Urea in feeds for sea water farmed Atlantic salmon: effect on growth, carcass quality and outbreaks of winter ulcer

The main objective of the present study was to evaluate whether dietary supplementation of urea might reduce the incidence of winter ulcer in sea water-farmed Atlantic salmon. Salmon destined to be S0 smolt were fed with a urea-supplemented diet (0 or 20 g kg⁻¹ urea) over an 8-week period prior to sea water transfer and were then fed supplemented diet (0, 5, 10 or 20 g kg⁻¹ urea) during the first and second winters in the sea. During the first winter positive relationships between dietary urea and plasma urea and between plasma urea and plasma osmolality were observed. Further, plasma osmolality displayed a negative relationship to mortality. Of the salmon that died during the first winter in the sea 90% had one or more skin ulcers. Both during the first and second winter there were fewer salmon with ulcer among fish fed with the diets supplemented with urea. Salmon fed with 20 g kg⁻¹ urea tended to have higher percentage water in the muscle. Mortality and incidence of salmon with ulcer seemed to relate to plasma osmolality amongst fish fed on diets that differed in levels of urea supplementation, suggesting that an osmotic imbalance may contribute to the development of winter ulcer in farmed salmon. Salmon fed with 20 g kg⁻¹ urea showed significantly greater body weight during the second winter in sea. Fish killed without prior starvation had significantly higher level of muscle urea in the 20 g kg⁻¹ urea group compared with fish fed with the unsupplemented diet. However, a 13-day starvation period reduced urea content in the muscle to the level of the control. No effects of dietary urea supplementation on the sensory quality of market size Atlantic salmon were observed.     

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.     

Digestibility of diets with precooked rye or wheat by Atlantic salmon, Salmo salar, L.

Four extruded diets, differing in grain supplementation, were fed to triplicate groups of Atlantic salmon ( Salmo salar , L.) with a mean weight of 0.5 kg in a digestibility trial. The diets contained 100 or 150 g kg⁻¹ of precooked rye or wheat, replacing fish meal. There were no significant differences in apparent digestibility coefficients (ADC) of protein, fat or starch which could be related to dietary carbohydrate source or inclusion level. The ADC of dry matter and energy were higher for the diets with wheat than for those with rye, and higher for the diets with wheat than for those with rye, and higher for the diets with 100 g precooked grain kg⁻¹ than for those with 150 g kg⁻¹. The mean ADC of starch was 52% for rye, and 53% for wheat.     

Supplementing copper to a fish meal based diet fed to Atlantic salmon parr affects liver copper and selenium concentrations

The present experiment was conducted to study growth and tissue responses in Atlantic salmon, Salmo salar L., fed a fish meal based diet supplemented with copper (Cu). The findings of the experiment were used to evaluate the need for dietary Cu supplementation. Atlantic salmon parr, initially weighing ≊ 7.5 g, were randomly distributed among 10 tanks, with 300 fish in each tank. Duplicate groups of fish were fed a fish meal based diet containing 3.5 mg Cu kg⁻¹, or this diet supplemented with 5, 10, 50 or 100 mg Cu kg⁻¹ (as CuSO₄*5 H₂O) for 12 weeks. Growth was recorded and blood haemoglobin measured. The Cu concentrations in whole body, liver, serum and selected muscle samples were measured, as was liver selenium (Se) concentration.
There were no difference in growth among the dietary treatments. There were, however, significant differences among the dietary groups in liver Cu and Se concentrations. The fish fed the diet supplemented with 5 mg Cu kg⁻¹ had increased liver Cu concentration compared with the other groups. Similar trends were found for serum Cu concentration and whole-body Cu concentration, but these effects were not significant. Liver Cu and Se concentrations were positively correlated and liver Se concentrations were inversely correlated to dietary Cu concentration, confirming an interaction between these two elements in salmon.
There may be a positive effect of a modest Cu supplementation level, and we suggest that a small amount of Cu (5–10 mg kg⁻¹) should be added to fish meal based diets.     

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.     

Effect of dietary L-carnitine supplements on growth and body composition of fingerling rohu, Labeo rohita (Hamilton)

Rohu, Labeo rohita (Ham.), fingerlings (average wt 3.38 g) maintained in 25 m² cement tanks were fed fish-meal-based, 300 g kg⁻¹ protein diets containing different levels (0, 0.25, 0.5, 0.75 and 1.0 g kg⁻¹) of L -carnitine in triplicate over a period of 126 days. Fish that received 0.5 g kg⁻¹ carnitine showed significantly higher growth than those fed the basal diet or the rest of the carnitine diets. Fat digestibility, food conversion efficiency and protein efficiency ratio were better in carnitine-fed fish; however, viscerosomatic and hepatosomatic indices decreased. Muscle proximate composition was affected as a result of carnitine treatment. The results of the present study demonstrate a positive effect of carnitine on the growth and body composition of rohu.     

Effect of dietary lipid level on muscle composition in Atlantic salmon Salmo salar

This study was conducted to determine the effects of feeding increasing lipid concentrations (310, 380 and 470 g kg^–1 lipid on dry weight) in diets based mainly on herring byproducts to Atlantic salmon Salmo salar . The diets were isonitrogenous, varying in dietary lipid content at the expense dietary starch. Average fish weight increased from 1.2 kg in April to 2.2–2.7 kg at the end of the feeding trial in September. Significantly greater growth was found in fish fed either the 380 g kg⁻¹ or the 470 g kg⁻¹ lipid diets compared with the 310 g kg⁻¹ lipid diet. Muscle lipid content increased in all dietary groups on a wet weight basis from 7.7 ± 1.4% to 12 ± 3% in salmon fed the 310 g kg⁻¹ lipid diet, and to 16 ± 2% in salmon fed the 380 g kg⁻¹ and 470 g kg⁻¹ lipid diets. In fish of similar weight there was a positive correlation between dietary lipid and muscle lipid concentrations. Low concentrations of muscle glycogen were detected in fish fed each of the diets, while muscle vitamin E concentrations slowly decreased as muscle lipid increased. Muscle fatty acid composition reflected dietary fatty acid profiles, containing similar percentages of total saturated, monoenic and n-3 fatty acids (20:5n-3 and 22:6n-3) in fish from all dietary treatment groups. However, a higher ratio of n-3/n-6 was found in muscle from fish fed the 470 g kg⁻¹ lipid diet compared with the other two groups. Blood chemistry values varied somewhat, but all values were within normal ranges for Atlantic salmon of these sizes.     

Use of full-fat winged bean Psophocarpus tetragonolobus seed meal as a protein feedstuff in fish-meal free diets for African catfish Clarias gariepinus

Mature winged bean Psophocarpus tetragonolobus seeds were quick-cooked and the full-fat meal derived was used to completely replace menhaden fish meal as a dietary protein source for the African catfish Clarias gariepinus . Five dry practical diets (400 g crude protein kg⁻¹ and 17.5 kJ gross energy g⁻¹ dry diet) containing menhaden fish meal (diet 1) or winged bean meal with or without graded levels of supplemental L -methionine (diets 2, 3, 4 and 5; 0, 5, 10 and 15 g kg⁻¹, respectively) were fed to catfish fingerlings (5.8  +  1.2 g) for 70 days. Weight gain, growth rate, feed conversion and protein utilization by catfish fed a winged bean meal diet without L -methionine supplementation (diet 2) was inferior ( P  > 0.05) to that in catfish fed the other diets, where performance differed nonsignificantly. Carcass protein of catfish was lower ( P  < 0.05) while liver protein was higher ( P  < 0.05) in catfish fed the winged bean meal diet without methionine supplementation. Results suggest that winged bean meal cannot replace fish meal as a protein source in catfish diets except with a minimum supplementation with 5 g L -methionine kg⁻¹ diet.     

Optimal dietary lipid level of silver barb, Puntius gonionotus fingerlings in relation to growth, nutrient retention and digestibility, muscle nucleic acid content and digestive enzyme activity

Five iso-nitrogenous (300 g kg⁻¹ diet) purified diets with graded level of lipid at 40 (D-1), 60 (D-2), 80 (D-3), 100 (D-4) and 120 (D-5) g kg⁻¹ diet were fed to Puntius gonionotus fingerlings for 90 days to determine their dietary lipid requirement. Two hundred and twenty-five fingerlings (average weight 2.34 ± 0.03 g) were equally distributed in five treatments in triplicate groups with 15 fish per replicate. Fifteen flow-through cement tanks of 100 L capacity with a flow rate of 0.5 L min⁻¹ were used for rearing the fish. Specific growth rate (SGR), feed conversion ratio (FCR), nutrient digestibility, retention, digestive enzyme activity, RNA : DNA ratio and whole-body composition were considered as the response parameters with respect to dietary lipid levels. Maximum SGR and minimum FCR with highest RNA : DNA ratio, whole-body protein content and digestive enzyme activity was found in D-3 group fed with 80 g kg⁻¹ diet lipid. Nutrient digestibility was similar in all the groups irrespective of the dietary lipid level. Maximum protein and energy retention was recorded at 80 g kg⁻¹ dietary lipid fed group. However, from the second-order polynomial regression analysis, the maximum growth of P. gonionotus fingerlings was found at 96.9 g lipid kg⁻¹ diet.     

Feed intake and growth of Atlantic salmon, Salmo salar L., fed diets supplemented with oxytetracycline and squid extract

This study examined the long-term effects of a feeding deterrent, oxytetracycline (OTC), and a feeding stimulant, squid extract, on feed intake, growth and dry matter (DM) digestibility in Atlantic salmon, Salmo salar L. Fish were fed one of four diets for 9 weeks: 1. commercial feed formulation (basic); 2. BM (basic plus 20 g kg⁻¹ OTC); 3. BMS (BM plus 10 g kg⁻¹ squid extract); 4. BS (basic plus 10 g kg⁻¹ squid extract). OTC initially reduced the palatability of the feed, but the fish seemed to become accustomed to the taste of OTC over time. Addition of squid extract to the medicated feed (BMS) seemed to mask the aversive taste of OTC, but the effect on feed consumption was of short duration. Addition of squid extract to the basic feed (BS) had no significant effect on feed intake, growth or feed digestibility. The growth of fish fed medicated diets (BM and BMS) was depressed, probably as a consequence of reduced feed digestibility. The two additives led only to temporary changes in feed acceptability, but both growth and DM digestibility were affected by OTC. Thus, we suggest that short-term studies may be inadequate to test whether deterrent or stimulant properties of feed ingredients are of practical importance in feed formulation.     

Carbohydrate level in the diet of silver barb, Puntius gonionotus (Bleeker) fingerlings: effect on growth, nutrient utilization and whole body composition

Five iso-nitrogenous (300 g crude protein kg⁻¹ diet) semi-purified diets with graded levels of carbohydrate at 220 (D-1), 260 (D-2), 300 (D-3), 340 (D-4) and 380 (D-5) g kg⁻¹ diet were fed ad libitum to Puntius gonionotus fingerlings (average weight 0.59±0.01 g) in triplicate groups (20 fish replicate⁻¹) for a period of 90 days to determine the effect of the dietary carbohydrate level on the growth, nutrient utilization, digestibility, gut enzyme activity and whole-body composition of fish. Fifteen flow-through cement tanks of 100 L capacity with a flow rate of 0.5 L min⁻¹ were used for rearing the fish. The maximum weight gain, specific growth rate, protein efficiency ratio, RNA:DNA ratio, whole-body protein content, protease activity, protein and energy digestibility and minimum feed conversion ratio (FCR) were found in the D-2 group fed with 260 g carbohydrate kg⁻¹ diet. The highest protein and energy retention was also recorded in the same group. However, from the second-order polynomial regression analysis, the maximum growth and nutrient utilization of P. gonionotus fingerlings was 291.3–298.3 g carbohydrate kg⁻¹ diet at a dietary protein level of 300 g kg⁻¹ with a protein/energy (P/E) ratio of 20.58 −20.75 g protein MJ⁻¹.     

Effect of fermentation on the nutritive value of sesame seed meal in the diets for rohu, Labeo rohita (Hamilton), fingerlings

Six isonitrogenous (350 g kg⁻¹ crude protein) and isoenergetic (17573 kJ kg⁻¹) experimental diets incorporating raw and fermented sesame ( Seasamum indicum ) seed meal at 200, 300, and 400 g kg⁻¹ into a fishmeal based diet were fed to rohu Labeo rohita fingerlings for 60 days and the growth performance and feed utilization efficiency of the fish was studied. The antinutritional factor phytic acid, from raw sesame seed meal, could be reduced below detection limit by fermentation with lactic acid bacteria ( Lactobacillus acidophilus ). Fermentation of the oilseed meal resulted in reduction of the tannin content from 20 to 10 g kg⁻¹. In terms of growth response, feed conversion ratio and protein efficiency ratio, a diet containing 400 g kg⁻¹ fermented sesame seed meal resulted in a significantly ( P  < 0.01) best fish performance. In general, growth and feed utilization efficiencies of fish fed fermented sesame seed meal diets were superior to those fed raw oilseed meal diets. Apparent protein digestibility (APD) values decreased with increasing levels of raw oilseed meal. APD was, however, significantly ( P  < 0.01) higher at all levels of incorporation of fermented sesame seed meal, while diets containing raw oilseed meal resulted in poor protein and lipid digestibility. Carcass protein and lipid contents of fish fed fermented sesame seed meal diets increased with increasing level of incorporation, being highest with 400 g kg⁻¹ fermented oilseed meal-containing diet. The results showed that sesame seed meal may be incorporated in carp diets up to 200 g kg⁻¹ and 400 g kg⁻¹ in raw and treated (fermented) forms respectively.     

Antioxidant status and immunity in Atlantic salmon, Salmo salar L., fed semi-purified diets with and without astaxanthin supplementation

Abstract. Parr of Atlantic salmon, Salmo salar L., were fed semi-purified diets supplemented with 60 mg astaxanthin kg⁻¹ and without astaxanthin supplementation for 10.5 months. The astaxanthin concentration in the non-supplemented diet was analysed to be 6–0 mg kg⁻¹ The growth of the fish was significantly affected by the dietary treatment. The mean daily weight gain in the groups fed the supplemented diets was 0.39% throughout the period, whereas the groups fed the non-supplemented diet had a mean daily weight gain of 0.18%. The dry matter and fat content were significantly higher in fish fed the supplemented diet. The astaxanthin concentration in the muscle of fish fed the astaxanthin-supplemented diet was 2–7 mg kg⁻¹ versus 0–3 mg kg⁻¹ in the non-supplemented fish. Antioxidant vitamins in the muscle (retinol, α-tocopherol) and liver (retinol, α-tocopherol and ascorbic acid) were two to 20 times higher in the fish in the supplemented group, suggesting antioxidant sparing effects. Blood haemoglobin and immunological parameters tended to be higher in fish fed the low astaxanthin diet although the difference was not significant. However, the resistance to challenge with Aeromonas salmonicida was higher in fish fed the astaxanthin supplemented diet. This may be due to a difference in weight at the time of the challenge which, in turn, may have influenced the body composition and smoltification of the fish. A relationship between dietary astaxanthin concentration and antioxidant status in both liver and muscle was observed, and this may also have had an influence on the observed differences in blood parameters and disease resistance.     

Dietary menadione nicotinamide bisulphite (vitamin K3) does not affect growth or bone health in first-feeding fry of Atlantic salmon (Salmo salar L.)

The aim of the present study was to elucidate if increasing levels of added vitamin K in the feed influenced fish growth, health or the incidences of bone deformities in Atlantic salmon ( Salmo salar L.) from onset of start feeding to ∼100 g in freshwater. Duplicate groups of Atlantic salmon fry (∼0.20 g) were fed eight levels (0, 2.5, 5, 7.5, 10, 15, 20 and 50 mg menadione kg⁻¹) of the vitamin K derivate menadione nicotinamide bisulphite (MNB) in a regression design for 28 weeks. All fish maintained high growth rates throughout the experiment, and showed no significant differences in specific growth rate, condition factor, whole body proximate analysis, blood coagulation time, vertebra morphology or mechanical properties of vertebrae. We found a dose-response between whole body vitamin K concentration and the dietary MNB supplementation level. Analysis of liver γ-glutamylcarboxylase activity revealed significant dose-dependent differences between groups given the 0, 10 and 50 mg MNB kg⁻¹ diets. In conclusion, Atlantic salmon seems to require low levels of dietary vitamin K, and the amount of vitamin K found naturally in the presently used feed ingredients may be enough to maintain optimal growth, health and bone strength in Atlantic salmon fry from start feeding.     

Effects of dietary phosphorus level on non-faecal phosphorus excretion from yellowtail (Seriola quinqueradiata Temminck & Schlegel) fed purified and practical diets

Non-faecal phosphorus (P) was determined for large yellowtail to estimate a minimum available P requirement (Experiment  1) and to justify inorganic P supplementation in a fish meal-based diet (Experiment 2). In Experiment 1, purified diets with incremental P concentrations were fed to yellowtail (mean weight 917 g) at a feeding rate of 1.5% of body weight. The peaks of non-faecal P excretion appeared 5–6 h after feeding in fish fed more than 4.5 g available P kg⁻¹ dry diet. Broken-line analysis indicated that the minimum available P requirement was 4.4 g kg⁻¹ dry diet. In Experiment 2, a purified diet (PR) containing 6.5 g available P kg⁻¹ and a fish meal-based diet with (F1) and without (F0) additional phosphorus were fed to yellowtail (mean weight 1.1 kg) at 1.5% (PR) and 2% (F0 and F1) feeding rates respectively. There was no significant difference in P excretion between fish fed the F0 (5.5 g soluble P kg⁻¹ dry diet) and the PR diet. However, significantly higher (34.5%) amounts of non-faecal P excretions (7.4 g soluble P kg⁻¹ dry diet) were found in fish fed F1 compared with the F0 diet. This suggested that there was an excess of dietary P in the F1 diet and that supplementation is not needed in fish meal-based diets for large yellowtail.     

Dietary vitamin E requirement of hybrid striped bass (Morone chrysops female × M. saxatilis male)

This study was conducted to determine the dietary vitamin E requirement of juvenile hybrid striped bass ( Morone chrysops female ×  Morone saxatilis male). Semi-purified diets supplemented with 0.2 mg Se kg⁻¹ from Na₂SeO₃ and either 0 (basal), 10, 20, 40, 60, or 80 mg vitamin E kg⁻¹ as  DL -α-tocopheryl acetate were fed to hybrid striped bass initially averaging 1.8 ± 0.1 g (mean ± SD) for 12 weeks. Fish fed the basal diet, which contained 5.8 mg α-tocopherol kg⁻¹ dry weight, were darker in colour and had reduced weight gain, as well as generally reduced haematocrit values compared with fish fed diets supplemented with vitamin E. In addition, fish fed diets containing less than 20 mg supplemental vitamin E kg⁻¹ had significantly ( P  < 0.05) reduced weight gain and feed efficiency compared with those fed diets supplemented with vitamin E at 20–80 mg kg⁻¹. Dietary supplementation of vitamin E caused incremental increases in the concentration of α-tocopherol in both plasma and liver tissues. However, hybrid striped bass fed graded levels of vitamin E did not exhibit a dose response in terms of ascorbic acid-stimulated lipid peroxidation of hepatic microsomes. Regression analysis of weight gain data using the broken-line model indicated a minimum vitamin E requirement ( ±  SE) of 28 ( ±  3) mg kg⁻¹ dry diet. Based on these data, the dietary vitamin E requirement of hybrid striped bass appears to be similar to that determined for other fish species.     

Acceptability and digestibility by tilapia Oreochromis niloticus of feeds containing cocoa husk

The acceptability, digestibility and nutrient utilization of feeds containing cocoa husk were determined for tilapia Oreochromis niloticus fingerlings reared in a recirculation system. Three semipurified isonitrogenous diets formulated to contain 0, 100 and 200 g kg⁻¹ of cocoa husk were fed to satiation three times daily. Although the feeds containing cocoa husk were acceptable to the fish, as indicated by their voracious consumption and positive weight gains, there were significant ( P  < 0.05) reductions in gross feed conversion efficiency with the cocoa husk feeds. Both apparent protein and dry matter digestibility were significantly ( P  < 0.05) reduced when 100 and 200 g kg⁻¹ cocoa husk was fed. Specific growth rates of 3.51 and 3.34% per day, resulting from the two cocoa husk feeds, respectively, were significantly ( P  < 0.05) lower than growth rates of control fish. Apparent net protein utilization was not significantly affected ( P  > 0.05) by the 100 g kg⁻¹ cocoa husk feed treatment. The consumption of the cocoa husk feeds could compensate for their low digestibility under acceptable fish yields and returns.     

Effects of dietary supplementation of alga Haematococcus pluvialis (Flotow), synthetic astaxanthin and β-carotene on survival, growth, and pigment distribution of red devil, Cichlasoma citrinellum (Günther)

Dietary carotenoids of various types and concentration can affect the pigmentation efficiency in an ornamental fish red devil, Cichlasoma citrinellum . Astaxanthin (AX) containing alga Haematococcus pluvialis , a synthetic AX, and a synthetic β-carotene (BC) were supplemented in formulated diets at two concentrations, 80 and 160 mg kg⁻¹, resulting in six pigmented diets. Formulated diet without carotenoids supplementation served as a control. These diets were fed to the fish, for 8 weeks. Astaxanthin dominated in body carotenoids deposition. Dietary BC hardly had contribution to body AX. Control fish had much lower AX content in skin, fin and muscle than fish fed pigmented diets, but had equal AX content in liver, intestine and gonad as those fish. Dietary synthetic AX had equal efficiency in depositing AX in skin and fin as natural AX but higher efficiency in gonad than natural AX. Fish fed AX supplemented at 160 mg kg⁻¹, either natural or synthetic AX, had higher AX content in skin than fish at 80 mg kg⁻¹ but had equal AX content in fin as fish at 80 mg kg⁻¹. Disregarding the treatment effects, the overall average AX content in tissue in descending order was gonad>fin≧(intestine=skin)>liver>muscle.     

Total sulphur amino acid requirement of the Indian major carp, Labeo rohita (Hamilton)

The quantitative dietary sulphur amino acid requirement of the Indian major carp, Labeo rohita (Hamilton), was determined by conducting a growth study. The experimental diets contained 400 g crude protein kg⁻¹ from casein, gelatine and supplemental crystalline amino acids. Diets containing six graded levels of methionine (3.2, 6.5, 9.0, 11.5, 14 and 16.5 g kg⁻¹) with a constant level of cystine (1.4 g kg⁻¹) were formulated and fed to triplicate groups of Labeo rohita fingerlings twice a day to satiation for 60 days. The optimum dietary requirement for methionine was estimated using the break-point regression analysis at 11.5 g kg⁻¹ of diet or 28.8 g kg⁻¹ of dietary protein. Thus the total sulphur amino acid (Met + Cys) requirement was determined to be 12.9 g kg⁻¹ of diet or 32.3 g kg⁻¹ of protein. Higher survival, specific growth rate and food conversion efficiency values were observed for fish fed the diet containing optimum levels of sulphur amino acids.     

Effects of dietary protein to metabolizable energy ratios and total protein concentrations on the performance of yellow perch Perca flavescens

Juvenile yellow perch Perca flavescens were fed semipurified diets with varying protein to metabolizable energy ratios (PME, g protein MJ⁻¹ metabolizable energy) and nutrient densities in three experiments to determine recommended dietary protein and energy concentrations. Experiment 1 fish (18.6 g) were fed diets containing 450 g crude protein kg⁻¹ dry diet and 14.5–18.8 MJ ME kg⁻¹ dry diet for 10 weeks. No differences were found in the growth of experiment 1 fish fed the different diets. Experiment 2 fish (21.9 g) were fed diets containing 15.7 MJ ME kg⁻¹ dry diet and 210–420 g crude protein kg⁻¹ dry diet for 8 weeks. Fish fed the diet containing 340 g kg⁻¹ protein (diet PME = 22) exhibited the greatest weight gain. Experiment 3 fish (27.1 g) were fed diets with a PME of 22 and varying nutrient density (yielding 205–380 g crude protein kg⁻¹ dry diet) for 8 weeks. No differences were found in the growth of experiment 3 fish. Yellow perch fed the semipurified diets exhibited increased liver fat content, liver size and degree of liver discoloration compared with fish fed a commercial fish meal-based diet. Liver changes may have resulted from high dietary carbohydrate levels. We conclude that a protein level of 210–270 g kg⁻¹ dry diet is suitable for juvenile yellow perch provided that the dietary amino acid profile and carbohydrate content are appropriate for yellow perch.