GIFT Strain Of Nile Tilapia Research Articles

Genome-wide identification of DNA methylation marks associated with resistance to Streptococcus agalactiae in the GIFT strain of Nile Tilapia (Oreochromis niloticus)

Epigenetic mechanism plays a pivotal role in the immune responses of fish. Streptococcus agalactiae (SA) infection is a significant challenge to tilapia aquaculture. DNA methylation involved in immune responses in tilapia against SA is unclear. Here, by using a QTLseq strategy integrated with whole-genome bisulfite sequencing-based DNA methylation analysis (methyl-QTLseq) and RNA sequencing (RNA-seq), we identified 3608 differentially methylated regions (DMRs) and 4355 differentially expressed genes (DEGs) in the spleen of Nile tilapia Oreochromis niloticus. Compared to the susceptible group, the up-regulated DMRs (2449) were approximately twice as many as the down-regulated DMRs (1159). Compared to the susceptible group, lower methylation levels for CpG, CHG and CHH in TEs and for CHG and CHH in genes and significant decreased expression for 8 of the 11 DNA methyltransferase genes in the resistant group were detected. 46 DEGs with differentially methylated promoter regions (DMPs) were significantly enriched in immune processes such as T cell differentiation and adaptive immunity. We detected 4 methyl-QTLs located on LG8:5332501–5,336,400, LG14:2307301–2,353,500, LG16:16889101–16,903,500, and LG22:25238401–2,536,880 across the tilapia genome. The methyl-QTL region located within the chromosome LG22:25238401–25,368,800 contains the most DMRs (91) and DMGs (7). Interestingly, most of the annotated genes that located within or under the peak of the methyl-QTL interval belong to the HOX protein family including hoxa1, hoxa2, hoxa4a and hoxa5a. Bisulfite sequencing PCR and expression analysis indicated that DNA methylation in the promoter regions of hoxa4a, lcp2a, and ccr9a regulated gene expression in spleen in response to SA infection. Overall, our study provides epigenetics evidences involving in immune responses against SA infection in tilapia.

Impact of dietary selenium supplementation on growth performance, bioaccumulation, antioxidant capacity, and gene expression in GIFT strain of Nile Tilapia (Oreochromis niloticus)

Impact of dietary selenium supplementation on growth performance, bioaccumulation, antioxidant capacity, and gene expression in GIFT strain of Nile Tilapia (Oreochromis niloticus)

Evaluating the inclusion of phytase sources to phosphorus-free diets for GIFT tilapia (Oreochromis niloticus): Growth performance, intestinal morphometry, immune-antioxidant responses, and phosphorus utilization

The current study aimed at evaluating the growth performance, phosphorus (P) retention, and welfare status of GIFT strain of Nile tilapia (Oreochromis niloticus) fed on P-free diets containing fungal phytase (FPhyt) and/or a novel hybrid bacterial phytase (HB-Phyt). The control reference diet (T1) was supplemented with dicalcium phosphate (DCP; 8.7 g total P/kg). Other five low-P (with no DCP; 5.9 g total P/kg feed) diets were supplemented with 500, 1000 FTU/g of FPhyt (T2-T3) or 500, 1000 FTU/g of HB-Phyt (T4 – T5), while T6 contained 1000 and 1000 FTU/g of both phytase sources. Each diet was allocated randomly to three 100-L tanks stocked with GIFT tilapia (n = 15 fish per tank, initial mean weight, 2.38 ± 0.22 g). Fish were fed on experimental diets up to satiation thrice a day for 60 days. Fish in T1, T3, T5, and T6 recorded highest growth performance; meanwhile, highest values of villi length/width and absorption area were observed in T3, T5, and T6 fish groups as compared with other groups. Highest values of hematological indices (red blood cell, hemoglobin, packed cell volume, white blood cell, and lymphocytes %) and immune-antioxidant biomarkers (superoxide dismutase, catalase, lysozyme, and respiratory burst activity) were highest in the case of fish in T3, T5, and T6 with no significant difference among them. Meanwhile, feeding fish on diets with 500 FPhytase (T2) or 500HB-Phyt (T4) showed lowest values of immune-antioxidant indices accompanied with highest value of malondialdehyde as compared with other treatments. Compared with other treatments, highest values of bone-P were observed in T3, T5, and T6, while highest whole-body P values were detected in T5 and T6 only, with no significant difference among them. The present study revealed much lower feed input per unit production accompanied with higher return on investment in GIFT fed on diets supplemented with 500 FTU/g of HB-Phyt than 1000 FTU/g of either FPhyt or HB-Phyt. Hence, the present study showed that the dietary inorganic P could be compensated by adding 1000 FTU/g of either FPhyt or HB-Phyt to fish diets. The growth and immune-antioxidant indices in fish fed with HB-Phyt were superior to FPhyt treatments. No synergetic effects of using both of FPhyt and HB-Phyt were detected in this study.

Effects of dietary copper (Cu) on growth performance, body composition, mineral content, hepatic histology and Cu transport of the GIFT strain of Nile tilapia (Oreochromis niloticus)

This study determined the influence of dietary copper (Cu) levels on growth and feed utilization, body composition, mineral content, liver histology and intestinal Cu transport, and identify dietary Cu requirement of the GIFT strain of Nile tilapia (Oreochromis niloticus). Six diets were prepared with Cu sulfate addition at levels of 0 (control), 5, 10, 20, 40, and 80 mg/kg, respectively. Analytical dietary Cu contents were 1.55, 2.97, 4.51, 7.25, 11.30, and 19.24 mg Cu/kg diet, respectively. Each experimental diet was fed to three replicates of GIFT tilapia (25 fish per tank, initial body weight 4.34 ± 0.01 g) in a recirculating freshwater system for eight weeks. GIFT tilapia fed 4.51 mg Cu/kg diet had higher growth performance and feed utilization. Cu contents in the whole-body, the liver and intestinal tract increased with dietary Cu levels. Moreover, dietary Cu addition also affected whole-body Mg content significantly, but did not affect whole body crude protein, lipid, zinc (Zn), iron (Fe), and calcium (Ca) content. GIFT tilapia fed with 4.51 mg Cu/kg diet had lower liver vacuoles relative area. Furthermore, dietary Cu addition also significantly influenced mRNA expression of genes involved in intestinal Cu transport, such as copper transporter 1 (ctr1), copper transporter 2 (ctr2), antioxidant 1 copper chaperone (atox1), cytochrome c oxidase copper chaperone (cox17) and copper-transporting ATPase alpha (atp7a). The regression analysis of weight gain and whole-body Cu retention against the dietary Cu levels suggested that 4.23 to 4.57 mg Cu/kg diet was optimal for GIFT tilapia. Statement of relevanceOur study determined the optimal dietary Cu requirement of GIFT strain of tilapia, which provided good references for dietary Cu addition for the fish species, and accordingly was helpful for its feed formulation and aquaculture production. Our study also demonstrated that dietary Cu addition influenced mRNA expression of genes involved in Cu transport, which provides a good basis for exploring Cu metabolism in fish.

Dietary arginine requirement in diets of GIFT strain of Nile tilapia, Oreochromis niloticus : Effects on growth performance, whole‐body composition, growth‐related gene expression and haemato‐biochemical responses

This study aims to evaluate the effects of dietary arginine supplementation on growth performances, whole-body composition, haemato-biochemical responses and growth-related gene expression in juvenile GIFT tilapia. Five corn-soy-based isonitrogenous (322 g/kg) and isoenergetic (17.4 MJ/kg) diets were formulated to contain graded levels of dietary arginine (14.7, 15.5, 16.4, 17.6 and 18.5 g/kg of diet). Each diet was randomly assigned to triplicate groups of 30 fish (4.4 ± 0.2 g) per experimental unit, which were fed thrice a day (09:00, 13:00 and 17:00 h) for 60 days. Growth performances and feed utilization were improved in fish fed arginine at 16.4 g/kg of diet compared with other dietary treatments. No significant differences were observed in the whole-body proximate composition, amino acid profile and haematological responses of fish fed graded levels of dietary arginine. However, significant interactions were observed in the blood biochemical responses and mRNA expression of MyoD, Myogenin, GH, IGF-1, GHR-1 and Pax7 in fish fed diets with graded levels of arginine, while dietary arginine levels had no effect on the mRNA expression of myostatin and IGF-2. Second-order polynomial regression analysis of weight gain and nitrogen gain against dietary arginine levels indicated that the optimum dietary arginine requirement for maximum growth and feed utilization of juvenile GIFT tilapia was estimated to be 16.7–16.8 g/kg of diet or 51.8–52.2 g/kg of protein.

Growth, nutritional efficiency, and profitability of juvenile GIFT strain of Nile tilapia (Oreochromis niloticus) reared in biofloc system on graded feeding rates

This study was conducted to evaluate the effects of the feeding rate (0%, 2.5%, 5.0%, 7.5%, and 10% of body weight per day; BW.d−1) on growth performance, nutritional efficiency, and profitability of Nile tilapia (Oreochromis niloticus) juveniles (3.1 ± 0.1 g) using the biofloc technology (BFT) system for 70 days. Fish were randomly stocked (15 fish. Tank−1) in 24 experimental units (50 L), while water quality parameters remained within acceptable limits for the species during the experiment. Animal performance parameters were influenced by feeding rates (P < 0.05), but not survival (P > 0.05), which remained around 81%. Final body weight, weight gain, and thermal growth coefficient increased significantly (P < 0.05); however, the gradual increase in feeding rates had reduced feed efficiency, protein, and energy productive values (P < 0.05). Whole-body lipid and gross energy increased significantly (P < 0.05) as the feeding rate increased, while the moisture content showed an opposite trend up to 5.0% BW.d−1. The results show that Nile tilapia juveniles raised in the BFT system should be fed between 4.3 and 6.1% BW.d−1 to exhibit improved profitability and growth.

Metabolic responses of juvenile GIFT strain of Nile tilapia ( Oreochromis niloticus ) to dietary L‐tryptophan supplementation

Metabolic responses of juvenile GIFT strain of Nile tilapia ( <i>Oreochromis niloticus</i> ) to dietary L‐tryptophan supplementation

Dietary vitamin E requirement of sub‐adult genetically improved farmed tilapia strain of Nile tilapia (Oreochromis niloticus) reared in freshwater

A two‐factor orthogonal test was conducted to determine the dietary vitamin E (VE, dl‐α‐tocopheryl acetate) requirement for sub‐adult GIFT strain of Nile tilapia (Oreochromis niloticus) at two lipid levels, and evaluate its effect on antioxidant responses. A basal diet containing 60 or 130 g/kg of soybean oil was supplemented with 0, 20, 40, 60, 120 and 240 mg VE/kg, respectively. Each diet was fed to three replicate groups of tilapia with initial weight (80.3 ± 0.7) g for 10 weeks. Results showed that the weight gain, feed efficiency and hepatic VE retention of fish were significantly increased by the increased VE in diets. In groups with 60 and 130 g/kg lipid, fish fed diets supplemented with VE had higher serum superoxide dismutase (SOD) and catalase activity, and lower malondialdehyde content than fish fed the VE un‐supplemented diet (p < .05). The proximate composition of fish had no significant difference in the group with 130 g/kg lipid, whereas crude lipid and ash content were significantly affected by dietary VE in the group with 60 g/kg lipid. Based on broken‐line regression analysis, dietary VE requirement to support the maximum weight gain and serum SOD were 43.2–45.8 and 66.0–76.1 mg/kg in diets with 60 and 130 g/kg lipid, respectively.

Quantifying the genetic parameters of feed efficiency in juvenile Nile tilapia Oreochromis niloticus

BackgroundImproving feed efficiency in fish is crucial at the economic, social and environmental levels with respect to developing a more sustainable aquaculture. The important contribution of genetic improvement to achieve this goal has been hampered by the lack of accurate basic information on the genetic parameters of feed efficiency in fish. We used video assessment of feed intake on individual fish reared in groups to estimate the genetic parameters of six growth traits, feed intake, feed conversion ratio (FCR) and residual feed intake in 40 pedigreed families of the GIFT strain of Nile tilapia, Oreochromis niloticus. Feed intake and growth were measured on juvenile fish (22.4 g mean body weight) during 13 consecutive meals, representing 7 days of measurements. We used these data to estimate the FCR response to different selection criteria to assess the potential of genetics as a means of increasing FCR in tilapia.ResultsOur results demonstrate genetic control for FCR in tilapia, with a heritability estimate of 0.32 ± 0.11. Response to selection estimates showed FCR could be efficiently improved by selective breeding. Due to low genetic correlations, selection for growth traits would not improve FCR. However, weight loss at fasting has a high genetic correlation with FCR (0.80 ± 0.25) and a moderate heritability (0.23), and could be an easy to measure and efficient criterion to improve FCR by selective breeding in tilapia.ConclusionAt this age, FCR is genetically determined in Nile tilapia. A selective breeding program could be possible and could help enabling the development of a more sustainable aquaculture production.

Molecular Cloning and Expression Analysis of IgD in Nile Tilapia (Oreochromis niloticus) in Response to Streptococcus agalactiae Stimulus.

IgD is considered to be a recently-evolved Ig and a puzzling molecule, being previously found in all vertebrate taxa, except for birds. Although IgD likely plays an important role in vertebrate immune responses, the function of IgD in Nile tilapia (Oreochromis niloticus) is virtually unknown. In the present study, a membrane form of IgD (mIgD) heavy chains were cloned from the GIFT strain of Nile tilapia (designated On-mIgD). The On-mIgD heavy chain’s cDNA is composed of 3347 bp with a 31 bp of 5′-UTR, 3015 bp open reading frame (ORF) and 301 bp 3′-UTR, encoding a polypeptide of 1004 amino acids (GenBank accession no: KF530821). Phylogenetic analysis revealed that On-mIgD heavy chains showed the highest similarity to Siniperca chuatsi. Quantitative real-time PCR (qRT-PCR) analysis showed that On-mIgD expression occurred predominately in head kidney, thymus, spleen, and kidney. After Streptococcus agalactiae infection, transcripts of On-mIgD increased and reached its peak at 48 h in the head kidney and thymus, and 72 h in the spleen, respectively. Taken together, these results collectively indicated that IgD could possibly have a key role to play in the immune response when bacterial infections in Nile tilapia.

Genetic and non-genetic indirect effects for harvest weight in the GIFT strain of Nile tilapia (Oreochromis niloticus)

Trait values of individuals are affected not only by their genetic makeup, but also by environmental factors and interactions with other individuals. The heritable effect of an individual on the trait values of other individuals it interacts with is known as an indirect genetic effect (IGE). Such IGEs may affect response to selection. Fish selected for high growth rate, for example, have been shown to be more aggressive and competitive, which may reduce the observed response in growth rate. The main objective of this study is to quantify the genetic and non-genetic indirect effects for harvest weight in the GIFT strain of Nile tilapia. A total of 6330 fish with harvest weight information were used to estimate genetic and non-genetic parameters. A bivariate analysis of harvest weight and survival was conducted by fitting different mixed models to investigate the presence of IGEs and other non-genetic effects. The full set of genetic parameters could not be estimated simultaneously with the inclusion of maternal common environmental effects. A confounding between maternal common environmental effects and direct genetic effects resulted from the mating strategy, where one sire was mated to only one or two dams. A 1 male to 2 females mating design is common in aquaculture, but it has limited power to estimate genetic parameters. Models without maternal common environmental effects showed significant IGE on harvest weight, which contributed 48% of total heritable variance. Models with maternal common environmental effects suggested the presence of IGE. The direct–indirect genetic correlation for harvest weight was negative (−0.38±0.19), indicating that traditional selection, if performed in an environment where the fish have to compete with each other for the resources, will increase competition. A strongly negative genetic correlation between direct effects on survival and indirect effects on harvest weight (−0.79±0.30) showed that individuals with better genes for survival suppressed growth rate of their social partners. Our results suggest that heritable competitive interactions affect harvest weight in Nile tilapia. Hence, breeding schemes may need to be adapted to avoid an increase in aggressiveness due to selection for growth rate in a competitive environment. Further studies are required to investigate the relevance of IGE and its implications on different systems of commercial aquaculture production. Statement of relevanceSociable fish will help to improve aquaculture production.

Dietary lipid levels impact lipoprotein lipase, hormone-sensitive lipase, and fatty acid synthetase gene expression in three tissues of adult GIFT strain of Nile tilapia, Oreochromis niloticus.

The objective of this study was to assess the effects of dietary lipids on growth performance, body composition, serum parameters, and expression of genes involved in lipid metabolism in adult genetically improved farmed tilapia (GIFT strain) of Nile tilapia, Oreochromis niloticus. We randomly assigned adult male Nile tilapia (average initial body weight = 220.00 ± 9.54 g) into six groups consisting of four replicates (20 fish per replicate). Fish in each group were hand-fed a semi-purified diets containing different lipid levels [3.3 (the control group), 28.4, 51.4, 75.4, 101.9, and 124.1 g kg(-1)] for 8 weeks. The results indicated that there was no obvious effect in feeding rate among all groups (P > 0.05). The highest weight gain, specific growth rate, and protein efficiency ratio in 75.4 g kg(-1) diet group were increased by 23.31, 16.17, and 22.02 % than that of fish in the control group (P < 0.05). Protein retention ratio was highest in 51.4 g kg(-1) diet group. The results revealed that the optimum dietary lipid level for maximum growth performance is 76.6-87.9 g kg(-1). Increasing dietary lipid levels contributed to increased tissue and whole body lipid levels. Saturated and monounsaturated fatty acids (MUFAs) decreased, and polyunsaturated fatty acids increased with increasing dietary lipid levels. With the exception of MUFAs, the fatty acid profiles of liver and muscle were similar. Dietary lipid levels were negatively correlated with low-density lipoprotein- cholesterol content and positively with triacylglycerol and glucose contents. In the lipid-fed groups, there was a significant down-regulation of fatty acid synthase (FAS) mRNA in liver, muscle, and visceral adipose tissues. There was a rapid up-regulation of lipoprotein lipase (LPL) mRNA in muscle and liver with increasing dietary lipid levels. In visceral adipose tissue, LPL mRNA was significantly down-regulated in the lipid-fed groups. Dietary lipids increased hormone-sensitive lipase (HSL) mRNA expression levels in the three tissues. These results strongly suggested that moderate dietary lipid levels were beneficial for adult tilapia growth performance and feed efficiency. However, excessive dietary lipid levels contributed to lipid deposition. Additionally, excessive dietary lipids may induce a competition between lipolysis and lipogenesis. FAS did not have tissue-specific regulation; however, the regulation of dietary lipids on LPL expression is tissue specific. FAS was a negative feedback regulator on fat deposition, and HSL was an indicator of fat content in tilapia.

Genetic parameters for reproductive traits in female Nile tilapia (Oreochromis niloticus): II. Fecundity and fertility

Harvest weight is the main trait in Nile tilapia (Oreochromis niloticus) breeding programmes. The effects of selection for harvest weight on female reproductive traits are unknown. In this paper we estimate genetic parameters for reproductive traits and their correlation with harvest weight using females from the generation 12 of the GIFT strain of Nile tilapia in the Mekong Delta of Viet Nam. Spawning records were obtained from single pair mating as well as group mating experiments. The traits were categorised into two groups: fecundity-related traits and fertility-related traits. Fecundity traits were: number of eggs (NEGG), relative fecundity as the ratio of number of eggs to female spawning weight (RFEC), egg weight (EGGW) and egg diameter (EGGD); fertility traits were: number of fertilised eggs (FEGG), number of hatched eggs (HAT), number of swim-up fry (SWUP), and fertilisation rate (FER, in %). Heritability estimates for fecundity traits were low, ranging from 0.05 to 0.08. Heritability estimates for fertility traits were also low, ranging from 0.06 to 0.12. Genetic correlations for HW with NEGG and TEGGW were positive (0.51 and 0.42, respectively), while correlations for HW with RFEC, EGGW, and EGGD were negative (−0.72, −0.48, and −0.50, respectively). The same trend was observed for body weight at spawning (SPW), but genetic correlations between SPW and fecundity traits were higher than those between HW and fecundity traits. Genetic correlations between HW and fertility traits were all moderate to high (0.46 to 0.69), except for FER (0.15±0.24). Genetic correlations between SPW and fertility traits were even higher (0.69 to 0.93). We conclude that both HW and SPW have favourable genetic correlations with NEGG, RFEC, and SWUP, which are the desired characteristics for Nile tilapia seed production. Selection for HW does not affect these traits. However, Nile tilapia females selected for large HW tend to produce smaller eggs. We recommend monitoring the phenotypic and/or genetic trend in this trait, as smaller eggs might, on the longer term, lead to lower fry survival.

Combined effect of temperature and salinity on the fertilization and hatching rate in the GIFT strain of Nile tilapia, Oreochromis niloticus

We evaluated the effect of temperature and salinity on the artificial fertilization rate(FR,%) and hatch-ing rate(HR,%) in the GIFT strain of Oreochromis niloticus using a Central Composite Design and Response Surface method.The fish were reared in temperatures ranging from 20?34?C and the salinities ranging from 0?18.Both FR and HR decreased as temperature and salinity approached the lower and higher bounds.HR and FR were significantly affected by the linear and quadratic of temperature and salinity(P0.001).However,there was no evidence for a synergistic effect between temperature and salinity(P0.05).After correcting for the negative cor-relation coefficient,the r2 values for the equations explaining temperature and salinity were 0.957 8 and 0.960 1,respectively(P0.01).Thus,these models can be used to forecast HR and FR in Nile tilapia.The highest FR(80.81%) and HR(77.63%) were observed eggs incubated at 27.14?C and 8.95 of salinity.Our results may be used to improve fertilization and hatching success in cultured strains of Nile tilapia.

A comparison of microsatellites and SNPs in parental assignment in the GIFT strain of Nile tilapia (Oreochromis niloticus): The power of exclusion

In this study, parental assignment was studied in the 10th generation of a pedigreed selected Nile tilapia (Oreochromis niloticus) population (GIFT) and their offspring, by comparing two types of molecular markers, microsatellites and SNPs, using an exclusion-based (Vitassign) and a likelihood-based (Cervus) method. For the experiment, G10 parents were divided in 4 groups (cohorts) and allowed to produce offspring by natural group mating. In total 173 offspring were tested against 238 parents, using either 12 microsatellites (PIC=0.639; exclusion power 68.0%) or 122 SNPs (PIC=0.341; exclusion power 99.9%). In this study, more than half of the candidate parents were either full- or half-sibs with other parents. Furthermore, 13.8% of the parents died before being sampled for DNA.When offspring were assigned to parents in the same cohort, using Vitassign, for microsatellites, allowing up to 2 mismatches, 37.6% offspring got unique assignments, 45.1% got multiple assignments, and 17.3% were not assigned; for SNPs with up to 15 mismatches allowed, 83.8% offspring got unique assignments while 13.9% got multiple assignments. Only 2.3% were not assigned. Using Cervus, for microsatellites, the mean ‘strict’ (>95% CF) assignment rate across the 4 cohorts was 18%, the ‘relax’ (80–95% CF) assignment rate was 43%, and 39% were not assigned; for SNPs, 39% ‘strict’ assignments were obtained (mean across 4 cohorts); the remaining offspring were not assigned. In general assignment rates were higher when cohort offspring were assigned to all parents combined, irrespective of method (Vitassign or Cervus) or marker used. However, consistency of assignments between microsatellites and SNPs was low: 28% with Vitassign and 16% with Cervus. Consistency of assignments between Cervus and Vitassign was high with SNPs (65%), but was low with microsatellites (31%). We conclude that missing parents and relatedness among candidate parents resulted in low assignment rates. Furthermore, low exclusion power of the microsatellite set resulted in low assignment rates and multiple parent pair assignments irrespective of method used. Exclusion methods and likelihood-based methods can be equally good for parental assignments, providing that good marker sets with high exclusion power are available.

Complete Genome Sequence of Streptococcus agalactiae ZQ0910, a Pathogen Causing Meningoencephalitis in the GIFT Strain of Nile Tilapia (Oreochromis niloticus)

Streptococcus agalactiae (group B streptococcus [GBS]) is a pathogen that causes meningoencephalitis in Nile tilapia (Oreochromis niloticus). Here, we reported the complete genome sequence of S. agalactiae strain ZQ0910, which was isolated from the GIFT strain of Nile tilapia in Guangdong, China.

Growth and survival rate of three genetic groups fed 28% and 34% protein diets

The strain by nutrition interaction in body weight and survival rate was examined by testing three genetic groups (Selection and Control lines of the GIFT strain, and Red tilapia) at two levels of protein in the diet (28% and 34%). The GIFT strain of Nile tilapia (Oreochromis niloticus) has been selected for high-breeding values for body weight, whereas the Control was contemporaneously maintained and selected for breeding values of body weight close to the population mean. The Red tilapia (Oreochromis spp) was unselected at the time of the experiment. There were a total of 6000 fish at stocking in the study (2000 fish per genetic group). During the grow-out period of 147 days, within each genetic group, the fish were randomly assigned to either a 28% or a 34% protein diet. Survival rate during grow-out averaged 72%. A total of 4335 fish were harvested, with individual body measurements and survival recorded. The effect of genetic group accounted for the largest proportion of variation in body weight and survival, followed by sex and protein level. Across the two dietary protein levels, the GIFT strain had the highest growth. The difference in body weight between the Control and Red tilapia was not statistically significant (P > 0.05). Responses in growth to dietary protein levels also differed between genetic groups. No differences (P > 0.05) in body weight were found in the GIFT selection and Control fish fed 28% or 34% protein diets. However, body weight of Red tilapia was greater in the high- than in the low-protein diet. In contrast to body weight, survival rate from stocking to harvest was affected by protein level. The high-protein diet significantly improved survival rate, averaging 24% across the three strains. The overall results indicate significant effects of genetic group and dietary protein level on both body weight and survival rate; however, the interaction between strain and dietary protein levels was small and possibly unimportant for these traits. It is concluded that the 28% protein diet used in the selection programme for the GIFT strain results in the selection of genotypes that can perform well under commercial feeds.

Morphological variation and mathematical analysis of effects of morphological traits on body-weight of GIFT tilapia after 3 generations of breeding

GIFT strain of Nile tilapia(Oreochromis niloticus) played an important role in world fishery.Several researches indicated that the growth performance of GIFT can still be improved.As an important indicator of breeding,body-weight was influenced by many morphological traits,and morphological traits that impact offspring body-weight might be changed after breeding,so comparative analyses of the impacts of morphological traits on body-weight between the offspring and parental generation became necessary.Sixty families of GIFT were introduced into FFRC as the parents(P) in 2006 for further study,three generations of offspring were bred(F1,F2,F3).In order to observe the achievement of breeding,body-weight(Y),body-length(X1),body-thickness(X2) and body-height(X3) of the P and F3 were measured,variation of four morphological traits of P and F3 were analyzed;correlation analysis,path analysis and regression analysis were used to calculate the correlation coefficient,path coefficient and the coefficient of determination,and the multiple regression equations between body-weight(Y) and morphological traits(X1,X2,X3)were established and analyzed.Results showed that: 1) compared with P,body-weight,body-length and body-thickness of F3 had a significant increase(P0.01),meanwhile a certain decline in the coefficient of variation(CV) was observed,body size of tilapia of F3 showed a trend of being consistent.Male of F3 had increased in some degree,significant increase of 4 traits of the male group was not observed.2) Trait af-fected the body-weight most of F3 converted to body-length,which was body-height×body-length in P.3) The influence of body-length,body-thickness and body-height on body-weight declined more in F3 than that in P.Results above indicated that,breeding made a positive effect on the growth speed of GIFT;for further study we should be more careful in selecting morphological traits,and some other morphological traits which might impact the body-weight should be taken into account for more accurate breeding project.

Genotype by production environment interaction in the GIFT strain of Nile tilapia ( Oreochromis niloticus)

Three discrete generations of GIFT fish (Nile tilapia strain, Oreochromis niloticus; a total of 10,065 fish with pedigree and phenotypic information) were tested in pond and cage culture environments to determine genotype by production environment interaction between both environments in Malaysia. Live weight (selected trait), standard length, body depth and width were recorded. A bivariate animal model was used to estimate variance and covariance components, whereby the homologous body traits in pond and cage environments were treated as genetically distinct traits. The heritabilities estimated for these body traits ranged from 0.19 to 0.40 in the pond environment, and from 0.23 to 0.34 in the cage environment. Across all traits the maternal common environmental effects ranged from 0.14 to 0.26 and were greater for the pond than for the cage environment. The genetic correlations between the pond and cage environments were 0.73 ± 0.09 for live weight, 0.81 ± 0.09 for standard length, 0.78 ± 0.10 for body depth, and 0.85 ± 0.13 for body width. Coupled with the total selection responses for live weight after two generations of selection, being 35% for the pond environment and 45% for the cage environment, we concluded that genotype by environment interaction for GIFT strain between pond and cage environments was not important. Hence, it would not be necessary to have two separate selective breeding programs for the GIFT strain in Malaysia.

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.