The effect of diet and photoperiod on ammonia efflux rates of the African catfish, Clarias gariepinus (Burchell, 1822)

Total ammonia efflux rates of the African catfish, Clarias gariepinus (Burchell), were measured under different combinations of photoperiod (LD 24:0. LD 0:24, LD 12:12) and feeding regime (50% protein diet, 41% protein diet and zero food). A time-dependent variation of ammonia efflux following feeding was observed, with postprandial excretion rates in the first 12 h being greater than those in the following 12 h. Ammonia efflux rates were directly related to the level of protein in the diet under all photoperiod conditions. Photoperiod had no effect on ammonia efflux rate, except in the LD 24:0-high protein diet group, which may indicate a stress response.     

Nitrogen budget for a low salinity, zero-water exchange culture system: I. Effect of dietary protein level on the performance of Litopenaeus vannamei (Boone)

A 4‐week study was conducted to evaluate the effects of different dietary protein levels (25%, 30%, 35% and 40%) on the growth and survival of juvenile Litopenaeus vannamei raised in a low salinity (4.6 g L⁻¹), zero‐water exchange culture system, as well as on the nitrogen budget and ammonia efflux rate. No significant differences were observed among the dietary treatments for final weight, weight gain or survival of shrimp, although the best performance was observed in the 25% protein treatment group. Both weight and survival decreased as the dietary protein increased. Significant differences (P<0.05) were observed in the ammonia concentration among dietary treatments during the first 2 weeks of the experiment. The highest concentration was measured in the 40% dietary protein treatment (5.88 mg NH4‐N L⁻¹). The nitrogen budget showed that the nitrogen loss increased as the dietary protein increased under the experimental conditions; the largest amount of nitrogen recovered as shrimp biomass (42.9%) was in the 25% protein treatment group, and the largest amount of unaccounted nitrogen (39.5%) was in the 40% protein treatment. Under these conditions, utilization of low‐protein diets resulted in better performance, presumably because they provided more carbon for heterotrophic bacteria and reduced the nitrogen loading of the system.     

Effect of dietary protein level on growth, survival and ammonia efflux rate of Litopenaeus vannamei (Boone) raised in a zero water exchange culture system

Litopenaeus vannamei postlarvae (1.96±0.07 g) were reared in a zero water exchange system for 25 days at 28°C. They were fed four commercial diets containing 25%, 30%, 35% or 40% crude protein in three replicate aquaria per dietary treatment. Total ammonia, nitrite, nitrate and pH were monitored weekly and total ammonia levels were additionally measured every 3 days using the flow injection analysis method. Total ammonia efflux rates were measured at days 0, 14 and 21, and survival and growth rates were recorded at the end of the experiment. No significant differences between water quality parameters such as temperature, salinity, dissolved oxygen and pH were found. Nitrite concentration remained low in all dietary treatments up to the second week increasing considerably from day 14 onwards suggesting the initiation of the nitrification process. Water total ammonia of all experimental groups exhibited a gradual increase up to day 13; however, following this time ammonia levels of all experimental groups decreased, probably due to either the action of bacterial nitrification or ammonia‐N uptake by the animals. High ammonia efflux rates were recorded at day 14, especially after the first hour of immersion in the 25% protein group, but no significant changes occurred in any experimental group after 3 h. No significant differences in weight gain, final weight or survival of shrimp were observed under these experimental conditions. The importance of zero water exchange systems and their effects on the nitrogen metabolism of crustaceans are discussed.     

Nitrogen excretion and absorption efficiencies of white steenbras, Lithognathus lithognathus CuvieSparidae, under experimental culture conditions

The various components of the nitrogen budget of white steenbras,Lithognathus lithognathus Cuvier (Sparidae), were determined under experimental culture conditions. A simple closed system respirometer was used where experiments were conducted to investigate faecal prodution, nitrogen excretion rates and absorption efficiencies at 16C and 20C. Faecal loss, as a percentage of the ingested nitrogen, amounted to 3.59%. Gross, carbon and nitrogen absorption efficiencies ranged from 8 6 to 9 8 % and were not significantly affected by fish size, ration size or temperature (P < 0.05). Net protein utilization (NPU) and the biological value (BV) ranged from 78 to95%. Ammonia and urea constituted 77.93 and 10.07%, respectively, of the total exogenous nitrogen excretion, the balance being made up of other dissolved organic nitrogen (DON). Endogenous ammonia excretion rates were significantly greater in small fish compared to large fish (P < 0.05). Total non-faecal losses as a percentage of the ingested ration amounted to 21.86%. Fish size and ration size increased nitrogen excretion, but temperature had no effect. Maintenance rations were 7.55 mg g-¹ dry weight day-¹ (0.76%dry body weight) and 5.99 mgg-¹ (0.60% dry body weight) for small and large fish, respectively. The high absorption efficiencies and high nitrogen indicated that white steenbras utilize the commercial trout pellet diet very efficiently.     

Oxygen consumption and ammonia-N excretion related to protein requirements for growth of white shrimp, Penaeus setiferus (L.), juveniles

An experiment was conducted to study the effect of protein level on the growth rate, survival, pre- and postprandial oxygen consumption, and ammonia (N-NH₃) excretion in white shrimp. Penaeus setiferus (L.), juveniles. Diets containing 10%, 20%, 30%, 40% and 50% protein were provided at a proportion of 15% of the dry weight of shrimp weighing 0.19 ± 0.01g. The instantaneous growth rate was recorded for 45 days. The optimum protein level, in terms of the best growth rate, was that of the 30% protein diet (1.1 5g45days^?1). All shrimp fed with the diets had significantly higher respiration rates after feeding because of the apparent heat increment (AHI). A greater postprandial nitrogen excretion (PPNE) excretion was also observed after feeding. Shrimp maintained on the 30% protein diet had the lowest AHI and PPNE coefficients (percentage of ingested energyl. and took the least time to reach the oxygen consumption and nitrogen excretion peak. The 0:N ratios varied according to protein level, with higher values (32 and 44, fasting and Feeding, respectively) with a 30% protein diet, and lower values (10 and 13. fasting and feeding, respectively) with 10% and 50% protein diets. These results indicate that P. setiferus juveniles use protein when fed with high (50%) and low (10%) protein diets, and lipid-protein substrates with a 30% protein diet. Under these conditions, P. setiferus grow better with a 30% protein diet where shrimp use food more efficiently.     

Fish meal replacement by plant and animal by-products in diets for the Australian short-finned eel, Anguilla australis australis (Richardson)

In this experiment, 23% of fish meal protein was replaced with protein from Australian soybean meal (SBM), lupin meal (LM), corn gluten meal (CGM) and meat meal (MM) in nutritionally balanced experimental diets. Growth and growth efficiencies of juvenile Australian short‐finned eel Anguilla australis australis (Richardson) elvers (2.23±0.4‐g average wet weight) were compared. Elvers were fed twice a day to a total of 5% body weight per day for 63 days. Total weight gain (g), specific growth rate (% day^?1), protein efficiency ratio (%) and productive protein value (%) were significantly higher (P<0.05) for elvers fed the MM diet than for those fed the LM diet. There were no differences in diurnal ammonia‐nitrogen excretion rates. However, diurnal urea‐nitrogen excretion rates were significantly (P<0.05) affected by diet and rates were two to three times higher for all diets, except CGM, 4 h following the afternoon feed. Diet significantly affected apparent digestibility (AD); ADs of protein for SBM and LM were significantly (P<0.001) higher than for control diet, CGM and MM; AD of energy for LM was significantly (P<0.05) lower than for all the other diets. Fish meal protein was replaced by CGM, SBM and MM without compromising growth rates of the Australian short‐finned eel. However, whole lupin seed meal (LM) depressed growth and growth efficiencies most likely because of the high indigestible carbohydrate content.     

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.     

Substituting fish meal with poultry by-product meal in diets for black Sea turbot Psetta maeotica

A 60 days feeding experiment was carried out with Black Sea turbot Psetta maeotica to determine the amount of poultry by‐product meal (PBM) that could replace fish meal (FM) in formulated diets without reducing growth performance. Juvenile Black Sea turbot (initial average weight, 30 g) were fed five isoenergetic (gross energy, 20.5 ± 0.21 kJ g^?1 diet) and isonitrogenous diets (protein content, 550 ± 0.35 g kg^?1). The control diet used white FM as the sole protein source, the other four diets were prepared to replace FM protein at levels of 25%, 50%, 75% and 100% with PBM. The fish readily accepted all experimental diets and no mortality were recorded during the trial. There were no significant differences in growth performance of turbot (P < 0.05) fed the diets with 25% and 50% replacement levels compared with fish offered the control diet (100% FM), however, final body weight and specific growth rate values in the 50% replacement diet were about 8% lower than those of the control. Total nitrogen excretion in fish fed 50% replacement diet were about 10% higher than the control group, even though these parameters were not found to be statistically different. At the levels of 750 and 1000 g kg^?1 of the protein, PBM inclusion caused a severe decrease in growth performance, feed utilization, protein efficiency ratio and per cent nitrogen retention. The results in the present study indicate that up to 25% of FM protein can be replaced by PBM protein without causing reduction in growth performance, nutrient utilization and nitrogen retention.     

Nitrogen budget for a low-salinity, zero-water exchange culture system: II. Evaluation of isonitrogenous feeding of various dietary protein levels to Litopenaeus vannamei (Boone)

This study evaluated the effects of isonitrogenous feeding (60 g dietary protein per kilogram of body weight per day) using experimental feeds with 25%, 30%, 35% and 40% protein on the nitrogen budget, ammonia efflux rate, growth and survival of juvenile Litopenaeus vannamei raised in a low-salinity (4 g L⁻¹) zero-water exchange culture system for 4 weeks. No significant differences in weight gain or instantaneous growth rate were observed between the dietary treatments with 35% and 40% protein after 3 weeks of study, or between treatments with 25% and 30% protein after 4 weeks of study. High mortality rates were observed for the 35% and 40% protein treatments, probably associated with high nitrite levels (4.80 and 7.36 mg NO₂-NL⁻¹ respectively) in water. Among the various dietary treatments, 39–46.3% of feed nitrogen was converted to shrimp biomass, 32.8–38.0% and 14.4–39.9% remained within the system as organic and inorganic nitrogen, respectively, and 32.5–39.3% was unaccounted for. The results of the present study showed high nitrogen utilization efficiencies. However, as the nitrogen loading of the zero-water exchange system increased, so did the nitrogen excretion of shrimp, causing a deteriorated general condition of the shrimp, demonstrated by the low ammonia efflux rates recorded at the end of the trial. This study confirms that low-salinity closed systems are particularly susceptible to nitrogen loading. Thus, in these culture systems, low-protein feeds may perform better as they provide more carbon for heterotrophic bacteria and less nitrogen to be degraded and transformed into nitrogenous wastes.     

Replacing fish meal with increasing levels of meat and bone meal,soybean meal and corn gluten meal,in diets of juvenile bluegill,Lepomis macrochirus

A 60‐day study was conducted to determine the response of juvenile bluegill Lepomis macrochirus to seven experimental diets, formulated using a blend of alternative protein sources as a replacement for fish meal. Adequate levels (digestible basis) of energy, protein and amino acids were maintained in diets 1–6, whereas slightly lower protein and energy levels were provided in diet 7. Feed cost per tonne ranged from $ 798.9 (diet 1, 550 g Kg^?1 fish meal) to $ 515.8 (diet 6, 0 g kg^?1 fish meal), or to $ 507.2 (diet 7, 0 g Kg^?1 fish meal). Three commercial diets were included in the study as reference diets: a high‐energy and a low‐energy trout diet, as well as a catfish diet. Quintuplicate bluegill groups (~22 g, n = 10 fish group^?1) were fed the experimental diets twice daily to apparent satiation. No major differences in feed consumption, feed efficiency and growth rates were detected among the bluegill groups fed the experimental diets. Trout diets generally produced higher fish fat deposition, whereas the catfish diet produced a poorer fish growth rate relative to the experimental diets. Under the reported conditions, results indicate diet 6, comprising predominantly soybean meal and porcine meat and bone meal, to be the most economical diet for juvenile bluegill.     

Evaluation of feed utilization and growth performance of juvenile striped catfish Pangasianodon hypophthalmus fed diets with varying inclusion levels of corn gluten meal

A nutrition trial with striped catfish (Pangasianodon hypophthalmus) juveniles was undertaken to evaluate the effect of replacing dietary fishmeal (FM) protein with corn gluten meal (CGM). A diet with FM as the main protein source was used as the control diet (FM). Five experimental diets (approximately 320 g kg^?1 crude protein) were formulated to progressively replace 20% (CGM20), 40% (CGM40), 60% (CGM60), 80% (CGM80) and 100% (CGM100) of FM protein. Fifteen fish per tank (initial weight 11.2 ± 0.6 g) were randomly distributed into 18 80‐litre fibreglass tanks connected to a closed recirculation system (temperature 30.3 ± 1.0 °C). The diets were tested in triplicate for 12 weeks. The final weight and specific growth rate (SGR) of fish fed diets CGM20, CGM40 and CGM60 were not significantly different compared to fish fed the FM diet. Feed intake (FI) tended to decrease with increasing dietary CGM level. Striped catfish fed FM, CGM20 and CGM40 had significantly lower feed conversion ratio (FCR) compared with fish fed CGM80 and CGM100 (P < 0.05). The protein efficiency ratio (PER) of fish fed the CGM80 and CGM100 diets was significantly lower than those of all other treatments (P < 0.05). Total ammonia‐nitrogen (TAN) excretion increased with elevated dietary CGM inclusion. The viscerosomatic index (VSI) of fish fed the CGM80 and CGM100 diets were significantly higher (P < 0.05) than those of fish fed the other treatments. The crude lipid content in the final body composition of the striped catfish was elevated significantly with increasing dietary CGM levels. Fish fed the CGM80 and CGM100 diets displayed haematocrit levels significantly lower (P < 0.05) than those fed the other diets. The haemoglobin content in fish was significantly higher in fish fed CGM20 and lower at CGM100 compared to fish fed the FM diet. The results of the present trial indicated that the optimum level of FM protein replacement with CGM determined by quadratic regression analysis was 25.1% on the basis of maximum SGR.     

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

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

Effects of dietary protein levels on the growth performance, digestive capacity and amino acid metabolism of juvenile Jian carp (Cyprinus carpio var. Jian)

This experiment was conducted to evaluate the effects of protein levels on the growth performance, digestive capacity and amino acid metabolism of juvenile Jian carp. Brown fish meal was used as the sole protein source in the present study. Six isoenergetic experimental diets containing 14.4 MJ kg^?1 of digestible energy and 220–495 g crude protein kg^?1 diets were fed to triplicate groups of 50 fish with a mean initial weight of 16.67 ± 0.01 g for 45 days. Per cent weight gain (PWG) and feed efficiency ratio (FER) improved with an increase in the dietary protein levels up to 330 g kg^?1 diet. The condition factor, relative gut length, intestinal folds height, hepatopancreas and intestine protein content improved with an increase in the protein levels up to 330–385 g kg^?1 diet. Trypsin, creatinkinase, Na⁺, K⁺‐ATPase and alkaline phosphatase activities generally followed the same tendency as that of growth parameters. Amylase and γ‐glutamyl transpeptidase (γ‐GT) activities were negatively correlated with increasing protein levels from 220 to 330 g kg^?1 diet, and no differences were found thereafter. Lipase activity was unaffected by protein levels. Lactobacillus amount was increased with protein levels up to 275 g kg^?1 diet, while Aeromonas amount followed the opposite pattern. Escherichia coli amount was not influenced by dietary protein levels. Glutamate–oxaloacetate transaminase (GOT) activities in the hepatopancreas and plasma ammonia concentration (PAC) were not influenced by protein levels between 220 and 275 g kg^?1 diet, but significantly increased with increasing protein levels from 275 to 440 g kg^?1 diet, and remained similar thereafter. Glutamate–pyruvate transaminase (GPT) activities significantly increased with protein levels >275 g kg^?1 diet. Based on the broken‐line model, the dietary protein requirement for PWG of Jian carp (16.7–55.0 g) was estimated to be 341 g kg^?1 diet with a digestible energy of 14.4 MJ kg^?1 diet.     

Effects of Dietary Protein and Lipid Levels with Different Protein‐to‐Energy Ratios on Growth,Feed Utilization,and Plasma Biochemical Parameters of Dianchi Golden‐line Barbell,Sinocyclocheilus grahami

An 8‐wk feeding trial was conducted to evaluate the effects of varying dietary protein and lipid levels with different protein‐to‐energy (P/E) ratios on growth, feed utilization, and plasma biochemical parameters of Sinocyclocheilus graham. Nine experimental diets were formulated to contain three protein levels (35, 40, and 45%), and each with three lipid levels (4, 8, and 12%), to produce a range of P/E ratios from 71.31 to 98.64 mg protein/kcal. Each diet was randomly assigned to triplicate groups of 25 fish. Fish grew best when fed the diet containing 45% protein and 12% lipid. However, fish fed the diet with 40% protein and 8% lipid had similar weight gain and specific growth rate as those fed the above diet but showed relatively better feed conversion ratio, protein efficiency ratio, and protein and energy retentions. Additionally, plasma total amino acids and blood urea nitrogen contents and γ‐glutamyltransferase, aspartate aminotransferase, and alanine aminotransferase activities in fish fed the diet containing 40% protein and 8% lipid were relatively low among the dietary treatments. These results may indicate that a diet containing 40% protein and 8% lipid with P/E ratio of 84.05 mg protein/kcal would be suitable for the optimal growth, feed utilization, and health of S. graham.     

Quantifying the dietary niacin requirement of the Indian catfish, Heteropneustes fossilis (Bloch), fingerlings

A growth study was conducted to determine the dietary niacin requirement of the Indian catfish, Heteropneustes fossilis (Bloch), fingerlings (Mean weight 9.41 ± 0.18 g). Semi‐purified diets with five levels (0, 5, 10, 20 and 40 mg kg^?1 diet) of supplemental niacin were fed to H. fossilis for 15 weeks. Each diet was fed to three replicate groups of fish. Results indicated that the highest (P < 0.05) weight gain was for the fish fed the diet supplemented with 20 mg niacin kg^?1, followed by fish fed the diets with 40, 10 and 5 mg niacin kg^?1, and the lowest in fish fed the unsupplemented control diet. Patterns of specific growth rate (SGR) and protein efficiency ratio (PER) were similar to those of the weight gain. Survival of fish fed the control diet and niacin‐supplemented diet was 58% and 91–100% respectively. Niacin deficiency signs such as anaemia, anorexia, lethargy and skin haemorrhage were observed in fish fed the control diet. The haematocrit values (Ht) were higher (P < 0.05) in fish fed the diets supplemented with niacin than in fish fed the control diet. The hepatosomatic indexes (HSI) of fish fed with or without niacin‐supplemented diets were not significantly (P > 0.05) different from each other. Both body protein and lipid content were higher (P < 0.05) in fish fed the diet supplemented with 20 and 40 mg niacin kg^?1, respectively, than those fish fed other diets. The niacin content in liver significantly (P < 0.05) reflected the supplementation level in the diet and ranged from 29.11 to 40.31 mg g^?1 tissue. The associated liver niacin content for growth was about 47 μg g^?1 tissue. Quadratic regression analysis showed that the dietary niacin requirement for maximal growth of H. fossilis under these experimental conditions was about 25 mg kg^?1 diet.     

Effect of high dietary intakes of vitamin E and n-3 HUFA on immune responses and resistance to Edwardsiella tarda challenge in Japanese flounder (Paralichthys olivaceus, Temminck and Schlegel)

A feeding experiment was conducted to investigate the effects of high dietary intake of vitamin E (supplied as dl ‐α‐tocopheryl acetate) and n‐3 highly unsaturated fatty acid (n‐3 HUFA) on the non‐specific immune response and disease resistance in Japanese flounder Paralichthys olivaceus. Nine practical diets were formulated to contain one of three levels of vitamin E namely, 0, 80 or 200 mg kg^?1 (the total α‐tocopherol contents in the diets were 21, 97 and 213 mg kg^?1 based on analysis), and at each vitamin E level with one of three n‐3 HUFA levels i.e. 0.5%, 1.5% or 2.0%. Each diet was randomly assigned to triplicate groups of Japanese flounder (initial body weight: 40.5±1.0 g, mean±SD) in a re‐circulation rearing system. Fish were fed twice daily to apparent satiation at 07:00 and 18:00 hours for 12 weeks. During the experimental period, water temperature was maintained at 18±1°C, salinity 31–35 g L^?1, and pH 7.8–8.2. Dissolved oxygen was not less than 6 mg L^?1, and there were negligible levels of free ammonia and nitrite. The results showed that the increase in dietary n‐3 HUFA from 0.5% to 1.0% significantly decreased muscle α‐tocopherol contents in fish‐fed diets with 21 and 97 mg α‐tocopherol kg^?1 diet (P<0.05). In 1.0% HUFA groups, alternative complement pathway activity (ACH₅₀) of fish fed the diet containing the 213 mg α‐tocopherol kg^?1 diet was significantly higher than noted for fish fed the diet containing 97 mg α‐tocopherol kg^?1 diet (P<0.05). Fish fed the diet with 213 mg α‐tocopherol kg^?1 and 2.0% n‐3 HUFA had the highest lysozyme activity (131.7 U mL^?1) among all the dietary treatments. Fish fed the diets containing 97 and 213 mg α‐tocopherol kg^?1 with 1.0% n‐3 HUFA had significantly higher respiratory burst activity than those fed the diets containing 21 mg α‐tocopherol kg^?1 with 0.5 and 1.0% n‐3 HUFA (P<0.05). In the disease resistance experiment, high intake of dietary vitamin E with 213 mg α‐tocopherol kg^?1 significantly decreased cumulative mortality and delayed the days to first mortality after a 7‐day Edwardsiella tarda challenge (P<0.05). In addition, under the experimental conditions, dietary vitamin E and n‐3 HUFA had a synergistic effect on the non‐specific immune responses and disease resistance in Japanese flounder (P<0.05).     

Protein synthesis and growth in juvenile Atlantic halibut, Hippoglossus hippoglossus (L.): application of 15N stable isotope tracer

The growth efficiency of juvenile Atlantic halibut, Hippoglossus hippoglossus (L.), was investigated by comparing wet weight specific growth rates (SGRs) over 28 days with protein synthesis rates measured using a non-invasive stable isotope (¹⁵N) tracer technique. A diet containing ¹⁵N-labelled protein was fed at a single meal and individual feed intake was measured by X-ray radiography to allow calculation of the amount of N consumed. Excreted ammonia and urea were collected from each fish and the ratio of ¹⁵N to ¹⁴N was used to calculate rates of protein synthesis. Peak rates of ammonia excretion occurred 12 h post-feeding. Rates of urea excretion did not change after feeding and remained relatively constant over the 48-h measurement period. Urea accounted for 17% of the measured nitrogen excretion and showed no enrichment with N. Mean protein growth rates were 1.31 ± 0.06% day^?1, while whole animal fractional rates of protein synthesis were 2.02 ± 0.24% day^?1. The mean protein synthesis retention efficiency was 77.41 ± 9.09%, which is higher than that recorded for most other teleosts. This suggests that halibut have a relatively low cost, high growth efficiency growth strategy.     

Dietary protein requirement of juvenile marbled spinefoot rabbitfish Siganus rivulatus

Rabbitfish are an Indo‐Pacific herbivorous marine fish that have good market demand and are suitable for aquaculture. The present work was performed to determine dietary protein inclusion necessary for optimal growth of juvenile rabbitfish Siganus rivulatus. Six diets with increasing levels of protein (10, 20, 30, 40, 50 and 60 g crude protein 100 g^?1 feed) and similar levels of gross energy (20 MJ kg^?1) were prepared and offered to S. rivulatus juveniles maintained in triplicate cages placed in two large water tanks for 49 days. Growth progressively improved with dietary protein for fish offered diets from 10% to 40% protein inclusion. Diets with greater protein levels did not improve fish growth beyond that observed in the 40% group. Daily feed intake, apparent protein utilization and feed conversion ratio decreased as dietary protein increased. Protein efficiency (PE) was greatest (1.47) in fish offered the 10% protein diet and least in fish offered the 60% protein diet (0.80). No differences in PE were observed among all other treatments (20–50%). Results of the present work suggest that minimum dietary requirement for suitable growth of S. rivulatus juveniles is 40% protein when digestible energy of the diet is 16–18 MJ kg^?1.     

Effect of dietary protein and lipid level on metabolic utilization of diets by european sea bass (Dicentrarchus labrax) juveniles

Two trials were performed with sea bass juveniles to study the effect of dietary protein (trial I) and lipid (trial II) levels on the metabolic utilization of diets at 25 °C. The effect of water temperature (18 and 25 °C) on metabolism was also tested in trial I. For that purpose, oxygen consumption and ammonia excretion were measured both in fed and in 9-days starved fish. In trial I, diets were formulated to be isoenergetic (GE: 19.4 kJ g^–1) and to have 36, 42, 48 and 56% protein; in trial II, diets were formulated to be isonitrogenous (48% protein) and to have 12, 18, 24 and 30% lipid. In trial I, feed intake (g kg^–1 day^–1), and daily ammonia excretion and oxygen consumption significantly increased with water temperature. However, when expressed relatively to intake there was no significant effect of temperature on ammonia excretion (% N intake) or heat production (% GE intake). Heat increment of feeding (% GE intake) was neither affected by diet composition nor by water temperature. The relative contribution of protein catabolism to total energy expenditure significantly increased with dietary protein level, but was not affected by water temperature. In trial II, both daily ammonia excretion and oxygen consumption were inversely correlated to dietary lipid levels. Nitrogen excretion, heat production, heat increment of feeding, non-fecal losses (% intake) and the relative contribution of protein to total energy expenditure were also inversely related to dietary lipid levels. Results of this study indicate that the main effect of water temperature was to modify feed intake, not the metabolic utilization of diets. Indeed, expressed relatively to nitrogen or energy intakes, both nitrogen and energy budgets were not significantly affected by water temperature. A decrease of dietary protein to energy ratio, by modifying either dietary protein or lipid levels, spared protein utilization for metabolism, and this effect was essentially due to a decrease of non-fecal nitrogen excretion and of the heat increment of feeding.     

Effects of dietary inclusion of the beta-adrenergic agonist, salbutamol, on growth performance and whole-body composition of rohu Labeo rohita (Hamilton) fingerlings fed diets containing two protein levels

A 60-day feeding experiment was conducted in the laboratory to evaluate the effect of oral administration of the beta-adrenergic agonist (BAA), salbutamol, on growth, nutrient utilization and whole-body composition of rohu Labeo rohita (Hamilton) fingerlings (average weight 5.51 ± 0.07 g) acting as a repartitioning agent in intermediary metabolism and redistributing nutrients for muscle synthesis. Two diets (diets 30/0 and 40/0) were formulated containing 30% and 40% crude protein to serve as basal diets containing the same ingredient composition. Another four diets (diets 30/3, 30/6, 40/3 and 40/6) were prepared in the same way to contain either 3 or 6 mg kg⁻¹ BAA salbutamol at each protein level making the total of six experimental diets. Rohu fingerlings were fed with the experimental diets in three replicate treatments at a restricted feeding regime equivalent to 2% of body weight (BW) day⁻¹. A significant (P < 0.05) interaction effect was found between dietary protein level and BAA treatment. Dietary incorporation of BAA at both protein levels significantly (P < 0.05) increased growth and nutrient utilization in terms of weight gain (%), specific growth rate (SGR), feed:gain ratio (FGR) and protein efficiency ratio (PER). BAA treatment at the 6 mg kg⁻¹ concentration led to a 12% rise in growth with the 30% protein diet and a 6% rise with the 40% protein diet, above their respective controls (without BAA treatment). However, no significant differences were found by raising the BAA concentration from 3 to 6 mg kg⁻¹. The apparent digestibility values for protein, lipid and energy were only higher with the 30% protein diets containing BAA. At both protein levels tested, BAA exerted a significant (P < 0.05) positive influence on protein retention and a negative influence on lipid retention efficiency, although the differences between the 3 and 6 mg kg⁻¹ BAA diets were not significant. This indicated that BAA acted as a repartitioning agent in suppressing lipid deposition in favour of protein accretion. BAA induced significantly (P < 0.05) higher whole-body protein and lipid relative to the untreated groups. The condition factor improved significantly (P < 0.05) in the BAA-treated dietary groups. The fillet percentage displayed a direct correlation and the frame percentage a negative correlation with BAA concentration in the diets. The results indicate that the BAA, salbutamol, was effective in producing growth enhancement, improved body composition (higher protein and lower lipid accretion) and efficient nutrient utilization at the 3 mg kg⁻¹ dietary incorporation level and thus has a potential for application in formulated diets for the Indian major carp, rohu, under culture conditions.