Relative bioavailability of zinc in supplemental inorganic and organic sources for Nile tilapia Oreochromis niloticus fingerlings

A 90‐day feeding experiment was conducted with sex reversed Nile tilapia (Oreochromis niloticus) fingerlings fed purified or practical diets supplemented with different zinc sources to evaluate fish growth performance and zinc and iron retention in fish bones, fillets, liver, skin and eyes. The relative bioavailability value (RBV) of zinc in the supplemental sources tested was also calculated. Fish were fed with isonitrogenous and isoenergetic purified or practical diets supplemented with 150 mg Zn kg^?1, as zinc sulphate monohydrate (ZnSO₄), zinc oxide (ZnO) or zinc amino acid complex (Zn‐AA). The feeding trial was conducted in 30, 50 L aquaria where four 0.66 ± 0.01 g (mean ± SD) fingerlings were initially stocked. No significant differences were observed for any growth performance variables (P > 0.05). In practical diets, only ZnSO₄ and ZnO presented bone zinc retention similar to that for the standard zinc source. Zinc concentration in the bone of fish fed practical diet supplemented with Zn‐AA (171 ± 3.62 μg g^?1) was significantly lower than that verified for the practical diets supplemented with the standard zinc source (200 ± 17.7 μg g^?1) or with ZnSO₄ (204 ± 19.9 μg g^?1). Assuming the concentration of zinc in bones as the response criterion, the supplemental zinc RBV from ZnSO₄ (105%) was higher than the RBV for Zn‐AA (95.1%) or ZnO (94.9%). Iron concentration in the bones of animals fed the non‐zinc‐supplemented purified diet was significantly higher than that observed for purified diet supplemented with Zn‐AA (P < 0,05). The results of the present work allowed us to conclude that ZnSO₄ in relation to ZnO or Zn‐AA was the supplemental zinc source with higher zinc bioavailability to Nile tilapia.     

Effect of dietary zinc level on growth,enzyme activity and body trace elements of hybrid tilapia,Oreochromis niloticus × O. aureus,fed soya bean meal‐based diets

A feeding experiment was conducted to determine the dietary zinc (Zn) requirement of hybrid tilapia fed on a diet with soya bean meal as the sole protein source. The quantity of phytic acid in the experimental diet was 15.5 g kg^?1. Juvenile hybrid tilapia were fed on diets containing 31–227 mg Zn kg^?1 in triplicates for 6 weeks. Haematology of the fish was not affected by various dietary Zn levels. Fish fed on a diet containing 31 mg kg^?1 endogenous Zn showed the lowest growth rates, feed utilization, and body and plasma Zn levels. Weight gain (WG), plasma Zn level and superoxide dismutase (SOD) activity increased when a higher quantity of dietary Zn of 127 mg kg^?1 was administered to the experimental fish. Beyond this level, the values of these parameters were relatively stable. On the other hand, within the dietary Zn range tested, whole‐body Zn and ash increased with higher dietary Zn levels. Analysis using a broken‐line model showed that the dietary Zn requirements of hybrid tilapia fed on soya bean meal‐based diets containing 15.5 g kg^?1 endogenous phytic acid were 115, 115 and 105 mg kg^?1 based on WG, whole‐body Zn retention and plasma Zn level, respectively.     

The effect of β‐1,3‐glucan derived from Euglena gracilis (Algamune™) on the innate immunological responses of Nile tilapia (Oreochromis niloticus L.)

Algamune^? is a commercial additive produced from Euglena gracilis, providing a rich source of the β‐1,3‐glucan paramylon. Isolated kidney phagocytes of Nile tilapia were incubated with graded doses (0, 8, 16, 32, 64 and 128 μg/ml) of Algamune^? and purified paramylon to gauge their ability to elicit the production of reactive oxygen species. A linear response was observed for extracellular superoxide anion for both sources but only Algamune^? for intracellular superoxide anion. After corroborating the immunostimulant properties ex vivo, a feeding trial was conducted to evaluate the dietary supplementation of Algamune^? (0, 100, 200, 400 and 800 mg/kg of diet) for Nile tilapia. Fish were fed for 3 weeks, after which, fish were sampled for blood and head kidney phagocytes. The remaining fish were challenged with Streptococcus iniae. Macrophage extracellular superoxide anion production was significantly elevated in fish fed diets with 200 mg of Algamune^? kg^?1 when compared to fish fed the basal diet. Even though the disease challenge did not show statistical differences, it is worth mentioning that fish fed intermediate doses of Algamune^? had lowest numerical mortality values. Therefore, Algamune^? was demonstrated to enhance some immunological responses of tilapia both in ex vivo and in vivo.     

Dietary calcium requirements of juvenile tilapia, Oreochromis niloticus × O. aureus, reared in fresh water

A feeding experiment was conducted to determine the dietary calcium (Ca) requirement for juvenile hybrid tilapia, Oreochromis niloticus × O. aureus reared in nature water. Purified diet supplemented with 0, 1, 2, 3, 4, 5, 7 and 10 g Ca kg⁻¹ diet providing of 0.6, 1.6, 2.6, 3.7, 4.7, 5.5, 7.5 and 10.7 g Ca kg⁻¹ diet, respectively, were fed to tilapia (mean initial weight: 0.52 ± 0.01 g, n = 3) for 8 weeks. Each diet was fed to three replicate groups of fish in a closed, recirculating fresh water rearing system. The rearing water contained 27.1–33.3 mg L⁻¹ Ca. The tilapia fed the diets supplemented with ≥3.7 g Ca kg⁻¹ had significantly (P < 0.05) higher weight gain, when compared with fish fed the diet with ≤1.6 g Ca kg⁻¹. Fish fed the unsupplemented control showed significantly lower weight gain when compared with the other groups (P < 0.05). Bone Ca concentration was highest in fish fed the diets with ≥4.7 g Ca kg⁻¹, intermediate in fish fed the diet with 2.6 g Ca kg⁻¹ and lowest in fish fed the control diet. Scale Ca concentration was higher in fish fed the diets with ≥3.7 g Ca kg⁻¹ than in fish fed the diets with ≤2.6 g Ca kg⁻¹. Serum alkaline phosphatase activity was 36% increased in fish fed the diets with ≥2.6 g Ca kg⁻¹ than fish fed the diets with <1.6 g Ca kg⁻¹. Analysis by broken‐line regression of weight gain, bone and scale Ca concentrations indicated that the adequate dietary Ca concentration for tilapia in water containing 27.1–33.3 mg Ca L⁻¹ was 3.5, 4.3 and 4.2 g Ca kg⁻¹ diet, respectively, supplied as Ca‐lactate.     

Dietary taurine enhances growth and feed utilization in larval Nile tilapia (Oreochromis niloticus) fed soybean meal‐based diets

This study was conducted to evaluate the effects of dietary taurine on growth performance and feed utilization of Nile tilapia (Oreochromis niloticus) larvae. Four plant protein‐based, isonitrogenous (400 g kg^?1 protein), isoenergetic (19 MJ kg^?1) diets supplemented with four taurine concentrations (0.0, 5.0, 10.0 and 15.0 g kg^?1; designated as T₀, T_0.5, T₁ and T_1.5, respectively) were prepared. The diets were fed to triplicate groups of fish larvae (0.024 g average body weight), to apparent satiation, three times per day for 60 days. Larval growth rates and feed utilization efficiency were significantly improved with increasing supplemental taurine up to 10 g kg^?1 and decreased with further taurine supplementation. The quadratic regression analyses indicated that the maximum larval performance occurred at about 9.7 g kg^?1 of total dietary taurine. Fish survival was significantly lower at 15 g kg^?1 dietary taurine than at other taurine levels. Body protein significantly increased, while body moisture and ash decreased, with increasing dietary taurine up to 10 g kg^?1 and decreased with further taurine supplementation to 15 g kg^?1. Body lipid was not significantly affected by dietary taurine concentration. A number of body amino acids (tryptophan, arginine, histidine, leucine, isoleucine, valine, alanine, glycine, threonine and taurine) significantly increased with increasing supplemental taurine up to 10 g kg^?1 and then decreased with further increase in dietary taurine levels. The rest of body amino acids were not significantly affected by dietary taurine. The present results suggest that about 9.7 g kg^?1 dietary taurine is required for optimum performance of Nile tilapia larvae fed soybean meal‐based diets.     

Protein‐sparing capability of dietary lipid in herbivorous and omnivorous freshwater finfish: a comparative case study on grass carp (Ctenopharyngodon idella) and tilapia (Oreochromis niloticus × O. aureus)

Two, 8‐week feeding trials were conducted to compare protein‐sparing capability of dietary lipid in herbivorous grass carp (Ctenopharyngodon idella) and omnivorous tilapia (Oreochomis niloticus × O. aureus). Utilizing a 2 × 3 factorial design, experimental diets containing two levels of crude protein (380 and 250 g kg⁻¹) and three levels of lipid (0, 40 and 100 g kg⁻¹) were formulated for use in both feeding trials. Growth performances showed better response of both fish fed 380 g kg⁻¹ protein diet than those fed 250 g kg⁻¹ protein diet. Despite the dietary protein level, weight gain (WG), specific growth ratio (SGR), feed conversion ratio (FCR) and protein efficiency ratio were much higher (P < 0.05) for grass carp fed 40 g kg⁻¹ lipid diet than those fed 100 g kg⁻¹ lipid diet; however, there were no significant differences in tilapia fed the two diets. The feed intake of grass carp fed lipid‐free diet was the lowest, but it tended to decrease with increase in dietary lipids in tilapia. Lipid retention (LR) was negatively correlated with dietary lipid concentration of both fish. Viscerosomatic index (VSI), hepatosomatic index (HSI), intraperitoneal fat ratio (IPF) and whole‐body and liver lipid content positively correlated with dietary lipid concentration of both fish. Plasma parameters and liver enzymes activities were also positively correlated with dietary lipid concentration of both fish. Liver lipid contents were higher and enzymes activities were lower in grass carp when compared with tilapia. These data suggested that there was no evidence of a protein‐sparing effect of dietary lipids in grass carp. Tilapia has relatively higher capacity to endure high dietary lipid level compared to grass carp.     

Apparent Absorption of Zinc from Supplemental Inorganic and Organic Sources to Nile Tilapia Oreochromis doticus Juveniles

Abstract— Nile tilapia Oreochromis niloticus fingerlings were fed with purified or practical diets, supplemented with 150 mg Zd/kg, from different sources. Dry matter (DM), crude protein (CP), ether extract (EE), and gross energy (GE) apparent digestibility coefficients (ADC), as well as zinc, copper, calcium, and phosphorus apparent absorption coefficients (AAC) were determined by the addition of 0.1% chromic oxide to the diets. The supplemental zinc sources utilized were commercial grade zinc sulfate monohydrate (ZnSO)₄, zinc oxide (ZnO) and a zinc amino acid complex (Zn‐AA). Analytical grade zinc sulfate heptahydrate was also utilized as a standard reference zinc source. There was a significant difference between purified (74.9%) and practical (41.3%) zinc AAC for the ZnO supplemented diets (P< 0.05). The supplemental zinc sources presented similar AAC when purified diets were utilized. However, ZnSO₄, was the best supplemental zinc source when practical type diets were used. There were no significant differences between supplemental zinc AAC from ZnSO₄, (68.9%), and supplemental zinc AAC from Zn‐AA (61.3%) in practical diets, but Zn‐AA diet showed a statistically lower zinc AAC when compared with the standard zinc source diet (75.6%). The practical diet supplemented with ZnO had the worst supplemental zinc AAC (41.3%). Dietary copper (74.2%), calcium (70.9%), and phosphorus (71.9%) AAC of the practical diets supplemented with ZnO were statistically lower (P < 0.05) than the respective AAC of the practical ZnSO₄, supplemented diets (83.6%, 84.1%, 87.1%). The ADC of the practical ZnO supplemented diet for DM (76.30/), CP (88.6%), EE (82.4%), and GE (81.6%) were statistically lower than the respective ADC of the ZnSO₄, practical diet (86.0,92.7,93.6,89.6%, respectively) and those ADC of the Zn‐AA practical diet (84.7,92.7,93.7, 88.2%, respectively) (P < 0.05). Hence, these results indicate that ZnSO₄, and Zn‐AA have equivalent intestinal absorption as supplemental zinc sources for Nile tilapia juveniles and both are superior to ZnO.     

Dietary leucine requirement of Juvenile Nile tilapia,Oreochromis niloticus

An 8‐week feeding trial was conducted to evaluate the effects of dietary leucine on growth performance, feed utilization, body composition and non‐specific immune responses of juvenile Nile tilapia. Five isonitrogenous and isoenergetic diets were formulated to contain graded levels of L‐leucine (5.3, 8.1, 10.9, 13.2, 15.6 and 18.1 g kg^?1 diet, respectively) from dietary ingredients and crystalline L‐leucine. Each diet was randomly assigned to triplicate groups of 20 juvenile fish (1.94 ± 0.01 g) three times daily to apparent satiation. Results showed that the weight gain (WG) and specific growth rate (SGR) increased as dietary leucine concentrations increased from 5.3 to 13.2 g kg^?1 and then decreased slightly with further increase in dietary leucine concentrations. Quadratic regression analysis (y = ?522.6x² + 1304.x + 132.6, R² = 0.684) on weight gain against dietary leucine levels indicated that the optimal dietary leucine requirement was estimated to be 12.5 g kg^?1 diet (corresponding to 43.1 g kg^?1 of dietary protein). Leucine supplementation had no impact on the survival and body composition of tilapia. Serum lysozyme activity of fish fed diet containing 13.2 g kg^?1 leucine significantly increased compared to fish fed diet containing 5.3 g kg^?1. Serum superoxide dismutase activity and immunoglobulin M (IgM) concentration were not significantly affected by dietary leucine supplementation.     

Effects of extruded and pelleted diets with differing lipid levels on growth,nutrient retention and serum biochemical indices of tilapia (Oreochromis aureus × Tilapia nilotica)

This study was conducted to evaluate the effects of extruded diets and pelleted diets with varying dietary lipid levels on growth performance and nutrient utilization of tilapia. Six diets, containing three levels of lipid at 40, 60 or 80 g kg^?1 (with the supplemental lipid of 0, 20 or 40 g kg^?1, respectively), were prepared by extruding or pelleting and then fed to tilapia juveniles (8.0 ± 0.1 g) in cages (in indoor pools) for 8 weeks. The results indicated that the fish that were fed the diet with 60 g kg^?1 of lipid had a higher weight gain (WG), specific growth rate (SGR), protein efficiency ratio (PER), lipid retention (LRE), energy retention (ERE), apparent protein digestibility, apparent dry matter digestibility and a lower feed conversion ratio (FCR) than those fed the diet with 40 g kg^?1 lipid in both the extruded diet and pelleted diet (P < 0.05). As the dietary lipid level increased from 60 to 80 g kg^?1, these parameters were not further improved, even digestibilities of the crude protein and dry matter decreased (P < 0.05). With the dietary lipid level increased, whole‐body lipid content significantly increased (P < 0.05), serum aspartate aminotransferase, alkaline phosphatase, total cholesterol and low‐density lipoprotein cholesterol (LDL‐C) tended to increase (P > 0.05), whereas whole‐body protein content, serum triglyceride (TG), high‐density lipoprotein cholesterol (HDL‐C) and HDL‐C/LDL‐C tended to decrease (P > 0.05). Fish fed with the extruded diets had a higher WG, SGR, hepatosomatic index (HSI), PER, protein retention (PRE), LRE, ERE, TG, apparent digestibility of protein and dry matter, as well as a lower FCR, than those fed with the pelleted diets at the same dietary lipid level (P < 0.05). These results suggested that tilapia fed with the extruded diets had a better growth and higher nutrient utilization than fish fed with the pelleted diets, when dietary lipid level ranged from 40 to 80 g kg^?1 and at dietary crude protein level was 280 g kg^?1. The optimum dietary lipid level was 60 g kg^?1 in both the pelleted and extruded diets, and extrusion did not affect dietary lipid requirement of the tilapia.     

Effect of fermented Enteromopha prolifera on the growth performance,digestive enzyme activities and serum non‐specific immunity of red tilapia (Oreochromis mossambicus × Oreochromis niloticus)

This study was conducted to evaluate the effect of dietary inclusion of different levels of fermented macroalga, Enteromorpha prolifera, on the growth performance, digestive enzyme activities and serum non‐specific immunity of red tilapia (Oreochromis mossambicus × Oreochromis niloticus). Fish were fed the control diet or the five diets supplemented with fermented E. prolifera for 7 weeks (diets 1–5 containing 10, 20, 30, 40 and 50 g kg^?1 of fermented E. prolifera respectively). The results showed that the percentage weight gain and specific growth rate (SGR) improved significantly in fish fed diets 3, 4 and 5, and regression analysis showed SGR reached the maximum in fish fed diet containing 37 g kg^?1 fermented E. prolifera, while the feed conversion ratio reduced significantly in fish fed diets 2, 3, 4 and 5, and regression analysis showed it reached its minimum in fish fed diet containing 41 g kg^?1 fermented E. prolifera. The pepsin, erepsin, gastric amylase, intestinal amylase, gastric lipase and intestinal lipase activities in fish fed diets 2, 3 and 4 were higher significantly than the control, with the exception of the pepsin activity in fish fed diet 4. The serum total superoxide dismutase, lysozyme, acid phosphatase and alkaline phosphatase activities enhanced significantly in fish fed diets 3 and 4. In conclusion, fermented E. prolifera had positive effects on the growth performance, digestive enzyme activities and serum non‐specific immunity of red tilapia and the recommended dose of fermented E. prolifera is 37–41 g kg^?1 in the diet of red tilapia.     

Optimizing zinc supplementation levels of rainbow trout (Oncorhynchus mykiss) fed practical type fishmeal‐ and plant‐based diets

Rainbow trout (23.1 ± 0.4 g) were fed either a fishmeal‐ or plant‐based diet supplemented with various levels of zinc (0, 15, 30, 60 or 120 mg kg^?1) for 12 weeks. Trout fed the fishmeal diet had significantly higher weight gain than with the plant‐based diet. Zinc supplementation in the fishmeal diet had no effect on growth performance, suggesting that additional dietary supplementation of zinc is not required. However, in trout fed the plant‐based diet, growth increased significantly up to 30 mg kg^?1 zinc after which growth was not affected. Trout fed the plant‐based diet containing no zinc exhibited severe growth retardation, and in fish fed the 0 and 15 mg kg^?1 zinc diets, cataracts were present. Use of broken‐line quadratic modelling suggests that dietary supplementation of zinc needed to prevent deficiency and promote adequate growth in rainbow trout fed the plant‐based diet in this study was 30.1 mg kg^?1 (80 mg kg^?1 total dietary zinc). This is higher than the NRC (2011, Nutrient Requirements of Fish and Shrimp) dietary recommended level of 15 mg kg^?1 for rainbow trout. Following the NRC recommendation could lead to zinc deficiency in rainbow trout fed a plant‐based diet.     

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.     

An estimation of dietary iron requirement of Atlantic salmon, Salmo salar L., parr

A study was conducted to determine the dietary iron requirement of fingerling Atlantic salmon Salmo salar L. During the first 4 weeks of the experiment, fish with an initial weight of 5 g were fed a casein–gelatine-based purified diet which contained 11 mg iron kg^?1. Thereafter duplicate tanks (200 fish in each) were fed the casein–gelatine purified diets containing supplemental iron levels of 0, 10, 20, 30, 40, 60, 100, 200 or 400 mg iron kg^?1 (added as FeSO_?4* 7H₂O) for 12 weeks. Weight gain, body length and mortality were monitored. Liver iron and ascorbic acid concentration were analysed in addition to whole-body iron, manganese and zinc concentration. Several haematological parameters were also measured. There were no significant differences in weight gain and survival of salmon fed diets containing different iron levels. Haematological values, hepatic and whole-body iron concentrations were, however, significantly affected by the dietary iron content. Liver vitamin C concentration decreased with increasing dietary iron levels. Dietary supplementation with iron significantly reduced whole-body manganese, but no effect of dietary iron on whole-body zinc was found. Based on haematology and hepatic iron concentration, the iron requirement of Atlantic salmon was determined to be between 60 and 100 mg iron kg¹.     

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.     

Dietary taurine improves reproductive performance of Nile tilapia (Oreochromis niloticus) broodstock

This study was conducted to evaluate the effects of supplemental taurine on reproductive performance of Nile tilapia (Oreochromis niloticus) broodstock fed soybean meal‐based diets. Four isonitrogenous (350 g kg^?1 protein), isocaloric (18 MJ kg^?1) diets were formulated to contain 0, 5, 10 and 15 g kg^?1 taurine. The diets were fed to triplicate groups of juvenile Nile tilapia (10–15 g average body weight) at a female: male ratio of 3 : 1, to apparent satiation, three times per day for 130 days. The size at first maturation decreased with increasing dietary taurine to 10 g kg^?1 and levelled off with further taurine supplementation. The time to first spawning was also significantly shorter at 10 g kg^?1 taurine level. Spawning performances, including spawning frequencies, total number of spawnings per tank, number of spawnings per female and absolute fecundity, were all significantly improved with increasing dietary taurine up to 10 g kg^?1. However, the quadratic regression analyses indicated that the maximum spawning performance occurred at 8 g kg^?1 of supplemental taurine. Eggs produced from broodstock fed 10 g kg^?1 taurine exhibited significantly higher hatchability and required shorter time for hatching and yolk‐sac absorption and also resulted in higher larval weight than at other dietary taurine levels. The highest egg protein, total amino acids and taurine were also obtained at 10 g kg^?1 taurine. These results suggest that 8 g kg^?1 dietary taurine is required for optimum reproductive outputs of Nile tilapia broodstock.     

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.     

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.     

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.     

Influence of dietary protein levels on growth performance and body composition of African bonytongue fingerlings,Heterotis niloticus (Cuvier, 1829)

Two experiments were conducted to examine the influence of dietary protein levels on growth and carcass proximate composition of Heterotis fingerlings. Four isoenergetic practical diets were formulated to contain dietary protein levels from 250 to 400 g kg^?1 diet. Replicate groups of young Heterotis (initial live weight 3.96 and 26.40 g in experiments 1 and 2 respectively) were handfed twice daily to apparent satiation for a period of 42 and 28 days respectively. Statistical analysis revealed that growth rate was significantly affected by dietary protein level (P < 0.01). The highest weight gain was observed in fingerlings fed with 300 and 350 g protein kg^?1 diet for fish size ranging between 3–15 and 26–62 g respectively. There was no significant difference between groups fed with 300, 350 and 400 g protein kg^?1 diet for Heterotis fingerlings (3–15 g) in the one hand; in the other hand, significant differences were found between fish (26–62 g) fed with 350 g protein kg^?1 diet and those receiving 300 and 400 g protein kg^?1 diet, with no significant difference between each other. The specific growth rate varied from 2.4% to 3.1% day^?1. The whole‐body protein, lipid, moisture and ash contents were not significantly affected by dietary protein levels (P > 0.05). The relationships between percentage weight gain and dietary protein levels suggested very similar dietary protein requirement (about 310 g crude protein kg^?1 diet) for Heterotis ranging from 3 to 62 g. The maximum growth occurred at about 345 g protein kg^?1 diet.     

The potential of dry olive cake in a practical diet for juvenile hybrid tilapia,Oreochromis niloticus × Oreochromis aereus

A feeding trial of 84 days was carried out to evaluate the effects of olive cake (OC) on growth, feed utilization, digestibility of nutrient, haematological values and some blood chemistry parameters of juvenile hybrid tilapia (Oreochromis niloticus × Oreochromis aereus). Four diets were prepared including OC at levels of 0, 120, 240 and 360 g kg^?1. Twenty fish per tank (initial weight 8.58 ± 0.09 g) were randomly distributed into 200‐L fibreglass tanks. Final body weight and specific growth rate of fish fed with diets OC12 were not significantly different compared to fish fed with the control diet. The best feed conversion rate and protein efficiency rate were obtained from the fish fed with the control and OC12 diets. Growth performance, feed conversion rate and protein efficiency rate of fish fed diets with OC incorporation levels of more than 12 per cent tended to decrease significantly (P < 0.05) compared to the control and OC12 diet groups. The apparent digestibility coefficients (ADC) of dry matter significantly decreased (P < 0.05) with the increase of dietary OC levels, whereas the ADC of protein was not affected by dietary treatment. The ADC of lipid of fish fed with control and OC12 diets were significantly (P < 0.05) higher than those of fish fed with OC24 and OC36 diets. Mean corpuscular haemoglobin, cholesterol and triglycerides were affected by dietary OC level. The findings of this study show that OC can be incorporated to diets of juvenile hybrid tilapia up to 120 g kg^?1 without any adverse effect on fish growth and feed utilization.