Graham A.E. Gall

Breeding new strains of tilapia : development of an artificial center of origin and linkage map based on AFLP and microsatellite loci

Based on ideas from plant breeding and the opportunities offered by molecular biology, a program was initiated in 1995 to derive genetically superior tilapia from a synthetic stock .artificial center of origin, ACO produced by inter-crossing five groups of fish: Oreochromis w . . x

Triploid rainbow trout identified by flow cytometry

Abstract Spontaneous and induced triploid rainbow trout were identified by analysis of the DNA content of red blood cells with flow cytometry. Two spontaneous triploids were found among 30 adult trout that failed to mature in a hatchery at 2 years of age. Fifteen induced triploids were recognized among fish previously treated as fertilized eggs with heat shocks to induce polyploidy. There was no evidence of diploid cells in the triploid individuals. Flow cytometry should be a useful technique for identifying polyploid individuals in future studies.

Detection of a chromosomal region with two quantitative trait loci, affecting cold tolerance and fish size, in an F2 tilapia hybrid

Abstract We searched for genetic linkage between microsatellite DNA markers and quantitative trait loci (QTL) for cold tolerance and fish size (body weight and standard length) in two unrelated F 2 families of interspecific tilapia hybrids ( Oreochromis mossambicus × Oreochromis aureus ). The first experiment was based on a family of 60 fish scanned for 20 microsatellites. A second experiment was conducted with a family of 114 fish scanned for 6 microsatellites in one linkage group, in order to test for QTL found in the first experiment. This two-step experimental design was used in order to protect against “false positive” associations. In both families, significant associations were found for two loci within the same linkage group. The two QTL, near UNH879 for cold tolerance, and near UNH130 for body size, were estimated to be 22 cM distant from each other, with no interaction found between the two traits. One of these loci, UNH879 , was also associated with sex determination. Distortion from the expected Mendelian genotypic ratio was observed for three markers: UNH130 , UNH180 and UNH907 , suggesting linkage with a QTL affecting survival. These results identify a chromosomal region in the tilapia genome harboring several QTL affecting fitness traits.

Effects of inbreeding on growth and reproductive traits in rainbow trout (Oncorhynchus mykiss)

Abstract Rate of inbreeding and inbreeding effects on body weight and reproductive traits were studied in three lines of rainbow trout from a Californian selection experiment, in which Line Y was selected for body weight at 364 days of age, Line E was selected for egg size and Line C was a random mated control. The coefficient of inbreeding, as estimated both from effective population size with the assumption of random mating and from observed pedigree increased from Gen. 0 to Gen. 5 by 7.8% and 7.5% in Line C, by 5.7% and 8.3% in Line E, and by 5.2% and 6.5% in Line Y, respectively. The effects of inbreeding on the various traits were measured by the regression of individual performance on the coefficient of inbreeding calculated from pedigree. The regressions of body weight on coefficient of inbreeding were positive but not significant in the age interval from 168 to 252 days of age, and negative but not significant from 280 to 336 days of age. After that, the regressions were significantly negative. Thus, inbreeding depression for body weight per 10% increase in inbreeding was 2.26% (♂ ♂+♀♀) at 364 days, and 3.92% (♂ ♂) and 5.77% (♀ ♀) at spawning as a percent of the mean. There was a tendency for inbreeding depression for body weight to increase with advancing age. A highly significant inbreeding depression was found for spawning age of females and egg number. Per 10% increase of the inbreeding coefficient, spawning age of females was delayed by 0.53% and egg number decreased by 6.10% of the mean, respectively. In contrast, inbreeding did not significantly affect spawning age of males or egg size. The three kinds of inbreeding originating from male, female and embryo had quite different effects on fertility-hatchability. Inbreeding of male had no deleterious influence on this trait. In contrast, inbreeding of female had a strong and significantly negative effect and inbreeding of embryo itself had a noticeable though not statistically significant negative effect on fertility-hatchability. Per 10% increase of the inbreeding coefficient of female and embryo, fertility-hatchability declined by 11.60% and 8.56% of the mean, respectively. The following rank order of traits with regard to the magnitude of inbreeding depression seems to be in agreement with the rank order of the expected correlations of traits with fitness: (1) fertility-hatchability of females; (2) hatchability of embryo; (3) egg number; (4) body weight of males and females at spawning; (5) body weight (♂ ♂) at 308–364 days of age; and (6) spawning age of females, body weight (♀ ♀) at 280 days of age, and egg size.

Response to selection for early spawn date in rainbow trout, Salmo gairdneri

Abstract The effectiveness of selection for early spawn date was determined for two year-classes of two rainbow trout broodstocks spawning at 2 years of age based on female spawning date. One stock was selected for early spawn date, and one was bred to maintain the existing spawn date. Average response in the selected stock was nearly 7 days per generation through six generations of selection. Assuming that selection differentials for males were equal to those observed for females, realized heritability estimates for spawn data were 0.55 ± 0.07 and 0.53 ± 0.05 for the two yearclasses. The broodstock bred to maintain spawn date showed no linear response, but there was cyclic variation in spawn date from generation to generation. Careful examination of the data suggested that the realized heritability estimate may be biased upward due to influences of management and selection involving other traits. Therefore, the estimates should be considered as the upper limit when predicting response to selection under commercial conditions. Also, there was some evidence of a negative effect of early spawning on egg size.

Genetic and environmental variation of female reproductive traits in rainbow trout (Oncorhynchus mykiss)

Abstract The variation and covariation of reproductive traits were studied by analyzing data from 2020 females divided into 377 full sib families and covering five generations of three lines—a random mated control line (C), an egg size (+) line (E) and a body weight (+) line (Y), in a selection experiment with rainbow trout conducted at Davis, California. Variance components were estimated from a single trait animal model and covariance components from a two-trait animal model by using a derivative-free restricted maximum likelihood algorithm. Pooled over the three lines, the estimates of heritability were 0.65 for spawning date, 0.14 for spawning body weight, 0.60 for egg size, 0.55 for egg number, 0.52 for egg volume and 0.13 for fertility-hatchability. The estimates in line C were lower for spawning date, spawning body weight and egg number, and higher for egg size and fertility-hatchability than those in line E and line Y. Full-sib family effects caused by factors other than additive genetic effects were considerable for spawning body weight but small for other traits. Genetic correlations were estimated from data pooled over the three lines. Spawning date had significant genetic correlations with spawning body weight, egg size and egg volume (0.51–0.73) as well as with egg number (0.25). Significant genetic correlations were also found for spawning body weight with egg size, egg number and egg volume (0.47–0.67); and for egg size with fertility-hatchability (0.35). As expected, the genetic correlations between egg number and egg volume and between egg size and egg volume (0.81 and 0.48) were strong and significant due to the partial auto-correlations originating from commonality among biological components and methods of measuring these traits. The estimated genetic correlations between spawning body weight and egg production traits (egg size, egg number and egg volume) were positive, so that direct selection for growth rate or egg production traits should result in favorable correlated responses. The low heritability of body weight, the moderately high heritability of egg volume, and the strong genetic correlation between spawning body weight and egg volume, suggest that combined selection for body weight and egg volume could be an effective alternative selection method for improving growth rate and also reproductive capacity in rainbow trout.

A genetics analysis of the performance of three rainbow trout broodstocks

Abstract The reproductive performance of three domesticated rainbow trout broodstocks spawning at 2 years of age was analysed using data collected over a period of 5 years. Data were collected for post-spawning body weight, volume of eggs spawned, egg size, egg number and fertility to the eyed egg stage. There were significant differences among the stocks attributable to both genetic and environmental causes. In addition, there were marked differences between year-classes, isolated from each other due to 2-year spawning. The differences appeared to be genetic in origin and demonstrated the effect of sampling the original parents. Heritabilities estimated from full-sib comparisons indicated male weight was more influenced by environmental stress at spawning than was female weight. Heritability estimates for egg volume, egg size and egg number ranged from 0.05 to 0.76 for individual stocks, but when averaged for the three stocks the range was from 0.32 to 0.52. Egg size was found to have the lowest heritability of the three traits. The heritability of fertility was found to be low and was the lowest for the stock with the poorest fertility. Genetic and phenotype correlations among the traits were also estimated. The relationship between body weight and egg volume and size were both positive as was that between egg volume and egg size. It was determined that egg volume was the principal determinant of egg number and that the relationship of number to size could be negative. The latter evidence was obtained by artificially adjusting the egg production traits to a constant female body size. The result suggested that females that produce larger numbers of eggs are likely to produce smaller eggs unless the change is associated with a marked increase in body weight. It is recommended that selection for egg size be included in all selection programs and that egg number be ignored in any selection program designed to increase body size.

Application of mixed-model techniques to fish breed improvement: analysis of breeding-value selection to increase 98-day body weight in tilapia

Abstract A post-selection analysis of a three-generation selection experiment was undertaken to assess the effectiveness of using estimated breeding values as the selection criterion for the improvement of body weight at 98 days of age. Two replicate selection lines and a control line were derived from a common base population. Fixed effects of generation, line, sex and tank, as well as the fixed-effect interaction of the generation with line, sex and tank, were the significant factors determining performance. The estimated heritability of the 98-day weight was 0.20±0.04, while the maternal direct-genetic and full-sib group effects as a proportion of phenotypic variance were 0.02±0.02 and 0.09±0.02, respectively. Although phenotypic means varied from generation to generation, the genetic gains calculated from the estimated breeding values were 2.61±0.05 and 2.42±0.37 g per generation for the replicate lines, which is equivalent to a 40% improvement in just three generations. Additionally, although the randomly selected control line showed a linear increase in performance of 4.10±1.27 g per generation, the change in the average breeding value was only 0.27±0.01 g per generation, indicating that the increase in performance was due to improved management and/or adaptation to the culture environment. The post-selection analysis clearly demonstrated the superiority of the mixed-model approach to selection, with the potential of increasing the selection response by 20–30% above the value expected from simple mass selection.

Heritability and selection schemes for rainbow trout: body weight

Abstract Genetic parameter estimates were obtained for nursery weight, yearling weight, 25-month-weight, and spawning weight from 892–2140 fish consisting of 49 half-sib families that reached sexual maturity at 30 months of age. The parents used to produce the half-sib groups had been manipulated to spawn 6 months out of season using photoperiod control. The fact the progeny spawned during the normal season for the broodstock demonstrated the existence of a strong genetic component determining spawning season. With the exception of nursery weight, the estimated heritability of body weight at all ages was 0.20 ± 0.11 when based on half-sib variance components. The dam components of variance were consistently larger than the sire components and estimates of common environmental effects ranged from 0.09 for mature weight to 0.19 for yearling weight, assuming the absence of dominance genetic effects. The estimated heritability of nursery weight was high (0.52 ± 0.15); the dam component of variance was smaller than the sire component suggesting some type of confounding of rearing method and distribution of families within the rearing system. Intraclass correlations for weight of full-sib groups at the four ages ranged from 0.19 for mature weight to 0.29 for yearling weight. A comparison of expected selection responses from individual, family, within-family and combined family and within-family selection demonstrated the superiority of combined selection. Combined selection is expected to produce a response per generation about 10%–30% above that of individual and family selection and about twice that expected for within-family selection.

Cold tolerance of tilapia species and hybrids

Several experiments were conducted,involving Oreochromis mossambicus, O. aureusand their F1 and F2 hybrids to studythe genetic basis of cold tolerance in tilapiinefishes. Groups of fish, of similar age and grown underidentical conditions, were housed in replicated netenclosures in a controlled cooling water system.Survival time through a regime of controlledtemperature reduction was the observed parameter forcold tolerance. Intra-population variation anddifferences among species, hybrids and repeated spawnswithin a species were examined. There was nocorrelation between cold tolerance and fish size(within the range of 23–105mm standard length), andthe distribution for the trait was not normal. O. mossambicuswas the most cold-sensitive group,followed by the F2, and the F1 which wassimilar to O. aureus. Genetic variation in coldtolerance seems to have a large dominance component,based on the similarity of the F1 hybrid to the O. aureus parent.