Search

Selective breeding to improve residual feed intake (RFI) in sea bass (Dicentrarchus labrax) is a major goal that would optimize economic gain while minimizing the environmental impact of production. Due to the difficulty in accurately measuring individual feed intake, no selective breeding program has yet been started. In a previous study, we identified a criterion phenotypically related to RFI variations: the loss of weight during feed deprivation, FD. Moreover, an additional composite criterion (CC) integrating both FD and weight gain during subsequent re-feeding (RF) was closely related to RFI, even though the relationship was only close to significance (P=0.06). The aim of the present study was to estimate the heritability of these two traits, in order to complete the analysis of their pertinence as indirect criteria for use in a selective breeding program to improve RFI. We set up a full factorial mating design combining 41 sires and eight dams to produce mixed families offspring, which were all raised in the same tank. At 50g. 1300 individuals were individually tagged and a fin clip was sampled for DNA extraction and parentage reassignment using five to six microsatellite loci, which showed they originated from 261 families. The evolution of individual body weight was recorded during a growth period of three weeks, followed by successive periods of three weeks feed deprivation and three weeks ad libitum re-feeding, repeated twice. Phenotypic and genetic correlations between the two feed deprivation periods or the two re-feeding periods were moderate (r = 0.45-0.51, and 0.71-0.73 respectively for phenotypic and genetic correlations) indicating that FD and RF are relatively repeatable. FD, RF and CC heritabilities were of the same magnitude (0.23 +/- 0.04, 0.19 +/- 0.04 and 0.22 +/- 0.04, respectively), and sufficient to consider the use of such criteria in a future breeding program.

Improving feed utilization efficiency (FUE) is one of the major challenges for the development of sustainable fish farming. However, to date, no selection program for improving this trait has started yet. This can be explained by the difficulty to measure individual intake with fish commonly reared in groups. The use of indirect and easy-to-measure criteria linked with FUE would be highly valuable in order to start a breeding program. The aim of the present work is to set the foundations of a future strategy for improving fish FUE based on such indirect criteria. Body weight loss during feed deprivation (FD) and gain during a successive re-feeding period (RF) were chosen as potential indirect criteria, under the assumption that these traits might reflect interindividual variations in maintenance requirements and turnover rates. The originality of the present study lies in the complementarities of the two model species used: rainbow trout clones are genetic replicates of the same individual, which makes the determination of individual FE and RFI easier, and sea bass families displaying a large genetic variability which allows accurate estimation of genetic parameters. Using rainbow trout clones, we demonstrated significant genetic variability for FUE as well as a genetic correlation between FUE and a composite trait integrating both FD and RF. In sea bass, the relevance of FD and RF as indirect criteria was validated: i) a trait integrating FD and RF is correlated with FUE in this species as well ii) FD and RF are heritable iii) FD et RF are stable over time. An optimised protocol for improving fish FE is proposed, which shall be applied to any fish species produced., L’efficacité d’utilisation de l’aliment (EUA) est un des verrous à lever pour le développement d’une pisciculture durable. Pourtant, aucun programme de sélection sur ce caractère n’a débuté. Ceci s’explique par le mode d’élevage en groupe des poissons qui rend difficile la mesure de l’ingéré. L’utilisation de critères indirects, faciles à mesurer dans les conditions d’élevage, serait un outil précieux pour démarrer un programme de sélection. L’objectif de ce travail est d’obtenir les données de base afin de proposer une stratégie d’amélioration génétique de l’EUA des poissons à partir de critères indirects. Nous avons choisi de tester la résistance au jeûne (FD) et la croissance compensatrice (RF) comme critères indirects, en faisant l’hypothèse que ces caractères reflètent les variations des besoins d’entretien et du turnover métabolique des individus. L’originalité de cette étude réside dans la complémentarité des deux modèles utilisés : les clones de truites arc-en-ciel qui, parce qu’ils sont des répétitions d’un même individu, facilitent la caractérisation individuelle de l’EUA, et le bar qui, parce que cette espèce présente une large base génétique, permet une estimation précise des paramètres génétiques. En utilisant 10 clones, nous avons mis en évidence que l’EUA possède une variabilité génétique significative, et est génétiquement corrélée un caractère intégrant FD et RF. Chez le bar, la pertinence de FD et RF comme critères indirects a été vérifiée : i) un critère combinant FD et RF est corrélé à l’EUA chez cette espèce également ii) FD et RF sont héritables iii) FD et RF sont stables dans le temps. Un protocole optimisé de sélection pour l’efficacité d’utilisation de l’aliment, applicable à toutes les espèces d’élevage, a été proposé à l’issue de ces travaux.

No commercial breeding programs have yet started to improve feed utilization efficiency in fish, mainly because of the difficulty in accurately measuring individual feed intake in fish reared in groups. Our general goal is to propose indirect criteria to be used for breeding of commercial lines. In a previous study undertaken with rainbow trout clones, a genetic correlation was detected between residual feed intake (RFI), and body weight variation during successive periods of feed deprivation (FD) and re-feeding (RF). To assess the pertinence of such indirect criteria for future breeding programs, we set up a large experiment using sea bass (Dicentrachus labrax), a recently domesticated species with broad genetic diversity. The objectives of the present study were to analyze the relationship of FD and RF with RFI, and to assess the consistency of such indirect criteria over time and their correlation with carcass quality. Fish originating from a full factorial design combining eight dams and 41 sires, were raised in the same tank. At 306 days post fertilization 2000 fish were individually tagged and their body weight recorded over a growth period of three weeks, followed by two successive periods of three weeks of feed deprivation and three weeks of ad libitum re-feeding. Fish performances were then classified, FD−, FD+, RF− and RF+ for fish exhibiting loss (FD) or gain (RF) of weight relatively lower (−) and higher (+) than the population mean. Fish were sorted into four groups (FD−/RF−, FD+/RF+, FD−/RF+, FD+/RF). Each of the 4 groups was split between three replicated tanks of 50 fish. Body weight gain and feed intake were measured for each replicate every three weeks over a six months period to estimate residual feed intake. The fish then underwent a period of three weeks of feed deprivation followed by a period of three weeks of ad libitum re-feeding. At the end of each period, individual weight gain variations were recorded, as well as muscle fat using ultrasonic measurement. The relationship with RFI variations was high for FD (P = 0.04, n = 12), and close to significance for a criterion merging FD and RF performances (P = 0.06, n = 12). FD but not RF was negatively correlated with muscle fat (P < 0.05, n = 600). In conclusion, selecting fish losing less weight during a three week feed deprivation period should lead to improve RFI, but also to increase muscle fatness. Using a combination of FD and RF as indirect criteria would result in slower progress in RFI, but would not impact carcass quality traits. The next step for inferring the potential genetic gain that can be expected is to assess the heritability of such criteria.

Little is known about the genetic basis of residual feed intake (RFI) variation in fish, since this trait is highly sensitive to environmental influences, and feed intake of individuals is difficult to measure accurately. The purpose of this work was (i) to assess the genetic variability of RFI estimated by an X-ray technique and (ii) to develop predictive criteria for RFI. Two predictive criteria were tested: loss of body weight during feed deprivation and compensatory growth during re-feeding. Ten heterozygous rainbow trout clones were used. Individual intake and body weight were measured three times at three-week intervals. Then, individual body weight was recorded after two cycles of a three-week feed deprivation followed by a three-week re-feeding. The ratio of the genetic variance to the phenotypic variance was found high to moderate for growth, feed intake, and RFI (VG/VP = 0.63 +/- 0.11, 0.29 +/- 0.11, 0.29 +/- 0.09, respectively). The index that integrates performances achieved during deprivation and re-feeding periods explained 59% of RFI variations. These results provide a basis for further studies on the origin of RFI differences and show that indirect criteria are good candidates for future selective breeding programs.