Selection For High Growth Research Articles

Genetic selection for high growth improves the efficiency of gilthead sea bream (Sparus aurata) in using novel diets with insect meal, single-cell protein and a DHA rich-microalgal oil

Genetic selection and novel raw materials for aquafeeds are current key tools in the ongoing effort to increase the productivity, efficiency, and sustainability of the aquaculture sector. Selective breeding could also improve the utilization of novel dietary formulations with emergent ingredients. Gilthead sea bream juveniles, either coming from a selective breeding program based on growth traits, or a non-selected population, were nutritionally challenged with two novel dietary formulations that were compared with a Control diet based on 15% FM and 6% FO dietary commercial levels for this species. The novel formulations included an insect meal diet (INS) at 5% of the diet to replace 33.3% of the dietary FM, or a single-cell protein diet (SCP) at 10% of the diet and to replace 66.7% of the dietary FM. Fish oil was also totally replaced in these diets by a blend of poultry oil and Veramaris algal oil. Better growth and feed utilization of the selected genotype compared to non-selected fish was observed, at any of the diets assayed. INS and SCP novel diets reduced general performance of fish by reducing feed intake. However, selected fish fed novel diets showed very similar growth and lower feed conversion ratio compared with non-selected fish fed a control diet. The novel formulations increased n-3 LC-PUFA in fish tissues, particularly DHA, irrespective of the genotype, as a result of the dietary inclusion of the DHA-rich microalgal oil. Neither genetic selection nor the use of novel raw materials affected fillet proximate composition and consequently, sea bream fillet quality in terms of texture and sensorial perception of consumers. Overall, the results reaffirm the positive effects of selective breeding programs in improving sea bream key productive indicators, as well as support the use of novel dietary formulations, using insect meal from H. illucens, single-cell protein from M. capsulatus as partial replacers of FM in diets for gilthead sea bream (33 and 66% of replacement, respectively), and a blend of DHA-rich microalgal and poultry oils as total replacer of FO.

Selection for high growth displaces costs of digestion from SDA to SMR in divergent ecotypes of rainbow trout

AbstractTo understand the drivers of variation in digestive performance and their effects on growth, we examined relationships among food consumption, digestive metabolism, food processing efficiency, and growth rate in juveniles of fast‐growing piscivore versus slow‐growing insectivore ecotypes of rainbow trout reared at satiation rations on the same diet (i.e., commercial food pellets). Relative to slow‐growing insectivores with lower basal metabolism, and despite a much larger maximum food ration, faster‐growing piscivores presented an unexpected pattern of higher digestive efficiency through a reduction in the absolute costs of postprandial metabolism coupled with shorter or similar gut residence time and higher assimilation efficiency. These results suggest that the increase in digestive metabolism following the ingestion of larger meals can be mitigated by displacing the costs of digestion from SDA to SMR. Reducing total digestion costs (SDA + SMR) while maintaining higher assimilation efficiency may be possible through potential adaptations including (1) increased intestinal absorption capacity; (2) economies of scale that shorten gut transit time with increasing ration level; or (3) a permanently larger digestive tract that increases maintenance costs but reduces the need for cyclic upregulation and associated overhead costs.

Selection for high growth improves reproductive performance of gilthead seabream Sparus aurata under mass spawning conditions, regardless of the dietary lipid source

Genetic selection programmes in gilthead seabream mainly focus on traits related to growth, disease resistance, skeletal anomalies, or fillet quality. However, the effect of selection for growth on the reproductive performance of seabream broodstock has not received much attention. The present study aimed to determine the effect of selection for growth traits, high (HG) or low (LG) growth, and broodstock feeding with fish oil (FO diet) or rapeseed oil (RO diet) as main lipid sources, on reproductive performance of gilthead seabream. For the first part of the spawning season (Phase I) HG and LG broodstock were fed a commercial diet and the HG broodstock produced a higher number of larvae and higher viable eggs, hatching and larval survival rates than LG broodstock, affecting egg fatty acid profiles. For the second part of the study (Phase II) broodstock were fed one of the two diets containing FO or RO. Fecundity in terms of viable eggs, hatchlings, and larvae produced, as well as fertilization rates, were improved in HG broodstock. Some fatty acids such as 18:0, 20:2n-6, 20:3n-3 or EPA/ARA were also affected by the growth selection. According to the two-way ANOVA analysis, feeding the RO diet did not significantly affect fecundity parameters, but slightly reduced fertilization and hatching rates in HG broodstock. Nevertheless, HG broodstock showed better spawning quality parameters than LG broodstock, even when they were fed the RO diet. Egg fatty acid profiles reflected diet composition, although DHA contents were not affected. In conclusion, broodstock selected for high growth had a positive effect on broodstock performance, and FO replacement by RO did not markedly affect reproduction providing that fatty acid contents were sufficient to fulfill the essential fatty acid requirements of gilthead seabream broodstock.

Assessment of a long-term selective breeding program for giant freshwater prawn Macrobrachium rosenbergii since 2007

Effects of long term selection for improved growth on traits of commercial interest are generally not well documented in aquaculture species, specifically in giant freshwater prawn (GFP) Macrobrachium rosenbergii. The present study analysed a total of 106,756 data records collected from a pedigreed GFP population over nine years (2007–2015) or nine generations (including base population) to evaluate genetic progress achieved for body weight and to examine correlated genetic changes in measurements of body dimensions (carapace length, abdominal length, carapace width and abdominal width), as well as fitness related traits (early maturity, EM and small blue claw male, SM). Linear mixed model fitting the random effects of individual prawn and common full-sib groups and the fixed effects of generation, line, pond by generation subclass, morphotypes for each sex and a linear covariate of grow-out day was used to analyse growth-related traits, whereas threshold logistic animal model was applied to binary data (EM and SM). The heritabilities were moderate for body weight and measurements of body dimensions (10 to 60%), but the estimates for EM and SM were low (0.13 ± 0.06 and 0.08 ± 0.01, respectively). The proportion of variance explained by the common full-sib effects was only 5–7% for measurements of body traits (weight and body dimensions). Genetic correlations among body traits were high and positive (0.93–0.97). These body traits however showed negative (i.e. favourable) genetic correlations with both EM and SM. Direct genetic gain for body weight and correlated changes in measurements of body dimensions and fitness related traits (EM and SM) were measured as differences in estimated breeding values (EBVs) between the selection line and control group within the same generation. The accumulative genetic gain in body weight after eight generations was 56%, averaging 7% per generation. Selection for high growth, however, did not have detrimental effects on measures of body dimensions and fitness related traits (i.e. EM and SM). In comparison to one of the founder stocks collected from Mekong river, the selection line had 50% greater body weight under the same testing environment in the latest generation 2015. Our findings provide information to refine the current breeding program to simultaneously improve traits of commercial interest in this important aquaculture species M. rosenbergii.

Selection strategies for beef cow size and condition

Context The present work was motivated by beef breeder concerns that selection for high growth and low fat in steers and low mature weight in cows will lead to cows that have low body condition and, therefore, productivity. Aims The aim of this was to partition cow weight into size (associated with height) and condition (variation net of height) and test whether the trait net weight is a worthy addition to breeding programs. Methods Angus cows (5901) were measured as heifers (4889) and at pre-calving and weaning of their first and second calf (minimum 2690) for weight, height and body condition traits (condition score, ultrasound eye-muscle area, P8 and rib fat depth, and intramuscular fat percentage). A novel trait was developed by fitting height as a covariate to weight, with the residuals termed net weight. Key results Net weight was both heritable and genetically correlated with cow condition score and ultrasound measures. However, despite having a lower heritability, condition score was a more effective measure for genetic improvement of cow condition. Conclusions A measure of cow condition should be included in genetic evaluation programs but net weight is unlikely to be that measure. Implications Condition score should be recorded at the time of mature cow weight for breeding programs.

Breeding for improved resistance to Edwardsiella ictaluri in striped catfish (Pangasianodon hypophthalmus): Quantitative genetic parameters.

Bacillary necrosis of Pangasius (BNP), caused by Edwardsiella ictaluri, is one of the most devastating diseases in stripedcatfish farming. To date, quantitative genetic inheritance of BNP resistance is not known in striped catfish Pangasianodon hypophthalmus. The main aim of this study was to estimate genetic parameters for BNP resistance in a breeding population of striped catfish undergoing four generations of selection for high growth. Specifically, the study examined whether BNP resistance is heritable to enable family selection and whether genetic improvement for enhanced BNP resistance may have detrimental effects on growth and survival rate. To test these hypotheses, 720 full- and half-sib families were challenged with E.ictaluri pathogen using injection and cohabitation methods over four years, from 2010 to 2012 and 2015. In total, the data included 398,234 animals in the pedigree, from which 18,849 animals had disease challenge test records and 39,103 siblings had growth performance. Both univariate and bivariate sire-dam linear and threshold mixed models were used to estimate (co)variance components for BNP resistance, survivals and growth traits. The estimates of heritability for the BNP resistance recorded as death or survival were low regardless of models used (0.10-0.16), whereas survival time (days post-challenge test) showed moderate heritability (0.35). The survival rate during hapa rearing had medium heritability (0.33-0.52). The genetic correlations of BNP resistance with body weight and survival were all positive (0.03-0.53), suggesting that selection of increased BNP resistance may have positive impacts on growth and survival traits, and these traits could be easily improved simultaneously in the selective breeding programme for striped catfish.

Genetic evaluation of a 15-year selection program for high growth in striped catfish Pangasianodon hypophthalmus

This study attempted to make a comprehensive genetic evaluation of a selective breeding program for striped catfish Pangasianodon hypophthalmus selected for high growth over 15 years from 2001 to 2015. Statistical analyses were carried out on 54,259 individual fish that were offspring of 554 sires and 926 dams (955 families in total). Both univariate and bivariate linear animal mixed models were used to estimate variance and covariance components for four groups of traits studied: (i) body traits (harvest body weight and standard length), (ii) carcass traits (fillet weight and fillet yield), (iii) fish body condition (condition index) and (iv) growth survival of each individual during grow-out phase. Medium to high heritability (0.31–0.54) were estimated for body traits, while carcass and condition index had medium heritability (0.17 to 0.20). Phenotypic and genetic correlations among body traits (weight and length) were high and close to one. The growth-related traits showed moderate and positive (i.e., favourable) genetic correlations with fillet yield (0.67–0.92) and condition index (0.28–0.49). Direct response to selection for high growth was 9.3% per generation. The selection program increased fillet weight and growth survival by 8.5% and 7.4%, respectively. However, there was insignificant correlated change in fillet yield (only 1.6%). Collectively, our results showed that there are substantial genetic variations in all traits studied and selection for high growth resulted in beneficial changes in fillet weight, fish body condition and survival during grow-out phase. The improved strain of striped catfish had 13.4% greater growth performance than their wild counterparts of the latest generation, suggesting that culture of the improved striped fish line may enhance productivity and economic return for small householder farmers and commercial producers.

Quantitative genetic changes in reproductive performance of giant freshwater prawn after 10 years of selection for increased growth rate.

Effect of long-term selection for improved growth on reproductive performance of giant freshwater prawn (GFP) Macrobrachium rosenbergii has not been reported in the literature. The present study aimed to measure correlated responses in reproductive traits and to estimate genetic parameters for these characters in a GFP population selected for high growth over ten generations from 2007 to 2016. A total of 959 breeding females (offspring of 515 sires and 810 dams) had measurements for seven reproductive traits (weight before spawn WBS; weight after spawn WAS; Fecundity FEC or number of larvae per female at hatching; first age to reach post-larvae PLAGE; zoea (e) weight ZOEAWT; larval survival during hatchery phase SURV1 and survival from PL to tagging SURV2. The restricted maximum likelihood (REML) and mixed model analysis were used to estimate genetic parameters and evaluate selection responses for the seven traits studied. Our REML analysis showed that heritability for these traits ranged from 0.04 to 0.42 (SE: 0.19-0.28). Female body weight either before or after spawning had strong positive phenotypic correlations with fecundity (0.52-0.98). By contrast, the phenotypic correlations of WBS/WAS with larval and fry survivals were not significant (-0.08-0.05). Genetic correlations among fecundity-related traits studied were not different from zero due to their high standard errors. Correlated responses in reproductive traits were measured by comparing least squares means of the selection line and control group. Females of the selected line for high growth had significantly greater weight before or after spawning than that of the control group. There were, however, no statistical differences between the two lines in the other traits. It is concluded that selection for high growth did not have detrimental impact on reproductive performance of breeding females in the present population of GFP.

High-Quality GaN Epilayers Achieved by Facet-Controlled Epitaxial Lateral Overgrowth on Sputtered AlN/PSS Templates.

It is widely believed that the lack of high-quality GaN wafers severely hinders the progress in GaN-based devices, especially for defect-sensitive devices. Here, low-cost AlN buffer layers were sputtered on cone-shaped patterned sapphire substrates (PSSs) to obtain high-quality GaN epilayers. Without any mask or regrowth, facet-controlled epitaxial lateral overgrowth was realized by metal-organic chemical vapor deposition. The uniform coating of the sputtered AlN buffer layer and the optimized multiple modulation guaranteed high growth selectivity and uniformity of the GaN epilayer. As a result, an extremely smooth surface was achieved with an average roughness of 0.17 nm over 3 × 3 μm2. It was found that the sputtered AlN buffer layer could significantly suppress dislocations on the cones. Moreover, the optimized three-dimensional growth process could effectively promote dislocation bending. Therefore, the threading dislocation density (TDD) of the GaN epilayer was reduced to 4.6 × 107 cm-2, which is about an order of magnitude lower than the case of two-step GaN on the PSS. In addition, contamination and crack in the light-emitting diode fabricated on the obtained GaN were also effectively suppressed by using the sputtered AlN buffer layer. All of these advantages led to a high output power of 116 mW at 500 mA with an emission wavelength of 375 nm. This simple, yet effective growth technique is believed to have great application prospects in high-performance TDD-sensitive optoelectronic and electronic devices.

Effects of selection for fast growth on survival rate during grow-out phase in giant freshwater prawn (Macrobrachium rosenbergii)

BackgroundCorrelated genetic response in survival to selection for high growth has not been reported in giant freshwater prawn (GFP) (Macrobrachium rosenbergii). The main aim of this study was to measure genetic changes and estimate heritability for this character (survival rate) and its genetic associations with body traits in a GFP population selected over eight generations from 2008 to 2015. Statistical analyses were conducted on 106,696 data records, using threshold logistic mixed model.ResultsThe estimated heritability for survival was 0.14 ± 0.04 and significant. Genetic associations of survival with body traits (weight, length and width) were weak, with the estimates of genetic correlations between the traits close to zero. Realised genetic changes in survival, calculated as the difference in estimated breeding values between the selection line and control group within the same generation, was in positive direction but the estimates were not significantly different from zero regardless of the expression unit used either in actual unit of measurement or genetic standard deviation unit. On the other hand, communal testing of stocks in the latest generation, namely G7 (2015), showed that the selection line had 18% higher survival rate than progeny of the wild prawns originated from Mekong river. This result suggests that inadvertent changes in survival occurred during domestication-selection.ConclusionsIt is concluded that selection for high growth had no significant effect on survival in the present population of M. rosenbergii.

Does selection in a challenging environment produce Nile tilapia genotypes that can thrive in a range of production systems?

This study assessed whether selection for high growth in a challenging environment of medium salinity produces tilapia genotypes that perform well across different production environments. We estimated the genetic correlations between trait expressions in saline and freshwater using a strain of Nile tilapia selected for fast growth under salinity water of 15–20 ppt. We also estimated the heritability and genetic correlations for new traits of commercial importance (sexual maturity, feed conversion ratio, deformity and gill condition) in a full pedigree comprising 36,145 fish. The genetic correlations for the novel characters between the two environments were 0.78–0.99, suggesting that the effect of genotype by environment interaction was not biologically important. Across the environments, the heritability for body weight was moderate to high (0.32–0.62), indicating that this population will continue responding to future selection. The estimates of heritability for sexual maturity and survival were low but significant. The additive genetic components also exist for FCR, gill condition and deformity. Genetic correlations of harvest body weight with sexual maturity were positive and those between harvest body weight with FCR were negative. Our results indicate that the genetic line selected under a moderate saline water environment can be cultured successfully in freshwater systems.

Are female reproductive status and male morphotypes of the giant freshwater prawn Macrobrachium rosenbergii altered by selection for high growth?

Understanding genetic changes in the hierarchical population structure of the giant freshwater prawn (GFP) Macrobrachium rosenbergii is important to improve productivity and profitability of prawn farming. We examined correlated responses in male morphotype and female reproduction status resulting from a selection programme for high growth in a GFP population undergoing four generations of selection. Two contemporary lines (selection and control) were maintained and produced simultaneously; the selection line was selected for high breeding values for harvest body weight and the control for average breeding values of the population. A total of 21,459 individual prawns were measured for body traits and morphotypes. Individual morphotype was recorded as a binary trait (0 and 1) and were analysed using a generalised threshold mixed model with a logit link function. Correlated genetic changes in three important male morphotypes (small, orange and blue claw males) were significant (p < 0.05–0.001) only in generation 2010 but not in the last generation (2012). Selection for high growth did not have an adverse effect on reproduction status of females, except that the selection line had a greater proportion of spawned females than the control (p = 0.01). Our results pointed out that selection for high growth may have had both positive and negative impacts on the social population structure of male morphotypes in GFP. Undesired changes in important morphotypes should be taken account of in genetic improvement programmes for GFP in order to minimise social competition effects and increase total biomass and consequently economic returns of the sector.

Genetic improvement for important farmed aquaculture species with a reference to carp, tilapia and prawns in Asia: achievements, lessons and challenges

AbstractThis study provides an overview of successful genetic improvement programmes for important farmed aquaculture species in Asia, with a focus on lessons and experiences gained as well as challenges remaining. In both fish and prawns (Macrobrachium rosenbergii), conventional selective breeding approaches have resulted in significant improvement in productivity, with genetic gains ranging from 8 to 12% per generation. Selection for high growth has also brought about beneficial changes in fillet weight of fish and edible meat in prawns without detrimental effects on flesh quality attributes and fitness‐related traits. Genetically improved animals show remarkable vigour and high adaptation to a range of culture environments/conditions in Asian countries. Despite these successes, however, the conduct and practical implementation of such breeding programmes still present several challenges. These include the expansion of breeding objectives, management of inbreeding in closed‐selection populations, controlling the effects of genotype by environment interactions, simultaneous production of large number of full‐ and half‐sib families for species with asynchronous spawning behaviour, maintaining pedigree records, dissemination of the improved strains for widespread production, as well as a reluctance by many to carry out systematically designed genetic improvement for aquatic animal species. There are also challenges with regard to the application of genomic information in genetic enhancement programmes and the development of genetically improved strains in response to climate and environmental changes. In this study, each of these challenges is discussed and solutions are proposed to increase efficiency of future genetic improvement programmes for economically important aquaculture species.

Genetic variation in survival of tilapia (Oreochromis niloticus, Linnaeus, 1758) fry during the early phase of rearing in brackish water environment (5–10ppt)

Tilapia fry viability is one of the important traits because it affects number of seed produced and marketed and, therefore, yield and economic return for hatcheries and the aquaculture industry. In the present study, we examined the effect of female body weight prior to spawning and fry birth weight on survival rates at 20 days of nursing (D20) and at 62 days (D62) (when tagged). Genetic parameters for D20 and D62 were estimated from 86,609 individual fry which were offspring of 63 sires and 77 dams in the sixth generation of a Nile tilapia (Oreochromis niloticus) population undergoing selection for high growth in brackish water environment. Both linear and threshold models were used to estimate genetic parameters for these two traits. The estimates of heritability for D20 after hatching were low and not significantly different from zero across the models studied. By contrast, D62 showed a large heritable additive genetic component on both the liability and observed scales (h2 = 0.24–0.79). The maternal and common environmental effects were 6–12% for survival at 20 days (D20), whereas they were small for survival from 21 days to tagging, D62 (1–5%). Genetic correlation between D20 and D62 was high and positive (0.72 ± 0.06). However, the estimate was significantly different from one, which suggests that D20 and D62 are under different genetic control and should be treated as different traits in selective breeding programs for tilapia. The results from the present study indicate for the first time that there is potential for simultaneous improvement of both survival rates at 20 days of nursing and at tagging in the future genetic improvement program for this tilapia population.

Flesh characteristics: estimation of genetic parameters and correlated responses to selection for growth rate in the GIFT strain

Flesh characteristics comprising chemical composition (protein, fat and moisture percentages and pH) as well as a sensory attribute (colour) were measured in 1951 fillet samples from two generations of two populations (a selection line, selected for increased harvest weight, and a control line, selected for average breeding values for harvest weight) of the genetically improved farmed tilapia (GIFT) strain of Nile tilapia. These data were jointly analysed with 5331 harvest weight records from three generations to estimate genetic parameters and correlated selection responses. Multiple trait animal models were used in the analyses. The potential for correlated responses was evaluated by estimating heritabilities and genetic correlations between body traits (weight, length, depth and width) and fillet traits (weight and yield) with the above mentioned flesh characteristics. The heritabilities for protein%, fat% and colour were low (0.06–0.11), whereas for moisture% and pH they were moderate (0.15–0.20). Genetic correlations among some flesh characteristics (moisture% with protein%, fat% and pH and with fat%) as well as between body and fillet traits with flesh characteristics, were significantly different from zero but low (−0.34 to 0.31). Correlated responses were evaluated by comparing the least squares means between the Selection and Control lines. Our results indicate that selection for high growth increased harvest weight in the Selection line relative to the Control line but it did not change the flesh characteristics of the GIFT strain.

Genetic parameters for economically important traits in yellowtail kingfish Seriola lalandi

The aim of the present study was to estimate genetic parameters for body and carcass traits, visual condition score, and deformity in yellowtail kingfish Seriola lalandi, an emerging aquaculture species in Australia. These novel data and genetic parameters are required to solve the problem of how to conduct efficient selection in this and related species. Analyses were performed on a total of 400 data records collected from a yellowtail kingfish breeding population at Cleanseas Tuna Ltd. farm. They were progeny of 22 full- and half-sib families (eight sires and six dams). Six newly developed and four published microsatellite markers were used to construct the pedigree. Genetic parameters were estimated using average information algorithm in ASReml with a multiple trait model. Fixed effects included sex, seal bite and deformity status. Random effects were the additive genetics of individual animal, and maternal and common environmental effects (i.e., dam-tank effect arising from a short period of separate rearing of offspring that came from two different broodstock tanks). The estimates of heritability for body and carcass traits were moderate (h2=0.15 to 0.30, s.e. ranging from 0.09 to 0.19). Fillet fat content showed an unusually high heritability (0.94±0.21) with a standard animal model, but was only moderate (0.41±0.26) when tank and dam were included as random effects. The estimate for condition score was 0.15±0.11, whereas the heritability for deformity was close to zero (h2=0.02). The genetic correlations between body and carcass (fillet weight and fillet yield) traits were high and positive (0.57 to 0.94, s.e. 0.05 to 0.46). Genetic correlations between body traits and condition score were moderate to high and positive (i.e. favourable). These results suggest that selection for high growth would result in concomitant increase in fillet weight, a carcass trait of paramount importance. It is concluded that there is substantial potential for genetic improvement of economically important traits especially growth performance and fillet weight in the current population of yellowtail kingfish.

General Rules for Selective Growth of Enriched Semiconducting Single Walled Carbon Nanotubes with Water Vapor as in Situ Etchant

The presence of metallic nanotubes in as-grown single walled carbon nanotubes (SWNTs) is the major bottleneck for their applications in field-effect transistors. Herein, we present a method to synthesize enriched, semiconducting nanotube arrays on quartz substrate. It was discovered that introducing appropriate amounts of water could effectively remove the metallic nanotubes and significantly enhance the density of SWNT arrays. More importantly, we proposed and confirmed that the high growth selectivity originates from the etching effect of water and the difference in the chemical reactivities of metallic and semiconducting nanotubes. Three important rules were summarized for achieving a high selectivity in growing semiconducting nanotubes by systematically investigating the relationship among water concentration, carbon feeding rate, and the percentage of semiconducting nanotubes in the produced SWNT arrays. Furthermore, these three rules can be applied to the growth of random SWNT networks on silicon wafers.

Quantitative genetic basis of fatty acid composition in the GIFT strain of Nile tilapia ( Oreochromis niloticus) selected for high growth

The quantitative genetic basis of fatty acid composition was examined in the Genetically Improved Farmed Tilapia (GIFT) strain of Nile tilapia selected for high breeding value for body weight and in the contemporaneous control selected for average breeding value. Gas chromatography analysis of 514 frozen fillet samples, obtained from the offspring of 104 sires and 154 dams from two generations in 2006 and 2007, showed that the fish possess all important fatty acids (FA), with the amount of omega-3 polyunsaturated fatty acids being 3.6%. The ratio of unsaturated to saturated fatty acids was greater than one (1.4) in the GIFT fillets, which is in line with the current dietary recommendation. Genetic analysis of FA was combined with 5532 performance and fillet records, and 2000 fillet samples analyzed for flesh composition and flesh quality attributes. A restricted maximum likelihood method applied to bivariate or trivariate mixed model was carried out in a full pedigree comprising a total of 18,970 animals to estimate genetic parameters and correlated responses in FA composition to the selection program. The estimates of heritability for individual FA varied from zero to medium, suggesting that FA composition of the GIFT fillet can respond to selection. Genetic correlations among FA within the same group (saturated, monounsaturated or polyunsaturated FA) were generally synergetic, but were antagonistic between groups. There were also both favourable and unfavourable genetic associations between important high chain polyunsaturated fatty acids and performance, fillet and flesh quality traits. Correlated changes in FA composition were measured by comparing least square means of the selection and control lines. Overall, selection for high growth resulted in very little change in FA composition. One notable change was that the content of heptadecanoic acid (C17:0) decreased in the selection relative to control line, which is beneficial for human health. In summary, the set of genetic parameters estimated and the response realized in the GIFT strain indicate that FA composition of tilapia or fish in general can be altered by genetic means.

Nanoheteroepitaxy of gallium arsenide on strain-compliant silicon–germanium nanowires

Heterogeneous integration of high-quality GaAs on Si-based substrates using a selective migration-enhanced epitaxy (MEE) of GaAs on strain-compliant SiGe nanowires was demonstrated for the first time. The physics of compliance in nanoscale heterostructures was captured and studied using finite-element simulation. It is shown that nanostructures can provide additional substrate compliance for strain relief and therefore contribute to the formation of defect-free GaAs on SiGe. Extensive characterization using scanning electron microscopy and cross-sectional transmission electron microscopy was performed to illustrate the successful growth of GaAs on SiGe nanowire. Raman and Auger electron spectroscopy measurements further confirmed the quality of the GaAs grown and the high growth selectivity of the MEE process.

Correlated response in fillet weight and yield to selection for increased harvest weight in genetically improved farmed tilapia (GIFT strain), Oreochromis niloticus

A data set consisting of 5532 slaughter records collected over three generations from a selection program for increased harvest body weight in the GIFT strain of Nile tilapia ( Oreochromis niloticus) was used to estimate genetic parameters and correlated responses in body (live weight, standard length, body width and body depth) and carcass (fillet weight and fillet yield) traits. A multi-trait model using restricted maximum likelihood method was applied to a full pedigree comprising a total of 18,970 animals. The estimates of heritability for body and carcass traits were of moderate magnitude (0.20 to 0.33). The proportions of variance explained by the maternal and common environmental effects were small, ranging from 4 to 8% for body traits and fillet weight, but were negligible for fillet yield. Genetic correlations among body traits were high (0.78 to 0.95), except between standard length and body width (0.56). High genetic correlations (0.78 to 0.96) were also obtained between body traits and fillet weight, whereas those between body traits and fillet yield were generally low (0.35 to 0.44). Genetic changes were measured as the difference in least squares means between the selection and control lines. The correlated increase in fillet weight was 23% in the latest generation studied or 0.97 phenotypic standard deviation units (σ P). The correlated response in fillet yield was negligible. In conclusion, selection for high growth significantly increased fillet weight. Strategies for the improvement of fillet yield in the GIFT strain are discussed.