Growth performance and body composition of pacu Piaractus mesopotamicus (Holmberg 1887) in response to dietary protein and energy levels

Improper dietary protein and energy levels and their ratio will lead to increased fish production cost. This work evaluated effects of dietary protein : energy ratio on growth and body composition of pacu, Piaractus mesopotamicus. Fingerling pacu (15.5 ± 0.4 g) were fed twice a day for 10 weeks until apparent satiation with diets containing 220, 260, 300, 340 or 380 g kg^?1 crude protein (CP) and 10.9, 11.7, 12.6, 13.4 or 14.2 MJ kg^?1 digestible energy (DE) in a totally randomized experimental design, 5 × 5 factorial scheme (n = 3). Weight gain, specific growth rate increased and feed conversion ratio (FCR) decreased significantly (P < 0.05) when CP increased from 220 to 271, 268 and 281 g kg^?1 respectively. Pacu was able to adjust feed consumption in a wide range of dietary DE concentration. Fish fed 260 CP diets showed best (P < 0.05) protein efficiency ratio and FCR with 11.7–12.6 MJ kg^?1; but for the 380 CP‐diets group, significant differences were observed only at 14.2 MJ kg^?1 dietary energy level, suggesting that pacu favours protein as energy source. DE was the chief influence on whole body chemical composition. Minimum dietary protein requirement of pacu is 270 g kg^?1, with an optimum CP : DE of 22.2 g MJ^?1.     

Growth and body composition of juvenile largemouth bass Micropterus salmoides in response to dietary protein and energy levels

To determine the dietary protein and energy requirements of juvenile largemouth bass, 1350 feed‐conditioned fishes (average weight 14.46 ± 0.81 g) were stocked in ninety 60‐L cages, set up in 1000‐L tanks at three cages/tank, and fed for 64 days with a dry, extruded feed containing six levels of crude protein (CP) (340–540 g kg^–1, with increases of 40 g kg^–1) and five levels of energy (150.7–171.7 kJ g^–1 feed, with increases of 5.2 kJ). The trial was set up in a 6 × 5 factorial, completely randomized design (n=3). Weight gain (WG), daily feed consumption (DFC), feed conversion rate (FCR), protein efficiency ratio (PER), specific growth rate (SGR), protein and energy retention were recorded and evaluated. There was no interaction between feed energy and protein levels with all parameters evaluated. Data analysis by the broken line method showed that the minimum dietary requirement for maximum daily weight gain of 8.0 g kg^–1 is 435.9 g kg^–1 CP; the best feed conversion ratio (1.04:1) was attained with a minimum of 448.2 g kg^–1 CP; a minimum of 162.1 kJ g^–1; DFC was reduced as dietary protein and energy levels increased; dietary levels of 460–500 g kg^–1 CP led to best PER (1.665); best values for protein (33.14 g 100 g^–1) and energy (26.87 g 100 g^–1) retention were observed for fish feeding on the 420 g kg^–1 CP ration. Limits of energy to protein ratio to feed largemouth bass are 25.01 and 26.89 mg protein kJ^–1, enabling feed conversion ratios of 0.96–1.10.     

Dietary leucine requirement of fingerling Indian major carp, Labeo rohita (Hamilton)

An 8-week feeding experiment was conducted to evaluate the dietary leucine requirement of fingerling Indian major carp, Labeo rohita (3.50±0.04 cm; 0.40±0.02 g) using amino acid test diets (40% crude protein; 17.90 kJ g⁻¹ gross energy) containing casein and gelatin as intact protein sources and l -crystalline amino acids. Growth performance and biochemical parameters were assessed by feeding six amino acid test diets supplemented with graded concentrations of leucine (0.75, 1.0, 1.25, 1.50, 1.75 and 2.0 g per 100 g) to triplicate groups of fingerlings to apparent satiation divided over two feedings at 07:00 and 17:30 hours. Performance of the fish was evaluated on the basis of live weight gain, feed conversion ratio (FCR), protein efficiency ratio (PER) and body protein deposition (BPD) data. Maximum live weight gain (315%), best FCR (1.35), highest PER (1.86) and BPD (33.9) were recorded at 1.50 g per 100 g dietary leucine. Statistical analysis of live weight gain, FCR, PER and BPD data reflected significant differences (P<0.05) among treatments. Live weight gain, FCR, PER and BPD data were also analysed using second-degree polynomial regression analysis to obtain more accurate leucine requirement estimate which was found to be at 1.57, 1.55, 1.52 and 1.50 g per 100 g of dry diet, corresponding to 3.92, 3.87, 3.80 and 3.75 g per 100 g of dietary protein respectively. Based on the quadratic regression analysis of the live weight gain, FCR, PER and BPD data, the optimum requirement of fingerling L. rohita for leucine is estimated to be in the range of 1.50–1.57 g per 100 g of the dry diet, corresponding to 3.75–3.92 g per 100 g of dietary protein.     

Dietary threonine requirement of fingerling Indian major carp,Labeo rohita (Hamilton)

An 8‐week feeding experiment was conducted in a water flow‐through system (26–28 °C) to determine the dietary threonine requirement of fingerling Labeo rohita (3.90±0.03 cm; 0.58±0.02 g). Growth, feed utilization and body composition of fish fed test diets (40% crude protein; 17.9 kJ g^?1 gross energy) with graded levels of l ‐threonine (0.75%, 1.0%, 1.25%, 1.50%, 1.75% and 2.0% dry diet) to apparent satiation were response variables used to assess threonine adequacy. Diets were made isonitrogenous and isoenergetic by adjusting the levels of glycine and dextrin. The amino acid profiles of the test diets were formulated to that of 40% whole chicken egg protein except for threonine. The performance of fish fed experimental diets was evaluated using calculated values for weight gain (g fish^?1), feed conversion ratio (FCR), protein efficiency ratio (PER) and protein productive value (PPV) data. Maximum weight gain (g fish^?1) (1.79), lowest FCR (1.39), highest PER (1.76) and PPV (0.33) were recorded at 1.50 g per 100 g dietary threonine. Statistical analysis of weight gain, FCR, PER and PPV data reflected significant differences (P<0.05) among treatments. Except for reduced growth performance in fish fed threonine‐deficient diets, no deficiency signs were noted. Weight gain, FCR, PER and PPV data were also analysed using second‐degree polynomial regression analysis to obtain a more accurate threonine requirement estimate, which was found, using each response variable, to be at 1.70, 1.63, 1.65 and 1.51 g per 100 g of dry diet, corresponding to 4.2, 4.07, 4.12 and 3.77 g per 100 g of dietary protein respectively. Based on the second‐degree polynomial regression analysis of the live weight gain, FCR, PER and PPV data, the optimum dietary level of threonine for fingerling L. rohita was found to be in the range of 1.51–1.70 g per 100 g of the dry diet, corresponding to 3.77–4.2 g per 100 g of dietary protein.     

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.     

Effects of Dietary Lipid and Energy to Protein Ratio on Growth and Feed Utilization of Juvenile Mutton Snapper Lutjanus analis Fed Isonitrogenous Diets at Two Temperatures

Growth and feed utilization of juvenile, hatchery‐reared mutton snapper Lutjanus analis (mean weight = 12.2 g) were compared for 40 d in laboratory aquaria on four isonitrogenous diets (45% crude protein) of varying lipid content (6, 9, 12 and 15%) with energy:protein ratios (E: P; kJ/g protein) of 33.9, 36.3, 38.8, and 41.2, respectively. Growth on these diets was compared under temperatures of 25 and 30 C. Final weights (Wt_r) and specific growth rates (SGR) were higher (P < 0.05) at lower dietary E: P ratios of 33.9 and 36.3 (Wt_r= 20.3–22.0 g; SGR = 1.25–1.35%/d) than at E:P ratios of 38.8 and 41.2 (Wt_r= 17.2‐17.7 g; SGR = 0.84–0.85%/d). Growth at 30 C (Wt_r= 21.5 g, SGR = 1.35%/d) was higher (P < 0.05) than at 25 C (Wt_r= 17.3 g; SGR = 0.82%/d). Feed consumption (FC) was higher (P < 0.05) at a dietary E: P ratio of 33.9 (1.57%/d) than at 36.3 (1.27%/d) or 38.8–41.2 (0.89–0.98%/d). Growth was highly correlated (P < 0.01) to E: P ratio and to feed consumption. Feed conversion ratio (FCR = 2.17–3.98), protein efficiency ratio (PER = 0.58–1.03) and apparent net protein retention (ANPR = 15.8–20.0%) were not significantly (P > 0.05) affected by dietary E: P ratio. Apparent net energy retention (ANER) was higher (P < 0.05) at E: P ratios of 33.9 and 36.3 (9.50–9.98%) than at E: P ratios of 38.8 and 41.2 (7.15–7.10%). Feed utilization parameters were significantly (P < 0.05) better at 30 C (FC = 1.36%/d; FCR = 2.6; PER = 0.88; ANER = 10.2%) than at 25 C (FC = 1.03%/d; FCR = 3.38; PER = 0.69; ANER = 6.72%), with the exception of ANPR (17.0–17.8%). Maximum growth and energy retention in juvenile mutton snapper using a diet containing 45% crude protein was obtained at dietary lipid levels of 6–9% and E: P ratios of 33.9–36.3 kJ/g protein. Studies which determine optimum protein levels and the effects of reducing E: P ratios below 33.9 kJ/g are needed to improve feed conversion and growth.     

Effect of dietary protein and lipid levels and protein to energy ratios on growth, survival and body composition of the mangrove red snapper, Lutjanus argentimaculatus (Forsskal 1775)

The approximate levels of dietary protein and energy that would sustain good growth and survival of the mangrove red snapper Lutjanus argentimaculatus (Forsskal) were determined in two feeding experiments. In the preliminary experiment, six fish meal‐based diets were formulated to contain three protein levels (35%, 42.5% and 50%) and two lipid levels (6% and 12%) for each protein, with dietary energy ranging from 14.6 MJ kg^?1 to 20.5 MJ kg^?1. The protein to energy (P/E) ratios of diets ranged from 20.6 mg protein kJ^?1 to 27.5 mg protein kJ^?1. Diets were fed for 100 days to triplicate groups of snappers with an average initial weight of 24.8 ± 0.4 g. No significant interaction between different levels of protein and lipid was observed. Survival rates (93.8% to 100%), feed conversion ratios (FCR) (2.61–3.06) and condition factors (K) were not affected by different dietary treatments. Regardless of lipid level, fish fed 50% protein diets had a significantly higher specific growth rate (SGR) than fish fed the 35% protein diets, but not compared with the 42.5% diets (P < 0.05). Increasing lipid to 12% in all protein levels resulted in no improvement in growth over the 6% level. Fish body moisture did not vary while lipid levels based on dry matter were high (27.9% to 33.7%). Snapper appear to require more than 40% dietary protein and a high dietary energy level for good growth. In the second experiment, fish (21.1 ± 0.1 g) in four replicate groups were fed for 94 days with three diets (39%, 44% and 49% protein with P/E ratios of 21.1, 23.3 and 25.5 mg protein kJ^?1 respectively) containing similar dietary energy levels of about 19 MJ kg^?1. Average final weight, SGR and FCR were significantly higher in diets containing 44% and 49% protein diets (P > 0.05). There were no differences in survival rates, protein efficiency ratio (PER) and nutrient composition of snapper flesh. All fish had fatty livers. Results indicated that the diet containing 44% protein with a P/E ratio of 23.3 mg protein kJ^?1 was optimum for snapper growth under the experimental conditions used in the study.     

Dietary isoleucine requirement of fingerling Indian major carp, Labeo rohita (Hamilton)

An 8‐week feeding experiment was conducted to quantify the dietary isoleucine requirement of fingerling Indian major carp, Labeo rohita (3.50 ± 0.04 cm; 0.40 ± 0.02 g) using amino acid test diets (400 g kg⁻¹ crude protein; 17.90 kJ g⁻¹ gross energy) containing casein, gelatin and l ‐crystalline amino acids. Six dietary treatments supplemented with graded levels of isoleucine (7.5, 10.0, 12.5, 15.0, 17.5 and 20.0 g kg⁻¹), in gradations of 2.5 g kg⁻¹ diet, were fed to triplicate groups of fingerlings to apparent satiation divided over two feedings at 07:00 and 17:30 h. Performance of the fish was evaluated on the basis of live weight gain, feed conversion ratio (FCR), protein efficiency ratio (PER), specific growth rate (SGR) and protein productive value (PPV). Statistical analysis of live weight gain, FCR, PER, SGR and PPV reflected significant differences among treatments. Live weight gain and conversion efficiencies were best with isoleucine at 15.0 g kg⁻¹ of diet. Live weight gain, FCR, PER, SGR and PPV data were also analysed using second‐degree polynomial regression analysis to obtain more accurate isoleucine requirement estimate which was found to be at 15.9, 15.3, 15.2, 15.8 and 15.7 g kg⁻¹ of dry diet, corresponding to 39.8, 38.3, 38.0, 39.5 and 39.3 g kg⁻¹ of dietary protein respectively. Based on the quadratic regression analysis of the live weight gain, FCR, PER, SGR and PPV, the optimum level of isoleucine for fingerling L. rohita is in the range of 15.2–15.9 g kg⁻¹ of dry diet, corresponding to 38.0–39.8 g kg⁻¹ of dietary protein. Maximum body protein, minimum moisture and fat were noted at 15.0 g kg⁻¹ of dietary isoleucine while the body ash remained constant among all the treatment levels. No mortality was recorded during the duration of the experiment.     

Evaluation of heat-processed cocoa pod husk meal as an energy feedstuff in production diets for the clariid catfish, Clarias isheriensis (Sydenham)

Isoproteic and isoenergetic diets containing 0%, 15%, 30% or 45% heat-processed cocoa pod husk meal (CPHM) were fed to Clarias isheriensis (16.8 ± 2.4 g) for 180 days. Growth rates of catfish fed varying levels of CPHM were similar (P > 0.05). Differences in feed-gain ratio (FGR) or protein efficiency ratio (PER) between treatments were not significant (P > 0.05). Histology of the liver showed no pathological effects of incorporation of CPHM. In a second experiment, C. isheriensis (19.1 ± 3.5 g) were fed isoenergetic diets containing 250, 300, 350 and 400 protein g kg^?1 (protein: energy ratios of 21, 25, 29 and 33 mg protein.kJ^?1 DE, respectively). Growth rate and FGR improved (P < 0.05) in proportion to the dietary protein level. PER decreased with increase in dietary protein. Carcass protein was lowest (P < 0.05) in catfish fed 250 g protein kg^?1, but did not differ among the other diets (P > 0.05). Body fat was highest in catfish fed 250 g protein kg^?1 and lowest in fish fed 350 g protein kg^?1. These results indicate that CPHM may be a suitable carbohydrate energy source for clariids at a P:E ratio of approximately 29 mg protein.kJ^?1 DE.     

Effects of Dietary Energy: Protein Ratio and Stocking Density on Growth and Survival of the Common Snapping Turtle Chelydra serpentinal1

Although the common snapping turtle Chelydra serpentina is cultured commercially in the United States, little information is available on nutritional and culture requirements. This study was conducted to evaluate the effects of dietary energy: protein ratio and stocking density on survival, growth, feed consumption, feed conversion, liposomatic index, dress-out percentage, and productive protein value of cultured, common snapping turtles. Hatchling turtles were stocked at 29 and 58 animals/m² and fed one of seven prepared diets. Six diets contained 30, 35, or 40% protein at two digestible energy (DE) levels (7 or 9 kcal DE/g protein); the seventh was a reference diet (66% protein and 5 kcal DE/g protein) formulated to equal or exceed the whole-body essential amino acid composition of wild, common snapping turtles. Turtles stocked at 58/m² exhibited greater mortality, lower weight gain, higher feed consumption, less-efficient feed conversion, lower liposomatic index, and lower productive protein value than turtles stocked at 29/m² (P < 0.05). The reference diet produced the greatest weight gain (P < 0.001). The superior performance of turtles fed the reference diet suggests that: 1) the protein (amino acid) content and/or energy: protein ratio of the reference diet was superior to that of the other diets tested; 2) improvements in growth parameters can be made with dietary manipulation; and 3) high levels of plant protein can be used in prepared, snapping turtle diets.     

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.     

Evaluation of growth, feed utilization, and economics of hybrid tilapia, Oreochromis niloticus×Oreochromis aureus, fed diets containing different protein sources in combination with distillers dried grains with solubles

A feeding trial was conducted in aquaria with juvenile hybrid tilapia (Oreochromis niloticus×Oreochromis aureus) to evaluate the use of different protein sources in combination with distillers dried grains with solubles (DDGS). Twelve 110‐L glass aquaria were stocked with 28 juvenile (2.7±0.5‐g) hybrid tilapia per aquarium. Three replicate aquaria were randomly assigned to each of the four dietary treatments. Diets were isonitrogenous and isocaloric. The control diet contained 12% fish meal and 41% soybean meal as the primary protein sources (Diet 1). Each experimental diet contained 30% DDGS by weight, in combination with 8% fish meal and 34% soybean meal (Diet 2), 26% meat and bone meal (MBM), and 16% soybean meal (Diet 3), or 46% soybean meal alone (Diet 4). Fish were fed to apparent satiation twice a day for 10 weeks. There were no significant differences (P>0.05) in average weight gain, specific growth rate (SGR), feed conversion ratio (FCR), and protein efficiency ratio (PER) among tilapia fed Diets 1, 2, and 3. Fish fed Diet 4 had significantly lower (P<0.05) average weight gain, SGR, and PER than fish fed Diets 1 and 3. Relative cost per unit weight gain for Diets 1, 2, and 3 were statistically similar (P>0.05), while cost per unit weight gain for Diet 4 was significantly higher (P<0.05) than other diets. Diet 3 represented approximately a 20% cost savings compared with the control diet, with no reduction in growth. This study indicates that diets without fish meal containing 30% DDGS in combination with MBM and soybean meal provide good growth in tilapia. A diet without animal protein did not support acceptable growth.     

Dietary histidine requirement of fingerling Indian major carp, Cirrhinus mrigala (Hamilton)

An 8‐week growth trial was conducted to determine the dietary histidine requirement of the Indian major carp, Cirrhinus mrigala fingerling (length 4.22 ± 0.45 cm; weight 0.61 ± 0.08 g; n = 40). Isonitrogenous (400 g kg^?1 crude protein) and isoenergetic (17.90 kJ g^?1 gross energy) diets with graded levels of l ‐histidine (2.5, 5.0, 7.5, 10.0, 12.5 and 15.0 g kg^?1 dry diet) were formulated using casein and gelatin as a source of intact protein, supplemented with l ‐crystalline amino acids. Twenty fish were randomly stocked in 70‐L indoor polyvinyl circular fish tank (water volume 55‐L, water exchange rate 1–1.5 L min^?1) and fed experimental diets at the rate of 5% of their body weight/day divided over two feedings at 08:00 and 16:00 h. Maximum live weight gain (295%), best feed conversion ratio (FCR) (1.48) and protein efficiency ratio (PER) (1.69) occurred at 7.5 g kg^?1 of dietary histidine level. When live weight gain, FCR and PER data were analysed using second‐degree polynomial regression, the break points indicated histidine requirements at 9.4, 8.6 and 8.5 g kg^?1 of dry diet respectively. Significantly (P < 0.05) higher whole body protein and low moisture values were recorded at 7.5 g kg^?1 histidine level. Body fat increased significantly (P < 0.05) with increasing histidine levels. However, at 7.5 and 10 g kg^?1 histidine diets body fat did not differ (P > 0.05) to each other. Ash content of fish fed diets containing various levels of histidine did not differ except at 2.5 and 5.0 g kg^?1 inclusion levels where significantly (P < 0.05) higher ash was recorded. Protein deposition was also found to be significantly (P < 0.05) higher in the 7.5 g kg^?1 histidine diet. Based on the polynomial regression analysis of FCR and PER data, it is recommended that the diet for fingerling C. mrigala should contain histidine at 8.5 g kg^?1 of dry diet, corresponding to 21.25 g kg^?1 of dietary protein for optimum growth and efficient utilization of feed.     

Effects of dietary protein on growth and body composition of Nile tilapia, Oreochromis niloticus L.

The effects of dietary protein (25%, 30%, 35%, 40% and 45%) on growth, survival, feed conversion ratio (FCR), protein efficiency ratio (PER) and body composition were investigated for four sizes (0.51, 45, 96 and 264 g) of Nile tilapia, Oreochromis niloticus L. In all four experiments, there was a progressive increase in growth with increasing dietary protein. In fry (0.51 g), significantly higher growth, survival and feed conversion were recorded for fish fed 40–45% rather than 25–35% protein diets. Similar trends for growth and FCR were also noted in 45 g fish. For larger (96 and 264 g) tilapia, significant differences in growth and FCR were found only between fish fed 25% and 30–45% protein diets. FCR and PER decreased with increasing weight of fish, and both were found to be negatively correlated with dietary protein level. Whole-body composition of the smallest fish was significantly influenced by dietary protein content. Percentage body protein of the fish fed 40–45% protein was higher than that of fish fed 25–35% protein diets, whereas lipid content decreased with increasing dietary protein level. In 45 g fish, both protein and lipid contents were higher in fish fed 25% and 30% protein diets than in those fed 35–45% protein diets. In larger tilapia, no significant influence of dietary protein level on body protein content was found. Percentage lipid decreased with increasing dietary protein level, and no definite trends in ash content were found. The results of these studies indicate that O. niloticus fry (0.51 g) should be reared on a practical diet containing 40% protein, and larger tilapia (96–264 g) on a diet containing 30% protein.     

Effects of dietary protein level on growth,feed utilization and digestive enzyme activity of the Chinese mitten crab,Eriocheir sinensis

A feeding trial was conducted using isoenergetic practical diets to evaluate the effects of the dietary protein level on growth performance, feed utilization and digestive enzyme activity of the Chinese mitten crab, Eriocheir sinensis. Four experimental diets were formulated containing 250, 300, 350 and 400 g kg^?1 protein and 16 kJ g^?1 gross energy. Each diet was randomly assigned to triplicate groups of juvenile crab with mean initial body weight 3.56 ± 0.16 g and mean shell width 15.31 ± 0.06 mm. Juvenile crab were reared in indoor flow‐through system consisting of 12 plastic tanks (1.0 m × 0.6 m × 0.5 m) and fed diets twice daily at 6–8% of body weight for 12 weeks. Performance was judged on the basis of growth (specific growth rate of weight, SGR_G; specific growth rate of shell width, SGR_SW), feed conversion ratio (FCR) and protein efficiency ratio (PER). A decreased FCR was observed with increasing dietary protein levels. Both SGR_G and SGR_SW significantly increased with increasing dietary protein levels up to 350 g kg^?1, whereas there were no significant differences for protein levels from 350–400 g kg^?1. Application of broken line regression analysis to SGR_G provided an estimate of 347.8 g kg^?1 dietary protein for maximal growth. The highest PER was observed in crab fed the diet containing 350 g kg^?1 protein (P < 0.05). The percent survival was not affected (P > 0.05) by the different dietary treatments. No significant differences were observed in the apparent digestibility coefficients of crude lipid and dry matter among dietary treatments (P > 0.05). However, the apparent digestibility coefficients of crude protein and energy in crab fed different protein levels significantly increased with increasing dietary protein level (P < 0.05). Both amylase and protease activities in the intestine of E. sinensis were studied. The amylase activity decreased significantly (P < 0.05) with increased dietary protein level and protease activity increased. Regression analysis showed a negative effect of inclusion of dietary protein level on amylase activity (P < 0.05). However, protease activities were found to be positively correlated (P < 0.05) with dietary protein level. The protein content of the crab significantly increased with dietary protein levels up to 350 g kg^?1 (P < 0.05), but no significant differences (P > 0.05) were founded with protein levels higher than 350 g kg^?1.     

Growth performance and feed utilization of Nile tilapia Oreochromis niloticus (Linnaeus, 1758) and tilapia galilae Sarotherodon galilaeus (Linnaeus, 1758) fingerlings fed plant protein-based diets

This study was designed to determine the effect of complete substitution of fish meal (FM) by three plant protein sources including extruded soybean meal (SBM), extruded full‐fat soybean (FFSB) and corn gluten meal (CGM) on growth and feed utilization of Nile tilapia Oreochromis niloticus and tilapia galilae Sarothrodon galilaeus. Four isonitrogenous of crude protein (ca. 28.0%) and isocaloric (ca. 19 MJ kg⁻¹) experimental diets were formulated. The control diet (diet 1) was prepared with FM as the main protein sources. Diets 2–4, each FM control diet, were completely substituted with SBM (diet 2), FFSB (diet 3) and CGM (diet 4). l ‐lysine and dl ‐methionine were added to plant protein diets to cover the nutritional requirements of tilapia. Each treatment was allocated to three net pens and fed for 17 weeks. Nile tilapia fed the control diet showed significantly higher (P≤0.05) values for final body weight (FBW), feed intake (FI), weight gain (WG) and specific growth rate (SGR), whereas fish fed the diet with CGM achieved the lowest values. Tilapia galilae fed SBM diet recorded the highest (P≤0.05) values for growth performance. Better feed conversion ratio (FCR) for both Oreochromis niloticus and Sarothrodon galilaeus was observed when fish were fed SBM diet, whereas the worse FCR was recorded for FFSB diet. Feed utilization parameters including protein productive value (PPV), fat retention (FR) and energy retention (ER) showed significant differences (P≤0.05) for both the species fed different dietary protein sources. The present results suggest that, for Nile tilapia, both SBM and FFSB supplemented with dl ‐methionine and l ‐lysine can completely replace dietary FM. Meanwhile, S. galilaeus fed SBM diet exhibited comparable growth and feed utilization with those fish fed a fish‐meal‐based diet.     

Dietary tryptophan requirement of fingerling Indian major carp, Cirrhinus mrigala (Hamilton)

An 8‐week feeding trial was conducted to evaluate the effects of dietary tryptophan concentration on weight gain and feed efficiencies of fingerling Indian major carp, Cirrhinus mrigala. Six isonitrogenous (40% crude protein) and isocaloric (17.90 kJ g^?1) amino acid test diets containing casein, gelatin and l ‐crystalline amino acids with graded levels of l ‐tryptophan (0.06, 0.16, 0.26, 0.36, 0.46 and 0.56 g 100 g^?1 dry diet) were formulated. Fish (4.25±0.30 cm, 0.62±0.02 g) were randomly stocked in triplicate groups in 70 L (water volume 55 L) flow‐through (1–1.5 L min^?1) indoor circular tanks and fed experimental diets at 5% of their body weight/day in two feedings at 08:00 and 16:00 hours. Maximum live weight gain (277%), lowest feed conversion ratio (FCR) (1.50) and highest protein efficiency ratio (PER) (1.66) were measured at 0.36% dietary tryptophan. The relationship between dietary tryptophan levels and weight gain, FCR and PER data were described using second‐degree polynomial regression analysis indicating the tryptophan requirement at 0.42, 0.39 and 0.38 g 100 g^?1 of dry diet respectively. Whole body moisture decreased with increasing tryptophan up to 0.36%. Significantly (P<0.05) higher protein content was evident in fish fed diet containing 0.36% tryptophan. Body fat increased significantly (P<0.05) in fish fed with different tryptophan concentrations except those fed 0.36% tryptophan where a significantly lower fat content was noted. Significantly (P<0.05) higher ash content was reported at 0.06% and 0.16% tryptophan levels. Survival was 100% in fish fed all the diets except those fed 0.06% tryptophan. Based on the results, diets for fingerling C. mrigala should contain tryptophan at 0.38 g 100 g^?1 dry diet, corresponding to 0.95 g 100 g^?1 dietary protein for optimum growth and efficient feed utilization.     

Effects of dietary protein and lipid levels on growth,feed utilization and body composition in Pseudobagrus ussuriensis fingerlings

An 8‐week feeding trial was conducted to investigate the optimum dietary protein and lipid levels for growth, feed utilization and body composition of Pseudobagrus ussuriensis fingerlings (initial weight: 3.40 ± 0.01 g). Twelve diets containing four protein levels (350, 400, 450 and 500 g kg^?1 crude protein) and three lipid levels (50, 100 and 150 g kg^?1 crude lipid) were formulated. Fish were randomly allotted to 36 aquaria (1.0 × 0.5 × 0.8 m) with 25 fish to each glass aquarium. Fish were fed twice daily (08:00 and 16:00) to apparent satiation. The results showed that weight gain and specific growth rate (SGR) decreased with increasing dietary lipid level from 50 to 150 g kg^?1 at the same dietary protein level. Fish fed the diets containing 150 g kg^?1 lipid exhibited higher feed conversion ratio (P < 0.05), lower protein efficiency ratio (PER) and nitrogen retention efficiency (NRE) relative to fish fed the diet containing 50 and 100 g kg^?1 lipid. Weight gain and SGR significantly increased with increasing dietary protein from 350 to 450 g kg^?1 at the same dietary lipid level, and even a little decline in growth with the further increase in dietary protein to 500 g kg^?1. Daily feed intake, NRE and PER were significantly affected by both dietary protein and lipid levels (P < 0.05) and tended to decrease with increasing dietary protein and lipid levels. Whole‐body protein content increased as protein levels increased and lipid levels decreased. Whole‐body lipid and muscle lipid content increased with increasing dietary lipid level, and decreased with increasing dietary protein at each lipid level. There was no significant difference in condition factor and viscerosomatic index among fish fed the diets. Hepatosomatic index was affected by dietary lipid level (P < 0.05), and increased with increasing dietary lipid level at the same protein level. These results suggest that the diet containing 450 g kg^?1 protein and 50 g kg^?1 lipid with a P/E ratio of 29.1 mg protein kJ^?1 is optimal for growth and feed utilization of P. ussuriensis fingerlings under the experimental conditions used in the study.     

The effect of varying dietary protein level on the growth, food conversion, protein utilization and body composition of tropical catfish Mystus nemurus (C. & V.) cultured in static pond water system

Tropical catfish, Mystus nemurus (C. & V.) (25.89 ± 0.7 g) were stocked semi-intensively in 0.03-ha earthen ponds at the rate of 10 000 ha”^-1 and fed six iso-energetic practical diets ranging from 27% to 50% protein for 8 weeks. Each diet was fed in three replicate ponds twice daily to satiation. Experimental fish were also reared extensively, in control ponds, without supplementary feed. Fish fed the 42% protein diet had the highest standing crop, weight gain and protein utilization values and the differences from other diets were statistically significant (P > 0.05). Protein efficiency ratio (PER) decreased as dietary protein increased. The experiment indicated that natural food organisms contributed to some degree if not significantly to the catfish production. Weight gain, food conversion ratio (FCR). PER and SGR (specific growth rate) indicated that a 42% protein diet with digestible protein-to-energy ratio (D/E) of 27.57 mg kj^_1 produced maximum growth in the static pond system.     

Effects of dietary protein levels on growth,feed utilization,protein retention efficiency and body composition of young <Emphasis Type="Italic">Heteropneustes fossilis</Emphasis> (Bloch)

An 8-week growth trial was conducted to assess the effect of dietary protein on growth, feed utilization, protein retention efficiency, and body composition of young Heteropneustes fossilis (10.02 ± 0.09 g; 9.93 ± 0.07 cm). Isocaloric (4.15 kcal g⁻¹, GE) diets with varying levels of protein (25, 30, 35, 40, 45, and 50% of the diet) were fed near to satiation to triplicate groups of fish. Optimum dietary protein was determined by analyzing live weight gain (LWG%), feed conversion ratio (FCR), protein efficiency ratio (PER), specific growth rate (SGR%), and protein retention efficiency (PRE%) data. Maximum LWG% (167), best FCR (1.42), PER (1.75), SGR (1.76), and PRE (31.7%) were evident in fish fed 40% protein diet (Diet 4). Body protein data also supported the above level. However, second-degree polynomial regression analysis of the above data indicated that inclusion of dietary protein in the range of 40–43% is optimum for the growth of young H. fossilis.