Energy and nitrogen partitioning in 250 g Atlantic cod (Gadus morhua L.) given graded levels of feed with different protein and lipid content

The effects of feed intake level on energy and nitrogen partitioning were studied in juvenile Atlantic cod (250 g) fed two fish meal based diets differing in protein and lipid content (54:31 and 65:16) at 10 °C. Replicate groups of cod were feed deprived for 32 days or fed one of the two diets at 25, 50, 75 or 100% of group satiation for 60 days. Feed intake and oxygen consumption were measured daily and weights and chemical composition of carcass, liver, viscera and whole body were measured at start and end. Diet digestibilities were assessed in a separate experiment.

The whole body and carcass growth rates at a given feed intake did not differ between dietary groups, but the liver grew faster in the fish fed the low protein diet, resulting in higher hepatosomatic indices at the end of the experiment in the groups fed this diet.

The efficiency of utilisation of digestible nitrogen for growth (k_DNg) was higher for the low protein diet (0.73 ± 0.02) than for the high protein diet (0.53 ± 0.05), resulting in higher nitrogen retention at a given nitrogen intake. No difference in percentage nitrogen retention was seen in full-fed fish however (31.2 ± 2.5 and 28.4 ± 1.6% for the low protein and high protein diets, respectively). This can be explained by higher nitrogen intake in the fish fed the high protein diet, resulting in a smaller proportion of the intake being used for maintenance.

There was no difference in energy utilisation between dietary groups. The digestible energy requirement for maintenance (DE_maint) was 53.8 ± 0.9 kJ kg^− 1 d^− 1 (42.3 ± 0.7 kJ kg^− 0.8 d^− 1) and the utilisation efficiency for growth (k_DEg) was 0.80 ± 0.02. The energy retention in full-fed fish was 31.3 ± 3.5 and 31.7 ± 1.0% for the low protein and high protein diets, respectively. The deposited energy was distributed in approximately equal proportions in the liver and carcass, whereas viscera accounted for a minor proportion. At a given energy intake, the fish fed the high protein diet deposited more energy in the carcass and less in the liver than did those fed the low protein diet.     

Effects of Cu-exchanged montmorillonite on growth performance, microbial ecology and intestinal morphology of Nile tilapia (Oreochromis niloticus)

A total of 360 Nile tilapia at an average initial body weight of 3.9 g were randomly allocated to 4 treatments, each of which had three replicates of 30 fish/tank and used to investigate the effects of Cu²⁺-exchanged montmorillonite (Cu-MMT) on growth performance, microbial ecology of the skin, gill and intestine, and intestinal morphology. The dietary treatments were: 1) basal diet, 2) basal diet + 1.5 g/kg MMT, 3) basal diet + 30 mg/kg copper as CuSO₄ (equivalent to the copper in the Cu-MMT treatment group), or 4) basal diet + 1.5 g/kg Cu-MMT. The results showed that supplementation with Cu-MMT significantly improved growth performance as compared to control and fish fed with Cu-MMT had higher growth performance than those fed with MMT or CuSO₄. Supplementation with Cu-MMT reduced (P < 0.05) the total intestinal aerobic bacterial counts and affected the composition of intestinal microflora with a tendency of Aeromonas, Vibrio, Pseudomonas, Flavobacterium, Acinetobacter, Alcaligence, Enterobacteriaceae decreasing as compared with control. Measurements of villus and microvillus heights at different sites of the intestinal mucosa indicated that dietary addition of MMT or Cu-MMT improved intestinal mucosal morphology. However, the microbial ecology of the skin and gill was not affected by the addition of CuSO₄, MMT or Cu-MMT. Supplementation with CuSO₄ had no (P > 0.05) effect on the growth performance, microbial ecology and intestinal morphology. The results showed that Cu-MMT exhibited antibacterial activity in vivo and protected intestinal mucosa from invasion of pathogenic bacterium and toxins, resulting in a positive effect on the growth performance.     

Effects of Dietary Chlorella ellipsoidea Supplementation on Growth, Blood Characteristics, and Whole-Body Composition in Juvenile Japanese Flounder Paralichthys olivaceus

The study was conducted to investigate the effects of dietary Chlorella powder (C) supplementation on growth performance, blood characteristics, and whole-body composition in juvenile Japanese flounder Paralichthys olivaceus . Four experimental diets were supplemented with C at 0, 1, 2 and 4% (C₀, C₁, C₂, and C₄) on a dry-weight basis. Three replicate groups of fish averaging 1.13 ± 0.02 g (Mean ± SD) were randomly distributed in each aquarium and fed one of four experimental diets for 12 wk. After 12 wk of the feeding trial, fish fed C₂ diet had higher weight gain (WG), feed efficiency (FE), and protein efficiency ratio (PER) than did fish fed C₀ and C₁ diets ( P 0.05); however, there was no significant difference among fish fed C₁ and C₄ diets, and among fish fed C₂ and C₄ diets ( P > 0.05). Fish fed C₂ and C₄ diets had a lower serum cholesterol level than did fish fed C₀ and C₁ diets ( P 0.05). Fish fed C₂ and C₄ diets had a lower body fat than did fish fed C₀ ( P 0.05). These results indicate that dietary supplementation of 2% Chlorella powder in the commercial diets could improve growth, feed utilization, serum cholesterol level, and whole-body fat contents in juvenile Japanese flounder.     

Thiamin Requirement of Nile Tilapia,Oreochromis niloticus

Juvenile Nile tilapia, Oreochromis niloticus, were fed to apparent satiation twice daily with purified diets containing 0, 1.0, 2.0, 4.0, 8.0, and 16.0 mg/kg and 0, 2.0, 4.0, 8.0, 16.0, and 32.0 mg/kg of thiamin in separate 14‐ and 8‐wk trials (Experiments 1 and 2, respectively). Fish fed the diet devoid of thiamin developed neurological disorders, anorexia, reduced growth, and feed efficiency and increased mortality (Experiment 2 only) within 4–6 and 8–10 wk for Experiments 2 and 1, respectively. Low red blood cell count (RBC) and hematocrit (Ht) were observed in fish fed the thiamin‐deficient diet. Serum pyruvate was elevated in fish fed the thiamin unsupplemented diet. Serum lactate was not affected by dietary thiamin levels. Whole body protein was unaffected by dietary levels of thiamin. Body moisture and ash increased whereas body lipid decreased in fish fed the thiamin unsupplemented diets. None of these abnormalities were observed in fish fed the thiamin‐supplemented diets. Using the response curves determined by PROC NLMIXED to estimate dietary thiamin levels required for various response variables, a dietary thiamin level of 3.5 mg/kg diet was adequate for optimum growth, feed intake and efficiency, survival, prevention of neurological symptoms, and maintaining normal levels of RBC, Ht, serum pyruvate, and proximate body composition.     

Efficacy of bithionol as an oral treatment for amoebic gill disease in Atlantic salmon Salmo salar (L.)

This study examined the efficacy of bithionol as an oral treatment for Atlantic salmon Salmo salar affected by amoebic gill disease (AGD). The current commercial management strategy of AGD is a costly 3 h freshwater bath. It is labour intensive and the number of baths needed appears to be increasing; hence, there is an effort to identify alternative treatments. Efficacy was examined by feeding AGD-affected Atlantic salmon twice daily to satiation with bithionol, an antiprotozoal, at 25 mg kg^− 1 feed. Three seawater (35‰, 17 °C) re-circulation systems were used each consisting of three tanks containing 32 Atlantic salmon smolts with an average (± SEM) mass of 90.4 g (± 5.2). Three feeds were examined in the trial including bithionol, plain commercial control and oil coated commercial control. Feeding commenced 2 weeks prior to exposure to Neoparamoeba spp. at 300 cells L^− 1 and continued for 28 days post-exposure. Efficacy was determined by examining gross gill score and identifying percent lesioned gill filaments twice weekly for 4 weeks post-exposure. Bithionol when fed as a two-week prophylactic treatment at 25 mg kg^− 1 feed delayed the onset of AGD pathology and reduced the percent lesioned gill filaments by 53% and halved the gill score from 2 to 1 when compared with both the plain and oil controls during an experimental challenge. There were no palatability problems observed with mean feed intake of bithionol over the trial duration with fish consuming higher levels of the bithionol diet compared to both the oil and plain controls. This study demonstrated that bithionol at 25 mg kg^− 1 feed, when fed as a two-week prophylactic treatment for Neoparamoeba spp. exposure, delayed and reduced the intensity of AGD pathology and warrants further investigation as an alternative to the current freshwater bath treatment for AGD-affected Atlantic salmon.     

Metabolic scope, swimming performance and the effects of hypoxia in the mulloway, Argyrosomus japonicus (Pisces: Sciaenidae)

The culture of the mulloway (Argyrosomus japonicus), like many other Sciaenidae fishes, is rapidly growing. However there is no information on their metabolic physiology. In this study, the effects of various hypoxia levels on the swimming performance and metabolic scope of juvenile mulloway (0.34 ± 0.01 kg, mean ± SE, n = 30) was investigated (water temperature = 22 °C). In normoxic conditions (dissolved oxygen = 6.85 mg l^− 1), mulloway oxygen consumption rate (M·o₂) increased exponentially with swimming speed to a maximum velocity (U_crit) of 1.7 ± < 0.1 body lengths s^− 1 (BL s^− 1) (n = 6). Mulloway standard metabolic rate (SMR) was typical for non-tuna fishes (73 ± 8 mg kg^− 1 h^− 1) and they had a moderate scope for aerobic metabolism (5 times the SMR). Mulloway minimum gross cost of transport (GCOT_min, 0.14 ± 0.01 mg kg^− 1 m^− 1) and optimum swimming velocity (U_opt, 1.3 ± 0.2 BL s^− 1) were comparable to many other body and caudal fin swimming fish species. Energy expenditure was minimum when swimming between 0.3 and 0.5 BL s^− 1. The critical dissolved oxygen level was 1.80 mg l^− 1 for mulloway swimming at 0.9 BL s^− 1. This reveals that mulloway are well adapted to hypoxia, which is probably adaptive from their natural early life history within estuaries. In all levels of hypoxia (75% saturation = 5.23, 50% = 3.64, and 25% = 1 .86 mg l^− 1), M·o₂ increased linearly with swimming speed and active metabolic rate (AMR) was reduced (218 ± 17, 202 ± 14 and 175 ± 10 mg kg^− 1 h^− 1 for 75%, 50% and 25% saturation respectively). However, U_crit was only reduced at 50% and 25% saturation (1.4 ± < 0.1 and 1.4 ± < 0.1 BL s^− 1 respectively). This demonstrates that although the metabolic capacity of mulloway is reduced in mild hypoxia (75% saturation) they are able to compensate to maintain swimming performance. GCOT_min (0.09 ± 0.01 mg kg^− 1 m^− 1) and U_opt (0.8 ± 0.1 BL s^− 1) were significantly reduced at 25% dissolved oxygen saturation. As mulloway metabolic scope was significantly reduced at all hypoxia levels, it suggests that even mild hypoxia may reduce growth productivity.     

Dietary copper requirements of juvenile grouper, Epinephelus malabaricus

To quantify dietary copper (Cu) requirements in grouper, Epinephelus malabaricus, copper sulfate was added to the basal diet at 0, 1, 2, 4, 6, 8, 10 and 20 mg Cu/kg diet providing the actual dietary value of 0.11, 1.66, 2.41, 4.37, 6.56, 8.97, 11.03 and 20.05 mg Cu/kg diet, respectively. Each diet was fed to triplicate groups of grouper (initial body weight 13.35 ± 0.01 g) in a recirculated rearing system for 8 weeks. The Cu concentration in rearing water was monitored during the feeding period and ranged from 1.0-1.5 μg/l. Weight gain (WG) and feed efficiency (FE) were higher (P < 0.05) in fish fed diets with 4.37 and 6.56 mg Cu/kg diet than those in fish fed diets with ≥ 11.03 and ≤ 1.66 mg Cu/kg diet. Hepatic thiobarbituric acid reactive substances (TBARS) value was lowest in fish fed diets with 4.37 and 6.56 mg Cu/kg diet, intermediate in fish fed diets with 11.03 and ≤ 1.66 mg Cu/kg diet, and highest in fish fed the diet with 20.05 mg Cu/kg diet. Differences between each of the three groups were statistically significant (P < 0.05). Both hepatic copper-zinc superoxide dismutase (Cu-Zn SOD) and plasma ceruloplasmin activities in fish fell into four groups. Cu-Zn SOD value was highest in fish fed the diet with 6.56 mg Cu/kg diet, second highest in fish fed the diet with 8.97 mg Cu/kg diet, intermediate in fish fed the diet with 20.05 mg Cu/kg diet, and lowest in fish fed the diet with 0.11 mg Cu/kg diet; plasma ceruloplasmin was highest in fish fed the diet with 6.56 mg Cu/kg diet, second highest in fish fed diets with 2.41, 4.37 and 8.97 mg Cu/kg diet, intermediate in fish fed diets with ≥ 11.03 mg Cu/kg diet, and lowest in fish fed diets with ≤ 1.66 mg Cu/kg diet. All values in each of the four groups were significantly different from the values of three other groups (P < 0.05). Analysis by broken-line regression of WG, hepatic SOD activity and TBARS value and linear regression of whole-body Cu retention of the fish indicate that the adequate dietary Cu concentration in growing grouper is about 4-6 mg Cu/kg diet.     

Physiological changes in rainbow trout held under crowded conditions and fed diets with different levels of vitamins E and C and highly unsaturated fatty acids (HUFA)

Rainbow trout (Oncorhynchus mykiss) maintained in crowded (100 kg m^− 3) and uncrowded (20 kg m^− 3) conditions were fed 42 days with five experimental diets having different levels of vitamin E (25.6 and 275.6 mg kg diet^− 1), C (0 and 1000 mg kg diet^− 1) and HUFA (highly unsaturated fatty acids, 12.5 and 320.5 g kg diet^− 1): −E−HUFA, −E+HUFA, +E−HUFA, +E+HUFA, −C+E+HUFA. Cortisol, plasma metabolites, tissue glycogen, fish composition, and tissue fatty-acid profile were evaluated at the end of the experimental period. In general, no changes in cortisol levels were associated with crowding, although +E+HUFA and −C+E+HUFA fish showed higher levels (mean ± SE, 55.5 ± 11.1 and 78.0 ± 11.3 ng ml^− 1) as a consequence of a possible interaction between chronic crowding and diet composition. Protein and glucose con-centration in plasma displayed no effect of crowding, but liver glycogen showed a general tendency to decrease in −E−HUFA, −E+HUFA, +E−HUFA, +E+HUFA, −C+E+HUFA crowded groups (70.2 ± 2.1, 52.1 ± 2.5, 73.4 ± 7.4, 91.7 ± 3.3, 74.2 ± 8.4 mg g^− 1 tissue, respectively) compared to uncrowded groups (108.9 ± 14.2, 82.7 ± 8.8, 92.4 ± 10.7, 99.1 ± 10.0, 103.5 ± 15.6 mg g^− 1 tissue, respectively), thus proving significant in −E+HUFA fish. Variations in total lipids, triglycerides, total cholesterol and HDL as well as LDL cholesterol in plasma were manifested under crowding conditions, displaying a certain influence of vitamin E and HUFA dietary content. Final body composition, in general, showed no change attributable to fish density, but some differences associated with diet composition were found in lipid and moisture percentages of crowded fish. Liver and muscle fatty-acid profile revealed a clear effect of the dietary lipid source that was more evident in muscle than in liver at normal fish density, and in some cases this effect was modulated by dietary vitamin E and C content and fish-culture conditions.     

Effect of dietary lysine and methionine supplementation on growth, nutrient utilization, carcass compositions and haemato-biochemical status in Indian Major Carp, Rohu (Labeo rohita H.) fed soy protein-based diet

An 8-week feeding trial was conducted in flow through system to examine the effects of dietary supplementation of lysine and methionine on growth, nutrient utilization, haemato-biochemical status and carcass compositions in Indian major carp, rohu, Labeo rohita fingerlings (average weight 6.32 ± 0.06 g). Four experimental soy protein-based diets D ₀ (without lysine or methionine supplementation), D ₁ (lysine supplementation alone), D ₂ (methionine supplementation alone) and D₃ (both lysine and methionine supplementation) were fed to triplicate groups. l -Lysine and dl -methionine were added to the diets containing 550 g kg⁻¹ soybean meals at 4 and 7 g kg⁻¹ of dry diet respectively. Significant higher weight gain, specific growth rate (SGR), protein efficiency ratio (PER), dry matter retention, nitrogen retention, total ash retention, whole carcass protein, haemoglobin concentration, haematocrit value, total erythrocytic count, total leucocytic count, plasma glucose and plasma total protein and lower FCR, per cent lipid retention and whole body moisture content were observed in fish fed soya protein-based diet supplemented with both lysine and methionine than that of fish of other dietary groups at the end of 8 weeks feeding trial. Although fish fed diet supplemented with either methionine or lysine did not show any significant differences of growth performances, feed utilization, carcass composition and haemato-biochemical status, fish of both of these dietary groups showed significantly better growth performances, feed utilization, carcass composition and haemato-biochemical status than that of fish fed diet without lysine and methionine supplementation.     

Determination of Dose Rate of Florfenicol in Feed for Control of Mortality in Channel Catfish Ictalurus punctatus (Rafinesque) Infected with Edwardsiella ictaluri, Etiological Agent of Enteric Septicemia

–A dose titration study was conducted to determine the appropriate dosage of florfenicol in feed to control mortality in channel catfish Ictalurus punctatus associated with enteric septicemia of catfish caused by Edwardsiella ictaluri. Six tanks (20 fish/ tank) were assigned to each of the following treatment: 1) not challenged with E. ictaluri and fed unmedicated feed; 2) challenged with E. ictaluri and fed unmedicated feed; 3) challenged and fed 5-mg florfenicol/kg body weight (kg bw); 4) challenged and fed 10-mg florfenicol/kg bw; or 5) challenged and fed 15-mg florfenicol/kg bw. Treatment was initiated the day after inoculation, and feed was administered by hand at 2.5% body weight for 10 consecutive days. Feeding activity was scored for all groups and was noted to be significantly less than the challenged, unmedicated group. Cumulative mortality in the challenged untreated group was 60%. The mortality in the unchallenged untreated group was 0%, and in die 5-, 10-, 15-mg florfenicol/kg bw group was 2.5%, 0.8%, and 2.5%, respectively. The mortality in each challenged, treated group and the non-challenged control group was significantly less than the challenged, unmedicated controls (P < 0.0001 for each contrast). There were no pairwise statistically significant contrasts among the florfenicol treated groups and the non-challenged control group. All 600 fish in the study were necropsied, cultured for bacteria, and examined by gross pathology. No specific lesions that could be associated with the antibiotic were observed. The efficacy of the 10 mg/kg dosage was confirmed in a separate dose confirmation study. In this study, fish in 30 tanks (20 fish/ tank) were infected with E. icraluri by immersion. Two days post-inoculation, fish in 15 tanks were hand-fed unmedicated feed, and 15 tanks were hand-fed medicated feed at a dosage of 10-mg florfenicol/kg bw at 2.5% body weight for 10 d. Feeding activity was scored and was noted to be significantly less than the challenged, unmedicated group. Cumulative mortality in the florfenicol group (14%) was significantly less than cumulative mortality in the untreated group (87.3%) (P < 0.0001). All 600 fish were submitted for bacterial culture, necropsied. and examined for gross pathology, and once again, no specific lesions that could be associated with the antibiotic were observed. The minimum inhibitory concentration of florfenicol against E. ictaluri in both studies was 0.25 ug/mL. Florfenicol was palatable, safe, and efficacious for control of mortality due to infection by E. ictaluri in catfish.     

Assessing the implications of variability in the digestible protein and energy value of lupin kernel meals when fed to rainbow trout, Oncorhynchus mykiss

A series of studies were designed to examine the degree of variability in the digestibility of protein and energy from lupin (Lupinus angustifolius) kernel meals when fed to rainbow trout (Oncorhynchus mykiss) and the potential implications of this variability. The digestibility of protein and energy from 10 different varieties of lupin kernel meal was assessed where the test ingredient comprised 30% of each test diet. Digesta was collected using faecal stripping techniques. Digestible protein value ranged from 331 to 508 g/kg DM and digestible energy values ranged from 10.6 to 13.3 MJ/kg DM. To examine the implications of variability in digestible protein and energy value, two lupin kernel meals from the extremes of the protein digestibility range (Lupin-1: AD_N ~ 70% and Lupin-2: AD_N ~ 100%) were chosen for assessment in two growth studies. Soybean meal and a reference diet with fishmeal as the only protein source were also included in the study. In the first growth experiment the test ingredients were included at equal concentrations (40%) in protein-limiting diets (350 g protein/kg DM) and fed at either of two ration levels (restricted and satiety). Diets were formulated on a crude basis so as to place the test variable on the variability in digestible protein value of the diets. In the restricted-fed treatments growth of fish fed the reference diet was highest, but not significantly better than lupin-H. Growth of fish fed the lupin-L diet was significantly poorer than both the reference and lupin-H diets, but not poorer than the soybean diet. The growth responses observed from this experiment clearly showed that the differences in feed intake and/or digestible protein value could be demonstrated in terms of significant differences in growth outcomes. In a second growth study high-nutrient dense extruded diets (400 g protein/kg and 23.5 MJ/kg) were prepared with a more practical level of 25% inclusion of the same test materials. Again the diets were formulated on crude basis so as to place the test variable on the variability in digestible protein and energy value of the diets. Growth of fish restrictively fed the lupin-H diet was highest, but not significantly better than the soybean, reference or lupin-L treatments restrictively fed. Growth of fish satietal fed the soybean diet was significantly poorer than the reference and lupin-H diets, but not compared to the lupin-L diet. The growth responses observed from this experiment showed that the differences in digestible protein and energy value could not be demonstrated in terms of significant differences in growth outcomes, and that feed intake variability and excess nutrient supply masked the effect of this variability; particularly at the satietal feed intake levels.     

Pharmacokinetics and the active metabolite of enrofloxacin in Chinese mitten-handed crab (Eriocheir sinensis)

The pharmacokinetics and active metabolite of enrofloxacin were estimated after single intramuscular administration (10.0 or 20.0 mg/kg body weight) to the Chinese mitten-handed crab (Eriocheir sinensis) in fresh water at 25.0 ± 1.0 °C. Levels of enrofloxacin and its metabolite ciprofloxacin in the main tissues (hemolymph, hepatopancreas, muscle, ovary and spermary) were simultaneously detected by HPLC. Enrofloxacin concentration–time profiles for the hemolymph in both tests were described by a two-compartment open model with first-order absorption. Distribution half-time (T_1/2), elimination half-time (T_1/2β), body clearance (CL/F), mean residence time (MRT_0–∞), area under the concentration–time curve from 0 to ∞ h (AUC_0–∞) and apparent volume of distribution (Vd/F), which derived from the pharmacokinetic model, were 0.427 h, 21.3 h, 0.133 l/h/kg, 60.0 h, 96.9 μg/ml/h and 4.08 l/kg, respectively, at a dose of 10.0 mg/kg body weight, and 0.216 h, 12.3 h, 0.189 l/h/kg, 85.8 h, 187 μg/ml/h and 3.35 l/kg, respectively, at a dose of 20.0 mg/kg body weight. Similarities were found between the hemolymph concentration–time curves of the two tests; for example, instant absorption process followed by the distribution phrase, and a second absorption peak at 6 h post-treatment. After intramuscular administration of 10.0 mg/kg body weight, absorption of enrofloxacin was observed in the main edible tissues (hepatopancreas, muscle, ovary and spermary), and the drug residue was the highest in the hepatopancreas, where the ‘drug sink’ phenomenon occurred. Comparative pharmacokinetics showed fast absorption, broad distribution and fast elimination of enrofloxacin in E. sinensis after intramuscular dosing. Regarding ciprofloxacin, the main active metabolite of enrofloxacin, though relatively low levels were detected in all the main tissues of the crab, its kinetics in the hemolymph in the two tests were not described by a one- or two-compartment open model.     

Dietary phosphorus requirement of juvenile Atlantic salmon, Salmo salar L.

The objective of this study was to determine the dietary phosphorus (P) requirement of juvenile Atlantic salmon, Salmon salar L. Triplicate groups of fish (mean initial weight 1.4 g) were fed semipurified, casein-gelatine-based diets containing one of five levels of P (4, 8, 10, 15 and 25 g kg⁻¹) from Ca(H₂PO₄)₂·H₂O, or a commercial feed (17 g kg⁻¹ P) for 9 weeks. Weight gains did not differ significantly among treatment groups fed the experimental diets but were slightly less than gains in fish fed the commercial feed. Feed efficiency (wet weight gain/dry feed consumed) was similar in all groups, averaging 1.45. Availability of dietary P, estimated from apparent retention and apparent digestibility, was 86%. Whole-body P concentrations declined in fish fed diets containing less than 10 g kg⁻¹ P. Fitting a logistic curve to dietary P vs. whole-body P concentrations indicated that a minimum of 11 g kg⁻¹ dietary P (9 g kg⁻¹ digestible P) was required by juvenile Atlantic salmon to maintain whole-body P concentrations at initial levels. Calculation of a dietary requirement using a simple factorial model which incorporated measurements of P availability, feed efficiency and normal whole-body P concentration indicated that the dietary requirement was approximately 10 g kg⁻¹. The dietary requirement established in this study (10–11 g kg⁻¹) is higher than previously reported for Atlantic salmon or other fishes. Possible reasons for the wide range of reported dietary P requirements in fishes are discussed.     

Effect of Dietary Protein Concentration and Feeding Rate on Weight Gain,Feed Efficiency,and Body Composition of Pond-Raised Channel Catfish Ictalurus punctatus1

Two experiments were conducted in earthen ponds to evaluate the effect of dietary protein concentration and feeding rate on weight gain, feed efficiency, and body composition of channel catfish. In Experiment 1, two dietary protein concentrations (28% or 32%) and four feeding rates (≤ 90. ≤ 112, ≤ 135 kg/ha per d, or satiation) were used in a factorial arrangement. Channel catfish Ictalurus punctatus fingerlings (average size: 27 g/fish) were stocked into 0.04-ha ponds at a rate of 24,700 fish/ha. Fish were fed once daily at the predetermined maximum feeding rates for 282 d (two growing seasons). In Experiment 2, three dietary protein concentrations (24, 28, or 32%) and two feeding rates (≤ 135 kg/ha per d or satiation) were used. Channel catfish (average size: 373 g/fish) were stocked into 0.04-ha ponds at a rate of 17,300 fish/ha. Fish were fed once daily for 155 d. In both experiments, five ponds were used for each dietary treatment. Results from Experiment 1 showed no differences in total feed fed, feed consumption per fish, weight gain, feed conversion ratio (FCR), or survival between fish fed diets containing 28% and 32% protein diets. As maximum feeding rate increased, total feed fed, feed consumption per fish, and weight gain increased. There were no differences in total feed fed, feed consumption per fish, or weight gain between fish fed at ≤ 135 kg/ha per d and those fed to satiation. Fish fed the 28% protein diet had a lower percentage carcass dressout and higher percentage visceral fat than fish fed the 32% protein diet. Dietary protein concentrations of 28% or 32% had no effect on fillet protein, fat, moisture, and ash. Feeding rate did not affect FCR, survival, percentage carcass dressout, or fillet composition, except fillet fat. As feeding rate increased, percentage visceral fat increased. Fish fed at ≤ 90 kg/ha per d had a lower percentage fillet fat than fish fed at higher feeding rates. In Experiment 2, dietary protein concentration or maximum feeding rate did not affect total feed fed, feed consumption per fish, weight gain, FCR, or survival of channel catfish. Feeding rate had no effect on percentage carcass dressout and visceral fat, or fillet composition. This was due to the similar feed consumption by the fish fed at the two feeding rates. Fish fed the 24% protein diet had lower carcass dressout, higher visceral fat and fillet fat than those fed the 28% or 32% protein diet. Results from the present study indicate that both 28% and 32% protein diets provide satisfactory fish production, dressed yield, and body composition characteristics for pond-raised channel catfish fed a maximum rate of 90 kg/ha per d or ahove.     

The effect of dietary protein replacement by crystalline amino acid on growth and nitrogen utilization of turbot Scophthalmus maximus juveniles

A study was conducted to evaluate the effect of partial replacement of dietary fish meal by crystalline amino acids on growth performance, feed utilization, body composition and nitrogen utilization of turbot juveniles.

Four diets were formulated to be isolipidic (12% DM) and isonitrogenous (8% DM). A fish meal based diet was used as control. In the experimental diets, a crystalline amino acid (AA) mixture was used to partially replace fish meal, corresponding to a non-protein nitrogen content of 19, 37 and 56%, respectively (diets 19AA, 37AA and 56AA, respectively). The overall amino acid profile of the experimental diets resembled that of the whole-body protein of turbot. Each experimental diet was fed to triplicate groups of 20 fish (initial body weight of 31.8 g) twice daily to apparent satiation for 42 days. During the trial water temperature averaged 18 °C.

Final body weight, weight gain (g kg ABW^− 1 day^− 1) and specific growth rate were not different between the control and 19AA diet but significantly decreased with the increase of crystalline-AA inclusion from 19 to 56%. Feed intake and feed efficiency of fish fed the control and diet 19AA were similar and significantly higher than those of fish fed the 56AA diet. At the end of the growth trial, there were no significant differences in whole-body composition among groups. Hepatosomatic index was also unaffected by dietary treatments.

Nitrogen retention (g kg ABW^− 1 day^− 1) of fish fed the control and the 19AA diets were similar and significantly higher than that of fish fed the other diets. Expressed as a percentage of the nitrogen intake, N retention was significantly higher with the control than with the 37AA and 56AA diets.

Daily ammonia excretion (mg kg ABW^− 1 day^− 1) of fish fed the control diet was significantly higher than that of fish fed the 37AA and 56AA diets, while daily urea excretion (mg kg ABW^− 1 day^− 1) did not significantly differ among treatments. Non-fecal nitrogen (ammonia + urea) excretion (mg kg ABW^− 1 day^− 1) was significantly higher for fish fed the control diet than in those fed the 37AA and 56AA diets. However, as percent of N intake, ammonia excretion and non-fecal N excretion were significantly higher in fish fed the 56AA diet than in those fed the control and 19AA diets.

Specific activity of glutamate dehydrogenase, alanine and aspartate aminotransferases did not significantly differ among experimental groups.

In conclusion, in diets with an overall amino acid profile resembling that of the whole-body protein of turbot, crystalline-AA may replace 19% of dietary protein without negatively affecting growth performances or feed utilization efficiency. However, higher protein replacement levels of protein-bound-AA by crystalline-AA severely depressed growth performance.     

Pyridoxine Requirement of Fingerling Red Hybrid Tilapia Grown in Seawater

Red hybrid tilapia (Oreochromis mossambicus × 0. niloticus) fingerlings were fed purified diets supplemented with pyridoxine hydrochloride at levels of 0, 3, 6, 12, 24, and 48 mg/kg diet for 10 weeks. Fish fed the diet without pyridoxine supplementation developed abnormal neurological signs, anorexia and convulsions followed by muscle spasms and lethargy after 9 days. These conditions progressed rapidly, and heavy mortality occurred at the end of week 2. Severe caudal fin erosion and mouth lesions were observed during the 3rd week. None of these symptoms were seen in fish fed pyridoxine-supplemented diets. At the end of 14 days, fish fed the pyridoxine-deficient diet had the lowest weight gain and poorest feed conversion (P < 0.01). Hematocrit values measured at the end of weeks 2, 6, and 10 were also consistently lower for fish on this treatment. Fish fed pyridoxine-supplemented diets for 10 weeks did not differ with regard to weight gain, feed conversion, and hematocrit. Histological study of various tissues revealed no apparent abnormalities in any of the treatment groups. It was concluded that 3 mg of pyridoxine/kg diet was sufficient for maximum growth, feed efficiency and survival, and prevention of various deficiency signs in red hybrid tilapia fingerlings grown in sea water.     

Replacement of fish meal by meat and bone meal in diets for large yellow croaker, Pseudosciaena crocea

A growth experiment was conducted to investigate the effects of replacement of fish meal (FM) by meat and bone meal (MBM) in diets on the growth and body composition of large yellow croaker (Pseudosciaena crocea). Six isonitrogenous (43% crude protein) and isoenergetic (20 kJ g^− 1) diets replacing 0, 15, 30, 45, 60 and 75% FM protein by MBM protein were formulated. Each diet was randomly allocated to triplicate groups of fish in sea floating cages (1.0 × 1.0 × 1.5 m), and each cage was stocked with 180 fish (initial average weight of 1.88 ± 0.02 g). Fish were fed twice daily (05:00 and 17:30) to apparent satiation for 8 weeks. The water temperature ranged from 26.5 to 32.5 °C, salinity from 32 to 36‰, and dissolved oxygen content was approximately 7 mg l^− 1 during the experimental period. Survival decreased with increasing dietary MBM and the survival in the fish fed the diet with 75% protein from MBM was significantly lower than other groups (P < 0.05). There were no significant differences in specific growth rate (SGR) among the fish fed the diets with 0 (the control group), 15, 30 and 45% protein from MBM. However, SGR in the fish fed the diets with 60 and 75% protein from MBM were significantly lower than other groups (P < 0.05). No significant differences in feeding rate were observed among dietary treatments. The digestibility experiment showed that the apparent digestibility coefficients (ADC) of dry matter, protein, lipid and energy of MBM were significantly lower compared with those of FM (P < 0.05). Essential amino acid index was found to be correlated positively with SGR in the present study, suggesting that essential amino acid balance was important. Body composition analysis showed that the carcass protein and essential amino acids were not significantly affected by dietary MBM. The lipid and n-3 highly unsaturated fatty acid (n-3 HUFA) in fish muscle, however, significantly decreased with increasing dietary MBM. These results showed that 45% of FM protein could be replaced by MBM protein in diets of large yellow croaker without significantly reducing growth. It was suggested that the reduced growth with higher MBM was due to lower digestibility and imbalance of essential amino acids.     

Purification and partial characterization of Cu, Zn superoxide dismutase from haemolymph of Oriental river prawn Macrobrachium nipponense

The copper plus zinc superoxide dismutase (Cu, Zn-SOD) was purified from haemolymph of the Oriental river prawn, Macrobrachium nipponense and partially characterized. Partial protein precipitation in crude extract was affected by using heat treatment and (NH₄)₂SO₄ fractionated precipitation methods. Fractionation of superoxide dismutase was performed by DEAE-cellulose 32 ion-exchange chromatography and followed by CM-cellulose cation-exchange chromatography. The molecular weight of it was about 66.1 kDa, as judged by SDS polyacrylamide gel electrophoresis. The enzyme was sensitive to cyanide and H₂O₂, and contained 1.08 ± 0.14 atom of copper and 0.98 ± 0.11 zinc per subunit shown in atomic absorption spectroscopy, which revealed that purified SOD was Cu, Zn superoxide dismutase. The purified enzyme had an absorption peak of 269 nm in ultraviolet region and the enzyme remained stable at 25–45 °C within 60 min. But it was rapidly inactivated at higher temperature (50 °C). The activity of purified shrimp Cu, Zn-SOD was remained stable over the range pH 5.8–8.3. Treated with 10 mM mercaptoethanol, the enzyme activity significantly increased. However, the enzyme activity was obviously inhibited by 10 mM CaCl₂, ZnCl₂, SDS, EDTA–Na₂ and 1 mM and 10 mM K₂Cr₂O₇. The results showed that it might be a kind of EC-SOD. And it was the first report of some characterizations of this EC-SOD in M. nipponense.     

Effect of Dietary Vitamin C on Weight Gain,Tissue Ascorbate Concentration,Stress Response,and Disease Resistance of Channel Catfish Ictalurus punctatus1

Juvenile channel catfish Ictalurus punctatus (average initial weight, 6.5 g/fish) were fed twice daily to apparent satiation with practical-type diets containing 0, 50, 150, or 250 mg supplemental vitamin C/kg from L-ascorbyl-2-polyphosphate for 10 wk under laboratory conditions. At the end of the feeding period, one half of the fish were stressed for 2 h by confinement and both stressed and nonstressed fish were exposed to a virulent strain of Edwardsiella ictaluri. Weight gain and feed conversion efficiency were lower for fish fed the basal diet than those fed diets containing supplemental vitamin C. No differences were observed in weight gain and feed conversion among fish fed diets containing supplemental vitamin C. There were no differences in feed consumption and survival (prior to experimental infection) among treatments. No vitamin C deficiency signs except reduced weight gain were observed in fish fed the basal diet. Serum cortisol concentrations were higher in stressed fish than in non-stressed fish. Dietary vitamin C level had no effect on serum cortisol concentration. As dietary vitamin C increased, ascorbate concentration in serum and liver increased. Confinement stress had no effect on serum and liver ascorbate concentrations. Cumulative mortality of channel catfish 21 d subsequent to experimental infection with E. ictaluri was higher for stressed fish than for nonstressed fish. Regardless of stress or nonstress, overall mortality for fish fed the basal diet was lower than the fish fed diets containing supplemental vitamin C. There were no differences in post-infection antibody levels among treatments or between stressed and nonstressed fish. Results from this study indicate that channel catfish require no more than 50 mg/kg dietary vitamin C for normal growth, stress response, and disease resistance.     

Ration level for salmonids: I. Growth, survival, body composition, and feed conversion in Atlantic salmon fry and fingerlings

Twelve groups of Atlantic salmon (Salmo salar L.), raised in fibre-glass tanks, were fed at 12 ration levels for 7 periods, each period lasting 28 days. The basic ration level was calculated from an expected maximum growth rate, depending on fish size and water temperature. This level was defined as “level 1.00”. The experimental ration levels varied from 0.50 to 3.25 in intervals of 0.25.

During the start-feeding period there was an average survival rate of 95%. After the remaining 6 periods the group which was fed least had a survival rate of 48%. The other groups had an average survival rate of 81%. In all 7 periods, increasing the ration levels from 0.50 to 1.00 resulted in increased growth. A further increase in ration level did not result in extra growth. The weight distribution of the fingerlings was bimodal, with the majority of fish in the scantiest fed groups being in the lower mode. The majority of the fish in the adequately fed groups were distributed in the upper mode.

The water temperature varied from 10 to 17°C, and the thermal sum was 2430 day-degrees. The average final weight of the fish which received ration levels from 1.00 to 3.25 was 28.3 g, while the fish on the scantiest ration weighed only 9.6 g at the end of the study. The feed conversion rate, which was 0.9–1.0 kg dry feed/kg growth for the two underfed groups, ranged from 1.0 to 3.0 in the other groups. The chemical composition of the fish varied according to fish size and ration level.