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The aim of the study was to evaluate the effects of dietary arginine (Arg) supplementation to either a plant protein-based diet or a fish meal-based diet on nitrogen (N) utilisation and ureogenesis in turbot and rainbow trout. Juvenile turbot (7.4 g) and rainbow trout (9.3 g) were fed for 12 weeks two types of diets (plant protein-based (PM) and fish meal-based (FM)) containing different levels of Arg (1.6%, 3% and 4% diet for PM diets and, 3% and 4% for FM diets). Besides, measurement of growth parameters and protein utilisation, ammonia and urea excretion rates were monitored. Plasma ammonia and urea concentrations and activities of selected enzymes of ornithine urea cycle (carbamoyl phosphate synthetase III, ornithine carbamoyltransferase and arginase) were measured. Both species fed PM-based diets had reduced growth performance compared to fish fed FM-based diets. Amino acid imbalance of the PM-based diets had a significant effect on plasma ammonia levels and ammonia excretion. Dietary Arg supplementation did not lead to any improvement in N utilisation or on ammoniogenesis. In both species, there was a linear relationship between dietary Arg and urea excretion. Our data confirm that ornithine urea cycle is incomplete in the liver and that argininolysis plays a major role in ureogenesis in both species.

Recent studies indicate that urea excretion is responsive to protein intake and that turbot, Psetta maxima, appear to differ from other species by their urea excretion pattern and levels. This study was undertaken to evaluate the influence of dietary nitrogen and arginine on ureagenesis and excretion in turbot. Juvenile turbot (29 g) were fed semi-purified diets containing graded levels of nitrogen (0–8% dry matter) and arginine (0–3% dry matter) for 6 weeks. Growth data showed that turbot have high dietary nitrogen (123 mg/kg metabolic body weight/day) and very low dietary arginine (9.3 mg/kg metabolic body weight/day) requirements for maintenance. Requirements for unit body protein accretion were 0.31 g and 0.15 g for nitrogen and arginine respectively. Post-prandial plasma urea levels and urea excretion rates showed that urea production was significantly (P

We evaluated the influence of dietary nucleic acid (NA) supplied either as an RNA extract (RNA) or as brewer's yeast (BY) on nitrogen (N) utilisation, N excretion and ureogenesis in a freshwater teleost, the rainbow trout (Oncorhynchus mykiss) and a marine teleost, the turbot (Psetta maxima). Five diets containing two levels of NA or BY were formulated for each species, and fed to juvenile rainbow trout (initial body weight (IBW): 21.7 g) and turbot (IBW: 11.8 g) over 8–10 weeks. Besides growth and N utilisation, we monitored total ammonia-N and urea-N excretion rates and measured the activities of selected enzymes (glutamate dehydrogenase, ornithine carbamoyltransferase, arginase and uricase). There was no clear N sparing effect of dietary NA or BY supplementations in either species. Feeding diets containing the RNA extract led to an almost two-fold increase in postprandial plasma urea-N and uric acid concentrations and in urea-N excretion rates. Glutamate dehydrogenase and arginase activities were decreased in fish fed NA supplemented diets. Uricase activities were inversely related to dietary NA levels. Data on N excretion and enzyme activities clearly suggest that ureogenesis is influenced by dietary NA in both species.

The incorporation of various bulk agents by substitution of an equivalent amount of the basal mixture was studied in terms of protein digestibility, growth performance and body composition in European seabass (Dicentrarchus labrax) juveniles. During the growth trial, triplicate groups of 40 seabass (mean initial weight: 7.0 g) were grown in seawater (salinity: 35; temperature: 18 degrees C) over 60 days. Fish were hand-fed, three times a day, one of seven experimental diets. Bulk agents tested at 10 or 20 % level of incorporation were silica, cellulose and a natural zeolite (chabamin). Feeding rates were adjusted in proportion to the percent dilution of the control diet without bulk incorporation. The incorporation of the bulk agents, at a 10 and 20 % level, did not affect protein digestibility or growth performance. Dietary bulk incorporation reduced feed efficiency values, particularly at the 20 % incorporation level. However, this reduction was mostly caused by the dietary nutrient dilution of the bulk-incorporated diets, rather than by a negative effect of the bulk agents as dietary ingredients. In comparison to the control treatment, bulk incorporation at 10 and 20 % level did not affect protein retention values. When compared with the control diet, 20 % bulk agent incorporation changed the evacuation profile of faeces and increased faecal egestion time.

A feeding trial was conducted with brown trout fry (initial body weight: 2 g) in order to estimate the best combination of feeding level and protein content. The factorial design consisted of feeding four dietary protein levels (47, 53, 58 and 63%) at four ration sizes (70, 85, 100 and 115% of a previous empirical reference). Fish were weighed at 21 and 42 days and at the end of the experiment that lasted 57 days. Two replicates were used for each protein×ration level combination. Diets had approximately the same energy level (about 18.5 MJ DE) and contained the same protein source with varying carbohydrate: fat ratio. Protein efficiency, estimated by productive protein value, was improved by low dietary protein level and feed restriction. Body composition was slightly but significantly affected by diet composition, with body lipid content decreasing with high dietary protein. The lowest ration (70%), even with the highest protein content, as well as the lowest protein content (47%), even with the highest feeding level, did not allow maximal growth which was nevertheless achieved with several protein content×ration size combinations. Combinations which yielded equivalent growth rates did not give the same feed efficiency, this criterion being best with 58 or 63% protein diets fed at 85% of the previous reference. Protein requirement was found to depend on feeding level; absolute requirement was estimated to be between 10 and 13 g balanced protein/kg body mass/day, while calculated absolute energy requirement was between 330 and 450 kJ DE/kg body mass/day. In these conditions, specific growth rate was of 2.7%. When compared to other fishes growing at the same rate, the absolute requirement of brown trout for protein appears to be rather low.

Resume Brown trout and rainbow trout (average weight 100 g) were reared in fresh water at 12OC under the same conditions beforc transfer of brown trout to sea water, in order to compare nitrogen utilisation in the two species. Apparent protein digestibility (ADC), nitrogen (ammonia and urea) excretion, protein productive value (PPV) and actual observed nitrogen mass balance were determined. Rainbow trout raised in fresh water had a higher growth rate (1.1 vs 0.8Yb.d-'), better food conversion ratio (0.7 vs 1.0), better ADC (91 vs 85%) and PPV (45 vs 35%) and lower ammonia excretion rates than brown trout reared in fresh water. Transfemng brown trout to sea water induced lower PPV (30%) and ammonia and urea excretion. Salinity did not rnodify metabolic efficiency in brown trout. Fat content was higher in brown trout (7.7-8.9% ww) than in rainbow trout (5.7-7.6% ww). Nitrogen mass balance indicated that compounds other than arnmonia and urea were produced in higher quantities by seawater brown trout. Behaviour, less domestication and specific ability to utilise protein could explain the differences between the two species.

Three species of marine fish, sea bass, sea bream and turbot, and two salmonids, rainbow trout and brown trout, were raised under similar feeding and environmental conditions in order to compare their nitrogen utilisation. Apparent digestibility of protein, ammonia and urea excretion patterns, plasma ammonia and urea concentrations and liver arginase activities were measured. No differences in protein digestibility were noticed among the five species. Ammonia and urea losses were quantitatively similar in all species, except in turbot, in which ammonia production was significantly lower. Ammonia excretion patterns were linked to ingested nitrogen and showed no inter-species differences. Conversely, urea excretion patterns were specific in turbot and sea bream. Plasma urea levels were higher in marine fish than in salmonids, with the highest values being reached in turbot. Some specificity with regard to liver arginase was also detected in the turbot. Turbot demonstrated some metabolic characteristics that could be connected with its elevated position in the phylogeny of fish.

Laboratory experiments on juvenile turbot. Scophthalmus maximus (L.), were carried out under controlled temperature (12°C) and feeding regimes in a flow-through system. Monitoring of total ammonia nitrogen (TAN) and urea nitrogen (Urea-N) was performed through continuous sampling of the effluent sea water. The effects of ingested nitrogen levels on TAN and Urea-N daily and hourly excretion rates were studied. Strong relationships were found between ingested nitrogen, and both TAN and Urea-N excretion for both daily and hourly maximum excretion rates. Turbot showed a low metabolic activity, confirmed by low excretion levels. Daily patterns for TAN and Urea-N production were different, suggesting specific physiological phenomenon for urea excretion mechanisms. The question of whether turbot are partly ureotelic or ureogenic is underlined.

The protein requirement of brown trout of INRA DC 87 strain was studied by feeding diets containing graded levels of protein. These diets were formulated to be isoenergetic on a digestible energy basis and contained protein from 38 to 65%. The fish were 1.15 g triploid fry reared in stream water. Triplicates of 300 fish per replicate were used for each diet. The fish were fed for 52 days a ration which was modified every 2 weeks according to biomass, but the actual overall ration corresponded to excess feeding. Proximate analyses were performed on whole body and epaxial muscle at the end of the trial. No significant growth improvement was obtained over 53% protein, while best feed efficiency was apparently observed with 57% protein. The lower the dietary protein, the better the nitrogen utilization (estimated by protein efficiency ratio or productive protein value). Body protein content was not related to dietary protein but low protein levels resulted in higher body lipid content. Essential free amino acid contents in the muscle were plotted against the dietary protein levels and the values of the protein level corresponding to the slope changes were compared with the estimations of the dietary requirement. One free amino acid (threonine) showed a slope changing point corresponding to the values of the requirement determined with specific growth rate, while two other amino acids (arginine and valine) led to values lower than the estimated requirement. Estimations of the absolute requirements in g protein per fish per day or g protein per 100 g fish per day were not accurate because of poor control of the actual feed intake. The optimal protein level of brown trout determined under these conditions seems to exceed that of the salmonids of the genus Oncorhynchus , but it could be similar to that of Salmo salar .

An experiment was carried out with 12 groups of a fast-growing strain of brown trout reared in seawater. Each treatment was fed to triplicate groups of 158 fish of 1.6 kg average body weight reared in 60-m3 floating cages. Four experimental diets corresponding to two levels (21 versus 29%) and two sources of added lipid (corn, i.e. vegetable, versus cod liver, i.e. marine) were tested. Crude protein content was similar (about 52%) in all diets. All fish were fed the same amount of calculated digestible energy. The level of fat had a slight but significant effect on growth rate and feed conversion; the higher dietary lipid level led to a faster daily growth index (+4.8%) and better feed conversion (−12%). Protein utilization, estimated by both protein efficiency ratio and productive protein value, was also improved in the high-lipid compared to low-lipid treatments. The same factor also significantly influenced fat and muscle water content which were higher and lower, respectively, in the high-lipid compared to low-lipid treatments. The source of added lipid did not influence growth rate, feed conversion, or protein efficiency. Lipid source had no effect on body composition except in the case of liver which contained more lipid and less water in the fish fed cod liver oil. The source of lipid had very pronounced effects on the fatty acid (FA) profile of muscle and liver lipids but the variations mainly concerned saturated (in liver only), monounsaturated and 18:2n−6 FAs (in both tissues). On the other hand, n−3 polyunsaturated FAs were significantly but only slightly modified by the source of lipid, corresponding for both tissues to that found in other salmonids. The level of 20:4n−6 remained constant. The elongation product of 18:2n−6, namely 20:2n−6, was incorporated in muscle and liver lipids while the Δ6 desaturation product, 20:3n−6, was only observed in liver.

1. 1. In 5.8 g turbot, fed AsA free diets, body AsA stores were depleted in 90 days, while growth was not affected before day 131. 2. 2. From day 94, hypertyrosinemia followed by tyrosine crystals deposition in tissues at mortality was observed in deficient fish. 3. 3. These symptoms were reinforced when the AsA deficient diet was also low in several vitamins: hypertyrosinemia appeared 40 days sooner and the frequency of deficiency symptoms was doubled. 4. 4. This interaction was in agreement with the vicariancy concept (sparing effect). 5. 5. No external sign of scurvy was found, though proline hydroxylation was depressed by AsA deficiency, both in skin and in vertebrae independently of the poly-hypovitaminosis.

Brown trout and rainbow trout (average weight 100 g) were reared in fresh water at 12 degrees C under the same conditions before transferring brown trout to sea water, in order to compare phosphorus utilisation in both species. Apparent phosphorus availability, orthophosphate excretion and phosphorus accretion in the fish were directly determined. Thus, actual phosphorus mass balance was built. Rainbow trout raised in fresh water had a higher phosphorus retention coefficient (maximum 50 %) than brown trout reared in fresh water (maximum 45 %). Transferring brown trout to sea water induced a reduction in phosphorus retention (maximum 39 %), Orthophosphate excretion, ranging 7-20 mg phosphorus per kg wet weight per day, represented 10-20 % of ingested phosphorus. Phosphorus availability was lower in brown trout raised in sea water (65 %) than brown trout raised in fresh water (75 %). Phosphorus balance measurements showed that 90 to 98 % of phosphorus flow could be accounted for., Des truites communes et des truites arc-en-ciel ont été élevées à 12 °C dans des conditions strictement identiques, avant le transfert des truites communes en eau de mer, dans le but de comparer l'utilisation du phosphore chez les deux espèces. La disponibilité apparente de phosphore, l'excrétion d'orthophosphate par les poissons, et l'accrétion de phosphore chez ces poissons ont été estimées par mesure directe. Ainsi, les réels bilans de masse ont pu être construits. Les truites arc-en-ciel élevées en eau douce présentent un meilleur coefficient de rétention du phosphore (maximum 50 %) que les truites communes élevées en eau douce (maximum 45 %). Le transfert de la truite commune en eau de mer a entraîné une diminution de la rétention du phosphore (maximum 39 %). L'excrétion d'orthophosphate, de 7 à 20 mg de phosphore par kg de poids vif par jour, représente 10¿20 % du phosphore ingéré. La disponibilité du phosphore chez la truite commune était plus faible en eau de mer (65 %) qu'en eau douce (76 %). Le rapport entre les entrées et les sorties de phosphore du système d'élevage, compris entre 90 et 98 %, montre que l'estimation du bilan de masse est correcte.

Sea bass fry were fed a fixed ration of one of six isonitrogenous diets differing in essential amino acid balance or physical and chemical state of the protein source (Hydrolysate vs. intact protein) to induce different growth rates. The reference diet was based on fish meal, whereas the other diets contained fish protein hydrolysate, greaves meal (i.e., defatted collagen meal) or hydrolyzed feather meal added at 30 or 50% of crude protein at the expense of fish meal protein. Digestibility as well as fractional rate of whole-body protein synthesis was assessed. Whole-body protein synthesis was determined for each group of fish using a single injection of flooding dose of tritiated phenylalanine. Protein digestibility of the diets varied only by 5.5%. Specific growth rate and fractional protein specific growth rate, i.e., fractional protein accretion, were higher in fish fed the reference diet than in those fed the diets in which 50% of fish meal protein had been replaced by greaves or hydrolyzed feather meal protein. Compared with the reference group, whole-body protein synthesis was higher in fish fed these latter diets as well as in those fed the diet containing 30% greaves meal protein. The fractional protein accretion to fractional protein synthesis ratio, i.e., the efficiency of protein deposition, was lower in fish fed poorer dietary amino acid balance than in the reference group. The substitution of fish protein hydrolysate for intact fish protein led to a similar, though less pronounced phenomenon: nonsignificant increase in protein synthesis accompanied by significant increase in protein degradation.(ABSTRACT TRUNCATED AT 250 WORDS)

1. A previous paper (Gatesoupe et al., 1977) showed that turbot had a specific requirement for omega 3HPUFA since equivalent dietary amounts of 18:3 omega 3 or omega 3HPUFA (0.55% of the diet) did not lead to the same growth performances. 2. In the present paper, we demonstrated that fish given a high level of dietary 18:3 omega 3 (3.7% of the diet), without omega 3HPUFA, presented better growth than those offered a lower level of 18:3 omega 3, and almost the same performances as fish receiving 0.57% omega 3HPUFA. 3. This suggested that turbot, like trout, might be able to use the 18:3 omega 3 as a precursor of the omega 3 series. Furthermore, according to the present relatively short-term experiment, elongation-desaturation reactions of the omega 3FA did not appear to be reduced with low dietary omega 3FA levels. 4. On the other hand, these types of reactions seemed to be totally missing with the 18:2 omega 6. Thus, it may be assumed that there was no direct relationship between growth and omega 3 elongating-desaturating activities, and that omega 3 lowering fish body content was not the cause, or at least not the only cause, of poor growth in long-term experiments.

Protein digestibility of soyabean meal, casein-gelatin mixture and fish hydrolysate was tested in the European sea bass, using increasing substitution levels in a reference diet. The protein digestibility of the latter composed of Norwegian fish meal had already been established (91 %). An accurate estimation of the apparent digestibility coefficient was made by linear regression, for the casein-gelatin mixture and soyabean meal, but not for fish hydrolysate (non significant correlation, p > 0.05). Protein digestibility estimated by extrapolation varied with the substitution level. The estimations obtained with the highest level used for each ingredient were close to those obtained by linear regression. However they exhibited a high variability for soyabean meal and, to a lesser extent, for fish hydrolysate. The availability of individual amino acids was also investigated in each protein source. For some amino acids it was different from that of total nitrogen, suggesting that the availability of essential amino acids should be used for accurate feed formulation. Metabolic fecal nitrogen and amino acids were determined using a protein-free diet, in order to estimate true availabilities. These coefficients were not significantly different from apparent availability coefficients.

Protein and lipid digestibility in European sea bass were investigated using six different methods of faeces collection: dissection, stripping, anal suction, immediate pipetting in tank water, continuous filtration and decantation. Protein digestibility varied from 82.5% for stripping to 94.2% for decantation, and lipid digestibility ranged from 94.1% for stripping to 97.3% for immediate pipetting. Differences between methods are discussed. It is concluded that for extensive work on nutrient digestibility with European sea bass, continuous filtration is the most appropriate technique.

Two series of experiments were performed on pellet adaptation, each with five batches of 100 sea bass larvae, reared until the age of 50 days at 18°C and fed with living food. Each experiment was followed for 25 days. Three different pellet formulas, with different amounts of Artemia powder incorporated, were compared with a diet of living prey only. The incorporation of 10% of Artemia powder to the pellets appeared to give better results. However, much clearer results were obtained with the different types of pellet composition, being mainly shown in terms of final survival rates. In spite of the stress due to the change of feeding habits, there is evidence that the same growth and survival can be achieved either on living food or on pellets.