Genetically Improved Farmed Tilapia Strain Research Articles

Acute hyperthermia and hypoxia tolerance of two improved strains of nile tilapia (Oreochromis niloticus)

Tilapia production in Ghana has been hit with episodes of stress and pathogen-induced mass fish kills which have anecdotally been linked to the culture of illegally imported Genetically Improved Farmed Tilapia (GIFT) strains of Nile tilapia, Oreochromis niloticus. This study was thus set up to comprehensively assess the stress tolerance of the GIFT strain and a native strain of Nile tilapia (the Akosombo strain) following exposures to hyperthermic and hypoxic stressors. In a series of experiments, oxygen consumption (MO2), aquatic surface respiration (ASR), thermal limits and hypoxia tolerance were assessed. The effects of these stressors on haematological parameters were also assessed. The GIFT strain was less tolerant of hypoxia and performed ASR at higher O2 levels than the Akosombo strain. Under progressive hypoxia, the GIFT strain exhibited higher gill ventilations frequencies (fV) than the Akosombo strain. The thermal tolerance trial indicated that the Akosombo strain of O. niloticus has higher thermotolerance than the GIFT strain and this was reflective in the higher LT50 (45.1℃) and LTmax (48℃), compared to LT50 and LTmax of 41.5℃ and 46℃ respectively. These results imply that it is crucial to consider how the GIFT strain performs under various environmental conditions and changes during culture. Particularly, raising the GIFT strain of Nile tilapia in earthen ponds rich in phytoplankton and subject to protracted episodes of extreme hypoxia may have a detrimental physiological impact on its growth and welfare.

Revaluating the dietary methionine requirements in an improved strain of nile tilapia (Oreochromis niloticus)

It has been shown with terrestrial animals that the genetic improvement increases the nutrient requirements of the animal, which becomes more efficient in using these nutrients to achieve their higher growth potential. This study was conducted to estimate the dietary methionine requirements of different generations of the Genetically Improved Farmed Tilapia (GIFT) strain of Nile tilapia at the juvenile stage (17.51 g–19.55 g initial body weight). To achieve this objective, a completely randomized 2 × 6 factorial design was applied, with the genetic background of fish (generation) as the first independent variable with two levels, the 16th and 17th generations, and the methionine content of the diet as the second independent variable, with 6 graded levels, 0.52, 0.62, 0.84, 0.94, 1.04 and 1.27% of methionine in the diets, respectively. At the end of the 42-day experiment, the interaction effect of the generation × diet was not significant (P > 0.05) for any of the response parameters studied. The genetic improvement led to 15% more growth in the 17th generation than the 16th generation of the GIFT strain of Nile tilapia, which was accompanied with better feed conversion ratio, protein productive value, and energy productive value in the former generation (P < 0.05). Whatever the generation considered, the optimum dietary methionine requirement for the growth of the improved GIFT strain of Nile tilapia was estimated in this study, using the broken-line model, between 0.75% and 0.80% of the diet (with a cysteine level of 0.50% of the diet), which is higher than 0.49% of the diet previously estimated for conventional Nile tilapia at the juvenile stage. Therefore, the genetic improvement applied to the GIFT strain of Nile tilapia likely led to a higher methionine and total sulfur amino acid requirement than the conventional strains. The results of this study support the need to update the existing nutrient requirement databases of fish, in order to ensure that diets are formulated to effectively satisfy the requirements of not only conventional, but also improved strains of fish, for the full expression of their accrued growth potential of the latter strains.

Chromosome-level genome sequence of the Genetically Improved Farmed Tilapia (GIFT, Oreochromis niloticus) highlights regions of introgression with O. mossambicus

BackgroundThe Nile tilapia (Oreochromis niloticus) is the third most important freshwater fish for aquaculture. Its success is directly linked to continuous breeding efforts focusing on production traits such as growth rate and weight. Among those elite strains, the Genetically Improved Farmed Tilapia (GIFT) programme initiated by WorldFish is now distributed worldwide. To accelerate the development of the GIFT strain through genomic selection, a high-quality reference genome is necessary.ResultsUsing a combination of short (10X Genomics) and long read (PacBio HiFi, PacBio CLR) sequencing and a genetic map for the GIFT strain, we generated a chromosome level genome assembly for the GIFT. Using genomes of two closely related species (O. mossambicus, O. aureus), we characterised the extent of introgression between these species and O. niloticus that has occurred during the breeding process. Over 11 Mb of O. mossambicus genomic material could be identified within the GIFT genome, including genes associated with immunity but also with traits of interest such as growth rate.ConclusionBecause of the breeding history of elite strains, current reference genomes might not be the most suitable to support further studies into the GIFT strain. We generated a chromosome level assembly of the GIFT strain, characterising its mixed origins, and the potential contributions of introgressed regions to selected traits.

Evaluation of growth performance of three strains of Nile tilapia Orechromis niloticus (L., 1758) and relation with water physico-chemical parameters reared in brackishwater ponds, Bangladesh

This study was executed to resolve the argument on the growth superiority of three Nile tilapia strain such as, existing strain of Nile tilapia (ESNT), genetically improved farmed tilapia (GIFT) and sex reversed Monosex cultured in brackishwater pond and to comprehend the relationship of water physico-chemical parameters with the growth. Analogous age group of fish each weighing about 0.62±0.09 g with iso-stocking density (5ind./m2) and a culture tenure of 120 days was considered. The physico-chemical variables were at their optimal level over the entire time span of culture. However, all physico-chemical variable beyond alkalinity and ammonia showed strong positive correlation with mean fish weight. The study revealed that, weight gain by GIFT strain was nearly 25.9% and 5.10% higher than Monosex and ESNT strain, respectively. The highest final mean body weight was achieved in the GIFT strain (223±8.60 g) and there was significant difference among the strains. The highest apparent SGR of 16.85%/day was attained in the GIFT strain without significant variation across the strain. GIFT strain gave significantly (p&lt;0.05) higher gross fish yield (9789.70 Kg ha-1) along with best feed conversion ratio (FCR) and survival, whereas they differed significantly among the three strains. The GIFT strain showed closest isomeric growth while the rest two had allotropic growth pattern. Thereby the results established that, strain difference significantly (p&lt;0.05) impacted the growth parameters and GIFT was the best strain. Overall results greatly minimizes the controversy on growth pattern of different strains of Nile tilapia reared in brackishwater ponds, Bangladesh.

Standardization of stocking density on genetically improved farmed tilapia (GIFT) Oreochromis niloticus in pond cage aquaculture system

Aim: To standardize the stocking density of GIFT strain of Nile tilapia (Oreochromis niloticus) to optimize survival, growth, biomass production and maximum economic gain in pond cage culture system. Methodology: Study was conducted in triplicate for 180 days in fish cages installed in cemented pond of 726 m-2 area and depth of 2.0 m. Stocking density of GIFT Tilapia was maintained @ 40 m-3 (C1), 50 m-3 (C2), 60 m-3 (C3), 70 m-3 (C4), 80 m-3 (C5) and 90 m-3 (C6), respectively. Water quality and growth parameters were studied at fortnight basis. Supplementary diet (D1) (30.0 % crude protein on dry weight basis) was provided @ 2% body weight. Survival rate, average growth rate, biomass production, specific growth rate (SGR), feed conversion ratio (FCR), length-weight relationship, condition factor, economics and benefit cost ratio were evaluated. Results: All water quality parameters were within the limit suggested for aquaculture. Maximum survival was achieved in C1 (96.25%) and survival rate reduced with increasing stocking density in cages. Decrease in SGR was observed with increasing stocking density. The average growth rate was highest in C1 (112.20 g) and lowest in C6 ( 61.80 g) whereas the maximum biomass (23.136 kg) was harvested from C4 with stocking density of 70 m-3 with best FCR (1.32). Benefit cost ratio was evaluated best in C4 (0.39). Interpretation: Pond cage aquaculture with improved stocking condition is suitable for GIFT tilapia growth, biomass production and maximum economic gain.

Growth, yield and profitability of genetically improved farmed tilapia (GIFT) and non-GIFT strains in Bangladesh

On-farm performance of the genetically improved farmed tilapia (GIFT) strain in monoculture and polyculture ponds in Bangladesh was assessed using a stratified random sample of 213 GIFT and 256 non-GIFT farmers. The GIFT strain of Nile tilapia (Oreochromis niloticus) was mostly farmed by small-scale farmers operating less than one ha of ponds and with a lower assets index than their non-GIFT counterparts. The GIFT strain had a faster growth rate (27% and 36% faster than that of non-GIFT tilapia in monoculture and polyculture, respectively). Although GIFT and non-GIFT farmers applied different stocking strategies with GIFT farmers growing much smaller fingerlings compared to non-GIFT farmers (7.3 g for GIFT and 17.2 g for non-GIFT, and 9.1 g for GIFT and 20.3 g for non-GIFT in monoculture and polyculture, respectively. Yields were statistically different between both strains in monoculture and polyculture (8.1 tons/ha per cycle for GIFT and 6.2 tons/ha per cycle for non-GIFT in monoculture, and 9.3 tons/ha per cycle for GIFT and 7.8 tons/ha per cycle for non-GIFT in polyculture). In polyculture systems, overall polyculture yield was statistically different at the 10% level (12.7 and 10.2 tons/ha for GIFT and non-GIFT ponds). In terms of profitability performance, GIFT tilapia is more profitable and cost-effective than non-GIFT. Findings from this study highlight the importance of adopting culture of high-performance strains to close yield gaps and realize the potential benefits of the GIFT strain.

The Effects of Feed Restriction and Isolated or Group Rearing on the Measurement of Individual Feed Intake and Estimation of Feed Conversion Ratio in Juvenile Nile Tilapia (Oreochromis niloticus) for Selective Breeding Purposes.

Accurately measuring the phenotype at the individual level is critical to the success of selective breeding programs. Feed efficiency is a key sustainability trait and is typically approached through feed conversion ratio (FCR). This requires measurements of body weight gain (BWG) and feed intake (FI), the latter being technically challenging in fish. We assessed two of the principal methods for measuring feed intake in fish over consecutive days: (1) group rearing 10 fish per group and video recording the meals and (2) rearing fish individually on a restricted ration. Juvenile Nile tilapia (Oreochromis niloticus) from the Genetically Improved Farmed Tilapia (GIFT) strain and the Cirad strain were entered into the study (128 GIFT and 109 Cirad). The GIFT strain were reared over three consecutive periods of 7 days each under different feeding, recording, and rearing scenarios (i) in groups fed an optimal ration (g100) or (ii) fed a 50% restricted ration (g50) both with video records of all meals and (iii) reared in isolation and fed a 50% restrictive ration. The Cirad strain were tested similarly but only for scenarios (i) and (iii). All fish were fed twice daily with a calculated ration. Correlations showed the same trends for the GIFT and the Cirad strains. For the GIFT strain, correlations were positive and significant for BWG and FI measured in scenarios (i) and (ii), 0.49 and 0.63, respectively, and FI measured in scenarios (i) and (iii) (0.50) but not for BWG measured in scenarios (i) and (iii) (0.29, NS). The phenotypic correlation estimated for FCR between scenarios (i) and (ii) with fish fed an optimal or a 50% restricted ration was low and not significant (0.22). Feed Conversion Ratio for GIFT fish reared in groups or in isolation and fed with a restricted ration [scenarios (ii) and (iii)] were not significantly correlated either. Social interactions between fish, potentially impacting their efficiency, may explain the results. Therefore, selective breeding programs seeking to improve feed efficiency will need to carefully plan the feeding rate and the rearing system used to estimate FCR in order to optimize selection for the targeted production system.

Animal by‐products with or without enzymatic hydrolysis completely replacement of fish meal in genetically improved farmed tilapia diets ( Oreochromis niloticus )

An 8-week feeding trial was performed to examine the potential of total replacement of fish meal with animal by-products with or without enzymatic components in juvenile genetically improved farmed tilapia (GIFT) diets, Oreochromis niloticus, (mean initial weight, 19.71 ± 0.28 g), reared in RAS system. Five isonitrogenous and isoenergetic diets were formulated with fish meal for the diets with total replacement of the isonitrogenous amounts of enzymatic fish meal (E-FM), chicken liver meal (CLM), enzymatic chicken liver meal (E-CLM), dried porcine solubles (DPS) and enzymatic dried porcine solubles (E-DPS) respectively. The results indicated that the weight gain rate (WGR) and specific growth rate (SGR) in the FM group were significantly higher than the E-FM and E-CLM groups (p < .05), but the specific growth rate (SGR) in the E-CLM group lower than the E-FM group. The feed conversion ratio (FCR) in FM and CLM was significantly lower than the E-FM, E-CLM and E-DPS groups (p < .05), and no significant difference was observed among the FM, CLM and DPS groups (p > .05). The values of the protein retention efficiency (PRE) and protein efficiency ratio (PER) in FM, CLM and DPS groups were significantly higher than the E-CLM group (p < .05). The values of feed intake ratio (FIR) in FM and CLM groups were significantly lower than the E-FM, E-CLM and E-DPS groups (p < .05). There was no significant difference in the whole body contents of moisture, crude lipid and crude ash among the FM and E-CLM groups (p > .05). The whole body contents of crude protein in the FM group were significantly higher than the E-FM, CLM, E-CLM DPS and E-DPS groups (p < .05). The apparent digestibility coefficients (ADC) of dry matter, crude protein and crude lipid in the FM, E-FM, E-CLM and E-DPS groups were not significantly different (p > .05). The serum glucose(GLU), total cholesterol (TCHO) and triglycerides (TG), or the activities of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were not affected by the different treatments (p > .05). There was no significant difference in serum total protein (TP) or albumin (ALB) and between the FM group and other groups (p > .05). There was no significant difference in the serum urea nitrogen (BUN) content in the FM, CLM, E-CLM and DPS groups (p > .05). Fish fed with the CLM and DPS diets had significantly lower hepatic GHR1, IGF1 and IGF2 gene mRNA expression levels than in fish fed the FM diet (p < .05). The present data showed that 6% of dietary fish meal can be totally replaced by the chicken liver meal and dried porcine solubles with no effect on the growth performance of GIFT strain tilapia.

Genomic selection for resistance to Streptococcus agalactiae in GIFT strain of Oreochromis niloticus by GBLUP, wGBLUP, and BayesCπ

China is the largest producer of tilapia in the world, and genetically improved farmed tilapia (GIFT) strain of Oreochromis niloticus is the main breed which is cultured widely in coastal and inland areas of China. Streptococcal disease, caused by Streptococcus agalactiae, is one of the most prevalent diseases in farmed tilapia that causes huge economic loss, leading to urgent needs for disease-resistant breed of tilapia. In view of the predictive accuracy and selective efficiency, genomic selection (GS) could be a feasible and optimal method to improve the S. agalactiae resistance in GITF. In this study, the genetic architecture of resistance to S. agalactiae and the accuracy of three GS methods at improving the resistance in GIFT were investigated by artificial challenge test (for phenotypes) and whole-genome re-sequencing (for genotypes). A total of 897 individuals were genotyped (776 individuals were used as the reference group) and 3,759,557 high-quality SNPs were obtained for downstream analysis. The genome-wide association study (GWAS) using weighted genomic BLUP (wGBLUP) and 1 M SNPs revealed that resistance to S. agalactiae in GIFT belongs to a polygenic genetic architecture. Seven suggestive trait-related SNPs were identified on chromosomes 4, 7, 11, and 18. These SNPs explained more than 1% genetic variance. Three GS (GBLUP, wGBLUP, and BayesCπ) methods had better estimation than pedigree-based BLUP, which indicated that the genomic selection approach could be a feasible and promising method to improve the S. agalactiae resistance in GIFT. Although wGBLUP and BayesCπ resulted in similar estimation accuracy, wGBLUP had priority when estimating time needs to be considered.

Selective breeding technique: Pandu and Kunti tilapia (Oreochromis niloticus) broodstock candidates at PBIAT Janti, Klaten-Central Java

Tilapia (Oreochromis niloticus) is a freshwater aquaculture commodity with high demand and economic value. With developing breeding technology, hybrid tilapia also grows in popularity. Pandu tilapia is a strain of Singapore tilapia, while Kunti tilapia is a GIFT (Genetically Improved Farmed Tilapia) strain. To ensure the continuity of good fingerling stock, the individual selection needs to be conducted on Pandu and Kunti Tilapia broodstock candidates. The family selection method was chosen using 125 pairs of broodstock candidates. The male and female ratio is 1: 1 with horizontal breeding where a broodstock was mated with another fish from its own family or strain to ascertain that there is no cross-breeding. Larvae hatched from the spawning were reared in a nursery pond, then graded. The top 50% fish was reared until reaching the adult stage and bred again. The broodstock candidates were then tested for its performance and mass spawned.

Single‐Nucleotide Polymorphism Discovery and Genetic Variation in YY‐Male and Mixed‐Sex Strains of Nile Tilapia Available in the United States

AbstractThe present study was focused on the discovery of single‐nucleotide polymorphisms (SNPs) and measuring genetic variation in three YY‐male and five mixed‐sex Nile Tilapia Oreochromis niloticus strains, which are available in the United States. We performed restriction site‐associated DNA sequencing for SNP discovery and genotyping. Overall, 31,813 SNPs were identified and used to measure both intra‐ and interstrain genetic variation. Mean expected heterozygosity (He) ranged from a low of 0.084 in the Miami YY strain to a high of 0.222 in the Miami mixed‐sex strain. Two of the three YY groups (Miami YY and Fishgen YY Red) had the lowest He values (0.084 and 0.085, respectively) and the second‐ and third‐lowest observed heterozygosity (Ho) values (both Ho = 0.107). The number of private alleles varied from 90 to 3,795 in different strains and tended to increase with increasing He. Inbreeding, as measured by FIS, was found to be low in all populations, ranging from −0.060 ± 0.004 (mean ± SE) in the Fishgen YY Dark strain to 0.04 ± 0.0093 in the GIFT (Genetically Improved Farmed Tilapia) strain; this indicates that the analyzed strains are currently being maintained with approximately random mating of individuals. Genetic differentiation between populations, as measured by pairwise FST, ranged from little differentiation (FST = 0.06 for the Ismailia Canal and GIFT strains) to strong differentiation (FST = 0.32 for the Miami YY and Lake Manzala strains). The discovered SNPs and quantification of genetic variation can be used for parentage determination and high‐throughput pedigree reconstruction as well as for determining the optimal interstrain crosses to achieve heterosis.

Evaluation of production performance and profitability of hybrid red tilapia and genetically improved farmed tilapia (GIFT) strains in the carbon/nitrogen controlled periphyton-based (C/N- CP) on-farm prawn culture system in Bangladesh

Performance of hybrid red tilapia (Mutant, Oreochromis niloticus×Oreochromis mossambicus) and GIFT tilapia strain (Oreochromis niloticus) in C/N-CP prawn (Macrobrachium rosenbergii) farming system was evaluated at the farmers' pond at Bailor union under Trishal upazilla of Mymensingh district, Bangladesh. The on-farm trial had two treatments: TR and TG (named according to the tilapia strains) with three replications. Six rectangular ponds of varying sizes (400–880m2) were used for this experiment. Hybrid red and GIFT tilapia stains were stocked with prawn at the stocking densities of 1 tilapia fingerlings (either red or GIFT strain) and 3 prawn juveniles m-2 in both treatments. Bamboo side shoot were posted vertically as periphyton substrate. This resulted in an additional substrate surface area of 1067m2 for periphyton development equaling 147% of the pond surface area. Considering the body weight of freshwater prawn only, feeding rates were 10% of body weight at the beginning of the study (up to 30days), and feeding application was gradually reduced to 3% in the last month assuming 80% survival. The abundance of total benthos and periphyton as well as total periphytic biomass were significantly higher (P<0.05) in TR than TG treatment and they were also differed significantly (P<0.05) among different months with a decreasing trends (exception to some extent) over the experimental period. The individual harvesting weight, individual weight gain, specific growth rate, Food Conversion Ratio (FCR), survival (%), gross and net yields of prawn were similar in two treatments. In contrast, the GIFT tilapia strain showed a higher (P<0.05) individual harvesting weight, individual weight gain, specific growth rate ((SGR, % bw d-1), survival, gross and net yields (1935 and 1825kgha-1, respectively) combined gross and net yields (2952 and 2784kgha-1, respectively), and economic return (3755 US$ with BCR 0.82) than the hybrid Red tilapia.

Genetic parameters for uniformity of harvest weight and body size traits in the GIFT strain of Nile tilapia.

BackgroundAnimal breeding programs have been very successful in improving the mean levels of traits through selection. However, in recent decades, reducing the variability of trait levels between individuals has become a highly desirable objective. Reaching this objective through genetic selection requires that there is genetic variation in the variability of trait levels, a phenomenon known as genetic heterogeneity of environmental (residual) variance. The aim of our study was to investigate the potential for genetic improvement of uniformity of harvest weight and body size traits (length, depth, and width) in the genetically improved farmed tilapia (GIFT) strain. In order to quantify the genetic variation in uniformity of traits and estimate the genetic correlations between level and variance of the traits, double hierarchical generalized linear models were applied to individual trait values.ResultsOur results showed substantial genetic variation in uniformity of all analyzed traits, with genetic coefficients of variation for residual variance ranging from 39 to 58 %. Genetic correlation between trait level and variance was strongly positive for harvest weight (0.60 ± 0.09), moderate and positive for body depth (0.37 ± 0.13), but not significantly different from 0 for body length and width.ConclusionsOur results on the genetic variation in uniformity of harvest weight and body size traits show good prospects for the genetic improvement of uniformity in the GIFT strain. A high and positive genetic correlation was estimated between level and variance of harvest weight, which suggests that selection for heavier fish will also result in more variation in harvest weight. Simultaneous improvement of harvest weight and its uniformity will thus require index selection.Electronic supplementary materialThe online version of this article (doi:10.1186/s12711-016-0218-9) contains supplementary material, which is available to authorized users.

Genetic parameters for survival during the grow-out period in the GIFT strain of Nile tilapia (Oreochromis niloticus) and correlated response to selection for harvest weight

The aims of this study were the estimation of genetic parameters for survival rate from tagging until harvest and the evaluation of the correlated response in survival rate to selection for harvest weight in the genetically improved farmed tilapia (GIFT) strain. The heritability for survival rate was low (0.038), and so was its genetic correlation with harvest weight (0.065), suggesting that selecting for the latter trait would have had no effect on survival. The calculation of the probability of survival by spawning season and line, fitting a model that included the random effects of individual animal and common environment, confirmed this prediction. There were very small and variable between line differences in the probability of survival, which generally favoured the selection line. We conclude that the focus of the GIFT programme on improving harvest weight was not detrimental to the survival of the fish during the grow-out phase.

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.

Effect of Feeding Frequency on Growth Rate, Body Composition and Gastric Evacuation of Juvenile GIFT Strain of Nile Tilapia (Oreochromis niloticus)

The specific objectives of this study were to determine the optimum feeding frequency in juvenile GIFT (Genetically Improved Farmed Tilapia) strain of Nile tilapia (Oreochromis niloticus), for growth rate, body composition, and gastric evacuation, as well as to investigate the passage of a single meal through the stomach in order to establish gastric evacuation rate. Six treatment groups of juvenile GIFT were fed to satiation with extruded feed, at 6 feeding frequencies: four, three, and two meals a day, and four meals, three, and two meals, every 2 days, for 6 weeks respectively. Each treatment (n=20) was replicated three times. As feeding frequency decreased, the growth rate of the juvenile GIFT decreased gradually. The feed intake of fish fed two meals a day was significantly lower than that of fish fed three meals a day (P &lt;0.05), whereas the feed efficiency ratio of fish fed two meals a day was significantly higher than that of fish fed three meals a day (P&lt;0.05). As feeding frequency decreased, moisture content of fish body increased and the fat and protein contents decreased gradually. Hepatosomatic indices of fish fed two, and three meals a day, were not statistically different to each other or to the remaining groups. The livers of all fish were normal. Gastric evacuation of the fish was best evaluated with the square root model. It was estimated that gastric feed contents gradually decreased and reached the prefeeding level within 15 h. Evacuation of 80% would require 9 h which appeared to correspond with the return of appetite. Our results suggest that two meals a day are optimal for growth performance of juvenile GIFT Nile tilapia.

Effects of IGF-1 genotype on weight gain and body shape in GIFT strain Oreochromis niloticus

Insulin-like Growth Factor 1(IGF-1) is one of important genes controlling growth and development in animals.By comparing with exon1-partial intron 2-exon 3-partial intron 4 sequences of IGF-1 from six indi-viduals of Genetically Improved Farmed Tilapia(GIFT) strain,we identified three SNPs on IGF-1 in this study,including intron1_A1307G,intron1_G1319T and intron3_C6T.PCR-RFLP was performed in intron1_A1307G and intron3_C6T genotypes detection on 121 individuals from five families of GIFT strain.The results of correlation analysis showed that intron1_A1307G was significantly associated with female fish weight gain and the ratio of body thickness/length(P0.05).The weight gain and thickness/length ratio of female fish with AA genotype were significantly higher than those of female fish with GG type(P0.05).However,the correlation of genotypes with those traits in male fish was not significant(P0.05).Intron3_C6T was significantly associated with weight gain in both male(P0.05) and female(P0.01).The weight gain of male fish with TT and CT genotype was significantly higher than that of male fish with CC type,while the weight gain of female with CT genotypes was significantly higher than that of female fish with TT.Intron3_C6T was also significantly associated with height/length ra-tio(P0.05) in female fish.The height/length ratio of female fish with TT and CT genotypes was significantly higher than that with CC(P0.05).In order to verify the performance of the screened markers in other families,we detected the correlation between intron1_A1307G,intron3_C6T genotypes and weight gain among 417 individuals from 60 families of GIFT strain(averaging seven individuals per family),and similar results were observed.The diverse genetic background and smaller size of samples resulted in the decreased correlation significance.These results showed that genetic background and sample size should be considered during molecular maker screening.And the two molecular markers of intron1_A1307G,intron3_C6T identified in this study could be used as refer-ence in GIFT strain breeding.

Effect of Dietary Fish Meal Replacement by Canola Meal on Growth Performance and Hepatic Intermediary Metabolism of Genetically Improved Farmed Tilapia Strain of Nile Tilapia, Oreochromis niloticus, Reared in Fresh Water

An 8‐wk feeding trial was conducted to evaluate the potential of replacing fish meal with canola meal in experimental diets for genetically improved farmed tilapia (GIFT) strain of Nile tilapia, Oreochromis niloticus (mean initial weight: 20.0 ± 0.62 g, means ± SD), reared in fresh water. Six isonitrogenous (30% crude protein) and isolipidic (10%) diets were formulated with canola meal included at six levels of 0 (control), 11, 22, 33, 44, and 55%, replacing 0, 15, 30, 45, 60, and 75% fish meal, respectively. Growth performance and feed utilization showed no significant differences among the treatments. In general, dietary canola meal supplementation showed significant effect on hepatic composition of tilapia, but not muscle composition. Viscerosomatic index tended to increase with increasing dietary canola meal levels from 0 to 44%, and then declined when dietary canola meal levels further increased from 44 to 55%. Dietary fish meal replacement by canola meal significantly influenced several hepatic enzymatic activities, including succinate dehydrogenase, lactate dehydrogenase, malic dehydrogenase, lipoprotein lipase, and hepatic lipase, suggesting that dietary fish meal replacement by canola meal had significant effects on nutrient metabolism in the liver. Based on the information above, 75% of dietary fish meal could be replaced by canola meal with no effect on growth performance of GIFT strain of Nile tilapia. Use of canola meal in practical diets for GIFT stain of Nile tilapia may allow producers and feed mills to formulate more economical diets.

Preliminary observations on growth and survival ofOreochromis spilurusx GIFTOreochromis niloticusF1reciprocal hybrids in fresh and seawater

Tilapia has a significant potential for culture in saline environments. There is an increasing demand among tilapia producers to develop a tilapia hybrid that can survive well in marine water conditions. This study compared mean weight (MWT), daily growth rate (DGR), specific growth rate (SGR), survival, feed conversion ratio (FCR), condition factor (K), production rate (PR) and rate of skin lesions, and tail and fin rot as well as eye cataract in the Genetically Improved Farmed Tilapia strain (GIFT) of the Nile tilapia, Oreochromis niloticus (NN) and the salt-tolerant Oreochromis spilurus (SS), and their F1 reciprocal hybrids; O. niloticus ♀ x O. spilurus ♂ (NS) and O. spilurus ♀ x GIFT O. niloticus ♂ (SN) in freshwater (0 g L−1) and seawater (40 g L−1). Fish (3.5 g) were stocked at 150-fish m−3 and fed with sea bream pellets (47% protein) for 180 days. Results showed that in seawater, the SN hybrid had the highest values for MWT (165.9 g), DGR (0.9 g fish−1 day−1), SGR (2.14% day−1), survival (96.3%), PR (23.9 kg m−3) and best FCR (1.53) followed by the NS hybrid and the NN parent. Both hybrids had significantly lower rates of skin lesions and fin and tail rot than the NN genotype. In freshwater, the NN had the highest values for MWT (255.1 g), DGR (1.40 g fish−1 day−1), SGR (2.38% day−1), K (2.13%) and PR (34.9 kg m−3) followed by the NS and SN hybrids. High estimate of heterosis for MWT (41.3%), DGR (42.5%), SGR (10.7%) and survival (22.1%) was obtained in the hybrids reared in seawater, indicating that a hybrid vigor was produced and the fast growth trait from the GIFT parent was successfully combined with the salinity tolerance trait from the O. spilurus parent. The better growth performance and survival of the SN hybrid in seawater indicate that this hybrid is more suitable for culture in seawater than its reciprocal hybrid.

SNP marker detection and genotyping in tilapia

We have generated a unique resource consisting of nearly 175 000 short contig sequences and 3569 SNP markers from the widely cultured GIFT (Genetically Improved Farmed Tilapia) strain of Nile tilapia (Oreochromis niloticus). In total, 384 SNPs were selected to monitor the wider applicability of the SNPs by genotyping tilapia individuals from different strains and different geographical locations. In all strains and species tested (O. niloticus, O. aureus and O. mossambicus), the genotyping assay was working for a similar number of SNPs (288-305 SNPs). The actual number of polymorphic SNPs was, as expected, highest for individuals from the GIFT population (255 SNPs). In the individuals from an Egyptian strain and in individuals caught in the wild in the basin of the river Volta, 197 and 163 SNPs were polymorphic, respectively. A pairwise calculation of Nei's genetic distance allowed the discrimination of the individual strains and species based on the genotypes determined with the SNP set. We expect that this set will be widely applicable for use in tilapia aquaculture, e.g. for pedigree reconstruction. In addition, this set is currently used for assaying the genetic diversity of native Nile tilapia in areas where tilapia is, or will be, introduced in aquaculture projects. This allows the tracing of escapees from aquaculture and the monitoring of effects of introgression and hybridization.