Utility of DNA barcoding in native Oreochromis species.

The importance of Oreochromis in worldwide aquaculture and regional fisheries motivates the study of their genetic diversity in their native range. In this article, all mitochondrial cytochrome c oxidase subunit I gene (COI) sequences of Oreochromis species are retrieved from Barcode of Life Data system to quantify the available DNA barcoding information from wild individuals collected within the native ranges of the respective species. It is found that 70% of the known species in the genus still lack a COI barcode, and only 15% of the available sequences are from within the respective native ranges. Many of the available sequences have been produced from specimens acquired from aquaculture and introduced, naturalized populations, making the assessment of variation within the original native range challenging. Analyses of the wild-collected fraction of available sequences indicated the presence of cryptic lineages within Nile tilapia Oreochromis niloticus and O. schwebischi, the occurrence of potential introgressive hybridization between O. niloticus and blue tilapia O. aureus, and potential ancestral polymorphism between Karonga tilapia O. karongae and black tilapia O. placidus. This article also reports a case of misidentification of O. mweruensis as longfin tilapia O. macrochir. These results stress the importance of improving the knowledge of genetic variation within the native ranges of Oreochromis species for better-informed conservation of these natural resources.

The diversity of ursodeoxycholic acid precursors from bile waste of commercially available fishes, poultry and livestock in Indonesia

Ursodeoxycholic acid (UDCA), a secondary bile acid (BA), has been used as a drug to treat various liver diseases. UDCA is synthesised from cholic or chenodeoxycholic acid (CA/CDCA), two primary BAs frequently used as the starting materials. Nowadays, swine, cattle, and poultry bile are the main sources of those BAs. However, other commercial animals could be promising sources as well. We identified two livestock, two poultries, and eight fishes that are commercially cultivated in Indonesia. Four free BAs including CA, CDCA, deoxycholic acid (DCA), and lithocholic acid (LA) were identified for their occurrences using thin-layer chromatography and high-performance liquid chromatography. CA was detected in cow, duck, red tilapia, gourami, the common carp, and grouper, whereas CDCA was only detected in two poultries and the common carp. The occurrence of DCA was common and abundant in most tested animals. In contrast, the presence of LA was found to be very low in all samples. The biliary bile of tilapia has been found to contain a high abundance of free CA (43% of the total bile). A simple extraction was able to purify CA from biliary bile of tilapia. This is a new promising and competitive source of CA.

Species-Specific Marker Discovery in Tilapia.

Tilapias (family Cichlidae) are of importance in aquaculture and fisheries. Hybridisation and introgression are common within tilapia genera but are difficult to analyse due to limited numbers of species-specific genetic markers. We tested the potential of double digested restriction-site associated DNA (ddRAD) sequencing for discovering single nucleotide polymorphism (SNP) markers to distinguish between 10 tilapia species. Analysis of ddRAD data revealed 1,371 shared SNPs in the de novo-based analysis and 1,204 SNPs in the reference-based analysis. Phylogenetic trees based on these two analyses were very similar. A total of 57 species-specific SNP markers were found among the samples analysed of the 10 tilapia species. Another set of 62 species-specific SNP markers was identified from a subset of four species which have often been involved in hybridisation in aquaculture: 13 for Oreochromis niloticus, 23 for O. aureus, 12 for O. mossambicus and 14 for O. u. hornorum. A panel of 24 SNPs was selected to distinguish among these four species and validated using 91 individuals. Larger numbers of SNP markers were found that could distinguish between the pairs of species within this subset. This technique offers potential for the investigation of hybridisation and introgression among tilapia species in aquaculture and in wild populations.

Quantitative trait loci on LGs 9 and 14 affect the reproductive interaction between two Oreochromis species, O. niloticus and O. aureus.

Effective farming of tilapia requires all-male culture, characterized by uniformity and high growth rate. Males of O. aureus (Oa) and females of O. niloticus (On) produce all-male offspring, but there is a behavioral reproductive barrier between the two species that prevents mass production. In crosses between Oa and On broodstocks, few hybrid females are attracted to the Oa male nests (denoted responders), and if they harbor the On alleles for the sex determination (SD) sites on linkage groups (LGs) 1, 3, and 23, all-male progeny are produced. Yet, without controlling for the alleles underlying SD, the parental stocks gradually lose their capability for all-male production. Hypothesizing that marker-assisted selection for female responders would allow production of sustainable broodstocks, we applied genotyping-by-sequencing to generate 4983 informative SNPs from 13 responding and 28 non-responding females from two full-sib families. Accounting for multiple comparisons in a genome-wide association study, seven SNPs met a false discovery rate of 0.061. Lowest nominal probabilities were on LGs 9 and 14, for which microsatellite DNA markers were designed within the candidate genes PTGDSL and CASRL, respectively. By increasing the sample size to 22 responders and 47 non-responders and by genotyping additional established microsatellites, we confirmed the association of these LGs with female responsiveness. The combined effects of microsatellites GM171 and CARSL-LOC100690618 on LGs 9 and 14 explained 37% of the phenotypic variance of reproductive interaction (p < 0.0001). Based on these findings, we propose a strategy for mass production of all-male tilapia hybrids through selection for genomic loci affecting SD and female responsiveness.

Identification and Evolution of TGF-ß Signaling Pathway Members in Twenty-Four Animal Species and Expression in Tilapia.

Transforming growth factor ß (TGF-ß) signaling controls diverse cellular processes during embryogenesis as well as in mature tissues of multicellular animals. Here we carried out a comprehensive analysis of TGF-ß pathway members in 24 representative animal species. The appearance of the TGF-ß pathway was intrinsically linked to the emergence of metazoan. The total number of TGF-ß ligands, receptors, and smads changed slightly in all invertebrates and jawless vertebrates analyzed. In contrast, expansion of the pathway members, especially ligands, was observed in jawed vertebrates most likely due to the second round of whole genome duplication (2R) and additional rounds in teleosts. Duplications of TGFB2, TGFBR2, ACVR1, SMAD4 and SMAD6, which were resulted from 2R, were first isolated. Type II receptors may be originated from the ACVR2-like ancestor. Interestingly, AMHR2 was not identified in Chimaeriformes and Cypriniformes even though they had the ligand AMH. Based on transcriptome data, TGF-ß ligands exhibited a tissue-specific expression especially in the heart and gonads. However, most receptors and smads were expressed in multiple tissues indicating they were shared by different ligands. Spatial and temporal expression profiles of 8 genes in gonads of different developmental stages provided a fundamental clue for understanding their important roles in sex determination and reproduction. Taken together, our findings provided a global insight into the phylogeny and expression patterns of the TGF-ß pathway genes, and hence contribute to the greater understanding of their biological roles in the organism especially in teleosts.

Effects of the acclimation to high salinity on intestinal ion and peptide transporters in two tilapia species that differ in their salinity tolerance.

Tilapiine species, widely distributed across habitats with diverse water salinities, are important to aquaculture as well as a laboratory model. The effects of water salinity on two tilapia species, that differ in their salinity tolerance, was evaluated. Oreochromis niloticus reared in brackish-water, showed a significant decrease in growth and feed efficiency, whereas O. mossambicus reared in seawater did not show any significant changes. The expression and activity of Na+/K+-ATPase (NKA), V-type H+-ATPase (VHA) and carbonic anhydrase (CA), as well as expression levels of genes encoding two HCO3- and three peptide transporters (nbc1, slc26a6, slc15a1a, slc15a1b and slc15a2) were measured in three intestinal sections of these two species, grown in freshwater and brackish/sea-water. Overall, the spatial distribution along the intestine of the genes examined in this study was similar between the two species, with the exception of tcaIV. The salinity response, on the other hand, varied greatly between these species. In O. mossambicus, there was a salinity-dependent increased expression of most of the examined genes (except slc26a6 and slc15a2), while in O. niloticus the expression of most genes did not change, or even decreased (tcaIV, nbc1 and slc15a1b). This study highlighted differences in the intestinal response to salinity acclimation between closely- related species that differ in their salinity tolerance. O. mossambicus, which has a high salinity tolerance, showed expression patterns and responses similar to marine species, and differed from the low-salinity-tolerance O. niloticus, which showed a response that differed from the accepted models, that are based on marine and diadromous fishes.

Growth arrest specific gene 2 in tilapia (Oreochromis niloticus): molecular characterization and functional analysis under low-temperature stress.

BACKGROUND: Growth arrest specific 2 (gas2) gene is a component of the microfilament system that plays a major role in the cell cycle, regulation of microfilaments, and cell morphology during apoptotic processes. However, little information is available on fish gas2. In this study, the tilapia (Oreochromis niloticus) gas2 gene was cloned and characterized for the first time. RESULTS: The open reading frame was 1020 bp, encoding 340 amino acids; the 5'-untranslated region (UTR) was 140 bp and the 3'-UTR was 70 bp, with a poly (A) tail. The highest promoter activity occurred in the regulatory region (-3000 to -2400 bp). The Gas2-GFP fusion protein was distributed within the cytoplasm. Quantitative reverse transcription-polymerase chain reaction and western blot analyses revealed that gas2 gene expression levels in the liver, muscle, and brain were clearly affected by low temperature stress. The results of gas2 RNAi showed decreased expression of the gas2 and P53 genes. CONCLUSION: These results suggest that the tilapia gas2 gene may be involved in low temperature stress-induced apoptosis.

Lipolytic response of adipose tissue and metabolic adaptations to long periods of fasting in red tilapia (Oreochromis sp., Teleostei: Cichlidae).

Adaptive changes of carbohydrate and lipid metabolism induced by 7, 15, 30, 60, 90, 150 and 200 days of fasting were investigated in red tilapia (Oreochromis sp.). Plasma glucose, lactate and free fatty acids (FFA) levels, liver and muscle glycogen and total lipid contents and rates of FFA release from mesenteric adipose tissue (MAT) were measured. Plasma glucose levels showed significant differences only after 90 days of fasting, when glycemia was 34% lower (50±5mg.dL-1) than fed fish values (74±1mg.dL-1), remaining relatively constant until 200 days of fasting. The content of liver glycogen ("15%) in fed tilapia fell 40% in 7 days of food deprivation. In 60, 90 and 150 days of fasting, plasma FFA levels increased 49%, 64% and 90%, respectively, compared to fed fish values. In agreement with the increase in plasma FFA, fasting induced a clear increase in lipolytic activity of MAT incubated in vitro. Addition of isobutylmethylxanthine (cAMP-phosphodiesterase inhibitor) and isoproterenol (non selective beta adrenergic agonist) to the incubation medium induced a reduction of lipolysis in fasted fish, differently to what was observed in mammal adipose tissue. This study allowed a physiological assessment of red tilapia response to starvation.

Complete mitochondrial DNA sequences of the Victoria tilapia (Oreochromis variabilis) and Redbelly Tilapia (Tilapia zilli): genome characterization and phylogeny analysis.

The Cichlid fishes have played an important role in evolutionary biology, population studies and aquaculture industry with East African species representing a model suited for studying adaptive radiation and speciation for cichlid genome projects in which closely related genomes are fast emerging presenting questions on phenotype-genotype relations. The complete mitochondrial genomes presented here are for two closely related but eco-morphologically distinct Lake Victoria basin cichlids, Oreochromis variabilis, an endangered native species and Tilapia zilli, an invasive species, both of which are important economic fishes in local areas. The complete mitochondrial genomes determined for O. variabilis and T. zilli are 16 626 and 16,619 bp, respectively. Both the mitogenomes contain 13 protein-coding genes, 22 tRNAs, 2 rRNAs and a non-coding control region, which are typical of vertebrate mitogenomes. Phylogenetic analyses of the two species revealed that though both lie within family Cichlidae, they are remotely related.

Fine-tuning for the tropics: application of eDNA technology for invasive fish detection in tropical freshwater ecosystems.

Invasive species pose a major threat to aquatic ecosystems. Their impact can be particularly severe in tropical regions, like those in northern Australia, where >20 invasive fish species are recorded. In temperate regions, environmental DNA (eDNA) technology is gaining momentum as a tool to detect aquatic pests, but the technology's effectiveness has not been fully explored in tropical systems with their unique climatic challenges (i.e. high turbidity, temperatures and ultraviolet light). In this study, we modified conventional eDNA protocols for use in tropical environments using the invasive fish, Mozambique tilapia (Oreochromis mossambicus) as a detection model. We evaluated the effects of high water temperatures and fish density on the detection of tilapia eDNA, using filters with larger pores to facilitate filtration. Large-pore filters (20 µm) were effective in filtering turbid waters and retaining sufficient eDNA, whilst achieving filtration times of 2-3 min per 2-L sample. High water temperatures, often experienced in the tropics (23, 29, 35 °C), did not affect eDNA degradation rates, although high temperatures (35 °C) did significantly increase fish eDNA shedding rates. We established a minimum detection limit for tilapia (1 fish/0.4 megalitres/after 4 days) and found that low water flow (3.17 L/s) into ponds with high fish density (>16 fish/0.4 megalitres) did not affect eDNA detection. These results demonstrate that eDNA technology can be effectively used in tropical ecosystems to detect invasive fish species.

Stock assessment of fishery target species in Lake Koka, Ethiopia.

Effective management is essential for small-scale fisheries to continue providing food and livelihoods for households, particularly in developing countries where other options are often limited. Studies on the population dynamics and stock assessment on fishery target species are thus imperative to sustain their fisheries and the benefits for the society. In Lake Koka (Ethiopia), very little is known about the vital population parameters and exploitation status of the fishery target species: tilapia Oreochromis niloticus, common carp Cyprinus carpio and catfish Clarias gariepinus. Our study, therefore, aimed at determining the vital population parameters and assessing the status of these target species in Lake Koka using length frequency data collected quarterly from commercial catches from 2007-2012. A total of 20,097 fish specimens (distributed as 7,933 tilapia, 6,025 catfish and 6,139 common carp) were measured for the analysis. Von Bertalarffy growth parameters and their confidence intervals were determined from modal progression analysis using ELEFAN I and applying the jackknife technique. Mortality parameters were determined from length-converted catch curves and empirical models. The exploitation status of these target species were then assessed by computing exploitation rates (E) from mortality parameters as well as from size indicators i.e., assessing the size distribution of fish catches relative to the size at maturity (Lm), the size that provides maximum cohort biomass (Lopt) and the abundance of mega-spawners. The mean value of growth parameters L∞, K and the growth performance index ø' were 44.5 cm, 0.41/year and 2.90 for O. niloticus, 74.1 cm, 0.28/year and 3.19 for C. carpio and 121.9 cm, 0.16/year and 3.36 for C. gariepinus, respectively. The 95 % confidence intervals of the estimates were also computed. Total mortality (Z) estimates were 1.47, 0.83 and 0.72/year for O. niloticus, C. carpio and C. gariepinus, respectively. Our study suggest that O. niloticus is in a healthy state, while C. gariepinus show signs of growth overfishing (when both exploitation rate (E) and size indicators were considered). In case of C. carpio, the low exploitation rate encountered would point to underfishing, while the size indicators of the catches would suggest that too small fish are harvested leading to growth overfishing. We concluded that fisheries production in Lake Koka could be enhanced by increasing E toward optimum level of exploitation (Eopt) for the underexploited C. carpio and by increasing the size at first capture (Lc) toward the Lopt, range for all target species.

The impact of rearing environment on the development of gut microbiota in tilapia larvae.

This study explores the effect of rearing environment on water bacterial communities (BC) and the association with those present in the gut of Nile tilapia larvae (Oreochromis niloticus, Linnaeus) grown in either recirculating or active suspension systems. 454 pyrosequencing of PCR-amplified 16S rRNA gene fragments was applied to characterize the composition of water, feed and gut bacteria communities. Observed changes in water BC over time and differences in water BCs between systems were highly correlated with corresponding water physico-chemical properties. Differences in gut bacterial communities during larval development were correlated with differences in water communities between systems. The correlation of feed BC with those in the gut was minor compared to that between gut and water, reflected by the fact that 4 to 43 times more OTUs were shared between water and gut than between gut and feed BC. Shared OTUs between water and gut suggest a successful transfer of microorganisms from water into the gut, and give insight about the niche and ecological adaptability of water microorganisms inside the gut. These findings suggest that steering of gut microbial communities could be possible through water microbial management derived by the design and functionality of the rearing system.

Stock assessment of fishery target species in Lake Koka, Ethiopia / Evaluación de las reservas pesqueras de especies objetivo en el lago Koka, Etiopia

Effective management is essential for small-scale fisheries to continue providing food and livelihoods for households, particularly in developing countries where other options are often limited. Studies on the population dynamics and stock assessment on fishery target species are thus imperative to sustain their fisheries and the benefits for the society. In Lake Koka (Ethiopia), very little is known about the vital population parameters and exploitation status of the fishery target species: tilapia Oreochromis niloticus,common carp Cyprinus carpióand catfish Clarias gariepinus.Our study, therefore, aimed at determining the vital population parameters and assessing the status of these target species in Lake Koka using length frequency data collected quarterly from commercial catches from 2007-2012. A total of 20 097 fish specimens (distributed as 7 933 tilapia, 6 025 catfish and 6 139 common carp) were measured for the analysis. Von Bertalanffy growth parameters and their confidence intervals were determined from modal progression analysis using ELEFAN I and applying the jackknife technique. Mortality parameters were determined from length-converted catch curves and empirical models. The exploitation status of these target species were then assessed by computing exploitation rates (E) from mortality parameters as well as from size indicators i.e., assessing the size distribution of fish catches relative to the size at maturity (L m),the size that provides maximum cohort biomass (Lopt) and the abundance of mega-spawners. The mean value of growth parameters L x, Kand the growth performance index 0' were 44.5 cm, 0.41/year and 2.90 for O. niloticus,74.1 cm, 0.28/year and 3.19 for C. carpioand 121.9 cm, 0.16/year and 3.36 for C. gariepinus,respectively. The 95 % confidence intervals of the estimates were also computed. Total mortality (Z) estimates were 1.47, 0.83 and 0.72/year for O. niloticus, C. carpioand C. gariepinus,respectively. Our study suggest that O. niloticusis in a healthy state, while C. gariepinusshow signs of growth overfishing (when both exploitation rate (E)and size indicators were considered). In case of C. carpio,the low exploitation rate encountered would point to underfishing, while the size indicators of the catches would suggest that too small fish are harvested leading to growth overfishing. We concluded that fisheries production in Lake Koka could be enhanced by increasing Etoward optimum level of exploitation (E opt)for the underexploited C. carpioand by increasing the size at first capture (Lc)toward the L opt range for all target species.

Un manejo pesquero eficiente es fundamental para que las pesquerías artesanales puedan continuar proveyendo alimento y sustento para los hogares, particularmente en los países en vía de desarrollo, en donde otras opciones a menudo son limitadas. Estudios sobre la dinámica poblacional de las especies objetivo de las pesquerías son, por lo tanto, imperativos para mantener las pesquerías y los beneficios para las sociedades. Esto también es válido para los recursos del Lago Koka (Etiopia) en donde hasta ahora se sabe muy poco sobre los parámetros poblacionales vitales y el estatus de las especies objetivo como la tilapia Oreochromis niloticus,la carpa Cyprinus carpioy el bagre Clarias gariepinus.El estudio aquí presentado tiene como objetivo determinar estos parámetros y evaluar el estado de la pesquería de estas especies en el lago Koka, utilizando los datos de frecuencia de tallas obtenidas de capturas trimestrales en el periodo 2007-2012. Un total de 20 097 especímenes fueron medidos (7 933 de tilapia, 6 025 de bagre y 6 139 de carpa). Los parámetros de crecimiento de von Bertalanffy fueron derivados del análisis de progresión de las modas usando ELEFAN I y aplicando la técnica de jackknife. Las tasas de mortalidad fueron estimadas de curvas de capturas basadas en longitudes y usando modelos empíricos. La tasa de explotación (E), se estimó con los parámetros de mortalidad y también considerando indicadores del tamaño a través de la distribución de tallas en las capturas y su relación con la talla de la primera madurez (L m),el tamaño que provee la biomasa máxima del cohorte (L opt)y la abundancia de los "mega-desovantes". Los valores calculados para los parámetros de crecimiento L m, Ky el índice de la capacidad de crecimiento 0' fueron: 44.5 cm, 0.41 año-1 y 2.90 para O. niloticus,74.1 cm, 0.28 año-1 y 3.19 para C. carpióy 121.9 cm, 0.16 año-1 y 3.36 para C. gariepinus,respectivamente. La tasa de mortalidad total (Z) fue estimada en 1.47, 0.83 y 0.72 año-1 para O. niloticus, C. carpioand C. gariepinus,respectivamente. Nuestros resultados sugieren que la población de O. niloticusse encuentra en un estado saludable, mientras C. gariepinusya muestra signos de sobrepesca por crecimiento. En el caso de C. carpiolas tasas de explotación tan bajas (E<0.5) que se encontraron, pueden apuntar a una sub-explotación, mientras que los indicadores de tallas sugieren que las pequeñas tallas obtenidas, pueden conducir a una sobrepesca por crecimiento. Concluimos que la producción pesquera en el lago Koka puede ser mejorada si se incrementa E al nivel E opt para C. carpioy aumenta el tamaño de la primera captura (Lc)al rango de L opt para todas las especies objetivo.

Automated detection of broadband clicks of freshwater fish using spectro-temporal features.

Large scale networks of embedded wireless sensor nodes can passively capture sound for species detection. However, the acoustic recordings result in large amounts of data requiring in-network classification for such systems to be feasible. The current state of the art in the area of in-network bioacoustics classification targets narrowband or long-duration signals, which render it unsuitable for detecting species that emit impulsive broadband signals. In this study, impulsive broadband signals were classified using a small set of spectral and temporal features to aid in their automatic detection and classification. A prototype system is presented along with an experimental evaluation of automated classification methods. The sound used was recorded from a freshwater invasive fish in Australia, the spotted tilapia (Tilapia mariae). Results show a high degree of accuracy after evaluating the proposed detection and classification method for T. mariae sounds and comparing its performance against the state of the art. Moreover, performance slightly improves when the original signal was down-sampled from 44.1 to 16 kHz. This indicates that the proposed method is well-suited for detection and classification on embedded devices, which can be deployed to implement a large scale wireless sensor network for automated species detection.

Intestinal transcriptome analysis revealed differential salinity adaptation between two tilapiine species.

Tilapias are a group of freshwater species, which vary in their ability to adapt to high salinity water. Osmotic regulation in fish is conducted mainly in the gills, kidney, and gastrointestinal tract (GIT). The mechanisms involved in ion and water transport through the GIT is not well-characterized, with only a few described complexes. Comparing the transcriptome of the anterior and posterior intestinal sections of a freshwater and saltwater adapted fish by deep-sequencing, we examined the salinity adaptation of two tilapia species: the high salinity-tolerant Oreochromis mossambicus (Mozambique tilapia), and the less salinity-tolerant Oreochromis niloticus (Nile tilapia). This comparative analysis revealed high similarity in gene expression response to salinity change between species in the posterior intestine and large differences in the anterior intestine. Furthermore, in the anterior intestine 68 genes were saltwater up-regulated in one species and down-regulated in the other species (47 genes up-regulated in O. niloticus and down-regulated in O. mossambicus, with 21 genes showing the reverse pattern). Gene ontology (GO) analysis showed a high proportion of transporter and ion channel function among these genes. The results of this study point to a group of genes that differed in their salinity-dependent regulation pattern in the anterior intestine as potentially having a role in the differential salinity tolerance of these two closely related species.

Chemical communication in tilapia: a comparison of Oreochromis mossambicus with O. niloticus.

In allopatric speciation species differentiation generally results from different selective pressures in different environments, and identifying the traits responsible helps to understand the isolation mechanism(s) involved. Male Mozambique tilapia (Oreochromis mossambicus) use urine to signal dominance; furthermore, 5ß-pregnane-3α,17,20ß-triol-3α-glucuronide (and its α-epimer, 5ß-pregnane-3α,17,20α-triol-3α-glucuronide), in their urine is a potent pheromone, the concentration of which is correlated with social status. The Nile tilapia (Oreochromisniloticus) is a close relative; species divergence probably resulted from geographical separation around 6 million years ago. This raises the question of whether the two species use similar urinary chemical cues during reproduction. The olfactory potency of urine, and crude extracts, from either species was assessed by the electro-olfactogram and the presence of the steroid glucuronides in urine from the Nile tilapia by liquid-chromatography/mass-spectrometry. Both species showed similar olfactory sensitivity to urine and respective extracts from either species, and similar sensitivity to the steroid glucuronides. 5ß-Pregnan-3α,17α,20ß-triol-3α-glucuronide was present at high concentrations (approaching 0.5mM) in urine from Nile tilapia, with 5ß-pregnan-3α,17α,20α-triol-3α-glucuronide present at lower concentrations, similar to the Mozambique tilapia. Both species also had similar olfactory sensitivity to estradiol-3-glucuronide, a putative urinary cue from females. Together, these results support the idea that reproductive chemical cues have not been subjected to differing selective pressure. Whether these chemical cues have the same physiological and behavioural roles in O. niloticus as O. mossambicus remains to be investigated.

Two homologs of rho-class and polymorphism in alpha-class glutathione S-transferase genes in the liver of three tilapias.

To clarify detoxification metabolism of tilapia, a natural and biological control for removing the leftover toxicants in fresh water, sequence structure, expression profile and polymorphisms of members of glutathione S-transferase (GST) genes were analyzed in Nile tilapia, blue tilapia and their hybrid. Full-length mRNA sequences of alpha-class GST (GSTA) and two homologs of rho-class GST (GSTR) were identified. Sequence analysis confirmed the similarity in conserved domain regions and their phylogenetic relationships with GST genes in other fishes. In addition, three single nucleotide polymorphisms of GSTA genes were identified in the three populations, two (C266T and G525A) of which showed significant association. The relative mRNA expression of GSTA gene was significantly (P<0.05) increased in the liver of Nile tilapia at 24h post-injection of MC-LR, significantly (P<0.05) decreased in blue tilapia whereas slightly decreased (P>0.05) in hybrid tilapia.

Molecular phylogeny and revised classification of the haplotilapiine cichlid fishes formerly referred to as "Tilapia".

African cichlids formerly referred to as "Tilapia" represent a paraphyletic species assemblage belonging to the so called haplotilapiine lineage which gave rise to the spectacular East African cichlid radiations (EARs) as well as to globally important aquaculture species. We present a comprehensive molecular phylogeny of representative haplotilapiine cichlids, combining in one data set four mitochondrial and five nuclear loci for 76 species, and compare it with phylogenetic information of a second data set of 378 mitochondrial ND2 haplotypes representing almost all important "Tilapia" or Tilapia-related lineages as well as most EAR lineages. The monophyly of haplotilapiines is supported, as is the nested sister group relationship of Etia and mouthbrooding tilapiines with the remaining haplotilapiines. The latter are consistently placed in eight monophyletic clades over all datasets and analyses, but several dichotomous phylogenetic relationships appear compromised by cytonuclear discordant phylogenetic signal. Based on these results as well as on extensive morphological evidence we propose a novel generic and suprageneric classification including a (re-)diagnosis of 20 haplotilapiine cichlid genera and nine tribes. New tribes are provided for the former subgenera Coptodon Gervais, 1853, HeterotilapiaRegan, 1920 and PelmatolapiaThys van den Audenaerde, 1969, in addition for "Tilapia" joka, Tilapia sensu stricto and Chilochromis, Etia, Steatocranus sensu stricto, the mouthbrooding tilapiines and for a clade of West African tilapiines.

[Genetic potential analysis of six tilapia populations by microsatellite DNA markers].

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.

[Age and growth of the hybrid tilapia Oreochromis niloticus x Oreochromis aureus (Perciformes: Cichlidae) in the dam "Zimapan" Mexico]. / Edad y crecimiento del híbrido de tilapia Oreochromis niloticus x Oreochromis aureus (Perciformes: Cichlidae) en la represa "Zimapán" Hidalgo, México.

Studies on age and growth in fishes are essential to establish models on population dynamics. The previous issues were determined in this study by scale growth analyses. Between September 2003 and May 2004, 382 organisms were captured using gill and atarraya nets. Eight samples were developed every month a long this study. Standard length in centimeters (L(e)), total weight in grams (P9t)), scale length in centimeters (L(esc)) and growth rings were determined. The size and weight ranged from 38 to 232 mm (L(e)) and 8.7 to 311.9 g (P(t)), respectively. The growth rings analyses reveal four age groups, being the second group the most representative with 34.3% of the total sampled. The scale ring analyses showed two growth rings, one develops between November-January and the other between April-May, in good correlation with low temperature and gonad development, respectively. The growth parameters were established as: L infinity = 281.1mm, W infinity = 877.1g, K = 0.33 and T(0) = 0.88 year(-1). The growth curves based on length and weight were described by using the von Bertalanffy model: L(e) = 28.11[1 -e (-0.33(t+0.88))] and P(t) = 877.17[1-e (-0.33(t+0.88))]3. Finally, it is concluded that commercial catches in this dam are between a year and year and half-old when exploited.