Benoit Fauconneau

Growth and meat quality relations in carp

Abstract Growth proceeds through an harmonious development of major tissues, namely bone, muscle and adipose tissues. Changes in chemical composition result from differential growth of these tissues. Little is known about the relative changes in morphometric traits during development of carp or about their genetic basis, but it seems that valuable criteria for selection on suitability for processing could be found in the mechanisms of bone and muscle development. The development of fatty tissues associated with growth of carp is stimulated by the use of lipid-enriched or high-energy artificial diets. Fat is accumulated in specific adipose tissues and the analysis of the relative development of these tissues could give valuable information on the over-accumulation of fat and its distribution in the whole body. Accumulation of fat has either positive or negative consequences for sensory evaluation depending on the source and the composition of fat. The main characteristics of muscle and connective tissues are presented in this paper. Different muscle tissues comprising different fibre types are found in cyprinids. These tissues together with adipose tissues compose the edible part of carp and explain most of protein retention. Protein content and composition are stable during development. Furthermore, a wide variability in the characteristics of muscle and connective tissues persists in commercial-size fish related to their mode of development. It is especially true for the main contractile protein: myosin. This is illustrated on expression of isoform of myosin but in early stages. The changes in the characteristics of the tissues and of the flesh after death and during postmortem storage and processing are reviewed. The structural components and the organization of tissues are very specific in fish and more sensitive to destruction. Thus, the degradative processes that affect the flesh during storage and processing have important consequences for sensory evaluation of the flesh which in freshwater species is generally rather soft and with neutral odour and taste. In this paper the possible role of biological characteristics of the flesh and of its constitutive tissues in quality is analyzed for the effect of body weight and for the effect of acclimation temperature. Temperature induces specific compensation for the maintenance of basic processes and the consequences for quality are analysed as well.

Feeding Behaviour and Food Utilisation in Tilapia, Oreochromis Niloticus: Effect of Sex Ratio and Relationship With the Endocrine Status

The feeding behaviour of male monosex, female monosex, and mixed groups of Oreochromis niloticus was studied under conditions of self-feeding. Feeding activity was observed almost exclusively during the light period. The food intake pattern was similar whatever the sex ratio, and voluntary food intake (VFI) appeared lower in the male monosex groups than in the others. Male monosex groups displayed higher specific growth rates (SGR) and a lower food conversion ratio than female monosex and mixed groups. The SGR of males was higher in the monosex than in the mixed groups, whereas females of mixed and monosex groups displayed no significant difference in SGR. The efficiency of food utilisation was also analysed: nutrient retention ratios were higher in male monosex than in female monosex and mixed groups. Males displayed a distinctly higher metabolic capacity. Differences in sex-related hormones (11 ketotestosterone = 11-KT, 17beta-Oestradiol = 17beta-E2) and a metabolic hormone (triiodothyronine = T3) were observed between males and females. The hypothesis of an involvement of these hormones in the higher metabolic capacity of males is discussed. The observed differences in feeding behaviour between the different groups also suggest an effect of social interactions on the efficiency of food conversion and thus on the differential growth of males and females.

In vivo protein synthesis in different tissues and the whole body of rainbow trout (Salmo gairdnerii R.). Influence of environmental temperature

The fractional protein synthesis rate (FSR) of tissue (liver, digestive tract, muscle and whole fish) proteins was measured in rainbow trout acclimated to 9 and 18 degrees C after a pulse injection of [U-14C] L-leucine. In each of the tissues two FSRs were calculated based on a different estimate of the specific radioactivity of leucine in the precursor compartment for protein synthesis. Whole fish protein synthesis (WFPS) was estimated to be 7 and 7.6 g protein per kg body weight and per day respectively at 10 and 18 degrees C. Muscle and digestive tract contributed the most (more than 30%) to WFPS. The rate of protein turnover in whole fish was very low, as in the muscle, when compared to liver and digestive tract.

The measurement of whole body protein synthesis in larval and juvenile carp (Cyprinus carpio)

Abstract 1. 1. A method for measuring protein synthesis in young fish was developed. Carp weighing 50 mg were immersed in radioactive solution containing a tracer dose of labelled amino acid: l -arginine U 14 C. Post-immersion kinetics of radioactivity and of specific activity of arginine in different compartments of fish were followed during a 24 hr period. 2. 2. In the different soluble compartments of fish radioactivity reached a plateau value in 4–6 hrs after immersion. This was also true for the specific activity of arginine in acid-soluble fraction of fish when specific activity of arginine into protein increased almost linearly. These kinetics were analysed as for the infusion method. 3. 3. Protein synthesis in young carp was estimated to be 344%/day with a range of 60–600%. 4. 4. 14 CO 2 excreted by fish was also recorded and the rate of arginine oxidation was calculated: 58 μmoles/day/g.

Effect of growth hormone on muscle protein synthesis in rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar).

This paper reports on the effect of administration of mammalian growth hormone (GH) on muscle protein synthesis as measured in white muscle using the phenylalanine flooding technique. The effect of exogenous GH was compared with that of insulin and prolactin, and with endogenous GH.The rate of protein synthesis in white muscle of rainbow trout 6 h after the injection of bovine GH or bovine insulin was twice (2.6 and 2.9% d−1) that of the control saline-injected fish (1.2% d−1). A metabolic effect of GH, as observed with insulin, is suspected.The rates of change in body weight and body length and the fractional rate of protein synthesis in muscle of rainbow trout were enhanced by mammalian GH administration. The effect of GH on muscle RNA/protein ratios was not significant. An opposite effect of antibodies against salmon GH (Lebailet al. 1989) on growth rate and muscle protein synthesis rate was found in rainbow trout. It is suggested that the effects of exogenous and endogenous GH on capacity and efficiency of muscle protein synthesis were similar.The long-term effects of mammalian GH on presmolt Atlantic salmon was also tested. The same trends were found with ovine prolactin supplementation in Atlantic salmon but not as high as those observed with ovine GH.

Identification of a muscle factor related to MyoD in a fish species

We have isolated the cDNA encoding a myogenic factor expressed in embryonic trout muscle by hybridization with a Xenopus MyoD cDNA. Nucleotide sequence analysis and amino acid comparison showed that this cDNA called TMyoD encodes a polypeptide of 276 amino acids with 70% identity to the entire Xenopus MyoD protein and 92% identity within the basic and myc-like region. Results from Northern blotting showed that the corresponding transcript is expressed both in adult and embryonic skeletal musculature and in an in vitro myogenesis system, but is undetectable in cardiac and smooth muscles and in non muscle tissues.

Free amino acid content in the skin mucus of goldfish, Carassius auratus L.: Influence of feeding

Free amino acid contents in skin extracts and influence of food and starvation on free amino acid content in skin mucus were analysed in sexually immature goldfish. Free amino acid concentration in skin mucus (91.1 mumol/g dry wt) was higher than in deep skin (54 mumol/g) or in whole skin (56.6 mumol/g) extracts. Free amino acid compositions were very similar in the latter extracts. They both differed from skin mucus extract in taurine, glutamic acid, glycine and histidine relative contents. Free amino acid composition in zooplankton used to feed goldfish was close to the composition found in corresponding skin mucus extracts, except in taurine content. Goldfish weighing 3 g (6 months old) and 17 g (1 year old) reared on zooplankton showed similar patterns of free amino acid composition in skin mucus. Comparison with free amino acid composition in skin mucus from goldfish fed on commercial food had big differences in glutamic acid, valine, methionine and lysine relative contents. During fasting, we observed an increase in the amount of mucus secreted and a concomitant decrease of the free amino acid concentration in the secretion. The origin of free amino acids found in skin mucus and their possible role in pheromonal and allelochemical communications of goldfish are discussed.

Oxidation of phenylalanine and threonine in response to dietary arginine supply in rainbow trout (Salmo gairdneri R.)

Abstract 1. 1. The effect of increasing amounts of dietary arginine on oxidation of other amino acids was tested. Two experiments were conducted in rainbow trout fed on diets containing grading amounts of arginine from 0.55 to 2.55%. 2. 2. The growth of fish and the efficiency of food conversion were measured and there were no significant differences between the different diets tested. 3. 3. After an oral administration of either l -[U-14C]phenylalanine or l -[U-14C]threonine, the rate of excretion of 14CO2 over a period of 3 hr and the radioactivity in the free pool and the protein pool of liver at the end of that period were measured. 4. 4. The rate of oxidation of phenylalanine and threonine was assessed using their respective specific activities in the free pool of liver. 5. 5. The rate of oxidation of phenylalanine increased from 246 ± 101 nmol/g body weight/3 hr at 0.55% dietary arginine supply to 679 + 85 nmol/g body weight/3 hr at 2.00% arginine then it decreased for higher arginine supply. 6. 6. The oxidation rate of threonine increased from 50 ± 22nmol/100g body weight/3 hr up to 774 ± 195 nmol/100 g body weight/3 hr for a dietary arginine supply of 2.45% then it decreased. 7. 7. It was concluded that oxidation of phenylalanine and threonine could not be used as an indirect indicator of arginine status.

Influence of feeding on protein metabolism in Atlantic salmon (Salmo salar)

Abstract Two experiments were conducted to study the post-prandial changes in protein synthesis rate of different tissues in juvenile Atlantic salmon after an i.v. injection of a large dose (1.5 μmole/g) of L-[2,3- 3 H]-leucine. In the first experiment, the changes in protein synthesis rate of the muscle and scales were followed over a period of 18 h after a meal, in salmon (mean body weight 43.4 g) starved for 1 week. The rate of protein synthesis in muscle increased until 18 h after feeding. No significant changes were observed in the protein synthesis rate of the scales. In the second experiment, the salmon (mean body weight 36.8 g) were regularly fed on a commercial diet. Immediate analysis of protein metabolism (2 h after the morning meal) as compared with analysis after an overnight fast showed no significant effect of feeding on the protein synthesis rate in liver, gill, digestive tract and muscle.

Biochemical growth characterization of fast and slow-growing rainbow trout strains: effect of cell proliferation and size

Concentrations of RNA and DNA, determined in two rainbow trout strains, Cornec and Mirwart, over a period of 9 months, were used to assess and characterize growth potential. More rapid growth and higher muscle nucleic acid concentrations in the Cornac strain trout, suggest a more metabolically active strain with higher rates of protein synthesis. On the other hand, the higher concentration of muscle DNA, in the Cornec strain, suggests a smaller cell size and a larger number of cells per unit weight issue. The faster decrease of DNA concentration, with increasing body weight, in the Mirwart strain, reflected a lower percentage of hyperplasia and consequently a lower capacity for growth.