Search

An 8‐week feeding trial with juvenile hybrid tilapia (Oreochromis niloticus × Oreochromis aureus) was conducted to assess the effects of dietary phenylalanine on growth, body composition, and biochemical parameters in plasma. Six diets were formulated with graded levels of l‐phenylalanine (0.43, 0.74, 1.01, 1.30, 1.60, and 1.91% of the diet). Each diet was randomly assigned to triplicate groups with 20 fish per replicate (5.63 ± 0.04 g). Weight gain, thermal growth coefficient (TGC), and protein retention efficiency (PRE) increased with the increasing levels of dietary phenylalanine, up to 1.30%, and declined slightly at higher levels. The ratio of whole‐body protein and lipid was significantly higher in fish fed 1.30% phenylalanine compared with those fed 0.43% phenylalanine (p

In teleosts, starvation induces an increase in appetite-related gene expression and peptide secretion in the hypothalamus. This reduces autonomic nervous activity and promotes food intake and body weight gain. We have previously demonstrated that single nucleotide polymorphisms (SNPs) in the 5′ flanking region of ghrelin affect gene regulation and are associated with superior growth traits in Nile tilapia (Oreochromis niloticus). Recent findings have also suggested that Ghrelin, Neuropeptide Y (NPY), and Prepro-orexin combine in the hypothalamus to regulate appetite in organisms, thus we hypothesized that SNPs in NPY and prepro-orexin may also indirectly regulate the growth of Nile tilapia. Accordingly, we examined the effects of SNPs in NPY and prepro-orexin in two populations of Nile tilapia—the GIFT (GF) and Egyptian (EG) populations—by cloning the 5′ flanking and coding regions of each gene and screening the SNPs in these regions to identify associations with superior growth traits. After preliminary screening and secondary prediction of function, 6 SNP loci (1 from NPY and 5 from prepro-orexin) were identified in the GF population, from which 9 diplotypes were constructed. Of these, four loci from prepro-orexin (g. −1108C > G, g. −1107C > G, g. −1063C > T, and g. −883C > T) and one diplotype were associated with superior growth traits. In the EG population, 4 SNP loci (1 from NPY and 3 from prepro-orexin) were identified and 6 diplotypes were constructed; however, none of these were associated with superior growth traits. Considering these findings, we discuss the necessity for functional prediction of SNP loci, and consider the differential conservativeness of the 5′ flanking and coding regions of appetite-related genes.

An 8-week feeding trial was conducted to determine the dietary threonine requirement of juvenile Nile tilapia Oreochromis niloticus. Six isonitrogenous and isoenergetic diets were formulated to contain graded levels of threonine, 0.73, 0.91, 1.14, 1.31, 1.56 and 1.72 % of dry weight, respectively. Each diet was randomly assigned to triplicate groups of 25 juvenile fish (2.97 ± 0.02 g), which were fed three times daily (8:30, 12:30 and 17:00) to apparent satiation. By the end of the feeding trial, weight gain (WG) was found to have increased with increasing dietary threonine levels up to 1.31 %, but WG then decreased in fish fed higher dietary threonine concentrations. Threonine concentration had no significant impact on survival, body composition or the measured haematological and immune parameters. There were, for example, no significant differences in serum lysozyme activity, superoxide dismutase activity, immune globulin M concentration and C-reactive protein content among dietary treatments. Using quadratic regression analysis of WG data, the optimal dietary threonine inclusion for juvenile tilapia was estimated to be 1.33 % of the diet (4.74 % of dietary protein).

In teleosts, ghrelin plays an important role in body weight gain. This hormone has been used in functional studies on food intake and foraging-related behaviors. However, the regulatory role of its 5′ flanking and coding regions is unknown. To examine the effects of single nucleotide polymorphisms (SNPs) in the ghrelin gene of Nile tilapia, we cloned sequences of its 5′ flanking and coding regions to analyze the regulatory elements binding sites and nonsynonymous mutation sites, and screened the SNPs in these two regions to find their association with mRNA expression levels and superior growth traits. No SNPs loci were found in the coding region. However, a SNPs locus (C−226 T) was identified in the amplified 5′ flanking region, for which we analyzed the distribution of three genotypes (CC, CT and TT) at frequencies of 17.80 %, 50.00 % and 32.14 %, respectively. TT is associated with an increased number of putative octamer transcription factor 1 binding sites (from 2 to 3); the TT genotype also exhibited more superior growth traits (body weight, total length, standard length, body depth) than either the CC and CT genotypes. Expression of ghrelin mRNA in Nile tilapia with the TT genotype was significantly up-regulated (P < 0.05) compared with the CC genotype. Thus, the polymorphism at the ghrelin locus C−226T is associated with superior growth in Nile tilapia, rendering the C−226T locus a potential marker for future selection of breeding stock to improve the quality and growth rate of farmed fish.

An 8-week feeding trial was conducted to determine the dietary threonine requirement of juvenile Nile tilapia Oreochromis niloticus. Six isonitrogenous and isoenergetic diets were formulated to contain graded levels of threonine, 0.73, 0.91, 1.14, 1.31, 1.56 and 1.72 % of dry weight, respectively. Each diet was randomly assigned to triplicate groups of 25 juvenile fish (2.97 ± 0.02 g), which were fed three times daily (8:30, 12:30 and 17:00) to apparent satiation. By the end of the feeding trial, weight gain (WG) was found to have increased with increasing dietary threonine levels up to 1.31 %, but WG then decreased in fish fed higher dietary threonine concentrations. Threonine concentration had no significant impact on survival, body composition or the measured haematological and immune parameters. There were, for example, no significant differences in serum lysozyme activity, superoxide dismutase activity, immune globulin M concentration and C-reactive protein content among dietary treatments. Using quadratic regression analysis of WG data, the optimal dietary threonine inclusion for juvenile tilapia was estimated to be 1.33 % of the diet (4.74 % of dietary protein).

The hybrid between Nile tilapia (Oreochromis niloticus,♀) and blue tilapia (O. aureus,♂) is an important strain in Chinese aquaculture industry. Two populations named AF (O. aureus, 29 samples) and NF (O. niloticus, 22 samples) were gathered from Freshwater Fisheries Research Center (FFRC). The other two named AG (O. aureus, 29 samples) and NG (O. niloticus, 28 samples) from Guangxi Fisheries Research Institute (GFRI). GFRI introduced AG and NG from AF and NF. The mitochondrial DNA D-loop was sequenced to assess the genetic diversity among four populations. A 580 bp fragment was sequenced. The 93 variable sites defined 39 haplotypes and three were shared. As a result, the genetic diversity of O. aureus AF and AG was much lower (H=0.497-0.532, K=0.69-0.714, π=0.0012-0.00124) than that of O. niloticus (H=0.849-0.866, K=24.286-24.807, π=0.04246-0.04337). Furthermore, the indices (H, K, π and D) was a slight increase between AF and AG, so did NF and NG. These results indicated that as the male parent, the AF and AG population was purebred and sustainable. And as the female parent, NF and NG had high genetic diversity. The conclusions might give reference to keep the germplasm diversity of tilapia and other introduced fishes.

An 8-week feeding trial was conducted to evaluate the effects of dietary arginine on growth performance, feed utilization, haematological parameters and non-specific immune responses of juvenile Nile tilapia (6.03 g). Five isonitrogenous and isoenergetic diets were formulated to contain graded levels of L-arginine (8.5 g kg−1, 11.5 kg−1, 15.3 kg−1, 18.8 kg−1 and 22.4 kg−1 dry diet) from dietary ingredients and crystalline arginine. Each diet was randomly assigned to triplicate groups of 25 juvenile fish (6.04 ± 0.02 g) three times daily (8:30, 12:30, and 17:00 hours) to apparent satiation. Results showed that the weight gain (WG) and special growth rate (SGR) increased with increasing dietary arginine levels up to 15.3 kg−1 and remained nearly the same thereafter. Arginine supplementation had no impact on the survival, body composition and haematological parameters of tilapia. However, the immune responses (plasma nitric oxide content, total nitric oxide synthase (T-NOS) and lysozyme activity) significantly (P

Genetic diversity plays a vital role for maintainingeconomically important traits in fish populations.The goal of this study was to assess the geneticvariability among four tilapia populations in China.Two populations named XA (Oreochromis aureus,30 samples) and AN (Egyptian Oreochromis niloticus,24 samples) were gathered from Freshwater Fish-eries Research Center (FFRC), and the other twonamed AL (O. aureus, 30 samples) and AJ (Egyp-tian O. niloticus, 30 samples) were from GuangxiFisheries Research Institute (GFRI). GFRI intro-duced AL and AJ from XA and AN, and selectedthem for generations. We want to know if AL andAJ have genetic changes after selection and gener-ations. Fifteen polymorphic microsatellite markerswere used. Our results indicated that the four tila-pia populations showed moderate genetic variabil-ity. The polymorphism information content (PIC)of the four populations was from 0.28 to 0.39; A e was from 1.67 to 2.15; the H e was from 0.35 to0.46; the genetic similarity indexes were from 0.94to 0.69 and also the clustering result showed thatthese four populations were highly related. Therewere no significant changes in genetic variationbetween late-introduced population and early-introduced population of O. aureus. Our resultshelped to understand the genetic variability of tila-pia populations in China and for future marker-assisted selection for important economic traits.Keywords: microsatellite, Nile tilapia, Blue tila-pia, heterozygosity, genetic diversity, selection,loss of genetic variationIntroductionTilapia belongs to Perciformes Cichlida and it isnative to Africa and Middle East. Tilapia (Oreochr-omis mossambicus) was introduced to China in theearly 1950s. Later, many species and strains (Or-eochromis niloticus, Oreochromis aureus, etc.) wereintroduced to China too (Li 2001; Li & Li 2001;Ye 2008). After their introduction to China, tila-pia has been undergone artificial selection forvarious economically important traits, such asfast growth, resistance to environmental stressorsand high percentage of males. Since the expandedproduction of tilapia started, China has been thelargest supplier of tilapia in the world till now(Li, Li, Tang & Cai 2009).Fresh Water Fisheries Research Center (FFRC) isthe most famous genetic and breeding resourcesCenter of Tilapia in China well known as the bestquality of purebred Tilapia parents. And now,FFRC was the head of China Agriculture Techni-que System-tilapia (CARS). The Blue tilapia(O. aureus, XA) was introduced from Auburn Uni-versity by FFRC in 1983, and they have selectedand bred a new Blue tilapia strain, named “Xia’ao1”. This strain is widely used for cross-breedingwith Nile tilapia to get all male tilapia fry inChina. The Nile tilapia samples (AN) used in thisstudy were introduced from Central laboratory forAquaculture Research, Abbassa, Ministry of Agri-culture and Land Reclamation of Egypt by FFRC in1999. Guangxi Fisheries Research Institute (GFRI)was the most famous tilapia fry productive unit inChina as the high male rate of cross-bred tilapiafry. GFRI introduced two strains of tilapia: XA(O. aureus) and AN (Egyptian O. niloticus) from

Twenty five microsatellite loci were used to analyze two blue tilapia populations ["Xia'ao 1" (ZA), Guangxi population] and four nile tilapia populations [Egypt strain (ZN), 88 strain (XN), Guangxi population (GN), American strain (MN)]. A total of 7775 fragments ranging from 100 bp to 400 bp in length were obtained. Three to eight alleles were amplified in 25 loci and 143 alleles in all the six populations. The average number of alleles in each locus was 5.72. The average values of observed heterozygosity (Ho) ranged from 0.7253 to 0.8160, the average expected heterozygosity (He) ranged from 0.5146 to 0.6834, the average polymorphic information content (PIC) ranged from 0.4212 to 0.6105, and the number of average effective alleles (Ae) ranged from 2.20 to 3.23. The highest genetic similarity index was 0.9130 (between ZA and GA); and the lowest was 0.4352 (between ZA and ZN). The results showed that the four nile tilapia populations contained a high level of genetic potential, and the two blue tilapia populations were moderate.