Efficacy of phytase on phosphorus utilization in practical diets fed to striped bass Morone saxatilis

Several experiments were conducted to determine the effects of phytase on dietary phosphorus (P) utilization by striped bass Morone saxatilis fed high phytate diets. The experiments were designed to determine the effectiveness of various dietary levels of a dry or liquid phytase concentrate incorporated in diets to improve the P utilization of striped bass. Fish were fed various basal diets containing over 700 g kg^?1 plant feed ingredients and 4.9–7.1 g kg^?1 P and 1.5–1.7 g kg^?1 non-phytin P. A diet supplemented with potassium monophosphate (PMP) and containing 9 g kg^?1 total P and 6 g kg^?1 non-phytin P with no added phytase was the positive control. The dietary treatments were assigned to duplicate tanks and diets were fed to juvenile striped bass for up to 14 weeks. The effectiveness of the phytase treatments was determined by measuring weight gain, feed conversion, serum, scale and vertebral calcium and P, as well as P absorption. Apparent P absorption was determined using 5 g kg^?1 chromic oxide as an indigestible marker in the diet. In experiment one, significant improvements (P < 0.05) were found in scale and vertebral phosphorus concentrations with 2400 Phytase Units (PU) kg^?1 (PU is the quantity of enzyme which liberates one micromole of inorganic P per minute from 0.015 tool L^?1 sodium phytate at 37°C and pH 5.5) added to the diet. In experiment two, significant differences were observed between serum phosphorus in the phytase and no-phytase groups, while there were no differences between the positive control (PMP supplemented) and the phytase-treated fish. It was concluded that 2400 PU kg^?1 of enzyme resulted in bone mineralization and serum phosphorus concentrations equal to that observed with 13 g kg^?1 dietary PMP addition (9 g kg^?1 total P).     

Effect of partial replacement of dietary monocalcium phosphate with neutral phytase on growth performance and phosphorus digestibility in gibel carp,Carassius auratus gibelio (Bloch)

A feeding trial was conducted to study the effect of partial replacement of dietary monocalcium phosphate (MCP) with neutral phytase on growth performance and phosphorus digestibility in gibel carp, Carassius auratus gibelio (Bloch). Control diet was prepared with 2% MCP but without phytase (P0). Other three experimental diets were prepared by replacement of MCP by 25%, 50% and 75% respectively in comparison with control with supplementation of neutral phytase at 500 U kg^?1 diet in each and designated as P25, P50 and P75 respectively. Gibel carp (initial body weight of 30.22 ± 1.98 g) were reared in twelve 300‐L cylindrical fibreglass tanks provided with filtered flow‐through tap water at 26–28°C. After 8‐week experiment, gibel carp fed with P50 had no obvious differences from the control group on weight gain (WG), specific growth rate (SGR), feed conversion ratio (FCR), protein efficiency rate (PER) and survival rate. Phytase supplementation did not affect body compositions or muscle compositions. Crude protein and phosphorus (P) contents in the faeces of fish fed with the phytase‐supplemented diets were significantly lower than those of the control group. The apparent digestibility coefficients (ADCs) of crude protein and P in gibel carp were increased when fish fed with the diets in which MCP was replaced by neutral phytase. This study suggested that partial replacement of dietary MCP at 50% with neutral phytase was considered as a recommended dietary supplemental level and increased dietary P and protein availability.     

Dietary phosphorus requirement of GIFT strain of Nile tilapia Oreochromis niloticus reared in freshwater

A study was conducted to estimate the optimum requirement of dietary available phosphorus for GIFT strain of Nile tilapia Oreochromis niloticus. Six purified diets were formulated to contain graded levels (0 (control diet), 2.9, 4.8, 7.6, 9.1 and 10.9 g kg^?1 diet) of available phosphorus. Each diet was fed to triplicate groups of 12 fish with initial average weight (46.03 ± 2.14) g for 8 weeks. The results showed that fish fed the three lowest phosphorus diets (0, 2.9 and 4.8 g kg^?1) had significantly lower weight gain rate, specific growth rate (SGR) and feed efficiency than those fed the other diets (P < 0.05). The survival rate of fish fed the control diet was significantly lower than that of the fish fed the other diets (P < 0.05). Whole body viscerosomatic index and crude lipid content decreased significantly with increasing dietary available phosphorus levels (P < 0.05), while the contents of crude ash, calcium, phosphorus in the whole body and vertebrae showed the opposite trend (P < 0.05). The blood chemistry analysis showed that dietary available phosphorus had significant effects on serum phosphorus concentration, enzyme activities of alkaline phosphatase and parathyroid hormone level. Quadratic curve analysis based on SGR indicated that the minimum dietary requirement of available phosphorus for maintaining optimal growth of tilapia was 8.6 g kg^?1.     

A comparison of the effect of dietary fungal phytase and dicalcium phosphate supplementation on growth performances,feed and phosphorus utilization of tra catfish juveniles (Pangasianodon hypophthalmus Sauvage, 1878)

Six isonitrogenous (320 g kg^?1) and isolipidic (60 g kg^?1) diets were formulated with graded levels (0, 5, 10 and 15 g kg^?1) of dicalcium phosphate (DCP) and fungal phytase (750 and 1500 FTU kg^?1 diet). Tra catfish (Pangasianodon hypophthalmus), 9.6 g, were fed the diets for 12 weeks. Each experimental diet was fed to eight replicates of fish to apparent satiation. At the end of the trial, fish fed the diets containing 15 g kg^?1 DCP, 750 and 1500 FTU kg^?1 phytase had higher growth performances, protein efficiency ratio and phosphorus retention than those fed the control diet, 5 g kg^?1 DCP and 10 g kg^?1 DCP diets (P < 0.05). Whole body ash and phosphorus concentration of fish fed the 10 g kg^?1 DCP and 15 g kg^?1 DCP diets were significantly higher than those of fish fed the control diet. Higher apparent digestibility coefficient of phosphorus was observed in fish fed the phytase supplemented diets. The present results indicate that supplementation of phytase at 750 FTU kg^?1 and 1500 FTU kg^?1 improves growth performances, feed and phosphorus utilization. The supplementation can completely replace dicalcium phosphate or other phosphorus sources in tra catfish feed and reduce the phosphorus discharge into environment.     

Partial replacement of fish meal by soybean meal with or without methionine and phytase supplement in diets for juvenile Chinese sucker,Myxocyprinus asiaticus

This study was designed to evaluate the effects of using soybean meal supplemented with or without methionine (M) and graded levels of phytase (P) to replace high‐level (60%) fish meal in the diets for juvenile Chinese sucker. Seven experimental diets (about 430 g kg^?1 crude protein on dry matter basis) were formulated from practical ingredients. The control diet (FM) was formulated to contain 400 g kg^?1 white fish meal (FM), whereas in the other six diets (diets 2–7), soybean meal (SBM) was used to replace 60% fish meal with or without methionine (3 g kg ^?1) and 0,500, 1000, 1500 and 2000 U kg^?1 phytase (designated as SBM, SM, SMP500, SMP1000, SMP1500 and SMP2000, respectively). Results from the feeding trial indicated that SBM without any methionine or phytase supplement replacing about 60% FM significantly affected the growth of fish (P < 0.05). Weight gain of fish fed diet SM was significantly higher than the fish fed diet SBM, but still much lower than fish fed the control diet (P < 0.05). SBM with methionine and phytase supplement significantly improved the growth of fish and apparent digestibility coefficients of phosphorus compared with the groups which fed diet SBM and diet SM (P < 0.05). Weight gain of fish fed SMP1000, SMP1500 and SMP2000 had no significant difference than fish fed control diet. Furthermore, fish fed SMP1500 showed optimum weight gain and ADC of phosphorus between these three groups. This suggested that soybean meal with 3 g kg^?1 methionine and 1500 U kg^?1 phytase supplement could successfully replace 60% fish meal in the diet for juvenile Chinese sucker without affecting growth and enhanced the apparent digestibility coefficient of phosphorus.     

Glycerol inclusion in the diet of Nile tilapia (Oreochromis niloticus) juveniles

The present study evaluated the effects of inclusion of glycerol in the diet of Nile tilapia juveniles on growth performance, biochemical changes in blood, and carcass composition. We used 300 Nile tilapia juveniles with an average initial weight of 29.15 ± 8.40 g and 11.55 ± 0.87 cm in length, distributed in 20 fiberglass tanks with a capacity of 250 L. The experiments followed a completely randomized design with five treatments and four replications during 79 days. The animals were fed diets containing four concentrations of glycerol (25 g kg^?1, 50 g kg^?1, 75 g kg^?1 and 100 g kg^?1) and a control diet without glycerol. HDL was the only biochemical parameter, that showed statistically different (P < 0.05) results; it was higher in the groups fed with 0 and 75 g kg^?1 glycerol compared to the other groups. No significant difference was observed in the results from the carcass composition of tilapia juvenile fed with the different glycerol levels, except for lipids (P < 0.05), which showed the highest values in fish fed with 50 g kg^?1 glycerol and the lowest in fish fed with 100 g kg^?1. Glycerol can be used in fish diets as an energy supplement without causing damage to growth performance or to the biochemical and carcass composition of Nile Tilapia juveniles.     

Citric acid substituted the inclusion of inorganic phosphorus in diet of rainbow trout (Oncorhynchus mykiss)

This study was conducted to evaluate the effects of citric acid (CA) supplementation in diet without inorganic phosphorus (P) on growth, muscle and bone composition, proteolytic activities and serum antioxidant property of rainbow trout. Six diets were designed as the negative diet without monocalcium phosphate (MCP) supplementation, the positive diet containing 10 g kg^?1 MCP and CA supplementation diets with 4, 8, 12, 16 g kg^?1 CA supplementation in negative diet, and then were fed to rainbow trout (113.6 g) for 60 days. Results showed that the fish fed 8 g kg^?1 CA, 12 g kg^?1 CA diet had higher weight gain, higher contents of crude ash and P in bone, and lower feed conversion ratio than those of fish fed negative diet (P < 0.05), and showed the similar levels as those of fish fed positive diet (P > 0.05). The proximate composition and P level of muscle were not affected by dietary CA and MCP. The proteolytic activity in intestine, but not in stomach and gastric digesta, was significantly improved by dietary CA and MCP (P < 0.05), when compared with negative control. The activities of serum superoxide dismutase of 12 g kg^?1 CA and 10 g kg^?1 MCP groups were significantly higher, and the malondialdehyde of 8 g kg^?1 CA and 12 CA g kg^?1 groups were significantly lower than those of negative control (P < 0.05). The above results indicated that the supplementation of CA could substitute the inclusion of MCP in rainbow trout diet and the supplementation level was suggested to be 8–12 g kg^?1.     

Growth performance,oxidative stress indices and hepatic carbohydrate metabolic enzymes activities of juvenile Nile tilapia,Oreochromis niloticus L., in response to dietary starch to protein ratios

The effect of various dietary starch to proteins ratios (STA/P) on growth performance, oxidative status and liver enzyme activities involved in intermediary metabolism in juvenile Nile tilapia was evaluated. Four isocaloric‐practical diets (12.73 MJ kg^?1 digestible energy) with increasing STA/CP ratios were formulated. These were designated D₀ (344 g crude protein (CP) and 163.5 g starch (STA) kg^?1), D₁ (310 g CP and 243 g STA kg^?1), D₂ (258 g CP and 322 g STA kg^?1) and D₃ (214 g CP and 401 g STA kg^?1). Each diet was fed to triplicate groups of 60 fish (2.7 g) for 45 days. Compared with the control diet (D₀), significantly (P < 0.05) depressed growth and feed efficiency were observed only in the groups fed on diet D₃. The activities of hepatic enzymes involved in glycolysis and lipogenesis pathways were significantly enhanced in groups fed on diet D₃ compared with other diets. A significant (P < 0.05) increase in catalase activity was detected only in groups fed on diet D₃. Similarly, a significant (P < 0.05) enhancement in superoxyde dismutase, glutathione S‐transferases and glutathione peroxidise was observed in groups fed on diets D₂ and D₃ compared with other diets. Results demonstrate the ability of juvenile Nile tilapia to spare protein by dietary carbohydrate.     

Apparent digestibility of nutrients in grass carp (Ctenopharyngodon idellus) diet supplemented with graded levels of neutral phytase using pretreatment and spraying methods

The effects of supplemental graded levels of neutral phytase using pretreatment and spraying methods on the apparent digestibility coefficients (ADCs) of protein, minerals and amino acids were investigated in grass carp (Ctenopharyngodon idellus) (mean weight, 20.92 ± 1.04 g). Seven experimental diets were prepared as: no‐phytase supplementation (control), pretreatment with phytase dose of 500 U (PP500), 1000 U (PP1000) and 1500 U (PP1500) per kg diet. With spraying method, the phytase was added to feed at the same three grades, namely 500 U (PS500), 1000 U (PS1000) and 1500 U (PS1500) per kg diet. After an 8‐week feeding trial, addition of phytase improved the crude protein, crude lipid, dry matter, ash, phosphorus and calcium digestibilities in comparison with the control, especially in the diets where phytase addition level was above 1000 U kg^?1 (P < 0.05). Phytase supplementation, both the pretreatment and spraying, significantly enhanced the ADCs of essential amino acid (EAA) and non‐essential amino acid. The ADCs of the nutrients were significantly influenced by phytase supplementation methods, supplementation levels and interaction of methods and levels. Based on the results, supplemental dietary phytase, regardless of application methodology, improved the ADCs of nutrients in grass carp, and the pretreatment mode of phytase application was more effective than spraying at the same phytase level. We suggest that the optimal level of phytase pretreatment is 1000 U kg^?1 diet, and the best addition level of phytase spraying is 1500 U kg^?1 diet or more phytase is required for spraying.     

The Efficacy of a Novel Microbial 6‐Phytase Expressed in Aspergillus oryzae on the Performance and Phosphorus Utilization of Cold‐ and Warm‐Water Fish: Rainbow Trout,Oncorhynchus mykiss,and Nile Tilapia,Oreochromis niloticus

The efficacy and tolerance of a novel microbial 6‐phytase were investigated in rainbow trout, Oncorhynchus mykiss, and Nile tilapia, Oreochromis niloticus. Reference diets were sufficient in available phosphorus (P). The test diet limiting in available P was supplemented with phytase at 500, 1000, or 2000 phytase units/kg feed. The enzyme was effective in increasing total P apparent digestibility coefficient in relation to increasing the dose of phytase in rainbow trout and Nile tilapia. Zinc apparent digestibility improved in relation to phytase supplementation in rainbow trout. P release due to phytase supplementation ranged from 0.06 to 0.18% P/kg feed in rainbow trout and from 0.13 to 0.26% P/kg feed in Nile tilapia. A 58‐d performance trial was conducted to evaluate tolerance of fish to phytase supplementation. Dietary treatments consisted of a basal diet without phytase or supplemented with 2000 and 200,000 phytase units/kg feed. Results indicate that this novel microbial 6‐phytase is well tolerated by fish. Significant improvements for growth as well as feed conversion ratio were observed when the phytase was fed at 2000 phytase units/kg feed. This phytase is proven efficient in releasing P from phytate and could be added when plants are used for fish meal replacement in diets for salmonid and omnivorous fish.     

Palm oil-laden spent bleaching clay as a substitute for marine fish oil in the diets of Nile tilapia, Oreochromis niloticus

A 8‐week feeding trial was conducted to determine the effect of substituting fish oil with palm oil‐laden spent bleaching clay (SBC), a by‐product from crude palm oil (CPO) refining, on growth, feed utilization, fatty acid composition and heavy metal accumulation in the muscle of Nile tilapia, Oreochromis niloticus. Four isonitrogenous and isolipidic practical diets were formulated to contain 0, 100, 200 or 300 g kg^?1 SBC. Growth performance of Nile tilapia was significantly better in fish fed the 100 g kg^?1 SBC diet compared with fish fed the 0, 200 or 300 g kg^?1 SBC diet. Growth and feed utilization efficiency of fish fed 200 or 300 g kg^?1 SBC were similar to fish fed the control diet without added SBC. Whole‐body composition, body‐organ indices and haematocrit of tilapia were not affected by dietary treatments. Fatty acid compositions in the muscle lipid of Nile tilapia were strongly influenced by dietary treatments with progressively elevated levels of total saturates and n‐6 PUFA because of the dietary influence of these fatty acids from residual CPO adsorbed onto SBC. A gradual decrease in total n‐3 PUFA concentrations were also observed with the ratio of n‐3 to n‐6 fatty acids in muscle lipids decreasing from 4.75 to 4.41, 3.23 or 2.37 after 8 weeks on the 0, 100, 200 or 300 g kg^?1 SBC diet, respectively. The arsenic, cadmium and lead concentrations in the experimental diets increased with increasing dietary levels of SBC but the concentrations of these heavy metals in the whole body and bone of Nile tilapia were not significantly different among fish fed the various diets. The present 8‐week study showed that in fishmeal‐based diets for Nile tilapia, palm oil‐laden SBC can totally replace added fish oil. The use of this presently discarded waste product from palm oil refining in tilapia diets will greatly contribute to reducing the impact of rising feed costs in the culture of tilapia in many tropical countries. Other potential benefits may include acting as a feed binder, removal of mycotoxins in fish feeds as well as adsorbing toxic substances present in the culture water.     

The potential for rice wine residual as an alternative protein source in a practical diet for Nile tilapia (Oreochromis niloticus) at the juvenile stage

This study investigated the utilization level of rice wine residual (RWS) in a diet for juvenile Nile tilapia. The effects of RWS in diets were evaluated for growth (at week 4), fillet composition, haematological and blood chemical parameters (at weeks 3 and 6) and intestinal morphology (at week 6). The dietary treatments (each diet in triplicate groups) consisted of seven isonitrogenous (320 g kg^?1 crude protein) servings that were formulated to include RWS at levels of 0 (control diet), 75, 150, 225, 300, 375 and 450 g kg^?1 dry diet (Diets 1–7, respectively) and a commercial diet (Diet 8). The growth performances of fish in the groups on Diets 1–4 did not differ significantly. There were no marked variations in fillet composition, serum lysozyme, haematological profiles and blood urea nitrogen (BUN) among treatment diets, except for haematocrit and BUN (week 3) and haemoglobin (week 6) of fish on Diets 6–7. While the blood glucose increased as the amount of RWS incorporation increased (P < 0.05), the cholesterol decreased (P < 0.05). Only intestinal morphometry of fish fed Diet 7 differed significantly from any of the other treatments. Taken together, RWS (at 225 g kg^?1 diet) has the potential for use in juvenile Nile tilapia diet without negative effects.     

The effect of dietary methionine concentrations on growth performance of juvenile Nile tilapia (Oreochromis niloticus) fed diets with two different digestible energy levels

A growth trial was conducted to examine the effect of dietary digestible energy (DE) content on methionine (Met) utilization and requirement in juvenile Nile tilapia (Oreochromis niloticus). Ten iso‐nitrogenous (288 g kg^?1 protein) practical diets, with two DE levels (10.9 MJ kg^?1; 12.4 MJ kg^?1) and five methionine supplementation levels (0, 1, 2, 4 and 6 g kg^?1), were hand‐fed twice daily to triplicate groups of Nile tilapia (initial body weight 8.95 ± 0.06 g) for 8 weeks. Weight gain (WG) and specific growth rate (SGR) increased significantly with increasing dietary methionine concentration at the same DE content (P < 0.001). At the same dietary methionine level, WG and SGR of fish fed high‐DE diets were significantly higher than that of fish fed low‐DE diets (P = 0.0001), although no interaction was found between dietary DE and methionine supplementation. Based on quadratic regression analysis between dietary methionine concentration and weight gain, optimal methionine requirement for maximum growth, expressed as g Met required kg^?1 diet (low‐ versus high‐DE diets), increased as diet DE concentration increased (7.34 versus 9.90 g kg^?1 diet, respectively; with cysteine 4.70 g kg^?1 diet). The results indicated that diet DE content affects methionine utilization and requirement in juvenile Nile tilapia, fish fed high‐DE diets required more methionine for maximum growth.     

Feed efficiency, nutrient retention and body composition of Nile tilapia, Oreochromis niloticus L., fed diets containing L-ascorbic acid, L-ascorbyl-2-sulphate or L-ascorbyl-2-polyphosphate

Seven purified diets were formulated and fed to seven groups of Nile tilapia, Oreochromis niloticus L., fingerlings for 12 weeks. Six of the formulated diets contained 5 or 50 mg kg^?1 of ascorbic acid equivalent supplied by either L-ascorbic acid (AA), L-ascorbyl-2-sulphate (AS) or L-ascorbyl-2-polyphosphate (APP). The seventh basal diet was ascorbate-free and served as the control. The results of diet analysis for ascorbic acid showed that it was not detected or negligible in the control diet and in the diets containing AA at the end of the experiment, whereas there was no loss of ascorbic acid from diets prepared with AS or APP. The results demonstrated that the feed efficiency and growth parameters in fish fed APP-5, AS-5, AA-5 or AA-50 diets were statistically similar to the same parameters in fish fed the control diet. The study indicated that diets supplemented with 5 or 50 mg kg^?1 ascorbic acid in the form of APP or AS were more effectively utilized as sources of vitamin C than equimolar AA in promoting growth, improving food efficiency, increasing nutrient retention and preventing scurvy in Nile tilapia. Fish fed the ascorbate-free diet and the diet containing 5 mg AA kg^?1 exhibited external signs of scurvy during the last growth period of the experiment. Diets containing 5 mg kg^?1 of ascorbic acid from AS or APP provided some growth with no overt signs of scurvy, indicating that this concentration of AS and APP might be near the minimum requirement for the species. The APP-50 diet was the most efficient, and significantly (P < 0.05), had the lowest value of the amount of dietary protein necessary for 100 g weight gain (dietary protein index, DPI), the highest values of feed conversion efficiency (FCE) and the highest values of nutrient retention, i.e. protein (PRV), fat (FRV), ash (ARV) and gross energy (ERV) compared to the other diets. Fish that received the APP-50 diet had a significantly (P < 0.05) higher weight and protein gains in tissues than the other fish groups. The increase in the feed efficiency and growth parameter values in fish receiving the APP-50 diet compared with the values for the same parameters in the AA-50 diet were calculated as percentages, and the results were: weight gain, 36.2%; protein gain, 40.9%; FCE, 53.3%; PRV, 58.1%; FRV, 34.9%; ARV, 57.4%; and ERV, 51.9%. The diet containing APP-50 was followed in order by the AS-50 diet. The AS-50 diet had statistically comparable (P > 0.05) values of weight gain, protein gain and FRV to the APP-50 diet. The increased feed efficiency and growth parameters values of fish receiving the AS-50 diet compared with the AA-50 diet were calculated as percentages, and the results were: weight gain, 2 7.9%; protein gain, 27.9%; FCE, 18.2%; PRV, 17.9%; FRV, 19.2%; ARV, 8.9%; and ERV, 18.2%. There were no significant (P > 0.05) differences between the groups in the percentages of moisture, protein and ash in whole fish at the end of the study, whereas lipid percentages were significantly (P < 0.05) lower in all the tested groups in comparison with the control fish. Increasing the level of ascorbic acid equivalent from 5 to 50 mg kg^?1 diet from APP, AS or AA reduced the percentage of fat in Nile tilapia bodies. These results indicate that all the tested vitamin C sources were effective in inducing lipolysis in Nile tilapia tissues.     

Supplemental graded levels of neutral phytase using pretreatment and spraying methods in the diet of grass carp,Ctenopharyngodon idellus

A feeding trial was conducted for 8 weeks to evaluate the effects of graded levels of neutral phytase supplementation using pretreatment or spraying method on growth performance, body composition, bone mineral content and serum biochemical parameter in grass carp, Ctenopharyngodon idellus. A control diet without phytase was added and six additional diets were arranged as a 2 × 3 factorial with two methods (pretreatment or spraying) and three levels of phytase (500, 1000 or 1500 U kg^?1). The results showed that supplemental phytase at different levels in the diet and with different application methods all improved weight gain, specific growth rate and protein efficiency ratio of grass carp (P < 0.05). The feed conversion ratio in phytase‐supplemented groups was lower than the control. Dietary phytase addition reduced the lipid content in the whole body of grass carp. Phytase supplementation with different method increased ash and mineral (P, Ca, Mg and Zn) contents in whole‐body and vertebra (P < 0.05). The increase in these mineral contents was also observed in the serum. Based on the results, we may conclude that: 1) supplemental dietary phytase, regardless of the application methodology, improved the growth performance and nutrient utilization in grass carp; 2) the pretreatment mode of phytase application was more effective than spraying at the same phytase level.     

Effect of phytic acid on growth and nitrogen retention in tilapia Oreochromis niloticus L.

Two experiments were conducted to determine the effect of phytic acid on nitrogen retention in tilapia (Oreochromis niloticus). The first experiment utilized graded levels of soybean meal (SBM) with or without hydrolysis of phytic acid. The second experiment utilized diets containing graded levels of purified phytic acid. In the first experiment, weight gain was inversely related to SBM inclusion beyond 250 g kg^?1 of the crude protein (CP). Broken‐line and quadratic models were applied to the growth data. The models suggest limiting inclusion to 380 and 170 g kg^?1 CP for untreated and phytase treated SBM, respectively. The two SBM treatments exhibited similar trends in efficiency parameters. However, significant differences (P < 0.05) within treatments appeared when phytase treated SBM surpassed 250 g kg^?1 CP, but not until 750 g kg^?1 CP with untreated SBM. At similar rates of SBM incorporation, apparent net protein utilizations with untreated SBM were significantly higher beyond 250 g kg^?1 CP (P < 0.05). In the second experiment, phytic acid did not affect efficiency parameters until the concentration was twice that in diets incorporating SBM as 1000 g kg^?1 CP in a 330 g kg^?1 CP diet. Phytic acid does not reduce nitrogen retention in tilapia, and its removal from SBM may decrease nitrogen retention.     

Dietary phytase and protease improved growth and nutrient utilization in tilapia (Oreochromis niloticus × Oreochromis aureus) fed low phosphorus and fishmeal‐free diets

A 10‐week study was conducted to evaluate the effects of supplemental phytase and protease in low phosphorus (LP) and fishmeal‐free diets (FMF) on growth and nutrient utilization of tilapia. Seven isonitrogenous diets were prepared as positive control diet (PC) containing 60 g/kg fishmeal and 18 g/kg monocalcium phosphate (MCP), LP diet (12 g/kg MCP), FMF diet, LP‐FMF diet, and three enzyme diets with phytase (LP + Ph), protease (FMF + Pr), and phytase + protease (LP‐FMF + Ph + Pr) supplementation in LP, FMF and LP‐FMF diets, respectively. Weight gain, nutrient (except Ca) retention and digestibility of LP, FMF and LP‐FMF groups were lower than those of PC group (p < 0.05). Compared to LP, FMF and LP‐FMF groups, the supplementation of phytase, protease and phytase + protease improved WG by 13.2%, 11.1% and 13.0% (p < 0.05). The three enzyme groups showed higher digestibility of protein and P, and higher intestinal villus length than those of LP, FMF and LP‐FMF groups (p < 0.05), respectively. Dietary phytase and Ph + Pr also promoted the retentions of crude protein and P (p < 0.05). The results indicated that the supplementation of phytase in LP diet and protease in FMF diet improved the growth and nutrient utilization, and phytase reduced MCP inclusion in the diet of tilapia.     

Effect of dietary l‐methionine concentrations on growth performance,serum immune and antioxidative responses of juvenile Nile tilapia,Oreochromis niloticus

An 8‐week feeding trial was conducted to determine the effect of dietary l ‐methionine supplementation on growth performance, serum immune and antioxidative responses of juvenile Nile tilapia Oreochromis niloticus. Six iso‐nitrogenous (282 g kg^?1 crude protein) diets were formulated to contain graded levels of methionine (0.32%, 0.54%, 0.75%, 0.93%, 1.14% and 1.33% of dry weight) at a constant dietary cysteine level of 0.83 g kg^?1. Each diet was randomly assigned to triplicate groups of 25 juvenile fish (2.3 ± 0.0 g), which were fed three times daily (8:30, 12:30 and 17:00 hours). The results showed that growth performance and feed utilization significantly improved when dietary methionine levels increased (P < 0.05). Using quadratic regression analysis of weight gain against dietary methionine levels indicated that, the optimal dietary methionine requirement for maximum growth of juvenile tilapia was 9.12 g kg^?1 of the dry diet in the presence of 0.83 g kg^?1 cystine. In addition, maximum C4 content and lysozyme activity were observed in fish fed 7.50 g kg^?1 methionine diet; maximum C3 content and superoxide dismutase activity were obtained in fish fed 9.30 g kg^?1 dietary methionine level. While there was no significant difference in serum glutathione peroxidase activity among all methionine supplemented treatments (P > 0.05). Methionine supplementation decreased malondialdehyde content in serum significantly (P < 0.05) when compared with the control diet, while there was no significant difference among supplemented treatments. These data suggested that l ‐methionine affected antioxidant status and promoted serum immune response in juvenile Nile tilapia, and at non‐stressed status, the requirement of dietary methionine in maintaining normal immunity and physiology is lower than that for maximum growth.     

Effect of supplemental dietary zinc sources on the growth and carbohydrate utilization of tilapia Smith 1840, Oreochromis niloticus × Oreochromis aureus

An 8‐week feeding trial was conducted to investigate the effect of supplemental dietary zinc sources on the growth performance and carbohydrate utilization of juvenile tilapia Smith 1840, Oreochromis niloticus × O. aureus. The goal was to compare the bioavailability of two zinc sources, zinc sulphate (ZnSO₄) or zinc methionine (ZnMet), by using two practical basal diets with 350 g kg^?1 (C350) or 400 g kg^?1 (C400) carbohydrates based on wheat as the carbohydrate source. The results showed that fish fed with a diet supplemented with 60 mg kg^?1 Zn from either ZnSO₄ or ZnMet had a significantly (P < 0.05) greater specific growth rate and protein efficiency ratio than those fed with the diets of ≤30 mg kg^?1 Zn. The composition of tilapia carcass was also found to be influenced by various levels of dietary zinc from the two zinc sources. The G6P‐DH in fish fed with the 20 mg kg^?1 ZnMet diet and the PK levels in fish fed with 20 mg kg^?1 ZnSO₄ and 30 mg kg^?1 ZnMet diet were significantly (P < 0.05) higher than those in fish fed with the C400 diet. The data suggest that supplemental dietary zinc from either ZnMet or ZnSO₄ significantly affects the growth performance and carbohydrate utilization of tilapia.     

Effects of dietary phytase supplementation on growth performance and apparent digestibility coefficients of Pacific White Shrimp Litopenaeus vannamei

A growth trial and a digestibility trial were conducted to evaluate the efficacy of phytase supplemented to practical shrimp feeds. The 5 weeks growth trial evaluated the effects of phytase supplementation in replete phosphorus (P) diets on the performances and compositions of juvenile Pacific white shrimp, Litopenaeus vannamei. No significant differences were observed in final biomass, final mean weight, weight gain, feed conversion ratio (FCR), protein retention and survival across all the treatments. Shrimp reared on the P deficient diet had significantly higher P retention and lower whole body P levels as compared to shrimp fed the other diets. Copper content in the whole shrimp body was significantly increased in the treatment supplemented with 1,000 IU kg^?1 feed phytase. The digestibility trial was conducted to study the combined effects of phytase supplementation levels and diet type (plant‐based versus fishmeal‐based) on apparent digestibility coefficients of Pacific white shrimp, Litopenaeus vannamei. There were no effects of diet type so the data was combined. Phytase incorporation at both 500 and 2,000 IU kg^?1 significantly improved protein digestibility, whereas P digestibility was enhanced when 2,000 IU kg^?1 phytase was supplemented to the diet. Apparent digestibility coefficients of alanine, arginine, aspartic acid, cysteine, glutamic acid, glycine, histidine, isoleucine, leucine, lysine, methionine, ornithine, phenylalanine, proline, serine, threonine, tyrosine and valine were significantly increased when fed diets contained 500 and 2,000 IU kg^?1 phytase supplementation. Results of this work demonstrate that under the conditions of the study growth was not enhanced by phytase supplementation in P replete diets. However, nutrient retention for Cu and digestibility of P, protein and a number of amino acids were enhanced.