Robert Métailler

Studies on nutrient digestibility in European sea bass (Dicentrarchus labrax) : 1. Methodological aspects concerning faeces collection

Abstract 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.

Comparison of nitrogenous losses in five teleost fish species

Abstract 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.

Effect of dietary lipid on growth performance and body composition of brown trout (Salmo trutta) reared in seawater

Abstract 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.

Excess dietary arginine affects urea excretion but does not improve N utilisation in rainbow trout Oncorhynchus mykiss and turbot Psetta maxima

Abstract 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.

Influence of dietary bulk agents (silica, cellulose and a natural zeolite) on protein digestibility, growth, feed intake and feed transit time in European seabass (Dicentrarchus labrax) juveniles

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.

The protein requirement of brown trout (Salmo trutta) fry

Abstract 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 .

Relationship between ration size and dietary protein level varying at the expense of carbohydrate and lipid in triploid brown trout fry, Salmo trutta

Abstract 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.

Effect of an ascorbic acid deficiency on tyrosinemia and renal granulomatous disease in turbot (Scophthalmus maximus) interaction with a slight polyhypovitaminosis

Abstract 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.

Studies on nutrient digestibility in European sea bass (Dicentrarchus labrax): 2. Effect of sodium alginate on protein and lipid digestibility

Abstract Protein and lipid digestibility in European sea bass were investigated using diets with increasing sodium alginate concentrations. This binder did not significantly affect protein and lipid digestibility when included in the diet at a rate of up to 8%.

Experiences de conditionnement d'alevins de bar (Pisces, Dicentrarchus labrax) a differents aliments composes

Abstract 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.