Jean-Marie Blanc

Relationship between number of pyloric caeca and growth in rainbow trout (Salmo gairdneri Richardson)

Abstract The relationship between fish length and number of pyloric caeca was studied in fullsib families, with different caeca number, which were obtained through genetic selection and reared in two different hatcheries. At Lees-Athas hatchery a significant positive correlation between caeca number and size of fish of the same age was demonstrated, both within and between families. An influence of rearing conditions upon this relationship was also observed as no significant correlation was found in Donzacq hatchery with the same families. In both hatcheries, families with many caeca exhibited better food conversion ratios than families with fewer caeca, the former showing either lower feed intake for the same growth rate or greater weight gain for the same feed intake. Two non-exclusive hypotheses could account for the growth-caeca number relationship: the caeca number could be either an indicative character reflecting initial growing conditions or a causal character, acting on intestinal morphology and food utilization. In either case, caeca number seems to be an interesting criterion in trout selection.

Evaluation of juvenile rainbow trout survival and growth in half-sib families from diploid and tetraploid sires

Abstract Five diploid and eight first-generation tetraploid males were mated with a pool of diploid females, with and without retention of the second polar body by heat shock, and the progenies were studied up to the sixth month after hatching. Apart from the poor fertilizing capacity of the tetraploid sires inducing low hatching rates, further survival and growth of the second-generation triploids were similar to those of the triploids obtained from diploid sires and heat shock. Second-generation tetraploids obtained from tetraploid sires and heat shock were inferior to the other ploidy types in post-hatching survival and growth. These characters were affected by a large variation of paternal origin, suggesting that genetic improvement would be possible.

Apparent digestibility of canthaxanthin in rainbow trout: effect of dietary fat level, antibiotics and number of pyloric caeca

Abstract Apparent digestibility coefficients (ADC) of lipid and canthaxanthin were studied in twelve rainbow trout families with 45 to 89 pyloric caeca, fed four experimental diets containing the same level (130 mg/kg) of synthetic canthaxanthin. Diets differed in lipid content (lipid-poor, 4%; lipid-rich, 15%) and by antibiotic supplementation (a combination of Flumequine 0.8 g/kg and Gentamycin 3.45 g/kg). The test families and their number of pyloric caeca did not induce any significant variation in the lipid or canthaxanthin ADC. Lipid ADC was significantly higher for the lipid-rich, antibiotic-supplemented diet (94.4%) than for the other diets (from 89.6% to 91.4%). Canthaxanthin ADC was significantly higher for the lipid-rich diets (64.3% without antibiotics, 54.1% with antibiotics) than for the lipid-poor diets (35.8% without antibiotics, 38.7% with antibiotics).

Inheritance of fertilizing ability in male tetraploid rainbow trout (Oncorhynchus mykiss)

Abstract Males presumed tetraploid were obtained from the previously reported mating of eight first-generation tetraploid sires with a common pool of diploid females and subsequent treatment of the eggs by heat shock. Sperm samples collected from these males and from diploid controls were used for cytometric measurements and fertilization tests. The results showed that one-third of the tested males performed like the diploid controls, which led to the assumption that these individuals arose from spontaneous androgenesis. Among the other males, whose performances were in line with their presumed tetraploid nature, important familial differences were observed and correlated to the performances of the corresponding parental sires. The estimate of the sire-son regression for fertilizing ability ( b =0.4±0.1) was indicative of an important inheritance allowing efficient improvement of this character by selection.

Dynamics of dietary canthaxanthin utilization in sexually maturing female rainbow trout (Salmo gairdneri Rich.) compared to triploids

Abstract Dynamics of canthaxanthin in rainbow trout was studied through a feeding experiment of 37 weeks by following canthaxanthin deposition and retention in muscle and ovary of maturing diploid females compared to sterile triploids. In the first 4 weeks canthaxanthin retention in diploids (3.6%) was about three times that of triploids. Later on, canthaxanthin retention in triploid muscle and diploid muscle and ovary reached similar and rather constant levels (2%) while the level in the diploid muscle was lower. The canthaxanthin deposit in the flesh of fish was higher in triploids than in diploids. Furthermore, the canthaxanthin concentration in muscle plus ovary from diploids did not differ significantly from the concentration in the muscle of triploids. After spawning, canthaxanthin concentration in the muscle of female diploids reached a level as high as that of triploids after 4 weeks.

Flesh colour of diploid and triploid rainbow trout (Salmo gairdneri Rich.) fed canthaxanthin

Abstract Colorimetric studies on the flesh of 12 diploid and triploid families of rainbow trout fed canthaxanthin have shown that triploids do not differ from diploids in average dominant wavelength and excitation purity. However, in luminosity, triploids are significantly inferior before as well as after canthaxanthin ingestion. Thus diploids and triploids show a similar ability to fix canthaxanthin. It was concluded that triploidy does not induce flesh colour changes of economic importance.

Direct and correlated responses to individual selection for large adult weight in the edible snail Helix aspersa Müller.

A selection experiment for large adult weight based on individual performance was conducted for three generations in Helix aspersa aspersa. A second line was kept as an unselected control line. Direct response measured as deviation from the control line was 3.55 g after three generations of artificial selection, which averaged 13%. Realized heritability was 0.38 +/- 0.04. Correlated responses to selection showed a significant increase in weight after hibernation, mean egg weight and mean weight of newly-hatched snails with selection. For adult age, egg number, and hatching rate, no significant change correlated to selection was found, but this is to be confirmed.

The early development of hybrids between brook charr (Salvelinus fontinalis) and arctic charr (Salvelinus alpinus)

Abstract Reciprocal hybrids between brook charr and Arctic charr were compared to parental species from fertilization to 10 weeks after the beginning of feeding. At the end of the experiment, higher survival rates (58.6% ± 1.5) were observed for brook charr (FF) than for Arctic charr (AA: 48.1% ± 2.2), while both hybrids were intermediate (Arctic charr dam × brook charr sire (AF): 57.5% ± 0.9; brook charr dam × Arctic charr sire (FA): 53.8% ± 1.4). All during the studied period, survival rates of hybrids were intermediate to parental species. Effects of parental species on the length of the incubation period (LIP) were significant but differed according to dam and sire species. LIP was 431.8 ± 0.9 degree-days for AF, 454.4 ± 2.2 for AA, 503.4 ± 0.9 for FF, and 518.6 ± 1.6 for FA. Individual sire effects on early survival and on the length of incubation period showed significant sire effects only on the length of the incubation period and only among brook trout sires in pure species.

Effect of selecting sires according to their number of pyloric caeca upon the growth of offspring in rainbow trout (Salmo gairdneri Richardson)

Abstract Two sires were selected, from each of four full-sib families, according to high (“sup”) and low (“inf”) caeca number. Pyloric caeca number, precocity and growth of offspring were studied in a factorial breeding plan of these eight sires crossbred with three dams. Compared with the progeny of sires “inf”, the progeny of sires “sup” exhibited (a) a higher caeca number, (b) slightly more precocious development (as shown by beginning of hatching, first feeding and degree of hydration during yolk resorption) and (c) a higher growth rate. Significant correlations were found, within dams, between fish length at 239 days and caeca number both within and between families of offspring. Although the physiological links between caeca number and growth are still obscure, the possibility of improving growth performance in rainbow trout by indirect selection on caeca number is discussed.

Evolution of genetic variability in a population of the edible snail, Helix aspersa Müller, undergoing domestication and short-term selection

The evolution of genetic variability is studied in six successive generations of a population originating from wild Helix aspersa. During the first three generations (G1 to G3), no artificial selection was applied. During the next three generations (G4 to G6), two lines were reared: a control line (C) and a line (S) selected for increased adult weight. Genetic variability is described by genealogical parameters (inbreeding, number of founders, effective number of founders and ancestors, effective number of remaining genomes) and by the additive genetic variance in adult weight. A large decrease in all parameters was observed between G1 and G2, suggesting strong natural selection: additive genetic variance in adult weight (transformed data) decreased from 0.0119 ± 3.8 × 10−3 to 0.0070 ± 1.7 × 10−3 (P < 0.05) and effective number of ancestors from 97.4 to 67.0. Selection also caused a large decrease during the first generation: additive genetic variance was 0.0079 ± 2.1 × 10−3 in G3 and 0.0040 ± 1.1 × 10−3 after the first selection cycle (P < 0.02). At the same time, the effective number of ancestors decreased from 59.2 to 29.5 and 24.2. This decrease is consistent with the theory of selection and the Bulmer effect.