B. Fauconneau

Partial or total replacement of fish meal by soybean protein on growth, protein utilization, potential estrogenic or antigenic effects, cholesterolemia and flesh quality in rainbow trout, Oncorhynchus mykiss

Abstract Groups of rainbow trout (initial body weight 83 ± 1 g) were fed diets (crude protein (CP) 46%; gross energy 21 kJ/g DM; crude fat 12%) containing graded levels of either a soyflour (CP 52% DM) or a soy protein concentrate (CP 72% DM) supplemented with L-methionine as partial or total replacement of fish meal protein. A growth trial was conducted over 12 weeks at a water temperature of 18 °C. Digestibility of the dietary ingredients and of the complete diets was determined using an indirect method. At the end of the growth trial, in addition to body composition analyses, the following parameters were measured: plasma vitellogenin and cholesterol, antigenic activity (passive haemagglutination) in the soy sources and antisoya antibodies in serum, phytoestrogens in the soy sources and in the bile. Sensory and physical evaluations of fish flesh were also made. Replacement of fish meal with soy protein concentrate (33 to 100% replacement) did not affect growth performance or nutrient utilization. However, replacement of fish meal with soyflour (up to 50%) reduced the growth rate, as did complete replacement with either casein alone, or casein and soyflour in equal amounts. Plasma vitellogenin levels were not significantly affected by the dietary levels of protein from soybean. No antisoya antibodies were detected in the serum of fish fed soy-based diets. Few phytoestrogens were present in the ingredients but only trace amounts were detected in the bile of trout fed 100% soy protein. Plasma cholesterol levels were reduced in fish fed soybean protein in comparison to those fed 100% fish meal. Physical and sensory quality of fish flesh were little affected by dietary treatments.

Effect of digestible carbohydrates on protein/energy utilization and on glucose metabolism in rainbow trout (Salmo gairdneri R.)

Abstract Diplicate groups of rainbow trout were fed low-protein (38%) diets containing high levels (38%) of five different carbohydrate sources (raw starch, extruded corn, extruded wheat, extruded corn starch or extruded wheat starch). A modified pair-feeding method was used to allow equal intakes of protein and of digestible energy by each group of fish. Growth parameters were followed over a period of 18 weeks; the digestibility of the diets, nitrogen and energy balances, and the respiratory and ammonia quotients of fish fed the different diets were determined. To study the long-term effects of dietary carbohydrates, plasma glucose profile and its control by bovine insulin was followed in fish fed over 30 weeks with selected test diets. The results show that inclusion of extruded cereals or extruded starch improves availability of dietary energy. High levels of carbohydrates to not adversely affect overall growth or nutrient retention efficiencies. Long-term feeding with carbohydrate-rich d diets does not confer on trout any adaptive capacity to regulate postprandial glycemia levels. Respirometric measurements appear to provide interesting data on the metabolic utilization of body substrates.

The effects of ovine growth hormone on protein turnover in rainbow trout

Ovine growth hormone (oGH) was administered to rainbow trout via an intraperitoneal cholesterol implant. After 21 days, plasma oGH levels were recorded as control group, less than 2 ng ml-1, i.e., not detectable, and oGH group, 19.2 +/- 2.8 ng ml-1. oGH-treated fish exhibited significantly increased whole-body growth rates, whole-body protein accretion rates, stimulated tissue protein synthesis, and tissue protein accretion rates. A dramatic decrease in white muscle protein concentration was also observed after oGH treatment. In some tissues (liver and stomach), elevated protein synthesis rates were the result of higher RNA/protein ratios. However, in other tissues (gill and ventricle), increased RNA activity accounted for the differences in rates of protein synthesis. The growth promoting effects of oGH on both whole-body and tissue protein turnover were generally accompanied with no change in the efficiency of deposition of newly synthesized protein. For the same ration size, the oGH group showed higher retentions of ingested nitrogen. It is concluded that oGH significantly enhances whole-body growth rates as a result of the stimulatory effect on protein synthesis rates with little effect on protein degradation.

Influence of environmental temperature on flow rate of foodstuffs through the gastrointestinal tract of rainbow trout

Abstract Experiments were carried out with rainbow trout ( Salmo gairdneri ) to determine the rate of passage of foodstuffs through the digestive tract, before and after a rise in environmental temperature from 9–10°C to 18°C in 1 day. Transit rate was analyzed from the rate of fecal excretion of a marker (Cr 2 O 3 ) incorporated in the diet. In a first experiment on trout weighing about 80 g, mean retention time (MRT) (Castle, 1956) and mean transit time (MTT) (Zierlier, 1958) of the marker, starting from the 9°C acclimated values (34 h for MRT and MTT), decreased as early as the first day after the temperature change (24 and 26 h respectively) and reached the 18°C acclimated values (19 and 21 h respectively) in 4–7 days. In a second experiment on trout weighing about 140 g the pattern of response of MRT and MTT to the temperature increase was similar to that observed in the first experiment: they were 27 and 29 h at 10°C, 16 and 19 h on the second day after the temperature change, and 13 h and 15 h after acclimation at 18°C, respectively. These changes related to environmental temperature were independent of any increase in food consumption. The differences in transit rate of marker between the two experiments could be attributed to the higher body weight and food consumption in the second experiment. Excretion of Cr 2 O 3 in the feces was analyzed in the second experiment through a four-compartment model involving the stomach, anterior and posterior intestine, and feces. Fractional evacuation rate of marker in each digestive tract compartment was calculated according to the model. All compartments were affected by the temperature increase. There was a transitory acceleration of transit rate, observed principally in the stomach. These alterations were achieved by the eighth day after the temperature change and it was concluded that acclimation to the new temperature was accomplished in 1 week.

Feed intake and growth of fast and slow growing strains of rainbow trout (Oncorhynchus mykiss) fed by automatic feeders or by self-feeders

Abstract Rainbow trout (8.5–9.5 g) of two strains (C and M) differing in growth potential were compared with respect to feeding motivation and feeding rhythms, over a 65-day experimental period, employing self-feeding or automatic feeding. Growth rate, feed gain ratio, feed intake and pattern of feeding activity of fish fed with self-feeders, were recorded, as was body composition of both strains. The final weight of fish of the fast-growing strain, strain C, fed using self-feeders, was significantly higher (82.6 g) than that observed for fish of the slow-growing strain, strain M (69.3 g). When the automatic feeders were used, no significant differences were found between the strains in terms of body weight gain (65 g). Results observed for feed gain ratio were also similar between the two strains. Although the voluntary feed intake (VFI) did not vary significantly with the genetic origin of the fish, strain C displayed a consistently higher VFI compared to strain M. The retention efficiency of nutrients and energy were similar between strains but significantly different between feeding systems. With regard to body composition, when fish were fed by means of self-feeders, no significant differences were found between the two rainbow trout strains. However, when fed automatically, dry matter and lipid content were highest in the strain M fish. The energy and protein content of the whole fish were not significantly influenced either by the feeding system or by the strain of the fish used.

Influence of sexual phenotype and genotype, and sex ratio on growth performances in tilapia, Oreochromis niloticus

In tilapia, precocious sexual maturity associated with continuous and asynchronous reproductive activity often results in unwanted reproduction and overcrowding in ponds where the food supply is limited. This constitutes a major limitation in the culture of most tilapia species. Furthermore, divergent growth performances linked to sex are regularly observed. Males present better growth performances than females. The first experiment of the present study analysed the influence of sexual genotype on phenotypic male growth rates. Males with three different sexual genotypes were produced: YY100 (YY male×YY female), XY100 (YY male×XX female) and XX100 (hormonally sex-inverted females). They were compared with classic (XY male×XX female) or all female (XX male×XX female) progenies. The objectives of the second experiment were to study the influence of social interactions through the use of different sex ratios: F100, F75, F50, F25, F0 (F100=100% females in the population). These two experiments were carried out in hapas implanted in pond with “Egypt-UCS” strain of Oreochromis niloticus. At the end of the first experiment (140 days post-fertilisation), the XY genotype presented the best growth performances and YY genotype the lowest. Final body weights of neomale (XX100) were significantly (P<0.05) higher than those of YY100 males. According to our results, the involvement of a genetic component in sex-related growth difference between males and females is strongly suspected. We stressed upon the involvement of genes bound to the sexual genotype (especially XY in comparison to YY and XX) independently of the sexual phenotype. Furthermore, sexual maturity is not the only phenomenon involved in the sexual dimorphism. From 102 days post-fertilisation until the end of the second experiment, females of the F25 population presented the best growth performances. Their final body weights were significantly higher than those of all the males except F50 population males. In general, female body weight tended to increase inversely to their proportion in the population. Males of the F50 population presented better growth rate than the other males. Thus, tilapias seems to be very sensitive to the effects of social interactions. This social behaviour could strongly influence growth differences between males and females.

Quality traits of brown trouts (Salmo trutta) cutlets described by automated color image analysis

Twenty-seven-month-old brown trout from two genotypes, i.e., control and lines selected for growth, were reared in seawater cages and fed two diets containing 16% and 26% fat (LFR and HFR) during the last 4 months of growth to maximise heterogeneity at slaughtering at 3.8 kg (n=48). Image segmentation methods were developed and applied to quantify quality traits on cutlets by color image analysis including flesh color (L*a*b), myoseptes (visible fat), myomera, and peripheral surfaces. Results were also compared to lipids evaluated by Soxhlet or by NMR. Color image analysis provided results on the effects of feeding and selection on the development of various tissues representing edible flesh.

Hormone profile in fast- and slow-growing strains of rainbow trout (Oncorhynchus mykiss) in response to nutritional state

Abstract The present study reports the hormone profile [growth hormone (GH) and thyroid hormones] in a fast- and slow-growing strain of rainbow trout under different feeding regimes. An examination as to whether growth rate could be related to the endogenous levels of these growth-promoter hormones was also undertaken. Fish were fed to satiation to establish routine feeding behaviour; others were submitted to a restricted ration level (2% of body weight) to nullify the feed intake effect, thereby allowing a comparison of the general metabolism of the fish, over a period of 16 weeks. Finally, fish were submitted to a 30-day fasting period, which functioned as a test to amplify the capacity of the animals to maintain high levels of circulating hormones. Differences in growth rate between the two rainbow trout strains, when fed to satiation, could not be associated with differences in hormonal status (pituitary and plasma GH, plasma T 3 and T 4 ). Nonetheless, fish of the fast-growing strain exhibited significantly higher circulating GH values than slow-growing fish, after the fasting period. Additional studies on both the thyroid hormones and GH receptor systems, and the cellular response to these hormones are warranted to further characterize this aspect of the endocrine regulation of body growth in the two rainbow trout strains.

Potential benefits of biotechnology in aquaculture: The case of growth hormones in French trout farming

Abstract Against the background of rapidly increasing fish demand and stagnant or declining marine harvest, aquaculture or fish farming has assumed a major role in France which is set to expand. Trout farming in particular has already displayed considerable growth and France is the leading producer in the EEC. Biotechnology holds the key to future changes in trout culture. One such technology, which trials show has potential to reduce production costs, is recombinant trout growth hormone (rtGH). This paper sets out to perform a preliminary ex ante assessment of the possible social benefits from the adoption of rtGH by French trout producers. Several scenarios, based on possible hypotheses of supply and demand growth, are considered. Scenarios assuming an association of the technology with diversification towards more highly processed trout products display the highest estimated welfare gains. A key factor which will determine the outcome of using rtGH is its acceptance by the public. There has already been strong adverse reaction in Europe to the use of genetically engineered growth hormones in meat production and to the use of bovine somatotropin to enhance milk yields. The possibility that there might be a similar response in the case of trout is examined by considering the possibility of a sharp drop in demand. Part 1 of the paper sets out the economic and technological background to biotechnological development of trout farming in France. Part 2 undertakes an ex ante assessment of potential changes in producer and consumer surplus from the adoption of rtGH applying alternative supply and demand shifts in the framework of partial equilibrium analysis.