The interactive effects of dietary protein and energy on feed intake, growth and protein utilization of juvenile mulloway (Argyrosomus japonicus)

The objectives of this study were to describe the interactive effects of varying digestible protein (DP) and digestible energy (DE) contents on the feed intake, growth, protein utilization and whole body composition of juvenile mulloway ( Argyrosomus japonicus ) and to determine the optimal DP : DE ratio for growth. This was achieved by feeding mulloway diets containing one of four different DP levels (250–550 g kg⁻¹) at two DE levels (16 or 21 MJ kg⁻¹). Juvenile mulloway were stocked at each of two different sizes (70 or 200 g) in triplicate groups for each dietary treatment and fed twice daily to apparent satiation over 58 days. The results indicated that feed intake was not governed solely by energy demands but was also dependant on the DP content of the diet. Protein utilization did not improve with diets containing decreasing protein and increasing lipid content indicating that mulloway have a limited capacity to spare DP. Optimal DP content was found to be 444–491 g kg⁻¹ depending on the DE content of the diet and the size of mulloway and is within the range reported for other sciaenid species. The use of formulated diets with 28.6 g of DP MJ DE⁻¹ will achieve optimal growth and protein deposition for 70–275 g mulloway.     

Evaluation of Digestible Energy and Protein for Growth and Nitrogen Retention in Juvenile Florida Pompano,Trachinotus carolinus

Juvenile Florida pompano (6.3 ± 0.50 g) were fed 1 of 12 diets formulated with an array of crude protein (340, 380, 420, 480, or 500 g/kg diet) and crude lipid (60, 100, 120, 160, or 180 g/kg diet) levels and estimated digestible protein to digestible energy (DP/DE) of 18.9–26.8 mg/kJ. In a second trial, apparent protein and energy digestibilities were empirically determined and coefficients used to calculate actual digestibilities. Digestible energy (DE) intake was 4.2–13.0 kJ/fish/d, and digestible protein (DP) intake was 0.13–0.32 g/fish/d. Average daily gain increased as a function of both DP and energy. Growth increased with increasing DP in all diets containing 24.0 mg/kJ DP/DE or greater until a plateau at 366 g DP/kg. Nitrogen gain was also a function of both DP and DE. Increasing energy at constant protein improved protein utilization. DP to maximize growth and nitrogen gain was between 356 and 366 g/kg. DE to attain maximum growth in juvenile Florida pompano is at least 15.4 MJ/kg with a DP/DE between 23.8 and 25.1 mg/kJ.     

Growth and efficiency of feed usage by Atlantic salmon (Salmo salar) fed diets with different dietary protein: Energy ratios at two feeding levels

The effect of dietary digestible protein/digestible energy (DP/DE) ratios and feeding level on growth, feed efficiency, nutrient and energy usage by Atlantic salmon ( Salmo salar ; initial body weight, 7.0 g/fish) at 15°C was investigated in a 16-week feeding trial. Three diets, differing in their DP and DE contents, namely 37/18 (regular diet, RD), 37/21 (high fat diet, HF) and 44/ 22 (high nutrient-dense diet, HND) g/MJ of dry feed were formulated. DP/DE ratios were 20, 18 and 20 g/MJ for the RD, HF and HND diets, respectively. Salmon were hand-fed three times a day at either 100% or 85% of the feed requirement estimated by a bioenergetics model. At each feeding level, DE intake (kJ/fish) was similar for all three diets. Diet composition did not affect growth rate. However, increasing the digestible energy density from 18 to 22 MJ/kg of dry feed resulted in a significant increase ( P  < 0.05) in feed efficiency. Restricting feed intake significantly decreased live body weight gains for all diets. However, feed efficiency was not affected by feeding level. Diet composition and feeding level did not affect carcass composition and nutrient and energy usage, with the exception of a higher ( P  < 0.05) carcass lipid of fish fed the HF100 diet compared with the fish fed the RD and HND diets and a higher ( P  < 0.05) lipid gain (g/fish) of fish fed the HF100 diet compared with fish fed all the diets at the restricted feeding level. Restricting feeding resulted in significantly lower ( P  < 0.05) energy gain (kJ/fish) compared with fish fed at 100%. Increasing the DE and nutrient density of the diet had no effect on growth but improved feed efficiency and lowered solid wastes (g of solid wastes per kg of fish produced) while dissolved wastes were not affected by dietary ormulation.     

Effects of dietary protein and lipid levels on growth,body composition and flesh quality of juvenile topmouth culter,Culter alburnus Basilewsky

Nine experimental diets at three protein (35%, 40% and 45% crude protein) and lipid (5%, 8% and 11% crude lipid) levels with variable digestible protein to digestible energy (DP/DE) ratios ranged from 21.9 to 27.8 g protein MJ^?1 were fed to topmouth culter (Culter alburnus Basilewsky) fingerlings (initial weight 6.5 ± 0.9 g) in triplicated groups (30 fish per replicated) for a period of 10 week to assess the optimum dietary DP/DE ratio and the protein sparing effect by utilizing dietary lipid. 27 cages of 1.5 m³ capacity placed in a lake located in Wuhan were used for rearing the fish. At the end of the experiment, maximum weight gain and thermal‐unit growth coefficient was found in fish fed diet D4 with 45% protein, 8% lipid and P/E ratio of 26.2 g protein MJ^?1, but without a significant difference compared to fish fed diet D5 with 40% protein, 8% lipid and DP/DE ratio of 25.3 g protein MJ^?1. The best flesh quality evaluated by muscle collagen content was found in fish fed D5. High fat accumulation with increasing dietary lipid levels was observed in whole body but not in muscle tissue. Hence, it may be concluded that the optimum formulation for maximum growth and quality of topmouth culter is a diet containing 40% protein and 8% lipid with a resultant DP/DE ratio of 25.3 g protein MJ^?1. In addition, the protein sparing effect by inclusion lipid was observed but limited.     

Investigation of the nutritional requirements of Australian snapper Pagrus auratus (Bloch & Schneider, 1801): effects of digestible energy content on utilization of digestible protein

This study used a curvilinear model to investigate the effects of different digestible energy (DE) levels on the digestible protein (DP) requirements of juvenile snapper Pagrus auratus. For each DE level (15, 18 or 21 MJ kg⁻¹), DP content was increased from about 210–560 g kg⁻¹ in seven evenly spaced increments by formulating a summit diet (highest DP content) and a diluent diet (lowest DP content) at the desired DE level and combining the summit and diluent diets in various ratios to achieve the desired DP content. This ensured the DE level remained relatively stable. Each of the 21 dietary treatments was fed to three replicate groups of snapper twice daily to apparent satiation for 57 days. At the completion of the trial, fish were weighed and killed for chemical analysis. Results indicated that the rapid growth of snapper weighing 30–90 g was highly dependent on the ratio of DP to DE and that optimum protein deposition did not occur until snapper were offered feeds with at least 350 g DPkg⁻¹, irrespective of DE level. According to the fitted models, diets formulated for snapper reared at temperatures from 20–25°C should contain approximately 23 g DP MJ DE⁻¹ to promote optimal weight gain and protein deposition. Based on the feeding regime used in this study, this could be achieved with practical diets containing a DP:DE ratio of 460:20, 420:18 or 350:15.     

Effect of dietary DP/DE ratio on apparent digestibility, growth and nitrogen and phosphorus retention in rainbow trout, Oncorhynchus Mykiss (Walbaum)

The effect of DP/DE ratio in diets for rainbow trout, Oncorhynchus mykiss (Walbaum), was investigated. To evaluate growth and body composition, groups of trout were fed three experimental diets with a constant level of gross energy (25.4 ± 0.12 MJ kg^?1 dry matter (DM)) and different digestible protein/digestible energy (DP/DE) ratios (diet A, 16. 35; diet B, 17.21; dietC, 18.23 g Mr^?1). Fat, protein and energy digestibility coefficients were not affected by the DP/DE ratio of the diets. Growth and feed utilization improved markedly as dietary DP/DE ratio increased (P < .01). The efficiency of fat, protein and energy utilization tended to increase with increasing DP/DE ratio of the diets. Nitrogen discharge in effluent water per kg of weight gain was not affected by dietary treatments (mean values for: diet A, 29.9; diet B, 29.8; diet C, 29.1 g N kg^?1 weight gain) while phosphorus discharge in effluent water fell using diets with a higher DP/DE ratio (mean values for: diet A, 7.3; diet B, 6.7; diet C, 5.9 g P kg^?1 weight gain).     

Animal performance and reproductive aspects of female Rhamdia quelen fed on different levels of digestible energy

This study was conducted to evaluate the effects of different diet energy levels on animal performance. Specifically, this investigation examined the reproductive and histological aspects of the liver and gonads of female silver catfish (Rhamdia quelen). These fish were fed for 210 days with diets containing 30% digestible protein (DP) and digestible energy (DE) that corresponded to 11.93, 12.98, 14.03, 15.07 and 16.12 MJ of DE kg^?1. The initial and final lengths, weights, and weight gains, the visceral, gonadal, and hepatosomatic indices, and the histological parameters hepatocytes area and gonadal stages were evaluated. In the reproductive season, the fish were submitted to an artificial reproduction protocol and the percentage of spawning females and their relative and absolute fecundity were evaluated. DE did not affect reproductive or animal performance aspects (P > 0.05). Cytoplasmic vacuoles in hepatocytes were observed in higher DE levels. Thus, female Rhamdia quelen can be fed a diet of 30% DP with 11.93 MJ of DE kg^?1 without reproductive or performance losses.     

Effect of different dietary protein and lipid levels on growth and survival of juvenile Australian redclaw crayfish, Cherax quadricarinatus (von Martens)

This study determined the effect of different dietary protein and lipid levels on growth and survival of juvenile redclaw Cherax quadricarinatus. Nine practical test diets were formulated to contain three crude protein (CP) levels [260, 310 and 360 g kg^?1, equivalent to 225, 260 and 296 g kg^?1 digestible protein (DP) respectively] at three crude lipid (CL) levels (40, 80 and 120 g kg^?1, equivalent to 38, 67 and 103 digestible lipids respectively), with digestible protein : digestible energy (DP : DE) ranging from 14.6 to 22.6 mg protein kJ g^?1. Three replicate groups of 15 crayfish (initial weight mean ± SD, 0.71 ± 0.13 g) per diet treatment were stocked in 40 L tanks, at 28 °C for 60 days. The highest mean weight, specific growth rate and biomass, with values of 7.0 g, 3.67% day^?1, and 370.2 g m^?2, respectively, were achieved by feeding a diet with P : L = 310 : 80 (P < 0.05). The treatments resulted in a survival rate of 80–91%, feed conversion ratio of 1.08–1.61 and protein efficiency ratio of 2.24–3.08. Results indicated that a diet containing 270 g kg^?1 DP (equivalent to 320 g kg^?1 CP), 75 g kg^?1 digestible lipid (DL) with a DP/DE of 18.4 mg protein kJ^?1, and 0.031 g protein per animal per day was optimum for juvenile C. quadricarinatus under the tested experimental conditions.     

Protein‐to‐energy ratio of 21.43 g MJ−1 improves growth performance of Nile tilapia at the final rearing stage under commercially intensive rearing conditions

This study evaluated the effect of ratio of dietary digestible protein (DP) to digestible energy (DE) on growth performance, fillet chemical composition and haematological profile of Nile tilapia subjected to transport‐induced stress at the final rearing stage (450 to 800 g) under commercial conditions. The trial was conducted using a 5 × 2 factorial layout (DP: 200, 230, 260, 290 and 320 g kg^?1) and (DE: 12.6 and 13.8 MJ kg^?1). Energy levels did not influence any analysed parameters in this research. Final weight and biomass gain were increased up to the ratio of 269 and 270 g PD kg^?1, respectively, and feed conversion ratio was reduced down to a 275 g DP kg^?1. Protein efficiency ratio linearly decreased from 200 g DP kg^?1 diet to 320 g DP kg^?1. There was no statistical difference in fillet chemical composition. Red blood cell count (RBC), haemoglobin (Hb), mean corpuscular volume (MCV) and mean corpuscular haemoglobin concentration (MCHC) were different before and after transport‐induced stress. Leucocyte differentiation after transport‐induced stress revealed lymphocytopenia and neutrophilia. We conclude that for tilapia weighing 450–800 g reared under commercially intensive conditions, a diet with 270 g DP kg^?1 and 12.6 MJ DE kg^?1 (21.43 g DP MJ^?1 DE) can improve the growth performance and ensure the fish health.     

Energy and protein requirements for maintenance and growth in gilthead seabream (Sparus aurata L.)

Factorial determinations of energy and protein requirements in growing Sparus aurata were carried out at 23–24°C. The energy content in the whole fish was dependent on fish weight and ranged from 5 to 11 MJ kg⁻¹ body mass for 1–250 g fish, whereas the protein content remained constant at 179 g kg⁻¹.
During starvation the fish lost 42.5 kJ body weight (BW) (kg)^−0.83 day⁻¹ and 0.42 g protein BW (kg)^−0.70 day⁻¹. The maintenance requirement for energy was calculated to be 55.8 kJ BW (kg)^−0.83 day⁻¹ and for protein 0.86 g BW (kg)^−0.70 day⁻¹. Utilization of digestible energy and digestible crude protein below and at maintenance was determined as 0.72 and 0.51, respectively. Utilization of digestible energy and digestible crude protein for growth above maintenance was determined as 0.46 and 0.28, respectively.
These values allow estimation of requirements for growing Sparus aurata .     

Influence of digestible protein levels on growth and feed utilization of juvenile meagre Argyrosomus regius

This study investigates the effect of digestible protein levels in experimental diets for meagre (Argyrosomus regius). A group of 253 fish, 52 g of mean weight, was distributed in 12 tanks, three replicates per treatment. Four isolipidic diets (170 g kg^?1 crude lipid) with different digestible protein levels (350 g kg^?1, 430 g kg^?1, 490 g kg^?1 and 530 g kg^?1) were formulated using commercial ingredients. The trial lasted 62 days. Meagre fed diets 430, 490 and 530 g kg^?1 obtained higher TGC (2.47, 2.57, 2.69 × 10^?3, respectively) than fish fed diet 350 g kg^?1 (2.14 × 10^?3). Group of fish fed diet with 350 g kg^?1 DP showed the lowest ammonia excretion level. According to the in vitro digestibility trial diets with 350 and 430 g kg^?1 DP released less amino acids in comparison with diet with 49% DP, although in vivo digestibility test did not show significant differences among diets 430, 490 and 530 g kg^?1 DP. Using the quadratic regression, optimal digestible protein intake according to the ECR for rearing juvenile meagre was recorded in 0.8 g DP/100 g fish and day.     

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.     

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.     

Digestible dietary protein and energy requirements of juvenile Asian horseshoe crabs,Tachypleus tridentatus and Carcinoscorpius rotundicauda

A 84‐day feeding experiment of two juvenile horseshoe crab species, including nine formulated diets with three digestible protein (DP) levels (36%, 40% and 44%) and three digestible energy (DE) levels (14, 16 and 18 kJ g^?1) versus the control, fed on frozen brine shrimp (Artemia salina), was conducted. The results showed that the survival rate of Tachypleus tridentatus ranged from 67% to 100%, while that of Carcinoscorpius rotundicauda varied from 44% to 100%. The results also indicated that the formulated diet containing 40% DP with 14 kJ g^?1 DE was the best, in terms of growth and feed utilization, for the two juvenile horseshoe crab species. Final body weight (FBW), thermal‐unit growth coefficient (TGC), feed efficiency (FE), nitrogen retention efficiency (NRE) and energy retention efficiency (ERE) of T. tridentatus fed 40% DP and 14 kJ g^?1 DE were significantly higher than that of T. tridentatus fed the control diet. However, for C. rotundicauda, only significantly higher FE, NRE and ERE were found in juveniles fed 40% DP and 14 kJ g^?1 DE than the control diet. The present findings revealed that the optimum DP/DE ratio for the two species was 28 g protein MJ^?1.     

The effects of dietary digestible protein and digestible energy content on protein retention efficiency of juvenile silver perch Bidyanus bidyanus (Mitchell)

Effects of varying dietary digestible protein (DP) and digestible energy (DE) on protein retention efficiency (PRE), weight gain, protein deposition and carcass composition for silver perch (Bidyanus bidyanus, Mitchell) were studied. Using digestibility data for silver perch, we formulated three series of diets with different DE contents (13, 15 or 17 MJ DE kg^?1). For each series, a ‘summit’ diet containing an excess of protein for silver perch (based on previous research) and a ‘diluent’ diet with only 10–13% DP were formulated. By blending the summit and diluent diets together in different ratios, five diets with different DP contents were produced for each DE series. A commercial diet was also included to give 16 experimental diets in total. Eight juvenile fish (mean initial weight 1.2 g) were stocked into each of 64 × 70‐L acrylic aquaria and then each of the 16 diets was randomly allocated to four replicate aquaria. Tanks were supplied with partially recirculated water (75%) at 25–27°C. Fish were fed restrictively, twice per day, based initially on 3.5% body weight day^?1 with 40% of the ration given at 08:30 hours and 60% given at 15:00 hours for 59 days. Quadratic functions were fitted to each energy series to describe the relationship between DP content of diets and PRE (the asymptote of these functions were used to predict maximum PRE). For low DE (13 MJ kg^?1), mid‐DE (15 MJ kg^?1) and high DE (17 MJ kg^?1), the dietary DP contents to give maximum PRE were 24.7%, 26.1% and 30.1% respectively. Carcass fat decreased with increasing DP and increasing DP:DE ratio. Varying the dietary protein and DE also influenced other indices of fish performance. ‘Optimum’ dietary protein therefore depends on several factors. For fish fed, restrictively, the protein content needed to maximize PRE is lower than the content needed to maximize weight gain or minimize carcass fat. For fish fed to satiation, the lowest protein content for maximum weight gain is lower than for fish fed restrictively.     

Optimum digestible protein and energy levels and ratio for greater amberjack Seriola dumerili (Risso) fingerling

A study was conducted to determine optimum dietary digestible protein (DP) and digestible energy (DE) levels and DP DE⁻¹ ratio for growth of greater amberjack Seriola dumerili fingerlings. A 3 × 3 factorial design with duplication was used in this study. Nine experimental diets were formulated to contain three levels of crude protein (CP; 420, 470 and 530 g kg⁻¹) and three levels of crude lipid (CL; 130, 180 and 230 g kg⁻¹). Nine groups of fingerling (initial weight 51.8 g) were fed each experimental diet for 40 days. Final body weight, feed efficiency, specific growth rate and energy efficiency were significantly affected by dietary protein and lipid level. These parameters tended to improve with increasing dietary protein level. Conversely, an increase of lipid level negatively affected these parameters. High growth rate and feed efficiency were obtained from fish fed the diet containing 393 g kg⁻¹ DP and 14.2 MJ kg⁻¹ DE (27.7 g MJ⁻¹ DP DE⁻¹). The high DP DE⁻¹ (27.7 g MJ⁻¹) indicates that greater amberjack fingerling are highly dependent on dietary protein as an energy source.     

Effects of varying dietary protein and energy supply on growth, body composition and protein utilization in gilthead seabream (Sparus aurata L.)

Diets formulated with increasing digestible energy (10–22 DE MJ kg⁻¹) contents and decreasing digestible crude protein (DCP)/DE ratios (34–15 g MJ⁻¹) were fed to triplicate groups of Sparus aurata in three consecutive trials. Fish were hand-fed to apparent satiation and voluntary feed intake was found to be dependent upon dietary DE content. Daily growth was regulated both by energy and protein intake and reached its maximum at high energy levels. Growth composition showed narrow limits regarding protein gain (157–190 g kg⁻¹) and a wider range regarding lipid (55–210 g kg⁻¹) deposition reflecting the dietary energy to protein supply. Energy utilization for growth was constant at a value of 0.50 regardless of energy intake. Efficiency of protein utilization for growth varied between 0.33 and 0.60 depending on the DCP/DE ratio in the diet. The optimal protein utilization for protein deposition was found to be at 0.47. These values allow daily energy and protein requirements for growing S. aurata to be quantified. This demonstrates that the optimal dietary DCP/DE supply changes with fish size, growth potential and daily feed intake.     

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.     

Optimum dietary ratio of digestible protein and energy for juvenile American eel, Anguilla rostrata, fed practical diets

Triplicate groups of juvenile American eel, Anguilla rostrata, initial weight 8.2 ± 0.24 g, were fed to satiation herring meal based diets formulated with digestible protein/digestible energy (DP/DE) ratios of 19, 20, 21, 22 and 23 g DP MJ DE^?1 (as‐fed basis) for 84 days. Data were collected to determine the effect of dietary DP/DE ratio on feed intake (FI), mean weight (MW), specific growth rate (SGR), feed conversion ratio (FCR), apparent digestibility (AD) of major nutrients, rate of phosphate excretion (RPE) and nutrient retention efficiency (RE). Highest MW, SGR and lowest FCR (P < 0.05) were achieved by feeding 22 g DP MJ DE^?1 with values (mean ± SE) of 22.9 ± 0.07 g fish^?1, 1.23 ± 0.033% day^?1 and 0.91 ± 0.075 g feed g gain^?1, respectively. With exception of lipid, digestibility of all nutrients were the same (P > 0.05) with mean AD coefficients for organic matter, protein, energy and phosphorous of 86.3, 94.1, 89.2 and 34.7%, respectively. Lipid AD was significantly higher (P < 0.05) when DP/DE ratio was 21, 22 or 23 g DP MJ DE^?1 at 92.3% as opposed to when DP/DE ratio was 19 or 20 g DP MJ DE^?1 at 90.3%. The DP/DE ratio had no significant effect (P > 0.05) on RPE and it averaged 0.05 ± 0.002 g phosphate kg fish^?1 day^?1. Nitrogen retention efficiency (NRE) significantly (P < 0.05) increased as DP/DE ratio increased to 21 g DP MJ DE^?1 and was similar thereafter (P > 0.05) at an average of 31.6 ± 0.67%. Energy retention efficiency (ERE) significantly (P < 0.05) increased to 42.9 ± 1.24% as DP/DE ratio increased to 22 g DP MJ DE^?1 and thereafter significantly (P < 0.05) decreased. Lipid retention efficiency (LRE) increased significantly (P < 0.05) to 75.7 ± 0.85% as dietary DP/DE ratio increased to 23 g DP MJ DE^?1. Non‐linear quadratic regression of ERE against dietary DP/DE ratio yielded an estimated optimum DP/DE ratio for juvenile American eel of 22.1 g DP MJ DE^?1.     

Fishmeal replacement with feather-enzymatic hydrolyzates co-extruded with soya-bean meal in practical diets for the Pacific white shrimp (Litopenaeus vannamei)

A feeding experiment was conducted to examine the potential of a commercial steam-processed-feather meal (SPFM) and feathers enzymatically hydrolysed for 60 or 120 min (EHF60 and EHF120) as substitutes for fishmeal (FM) in diets for white shrimp juveniles. Enzymatically hydrolised feathers or SPFM were blended through an extruder with soyabean meal (SBM) in a 1:1 ratio (EHF-SBM, SPFM-SBM). Isoproteic and isolipidic diets were formulated to contain 9% EHF60-SBM, 9% EHF120-SBM and 18% EHF60-SBM. These diets were compared with a diet containing 13.7% SPFM-SBM and a control diet designed to contain 18.4% FM and no feather. Quadruplicate groups of 15 shrimp (0.33 g initial-body weight) were fed twice a day on each diet for 4 weeks. The weight gain of shrimp fed on the three EHF-SBM diets did not differ from that of shrimp fed on the FM-control diet; however, shrimp fed on the SPFM-SBM diet gained less weight. The EHF60 and EHF120 coextruded with SBM in a 2:1 ratio were evaluated in a commercial rearing pond. Both ingredients included at 20% in the test diets were compared with a control diet containing 17.8% FM. Triplicate groups of juvenile shrimp (3.4 g initial-mean weight), randomly allocated in 1 m³ plastic cages, were fed with the test diets during 30 days. Growth (weight gain, specific-growth rate (SGR)) and nutritional value of the diets, food conversion ratio (FCR), protein-efficiency ratio (PER), digestibility were similar. In summary, these results indicate that white shrimp can be fed with a practical diet containing 20% EHF-SBM (2:1) without impairing growth or food conversion. The use of 20% EHF-SBM (2:1) allowed the fish-meal portion to be reduced by nearly by 55%.