Tilapia Populations Research Articles

Sustainable Ecosystem Management Strategies for Tackling the Invasion of Blackchin Tilapia (Sarotherodon melanotheron) in Thailand: Guidelines and Considerations.

The invasion of blackchin tilapia in Thailand is a critical ecological threat affecting native biodiversity and destabilizing ecosystems. It is also resulting in significant ecological and socio-economic impacts. Originally from West Africa and introduced globally for aquaculture, blackchin tilapia thrive in Thailand's brackish and freshwater ecosystems because of their high reproductive rates, environmental adaptability, and trophic plasticity. This review evaluates potential solutions for the invasion of blackchin tilapia in Thailand from a scientific perspective. The successful invasion of blackchin tilapia in Thailand can be attributed to several key factors, including late detection of the species, the delayed government response, the absence of effective management strategies, and the species' high invasive potential. Given its wide distribution, large population size, and high reproductive rate, the eradication of the entire blackchin tilapia population is unlikely. Management efforts should focus on containment and impact reduction. Early detection and monitoring at the invasion front remain crucial to limit the species' spread. Developing an online platform for tracking invasive species would aid these efforts. Public education and outreach are essential for promoting responsible behaviors for preventing further spread. Encouraging the utilization of blackchin tilapia as a food source and for commercial purposes could help suppress its population while supporting local economies. Biological control and other potentially harmful strategies should be avoided unless supported by strong scientific evidence to ensure minimal risks to ecosystems. Scientific research into controlling blackchin tilapia should be encouraged to develop suitable strategies, including using sterile triploid tilapia. The "polluter pays" policy should be implemented to cover the costs associated with invasive species. Coordinated efforts between researchers, policymakers, and the public are crucial for formulating effective management strategies to promote a balance between economic benefits and long-term environmental sustainability.

Population Dynamics of Nile Tilapia (Oreochromis niloticus, L. 1758) in Lake Nubia, Sudan

This study aims to investigate the population dynamics of Nile tilapia (Oreochromis niloticus, Linnaeus, 1758) in Lake Nubia, Sudan. Monthly samples were collected from fishermen from January to December 2021, and recorded total lengths (TL) of 996 specimens nearest to 1.0 mm using a standardized measuring board; the lengths (TL) exhibited a range from 5.2 to 41.3 cm. Population parameters were assessed using the ELEFAN I routine within FiSAT II software, which produced von Bertalanffy growth parameters as follows: an asymptotic length (L∞) of 43.05 cm, a growth curvature (K) of 0.230 yr⁻¹, and a theoretical length at age zero (t0) of -0.1816. The growth performance index (Φ') was calculated to be 2.639. The instantaneous mortality rates were evaluated, revealing total mortality (Z) at 0.65 yr⁻¹, natural mortality (M) at 0.63 yr⁻¹, and fishing mortality (F) at 0.02 year⁻¹; While the exploitation rate (E) was determined to be 0.04 yr⁻¹. The size at first capture (Lc) was obtained as 5.2 cm, while L50 was estimated at 10.07 cm, both being below the size at first maturity (Lₘ) of 13.5 cm, and the longevity (Tmax) was noted to be 12.86 years. The results indicated poor utilization of the Nile tilapia population in Lake Nubia, and its size at first capture and L50 was below the size at first maturity. This situation is an indication of the need for a continuous process of monitoring and managing to reduce the harvesting of smaller individuals and to improve productivity toward achieving levels that optimize sustainable yield.

Population Dynamics of Nile Tilapia (Oreochromis niloticus, Linnaeus.1758) from Khashm El-Girba Reservoir, Atbara River, Eastern Sudan

This study was conducted to assess the population parameters of Nile tilapia, Oreochromis niloticus, in the Khashm El-Girba Dam Reservoir in Eastern Sudan. Fish samples were collected from December 2019 to November 2020. Length-frequency data were collected from 1,671 specimens ranging from 5.1 to 34.2 cm in total length (TL). Analysis of the population parameters was determined using the ELEFAN I routine and the FiSAT II software computer program revealed that the estimated the Von Bertalanffy growth parameters were as follows: asymptotic length (L∞ = 36.75 cm), growth rate (K = 0.650 year -1) and age at length zero (t0 = -0.629) and the growth performance index (Φ') was calculated at 2.943. The instantaneous total mortality (Z), natural mortality (M), and fishing mortality (F) rates were determined using the length-converted catch curve and empirical models. The values obtained were Z = 2.38 year -1, M = 1.22 year -1, and F = 1.16 year -1, respectively. The exploitation rate (E) of the Nile tilapia was calculated at 0.49 year -1. The size at first capture (Lc) was estimated at 15.64 cm, which is slightly greater than the size at first maturity (Lm = 14.5 cm) and longevity (Tmax) was found to be 4.62 years. These findings indicate that the stock of the Nile tilapia population in Khashm El-Girba reservoir is overexploited, and that monitoring and management practices need to be employed to maintain the stocks at the optimum exploitation level.

Pathogenicity of Aeromonas veronii from Nile Tilapia (Oreochromis niloticus) and Efficacy of Fish Oral Vaccine against Motile Aeromonad Septicemia in Tank Trials

Motile aeromonad septicemia (MAS), caused by the Aeromonas species, has been a serious problem in fish health management, particularly in Nile tilapia (Oreochromis niloticus). This study characterized an Aeromonas species isolated from farmed tilapia fingerlings in Binangonan, Rizal, Philippines, and tested for its pathogenicity in tank trials. The isolate, designated as Aeromonas veronii DFR01 (Diseased Fish Rizal), was identified based on 16S rRNA phylogenetic analysis, 16S rRNA homology, and MALDI-TOF mass spectrometry. Its biochemical profile was generated from API and Biolog Gen III systems. A median lethal dose of A. veronii DFR01 was determined to be 107 CFU/mL in tank trials and was utilized as a whole-cell inactivated antigen for oral vaccine development. The immunized tilapia fingerlings produced elevated levels of immunoglobulin M (IgM) in the blood as determined by an enzyme-linked immunosorbent assay (ELISA). There was a significant increase in IgM levels 14 days post-vaccination. A quantitative polymerase chain reaction (qPCR) showed increasing levels of IgM gene expression after vaccination until 38 days of culture. Vaccinated fish showed 25–35% cumulative mortality after the challenge, while non-vaccinated-challenged fish showed 75% mortality. The findings of this research suggest that the fish oral vaccine may prove beneficial for farmed tilapia populations. The vaccine elicited improved immune responses in the fish and resulted in higher survival rates.

Unlocking Nile tilapia (Oreochromis niloticus Linn., 1758) selective breeding programmes in Uganda through geographical genetic structure mapping

AbstractNile tilapia (Oreochromis niloticus), native to Africa and the Levant, is an important species for both aquaculture and capture fisheries. Despite these attributes, Nile tilapia has been negatively impacted by anthropogenic activities ranging from overfishing and habitat destruction to translocations. These human‐mediated activities have threatened the genetic evolutionary integrity of native populations of Nile tilapia and congeneric species through admixture, demographic bottlenecks and introgressive hybridization. In this context, the genetic contrast between farmed/bred strains and wild Nile tilapia populations in the major lakes of Uganda remains understudied. Understanding the genetic structure of Nile tilapia populations in the major water bodies of Uganda (lakes Victoria, Kyoga, Edward, George, Albert and Nile River) is a key resource to guide selective breeding programmes, thus minimizing the effects of maladaptation under both aquaculture and natural stocks. Although the population genetics of Nile tilapia in Uganda's major lakes have been studied, this was based on limited sampling scope, especially in the wild, and the key information on the species could have been overlooked. We fill this knowledge gap by genotyping 756 Nile tilapia individuals from multiple populations for each major water body of Uganda using a panel of 34 microsatellite loci based on the microsatellite genotyping‐by‐sequencing (SSR‐GBS) technique. The results indicate two discrete gene pools/stocks: the Edward‐George system and the Albert‐Kyoga system‐Victoria. Evidence of loss of genetic diversity and admixture of some Nile tilapia stocks was found, most likely resulting from anthropogenic perturbations. This study contributes useful information key for understanding the potential Nile tilapia broodstock sources for selective breeding programmes, aimed at improving aquaculture production in Uganda.

Effect of the combination of fluoxymesterone and a commercial blend of additives on the sex proportion, growth, and survival of Nile tilapia (Oreochromis niloticus) fry

In the commercial culture of Nile tilapia (Oreochromis niloticus), monosex, all-male populations obtained through steroid sex reversal is the most commercially used method to eliminate unwanted reproduction and increase final productive and economic yield. However, the rapid growth of Nile tilapia culture has led, in some regions, to an increase in infectious diseases and mortality in all stages of commercial culture. To reduce this, without the abuse of antibiotics or similar substances, feed additives are currently used in all stages, including the fry period, during the sex reversal process. The objective of this work was to evaluate the effect of synthetic steroid Fluoxymesterone (FM) at various concentrations in combination with a commercial Blend of additives (BA) on the percentage of males, growth, and survival of Nile tilapia fry. Five treatments (FM20, FM5+BA, FM10+BA, FM20+BA, and BA+FM20) and a control group were evaluated. Treatments differ in the order in which the commercial blend (2 g) was added and the FM concentration (5, 10, and 20 mg). The feeding trial lasted for 30 days using a sexually undifferentiated population of Nile tilapia. The results showed a decrease in the percentage of males in all treatments supplemented with the BA, compared to the FM20 treatment (containing 20 mg without BA). Growth and survival were positively affected by the inclusion of the BA in all treatments, showing higher values than those observed in the control group. Further studies are necessary to determine the FM-BA interaction.

Resistance of juvenile Nile tilapia Oreochromis niloticus from Brazilian populations to Streptococcus agalactiae (serotype Ib and ST-NT)

Nile tilapia is the main farmed fish in Brazilian aquaculture. Streptococcus agalactiae (GBS) is responsible for high mortality rates in fish farms. Genetic improvement is considered an effective alternative for producing resistant animals in aquaculture. The objective of this study was to estimate genetic parameters for resistance to GBS infection in a breeding population of Nile tilapia from Brazil, based on disease challenge using a circulating serotype (Ib and ST-NT). Furthermore, genetic correlations between resistance to GBS and average daily gain (ADG) were estimated to determine whether these traits can be included in selective breeding programs. Survival (SS) and time until death (TD) were the evaluated traits. The survival of the most resistant families was approximately 30%, indicating high phenotypic variation in resistance to the infection. Low to moderate heritability values for resistance traits in the Nile tilapia population were estimated, ranging from 0.14 to 0.27. Heritability for ADG was moderate to high (0.40) based on a growth trial involving 43 families (735 animals). Phenotypic correlations between the resistance traits (SS and TD) and ADG were positive and low, ranging from 0.09 to 0.18, whereas genetic correlations were close to zero. Phenotypic and genetic correlations between SS and TD were considered high and positive, ranging from 0.38 to 0.72. The results suggest that selection for resistance against GBS does not negatively affect juvenile weight gain in Nile tilapia.

Genome-wide association studies in a F1 tilapia population reveal novel genetic loci associated with salinity tolerance

Salinity tolerance is a complex trait of ecological and economic importance in tilapia aquaculture. To further dissect the genetic architecture underlying this trait, we performed a genome-wide association study (GWAS) using ddRAD-seq in an F1 tilapia population of GIFT tilapia, which is derived from selective breeding. Unlike previous studies localized to ∼23 Mb on chrLG18, we identified 11 novel genome-wide significant SNPs spanning a 4.6 Mb region (24,593,966 to 29,240,173 bp) on chrLG18 associated with salinity tolerance. GO enrichment analysis of the genes within this QTL region on chrLG18 showed significant enrichment of genes involved in fatty acid metabolism. The significant associations with salinity tolerance for the two missense mutations, LG18_25,305,119 (c.C388T) and LG18_25,305,122 (c.A391G), in the slc25a24l gene have been confirmed by Sanger sequencing. Individuals homozygotes for the T allele of LG18_25,305,119 and G allele of LG18_25,305,122 demonstrated over 2-fold longer average survival times under high salinity challenge compared to the individuals with disadvantageous genotypes. The mutated 131th amino acid (I/V) in SLC25A24L corresponding to the location of the nonsynonymous SNP LG18_25,305,122 showed a strong association with habitat salinity differences when comparing orthologs between freshwater and marine fish species. Our findings provide novel insights into QTLs, candidate genes and mutations conferring enhanced osmoregulatory capacity in tilapia.

Production of fertile YY pseudofemales in Nile tilapia with LG23 as the sex chromosome

Nile tilapia display conspicuous differences in growth rates between genders, as males tend to outpace and outgrow females. The production of all male Nile tilapia populations using genetically male tilapia (GMT) technology represents the most efficient and scientifically grounded approach. Most of the Nile tilapia stocks in aquaculture use LG23 as sex chromosome. The crux of GMT lies in the acquisition of YY supermales and YY pseudofemales (pF). Nonetheless, the utilization of GMT is impeded by the lower fertility and even infertility of feminized YY-pF. In this study, we found that YY-pF exhibited male-like genital papillae, and exhibited significantly higher androgen levels and lower E2 levels compared with that of fertile XY-pF. YY-pF carries two copies of Amhy but lacks Amh, and XY-pF possesses one Amhy and one Amh. In XY-pF, the expression of Amh/Amhy was only observed in granulosa cells of phase I and II follicles, while in YY-pF, Amhy expression persisted from phase I to IV. On the contrary, Cyp19a1a was found to be highly expressed in granulosa cells of phase III and IV follicles in XY-pF, but significantly reduced in granulosa cells of phase III and IV follicles in YY-pF, exhibiting a reciprocal expression pattern with Amhy. Consistently, YY-pF with one copy of Amhy mutation (YY-Amhy+/−-pF) were fertile. These results indicated that prolonged expression of Amhy led to a decrease in the expression of Cyp19a1a, followed by a decrease in serum E2 levels and an increase in androgen levels. Based on these data, we treated YY-pF with both E2 and trilostane (androgen synthetase inhibitors) simultaneously at the vitellogenic stage to make it fertile. The acquisition of fertile YY-pF laid the foundation for the widespread application of GMT.

Lack of mitochondrial introgression and limited genetic connectivity among Manyara tilapia (Oreochromis amphimelas) populations in Tanzanian Saline Rift Valley Lakes

AbstractThe Manyara tilapia (Oreochromis amphimelas), native to the Saline Rift Valley Lakes (SRVLs) in north‐central Tanzania, has recently experienced population declines mainly due to overfishing and severe droughts. This, combined with the introduction of Nile tilapia (O. niloticus), which poses a risk of hybridisation, could potentially erode essential genetic traits necessary for their survival. To address these concerns, our study analysed partial cytochrome oxidase subunit I sequences (627 base pairs) from 139 Manyara tilapia and 79 Nile tilapia specimens collected from the SRVLs to test two hypotheses: (i) whether there is no transfer of mitochondrial DNA between these species, and (ii) whether Manyara tilapia populations in the SRVLs have remained genetically connected despite reported declines. The results revealed six distinct haplotypes for Manyara tilapia and three for Nile tilapia. These haplotypes formed separate clusters for each species, with no shared or closely related haplotypes, indicating limited or no transfer of mitochondrial DNA between them. Additionally, we found evidence of restricted genetic connectivity among Manyara tilapia populations in the SRVLs, with populations in Lakes Manyara and Eyasi displaying limited genetic exchange among themselves and with those in other SRVLs. Our findings highlight the importance of sustained conservation efforts in protected areas around Lake Manyara and Lake Eyasi to safeguard the unique populations of Manyara tilapia in these lakes. However, limited connectivity with other SRVLs suggests that conservation initiatives in these areas may have a limited impact on these lakes. Thus, future efforts should prioritise stocks in Lakes Kindai, Singida and Sulunga, focusing on protecting fish refugia, particularly the rivers connected to these lakes, which serve as critical habitats during the dry season and as important reservoirs for replenishing these populations.

Morphometric and genetic characterization of cultured and wild populations of tilapia, Oreochromis niloticus in India.

To study genetic variation in Indian populations of tilapia, Oreochromis niloticus, both truss morphometrics and genetic characterization have been performed. In the present study, 88 individuals from two farm populations (GIFT and West Bengal) and one reservoir population (Gujarat) were selected to analyse variations at ten morphometric landmarks and eight microsatellite loci. Truss morphometric analysis showed PCI, PCII, and PCIII expressing 29.1%, 21.36%, and 15.48% of the variance, respectively. Results showed no clear shift in shape between the studied populations of O. niloticus, indicating low morphological variability among them. The number of microsatellite alleles ranged from 3to 9, while expected heterozygosity (HE) and observed heterozygosity (HO) values ranged from 0.56 (WB) to 0.68 (Guj) and 0.59 (GIFT) to 0.72 (Guj), respectively. The Gujarat and West Bengal populations had the smallest pairwise distance (0.0123) between them, indicating that they were genetically closer. Individuals from GIFT, however, showed the largest distance from the other populations. DNA marker variations revealed the highest genetic variability in the Gujarat population and the lowest variability in the GIFT population. The results of this study will help establish a base population for genetic improvement program and conservation of wild populations.

Comparative studies on the phenotypic variability among the population of Nile tilapia (Oreochromis niloticus) caught from rivers Taraba and donga

Comparative studies on the phenotypic variability among the population of Nile tilapia (Oreochromis niloticus) caught from rivers Taraba and donga

Genetic diversity and population structure of farmed and wild Nile tilapia (Oreochromis niloticus) in Uganda: The potential for aquaculture selection and breeding programs

Nile tilapia is one of the most important aquaculture species globally, providing high-quality animal protein for human nutrition and a source of income to sustain the livelihoods of many people in low- and middle-income countries. This species is native to Africa and nowadays farmed throughout the world. However, the genetic makeup of its native populations remains poorly characterized. Additionally, there has been important introgression and movement of farmed (as well as wild) strains connected to tilapia aquaculture in Africa, yet the relationship between wild and farmed populations is unknown in most of the continent. Genetic characterization of the species in Africa has the potential to support the conservation of the species as well as supporting selective breeding to improve the indigenous strains for sustainable and profitable aquaculture production. In the current study, a total of 382 fish were used to investigate the genetic structure, diversity, and ancestry within and between Ugandan Nile tilapia populations from three major lakes including Lake Albert (L. Albert), Lake Kyoga (L. Kyoga) and Lake Victoria (L. Victoria), and 10 hatchery farms located in the catchment regions of these lakes. Our results showed clear genetic structure of the fish sourced from the lakes, with L. Kyoga and L. Albert populations showing higher genetic similarity. We also observed noticeable genetic structure among farmed populations, with most of them being genetically similar to L. Albert and L. Kyoga fish. Admixture results showed a higher (2.55–52.75%) contribution of L. Albert / L. Kyoga stocks to Uganda's farmed fish than the stock from L. Victoria (2.12–28.02%). We observed relatively high genetic diversity across both wild and farmed populations, but some farms had sizable numbers of highly inbred fish, raising concerns about management practices. In addition, we identified a genomic region on chromosome 5, harbouring the key innate immune gene BPI and the key growth gene GHRH, putatively under selection in the Ugandan Nile tilapia population. This region overlaps with the genomic region previously identified to be associated with growth rate in farmed Nile tilapia.

Exploring the morphological dynamics of Nile tilapia (Oreochromis niloticus Linn. 1758) in Victoria Nile as depicted from geometric morphometrics

BackgroundVarious anthropogenic activities continue to threaten the fish biodiversity of the East African water bodies such as the Victoria Nile. Although the Victoria Nile is a significant source of livelihood for human populations, the biology and ecology of Nile tilapia in this ecosystem remain understudied with little or no information on the morphology of the fish given varying and immense anthropogenic activities. Here, we use geometric morphometrics to examine the morphology/shape variations of Nile tilapia populations in Victoria Nile to gain insights into their current ecological state.ResultsOur results indicate unexpectedly smaller Nile tilapia body weights in Victoria Nile than in L. Victoria. Despite this, nearly all the populations displayed a relative condition factor (Kn) of greater ≥1 suggesting a healthy stock. However, two populations, LMF and VN_Bukeeka demonstrated Kn values of less than one (< 1). We also report that some Upper and Lower Victoria Nile populations display morphological similarities. Apart from L. Albert, Nile tilapia populations from Lakes Victoria and Kyoga are morphologically divergent from the riverine ones. We note that Nile tilapia from Nalubale Dam Reservoir is morphologically distinct from the close neighbouring Victoria Nile populations which are likely allied to the influence of the Nalubale Hydroelectric power dam as a barrier.ConclusionNile tilapia’s morphological variation appears to be influenced by various anthropogenic disturbances notably, overfishing, hydroelectric power dams, and fish translocational history in Uganda. Management should enforce regulatory frameworks to avert human-mediated activities as these are likely to compromise the sustainability of the fisheries. Further studies are required to follow these populations with molecular genetics and environmental data to gain a deeper understanding of the fish species for informed sustainable management and conservation options.

Growth response and estimating heritability of synthetic base population (F0) of red tilapia (Oreochromis spp.) through family selection

Red tilapia (Oreochromis spp.) is widely cultivated because it has high economic value. However, at the same age, the growth and thickness of red tilapia flesh are lower than that of black tilapia, which is necessary to improve genetics, one of which is a breeding program. The purpose of this study was to evaluate growth performance and estimate the value of the genetic parameter of the synthetic based population (F0) of red tilapia. Spawning was done naturally using happa with 30 males and 90 females. The number of families produced was 30 families, consisting of male and female sub populations. Enlargement activities were carried out for 90 days with a stocking density of 7 fish/m2 and a frequency of feeding 2 times a day. The estimated heritability was 0.26±0.07 with a response to selection of 18.52 g (male) and 0.35±0.09 with a response to selection of 20.69 g (female). Based on these parameters, the selection process for the next generation can still be done by increasing the number of families.

Reproductive performances of triploid male and female Nile tilapia Oreochromis niloticus (Linnaeus, 1758) at different ages

Abstract. Carman O, Mukti AT, Zairin JR M, Alimuddin. 2023. Reproductive performances of triploid male and female Nile tilapia Oreochromis niloticus (Linnaeus, 1758) at different ages. Biodiversitas 24: 4235-4242. Triploidization has been known as a chromosome set manipulation strategy to produce sterile fish. This study aimed to examine the reproductive and sterility performances of triploid male and female Nile tilapia Oreochromis niloticus (Linnaeus, 1758) at different ages. The triploidization process using heat shock of 41°C for four minutes at four Minutes After Fertilization (MAF) of the zygote old made the population of triploid tilapia. Two steps of fish rearing were conducted, namely indoor fish rearing and outdoor fish grow-out. Fish were reared in a controlled laboratory (indoor) at the Reproduction and Genetics Laboratory of Aquatic Organisms, Department of Aquaculture, Faculty of Fisheries and Marine Science, IPB University for four months, and then fish grow-out was performed in a controlled pond for two months. Reproductive performances such as Hepatosomatic Index (HSI), Gonadosomatic Index (GSI), gonadal development, and sterility of triploid and diploid for both male and female tilapias were analyzed. These results showed that triploid tilapia generally indicated late gonadal development and growth compared to diploids before and during maturation. Triploid female tilapia showed a lower HSI than diploid female tilapia (P&lt;0.05). Otherwise, triploid and diploid males showed the same HSI. GSI of triploid males and females were lower than diploid males and females (P&lt;0.05) at every age, namely three-, four-, five- and six-month-old fish. Based on the size and histology of the gonad, triploid male and female tilapias showed sterile characteristics with gametogenesis inhibition.

Immune responses to Tilapia lake virus infection: what we know and what we don't know.

Tilapia lake virus (TiLV) is a novel contagious pathogen associated with a lethal disease affecting and decimating tilapia populations on several continents across the globe. Fish viral diseases, such as Tilapia lake virus disease (TiLVD), represent a serious threat to tilapia aquaculture. Therefore, a better understanding of the innate immune responses involved in establishing an antiviral state can help shed light on TiLV disease pathogenesis. Moreover, understanding the adaptive immune mechanisms involved in mounting protection against TiLV could greatly assist in the development of vaccination strategies aimed at controlling TiLVD. This review summarizes the current state of knowledge on the immune responses following TiLV infection. After describing the main pathological findings associated with TiLVD, both the innate and adaptive immune responses and mechanisms to TiLV infection are discussed, in both disease infection models and in vitro studies. In addition, our work, highlights research questions, knowledge gaps and research areas in the immunology of TiLV infection where further studies are needed to better understand how disease protection against TiLV is established.

Fish Gut Microbiome Analysis Provides Insight into Differences in Physiology and Behavior of Invasive Nile Tilapia and Indigenous Fish in a Large Subtropical River in China.

The gut microbiome is thought to play vital roles in host fitness and local adaptation to new environments, thereby facilitating the invasion of the host species. The Nile tilapia (Oreochromis niloticus) (NT) is an aggressive and omnivorous species that competes with native fishes for food resources, and it has successfully invaded much of the Pearl River basin in China. Here, we investigated the gut microbiomes of invasive Nile tilapia and indigenous black Amur bream (BA) in the same river section using high-throughput 16S rRNA gene sequencing. The results indicated that the gut microbiome of NT had several special characteristics, e.g., higher alpha diversity and greater niche breadth, compared with the bream. The gut microbiota of the small size of Nile tilapia (NTS) and small size of black Amur bream (BAS) groups were dominated by Proteobacteria, while those of the NTS and large size of Nile tilapia (NTL) and BAS and large size of black Amur bream (BAL). BAL and NTL were characterized by Firmicutes and Fusobacteriota, respectively. We found that Pseudomonas, Cetobacterium, Ralstonia, and Romboutsia were biomarkers of the NTS, NTL, BAS, and BAL groups, respectively. Moreover, the results collectively suggested that the clustering coefficients of BAL and NTL networks were greater than those of BAS and NTS networks, and BAS had the smallest network among the four groups. Positive interactions between two ASVs dominated the BAS, NTS, and NTL networks, while the proportion of negative interactions between two ASVs in the BAL network was remarkably increased. Low levels of interspecies competition in the NT gut microbiome would contribute to high diversity in the dietary niches and would also benefit the survival and local adaptation of the host. Our results identified specific biomarkers of gut microbial species in invasive Nile tilapia and provided useful information concerning how to monitor and manage invasive Nile tilapia populations.

Population structure and genetic diversity of Nile tilapia (Oreochromis niloticus) using microsatellite markers from selected water bodies in southwest Ethiopia.

The Ethiopian southwest drainage has been designated a huge potential for fishery and aquaculture development. However, the genetic diversity of Nile tilapia along the main water bodies has yet to be uncovered. Therefore, this study used microsatellite markers to assess the genetic structure and diversity of Nile cichlid (Oreochromis niloticus) populations. One hundred and sixty-seven fish were collected from Alwero Dam, Baro River, Gilgel Gibe I Dam and Gojeb River southwest of Ethiopia. Genomic DNA was extracted from 40 tissue samples using a Qiagen DNA tissue extraction kit and genetic polymorphism was estimated using GenAlEx6.502 software. The result showed that four loci were polymorphic and produced 3-6 alleles per locus, while the number of effective alleles (Ne) and the number of distinct alleles (Na) were 1.370 and 2.063, respectively. Observed heterozygosity (Ho) and expected heterozygosity (He) were expanded between 0.100.50 and 0.115-0.265, respectively. Baro River population revealed the highest mean expected heterozygosity of 0.265, whereas the lowest expected mean heterozygosity of 0.115 was from the Alwero Dam. The genetic differentiation between populations (FST) resulted in a moderate to a very high degree of divergence between the populations. The Alwero Dam and Gojeb River populations were the most divergent populations (FST=0.524), unlike those from the Alwero Dam and Baro River. The genetic variation among individuals within populations was 69%, whereas 31% appeared among populations and no variation within individuals to the overall variance. This study confirmed the presence of significant genetic variations and differentiation among populations except between Gilgel Gibe I Dam and Gojeb River. This study highlights the genetic structure and differentiation amongst wild Nile tilapia (O. niloticus) populations in south-western Ethiopia and paves the way for selective aquaculture breeding programs in the study area.

Impact of selection for growth and stocking density on Nile tilapia production in the biofloc system

Environmentally friendly aquaculture systems such as the biofloc technology (BFT) are gaining prominence, as well as the use of genetically superior fish and better adapted strains. However, sustainable systems must be economically efficient as well. According to literature, Nile tilapia takes a longer time to reach commercial weight in BFT if compared to traditional systems, reducing profitability. A better adapted strain, with faster growth, feed efficiency and tolerance to the intensive conditions of the BFT, should be an alternative to improve the profitability of the system. This study evaluated the economic and growth performance of Nile tilapia populations from two distinct generations, the base generation (G0) and generation 5 (G5), from a genetic improvement program based on genetic selection for body weight in BFT and recirculating aquaculture system, under two different stocking densities (12.5 and 37.5 ind. ‧ m−3) in BFT. A total of 320 male fingerlings (160 from G0 and 160 from G5) were randomly distributed in a factorial arrangement (2 × 2, four treatments) with four replicates (800 L tanks) for each treatment (16 sample units in total). The means were compared using two-way ANOVA and SNK's test (p < .05) and the confidence interval (95%) of the differences between them. The water management measures were enough to keep the water indicators within the acceptable ranges for tilapias. Survival rate was high (> 90%) for all treatments. The daily weight gain (DWG) was greater for G5 compared to G0 and resulted in a reduction of >57 days in slaughter time (750 g of harvested weight) for G5 compared to G0 and a 0.22 reduction in feed conversion ratio. The G5 promoted an average reduction of US$ 246.38 ‧ 100 m−3 for total operating cost and added US$ 275.97 ‧ 100 m−3 in operating profit compared to G0. Considering the economic analysis in relation to one ton of tilapia produced, G5 reduced the total operating cost and increased the operating profit only in the lowest stocking density. The increase in stocking density reduced the DWG for both generational groups, resulting in an increase of average time to slaughter of 43.61 days, however, 37.5 tilapia ‧ m−3 promoted a larger operating profit per 100 m−3 (+ US$ 832.60) and per ton of tilapia produced (+ US$ 338.90 for G0 and + US$ 148.39 for G5). This study demonstrates the importance of using genetically improved tilapia together with an adequate stocking density management to achieve better productivity and to make economically more viable an environmentally friendly system.