interaction with dietary calcium. Twelve isoenergetic and isoproteic diets were prepared using a basal artificial diet containing vitamin-free casein, dextrin, starch, corn oil, fish oil, vitamin mixture and a mineral mixture free of calcium and phosphorus. Calcium and phosphorus levels were determined in the casein. To the basal diets were added different concentrations of phosphorus as potassium monophosphate (0.5, 1.0, 1.5 and 2.5 g kg^–1) and calcium as calcium carbonate (0.5, 0.75, 1.0, 1.5, 2.0, 2.5, 3.0 and 4.0 g kg^–1). These concentrations resulted in varying Ca–P ratios (1:1, 1.33:1, 1.5:1, 1.6:1 and 2.0:1). Calcium and phosphorus concentrations in the water were 84 mg kg^–1 and 0.003 mg kg^–1, respectively. The diet with 0.5 g kg^–1 phosphorus resulted in deficiency signs such as reduced growth, high conversion ratio, high fat content and low bone mineralization. Increased levels of dietary calcium and phosphorus both gave improved growth and mineralization. Mineralization continued to increase with dietary phosphorus levels above that required for maximum growth. The optimum level of phosphorus in the diet was 1.5 g kg^–1, the optimum calcium level was 1.8 g kg^–1 and the optimum Ca–P ratio was 1.3. Carcass lipid levels were inversely related to dietary phosphorus.     

Methionine requirement of juvenile Japanese flounder Paralichthys olivaceus estimated by the oxidation of radioactive methionine

Growth and amino acid oxidation studies were conducted to estimate methionine requirement of juvenile Japanese flounder, Paralichthys olivaceus , by using the purified diets containing 500 g kg^–1 crude protein from casein, gelatine and crystalline amino acids (CAA). Diets with six graded levels of methionine (5.3, 8.3, 11.3, 14.3, 17.3 and 20.3 g kg^–1 diet) were fed to triplicate groups of the juvenile (initial weight 2.8 ± 0.05 g) twice a day for 40 days. To prevent leaching losses, CAA were precoated using carboxymethylcellulose (CMC), and further diets were bound by CMC and κ-carrageenan. Based on broken-line analysis of percentage weight gain and feed conversion efficiency, the methionine requirements of Japanese flounder in the presence of 0.6 g kg^–1 of cystine were 14.9 and 14.4 g kg^–1 dry diet, respectively. After the growth study was finished, a direct estimate of methionine requirement was made by examining the influence of dietary methionine level on ¹⁴C-methionine oxidation by determining radioactive carbon dioxide, protein and nonprotein fractions of the whole body. The dose–response curve between expired radioactive CO₂ and dietary methionine levels showed that the optimum methionine level for the flounder was estimated to be within the range of 14.3–17.3 g kg^–1 of diet in high agreement with values obtained from the growth study.     

Evaluation of carbohydrate rich diets through common carp culture in manured tanks

Four diets (T₀–T₃) were formulated reducing the fishmeal (Indian) component by 100 g kg^–1 from 300 to 0 g kg^–1 and including proportionately increasing quantities of maize. Diets were fed for 120 days at 50 g kg^–1 body weight to triplicate groups of common carp (av. wt. 2.11–2.18 g) stocked at 1 m^–2 in mud bottomed cement tanks (18 m²), fertilized with poultry manure. Fish growth, SGR and FCR in the different treatments were statistically not significantly different ( P  > 0.05). PER was lowest for the 300 g fishmeal kg^–1 diet treatment (diet T₀), increasing with decrease in dietary fishmeal content (diets T₁–T₃). Fish survival ranged from 96.29 to 100%. Diets influenced carcass composition and digestive enzyme activity. A significant increase in lipid deposition was recorded with increasing dietary carbohydrate content. Amylase, protease and lipase activities were higher in fish fed with diets T₂ and T₃. The protein sparing effect of dietary carbohydrate and the economic implication of eliminating fishmeal from the diet are discussed.     

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.     

Effects of dietary phosphorus and lipid levels on utilization and excretion of phosphorus and nitrogen by rainbow trout (Oncorhynchus mykiss). 1. Laboratory-scale study

Nutritional strategies to reduce both phosphorus (P) and nitrogen (N) excretion relative to growth of rainbow trout were tested in a 2 × 3 factorial experiment. The two factors were `dietary P level' and `dietary lipid level.' Reduction in dietary P from 14 to 8 g kg^–1 dry diet was achieved by partial substitution of dietary fish meal with a combination of full-fat soyabean meal, corn gluten and spray-dried blood meal. Triplicate tanks of 35 rainbow trout per tank were fed experimental diets for 16 weeks and grew from approximately 40 to 250 g, in 15 °C spring water. All tanks were fed the same percent biomass per day. Diets were isonitrogenous, and dietary energy varied with dietary lipid. Diet digestibility data and results of the experiment were used to construct N and P budgets for the fish fed the various diets. A reduction in dietary fish meal from 500 to 200 g kg^–1 dry diet, corresponding to a reduction in dietary P from 14 to 8 g kg^–1 dry diet, resulted in >50% reductions in both solid and dissolved P waste, but did not affect growth, feed efficiency ratio (FER) or sensory characteristics of rainbow trout. Increasing dietary lipid from 170 to 310 g kg^–1 dry diet led to higher growth rate and FER, and lower total N waste relative to weight gain, but did not change protein retention. Increasing dietary lipid level increased deposition of lipid in whole bodies of rainbow trout, and resulted in discernible differences in sensory characteristics of trout fillets.     

The influence of different levels of dietary vitamin E on sea bass Dicentrarchus labrax flesh quality

Sea bass Dicentrarchus labrax fillet quality was investigated after feeding with four diets (A, B, C or D) containing different levels of dietary vitamin E (139 mg kg^–1, 254 mg kg^–1, 493 mg kg^–1 and 942 mg kg^–1, respectively). Six-hundred and eighty fish (mean initial weight 208 g) were equally divided into four 20 m³ tanks and fed for 87 days. Filtered seawater with a temperature ranging from 18.2 to 26.3 °C was supplied continuously. At the end of the experiment, fish were stored at 1 °C for 12 days. At one, three, six, nine and 12 days, 20 fish per group were processed for proximate composition, vitamin E and induced thiobarbituric acid reactive substances (TBARs) analyses. No significant differences in proximate composition were registered between groups. The flesh lipid content ranged from 88.0 g kg^–1 (group B) to 96.8 g kg^–1 (group A). Vitamin E fillet content was significantly different between groups, reaching levels of 98.0, 150.7, 225.2 and 302.0 μg g^–1 lipids for group A, B, C and D, respectively. Induced TBARs values were statistically different only for group A compared with the other groups. No significant variations were registered in relation to preservation time. Because of the positive influence of vitamin E on seafood quality and the correlation between its dietary level and flesh deposition, the α-tocopherol content of the diet should be well above fish minimum requirements.     

Acute LD50 and kidney histopathology following injection of erythromycin (Erythro-200) and its carrier in spring chinook salmon, Oncorhynchus tshawytscha (Walbaum)

We evaluated the toxicity of commercial injectable erythromycin (Erythro-200) and the injectable drug carrier alone (PEG-400, ethyl alcohol and ethyl acetate) in sub-adult spring chinook salmon, Oncorhynchus tshawytscha (Walbaum). Both compounds were toxic to salmon when administered in high dosages. The 50% lethal dose (LD₅₀) of the erythromycin within its carrier (Erythro-200) at 12 °C was estimated at 429 mg erythromycin kg^–1 or 2.145 mL kg^–1 when measured by volume. The LD₅₀ of the drug carrier alone was 2.95 mL kg^–1 by volume or equivalent to 3.21 g kg^–1 of the carrier. We evaluated and scored the histopathology in kidney sections removed from fish 96 h after injection with Erythro-200, the drug carrier alone, or sterile phosphate buffered saline (PBS) that served as a reference control. Kidneys from fish injected with saline had lowest average pathology scores; those injected with the carrier had moderate scores; and the pathology score was highest in tissues from erythromycin-injected fish. In tests at 12 °C, vacuoles were more prominent in proximal and distal tubules of fish injected with higher dosages of 403 and 545 mg erythromycin kg^–1 than in tissues from fish injected with 299 mg kg^–1.     

Effect of methionine on intestinal enzymes activities, microflora and humoral immune of juvenile Jian carp (cyprinus carpio var. Jian)

An 8-week feeding experiment was conducted to determine the effect of dietary methionine supplementation on intestinal microflora and humoral immune of juvenile Jian carp (initial weight of 9.9 ± 0.0 g) reared in indoor flow-through and aerated aquaria. Eight amino acid test diets (350 g kg⁻¹ crude protein, CP), using fish meal, soybean-condensed protein and gelatin as intact protein sources supplemented with crystalline amino acids, were formulated to contain graded levels of methionine (0.6–22.0%) at a constant dietary cystine level of 3 g kg⁻¹. Each diet was randomly assigned to three aquaria. Growth performance and feed utilization were significantly influenced by the dietary methionine levels ( P  < 0.05). Maximum weight gain, feed intake occurred at 12 g kg⁻¹ dietary methionine ( P  < 0.05). Methionine supplementation improved hepatopancreas and intestine weight, hepatosomatic and intestine index, intestinal γ-glutamyltransferase and creatine kinase activity, Lactobacillus count, Bacillus count, lysozyme activities, lectin potency, sim-immunoglobulin M content, addiment C3,C4 contents and serum total iron-binding capacity and declined Escherichia coli and Aeromonas counts. Quadratic regression analysis of weight gain against dietary methionine levels indicated that the optimal dietary methionine requirement for maximum growth of juvenile Jian carp is 12 g kg⁻¹ of the dry diet in the presence of 3 g kg⁻¹ cystine.     

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.     

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.     

Dietary methionine requirement of juvenile Arctic charr Salvelinus alpinus (L.)

The dietary methionine requirement of juvenile Arctic charr Salvelinus alpinus (L.) was assessed by feeding diets supplemented with graded levels of DL-methionine (9, 12, 15, 18, 21, and 24 g kg⁻¹dietary protein) for 16 weeks at 12°C. All diets contained 400 g kg⁻¹ protein, 170 g kg⁻¹ lipid, 66 g kg⁻¹ ash and an estimated 17.5 MJ digestible energy (DE) kg⁻¹. When live-weight gain was examined using quadratic regression, the estimate of methionine requirement for optimal growth was 17.6 g kg⁻¹ of dietary protein (DP) or 7 g kg⁻¹ of the diet. Requirements estimated on the basis of carcass protein and energy gains were 18.8 and 17.9 g kg⁻¹ DP, respectively. Plasma methionine concentrations and ocular focal length variability measurements did not provide a sensitive measure of requirement, because each responded in a linear fashion to increasing dietary methionine levels. Based on the prevalence of cataracts, the methionine level required to prevent lens pathology (26.7 g kg⁻¹ DP) appears to be higher than that required for maximum growth.     

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).     

Nutritional evaluation of waste date fruit as partial substitute for soybean meal in practical diets of juvenile Nile tilapia, Oreochromis niloticus L.

The potential of waste date meal (WDM; low-quality date palm, Phoenix dactylifera L.) as a carbohydrate source in formulated diets for Nile tilapia was evaluated. Four isocaloric-practical diets (15.7 kJ g⁻¹) were formulated incorporating WDM at 0, 100, 200 and 300 g kg⁻¹ levels as partial substitutes for soybean meal (SBM). These were designated D₀ [284 g crude protein (CP) and 383 g carbohydrate (CHO) kg⁻¹ diet], D₁ (279 g CP and 446 g CHO kg⁻¹ diet), D₂ (207 g CP and 495 g CHO kg⁻¹ diet) and D₃ (175 g CP and 578 g CHO kg⁻¹ diet). Each diet was fed to three replicate groups of 30 fish [20.20 ± 0.09 g (±SE)] for 75 days. No feed-related mortality was observed during the entire experimental period. Final body weight (FBW) and specific growth rate (SGR) in the different treatments were statistically not significantly different ( P  > 0.05). Protein efficiency rate (PER) was lowest in diet D₀ and increased with decrease of SBM content (D₁–D₃). A significant increase in whole body lipid content was recorded in fish fed diets D₂ and D₃. Results showed that WDM could be a substitute for SBM up to 300 g kg⁻¹ in practical Nile tilapia diets without compromising growth.     

Comparative performance of juvenile red abalone, Haliotis rufescens, reared in laboratory with fresh kelp and balanced diets

Juvenile Haliotis rufescens were reared in the laboratory in order to investigate the extent to which fresh kelp and formulated feeds with 250 g kg⁻¹ (25P) and 380 g kg⁻¹ protein content (38P) affected their growth rate, gut residence time (GRT), food consumption ( C ), food conversion ratio (FCR) and digestibility. Abalone from 38P attained the highest growth rate (70.5 ± 4.2 μm day⁻¹; 98.3 ± 6.95 μg day⁻¹), followed by 25P (47.9 ± 2.79 μm day⁻¹; 67.4 ± 2.82 μg day⁻¹) and kelp (23.6 ± 3.36 μm day⁻¹; 28.2 ± 4.11 μg day⁻¹). No significant differences were observed in consumption rate among treatments (0.61–0.68% body weight per day), yet kelp-fed abalone exhibited higher FCR (2.44), protein efficiency ratio (4.42), and apparent digestibility of dry matter (69.5%), protein (69.8%) and gross energy (79.2%) than 38P organisms (59.8, 62.4 and 62.2%, respectively). They also showed longer GRT (23.1 ± 0.93 h). This study demonstrated that formulated diets with 250 g kg⁻¹ and 380 g kg⁻¹ protein inclusion can sustain higher growth rates of juvenile H. rufescens than fresh algae. These differences seem to be due to the amount of dietary protein. Kelp meal appears to improve the consumption and digestibility of balanced diets, and its inclusion in formulated diets is recommended.     

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.     

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.     

The need for riboflavin supplementation in high and low energy diets for Atlantic salmon Salmo salar L. parr

A two-factor study was conducted to evaluate the effects of dietary riboflavin and lipid levels on the growth, health performance and riboflavin status of Atlantic salmon ( Salmo salar ). Atlantic salmon parr were fed four fishmeal-based diets with or without supplementation of 20 mg riboflavin kg^–1, at two lipid levels, 150 or 300 g kg^–1. Each diet was fed to triplicate tanks of fish for 12 weeks. Unsupplemented diets contained between 6 and 8 mg riboflavin kg^–1. There were no significant differences in growth as a result of riboflavin supplementation. No mortality or histomorphological changes in eye tissues were observed. Dietary treatments did not affect blood haemoglobin values. After 12 weeks, muscle lipid content seemed to be reduced by riboflavin supplementation irrespective of dietary lipid level. Riboflavin status of whole body, muscle, liver, kidney and eye lenses is reported. Saturation levels of riboflavin in liver and muscle were reached with unsupplemented diets. The concentrations of riboflavin and lipid in liver were negatively correlated. There was a tendency of higher whole body riboflavin concentration in fish fed high-lipid diets. Based on growth, absence of deficiency signs and maximal tissue saturation of riboflavin, it can be concluded that the requirement for riboflavin was met by the natural riboflavin content in the raw materials of the feed. However, independent of dietary lipid level, dietary riboflavin supplementation may increase lipid utilization in rapidly growing salmon parr.