Browsing by Author "Nehemia, Alex"

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Anthropogenic activities along the lake nyasa catchments alter the habitat and genetic diversity of a lake salmon, opsaridium microlepis
(Heliyon, 2024) Nehemia, Alex; Mwakalesi, Alinanuswe J.
The Lake Salmon, Opsaridium microlepis is an economically important fish along the Lake Nyasa. However, the species is under threat of extinction due to anthropogenic activities such as agri culture, mining, urbanization, and deforestation. Consequently, the fish species is currently regarded as a threatened species, and the International Union for Conservation of Nature (IUCN) has red-listed the species due to an apparent decline in abundance. The current study assesses the potential impact of human activities on the genetic diversity of O. microlepis using partial mito chondrial cytochrome oxidase subunit I (COI) sequences and microsatellite loci. The results indicate that genetic diversity is lower in the areas affected by human activities compared to relatively pristine areas. The results from this study may suggest that human activities taking place in the catchments are likely to contribute to the alteration of the genetic diversity of O. microlepis species. Thus, immediate measure is required to control anthropogenic activities in the areas to protect the species and other aquatic organisms from possible threats of extinction.
DNA barcoding reveals endangered and protected elasmobranchs in Tanzanian fish markets
(Western Indian Ocean Journal of Marine Science, 2023) Rumisha, Cyrus; Simwanza, Rehema J.; Nehemia, Alex; Mdegela, Robinson H.; Kochzius, Marc
Western Indian Ocean countries have banned elasmobranch finning and enacted legislation to of Marine Science 22(1): 57-65protect endangered elasmobranchs, however finned and morphologically deformed specimens [doi: 10.4314/wiojms.v22i1.6]are still landed and traded on Tanzanian fish markets. Such specimens are difficult to identify Received:morphologically, and it is possible that protected elasmobranchs are among these. This study September 19, 2022used DNA barcoding to uncover protected elasmobranchs in 102 specimens traded on Tan- Accepted:zanian fish markets. The sampled specimens revealed 23 elasmobranch species, 12 of which April 04, 2023(52.1 %) were classified as endangered (EN) or critically endangered (CR) on the IUCN Red List. Published:Three of the identified species (great hammerhead Sphyrna mokarran, oceanic whitetip shark June 16, 2023Carcharhinus longimanus, and pelagic thresher Alopias pelagicus) are protected by Tanzanian laws. Copyright:Hence, it is advised that steps be taken to strengthen law enforcement at landing sites and fish Owned by the journal.markets in the country. Furthermore, the Third Schedule of Fisheries (Amendment) Regula- The articles are open accesstions of 2009 should be updated to include 11 EN and CR elasmobranchs that are not on the list. articles distributed underAdditionally, national and regional elasmobranch conservation plans should be developed to the terms and conditions of the Creative Commons Attribution (CC BY 4.0) licence. prevent the exploitation of endangered elasmobranchs.
DNA barcoding validates new sightings of tridacna elongatissima in Tanzania and Mozambique (Western Indian Ocean)
(Springer, 2022) Velkeneers, Xander; Dissanayake, P. A. K. N.; Huyghe, Filip; Nehemia, Alex; Ratsimbazafy, Hajaniaina Andrianavalonarivo; Kochzius, Marc
There are currently 12 recognised extant species of giant clams (Cardiidae: Tridacninae) inhabiting the tropical waters of the Indo-Pacific. Six species have been newly described or rediscovered since 1982, such as the recently resurrected species Tridacna elongatissima in the Western Indian Ocean. In order to investigate the distri- bution range of this species, 24 specimens have been col- lected and identified by DNA barcoding. This study provides the first record for T. elongatissima in Tanzania and expands both the northern (Zanzibar, Tanzania) and southern (Ponta de Ouro, Mozambique) ranges of this species.
Ecological impact of salt farming in mangroves on the habitat and food sources of austruca occidentalis and littoraria subvittata
(Elservier, 2019) Nehemia, Alex; Chen, Margaret; Kochzius, Marc; Dehairs, Frank; Brion, Natacha
The impact of salt farming on the habitats and food sources of Austruca occidentalis and Littoraria subvittata was studied in mangroves along the coast of Tanzania using stable isotopes ( 13 C and 15 N) and sediment particle size analysis. The 13 C and 15 N stable isotope composition in mangrove leaves, sediments and invertebrate tissues, were used to evaluate whether there are differences in feeding ecology of the crab Austruca occidentalis and the snail Littoraria subvittata collected from natural mangroves and mangroves around the salt ponds. Organic C, total N content and particle size distribution in sediments were used to assess if there are differences in habitat characteristics of mangroves around the salt ponds. Mangrove leaves and sediments were found to be 13 C en- riched around salt ponds compared to those from natural mangroves. Likewise the macroinvertebrates collected from mangroves around salt ponds were found be enriched in 13 C relative to undisturbed mangroves. In addition, mangrove sediments around salt ponds were poorer in organic carbon and nitrogen and had more sand content compared to sediments from natural mangroves. These results indicate that salt pond activities have contributed to the modification of the habitats of macroinvertebrates by causing δ 13 C stable isotopes enrichment and al- teration of sediment characteristics in the ecosystem.
Genetic diversity, population genetic structure and demographic history of the Ribbontail stingray Taeniura lymma (Fabricius, 1775) (elasmobranchii: myliobatiformes: dasyatidae) along the Tanzanian coastline
(Taylor & Francis, 2024) Nehemia, Alex
The Ribbontail stingray Taeniura lymma is an economically important fish and attractive species for the aquarium trade industry. Overfishing, habitat degradation, and pollution, however, pose a threat to this species. This study used partial mitochondrial cytochrome oxidase subunit I (COI) sequences (603 base pairs long) from 96 samples of T. lymma collected at five fish-landing sites (Deep Sea-Tanga, Malindi-Unguja, Kaole-Bagamoyo, Kivukoni-Dar es Salaam, and Bandarini-Mtwara) located along the coast of Tanzania to determine the species’ genetic diversity, population genetic structure, and demographic history. The findings revealed an average nucleotide diversity of 0.24 ± 0.16% and a haplotype diversity of 0.75 ± 0.04. Nucleotide and haplotype diversities were relatively low at Kaole-Bagamoyo compared to the other studied localities. An Analysis of Molecular Variance (AMOVA) indicated limited but statistically significant genetic differences among populations (Overall FST = 0.09, p < 0.01). Pairwise AMOVA revealed genetic difference between the Deep Sea-Tanga population and all other populations studied with exception of Malindi-Unguja. Analyses of mismatch distribution, demographic history, and a haplotype network support a scenario of historical population expansion in the studied species. Immediate effort is required to protect population exhibiting low genetic diversity in this commercially important ray.
Genetic erosion in the snail littoraria subvittata (reid, 1986) due to mangrove deforestation
(Journal of molluscan studies, 2016) Nehemia, Alex; Huyghe, Filip; Kochzius, Marc
In tropical coastal ecosystems mangrove forests are important as feeding, spawning, breeding and nursery grounds for many marine species. High human population pressure in coastal areas has led to the loss and deterioration of mangrove habitats. Solar salt production can affect these habitats along the East African coast. Littorinid snails live on mangrove trees, forming an important component of the mangrove ecosys- tem and have been used as bioindicators of environmental health and community stress. Littoraria subvittata is the most abundant littorinid species in mangroves along the East African coast. Partial mitochondrial cytochrome oxidase subunit 1 (COI) gene sequences of 298 individuals were used to assess the impact of mangrove deforestation at salt ponds on the genetic diversity and structuring of L. subvittata populations, as well as to infer the demographic history of the species. Nucleotide and haplotype diversities were found to be lower in samples from mangroves at salt ponds than in samples from natural mangroves. The mean nucleotide diversity was 0.049 ± 0.036% and 0.115 ± 0.068% in mangroves at salt ponds and natural mangroves, respectively. The mean haplotype diversity was 0.23 ± 0.14 and 0.50 ± 0.14 in mangroves at salt ponds and natural mangroves, respectively. Analysis of molecular variance (AMOVA) detected a sig- nificant population structure (Ф st = 0.049; P < 0.0001) for the combined populations. Hierarchical AMOVA detected a significant population genetic structure only between populations from mangroves at salt ponds and natural mangroves (Φ ct = 0.022; P < 0.05), but not between any other groupings. Populations from natural mangrove sites showed a significant genetic structure (Ф st = 0.054, P < 0.0001), while populations from sites at salt ponds could not be differentiated (Ф st = −0.0026, P = 0.64). Reduced effective population size was observed in most samples from mangrove sites at salt ponds compared with natural mangrove. The direction of migrants was mostly from salt ponds to natural mangroves. These results show that salt ponds have a negative impact on the genetic diversity of L. subvittata populations and modify the population’s genetic structure.
Genetic variation and lack of hybridization in five cichlid fish species in the Malagarasi River basin, Tanzania
(Elsevier, 2025) Nehemia, Alex
Among the most widely cultured groups of freshwater fish species are tilapiine cichlids. This has contributed to introduction of cichlid fish species in area where they were not native. Consequently, has contributed to negative ecological effects on local species and their habitats through competition, habitat alteration and loss of unique population genetic structures due to hybridization. This research study aimed to assess the genetic status of five cichlid fish species red listed by the International Union for Conservation of Nature (IUCN) as least concerned species. A mitochondrial Cytochrome Oxidase Subunit I (COI) gene fragment from 112 individuals collected from three sampling sites were used to determine the present genetic diversity of the cichlid species inhabit the Malagarasi River system which discharge water into Lake Tanganyika. The highest nucleotide diversity (0.02 ± 0.01) and haplotype diversity (0.94 ± 0.04) were recorded from Haplochromis pharyngalis. The lowest levels of nucleotide and haplotype diversity were recorded from Oreochromis leucostictus. The Analysis of Molecular Variance (AMOVA) resulted into statistically significant genetic differences (Φst: 0.96, P < 0.001) among the cichlid species studied. The minimum spanning haplotype network and maximum-likelihood phylogenetic an alyses support the AMOVA findings as no species is sharing any haplotype with other species. The values of neutrality tests suggested that the studied cichlid fish species are stable and not expanding. These findings highlight the necessity of conservation interventions in the area especially for the species which displayed low nucleotide and haplotype diversity.
Length-Weight relationship and condition factor of tilapia species grown in marine and fresh water ponds
(Agriculture and Biology Journal of North America, 2012) Nehemia, Alex; Maganira, Justin D.; Rumisha, Cyrus
The aim of this study was to describe the differences in Length-Weight relationship and condition factor of Tilapia zillii and Oreochromis urolepis urolepis reared in full strength sea water (FSSW) and fresh water (FW) ponds. The environmental condition in FSSW and FW ponds were also analyzed to determine their impacts on Length-Weight relationship and condition factor on both species. The regression coefficient "b" exhibit negative allometric growth in FW and positive allometric growth in FSSW for both species. The value of exponent "b" and condition factor (K) for T. zillii in FW and FSSW (in the bracket) were found to be 2.94 (3.3) and 2.07 (0.74) respectively. On the other hand the value of exponent "b" and condition factor (K) for O. urolepis urolepis in FW and FSSW (in the bracket) were found to be 2.81 (3.46) and 0.86 (0.53) respectively. Though both species performed well in FW, the study also revelead that farming of these tilapia species in FSSW can be feasible if water quality parameters are properly monitored.
Mitochondrial genetic diversity and demographic history of critically endangered oreochromis karongae (trewavas, 1941) along lake nyasa, Tanzania
(John Wiley & Sons, 2024) Nehemia, Alex; Mwakalesi, Alinanuswe J.
Fish provide food and income opportunities for millions of people in Lake Nyasa, also known as Lake Malawi in Malawi and Lake Niassa in Mozambique. Oreochromis karongae (Trewavas, 1941), which is native to Lake Nyasa, Lake Malombe and the Shire River, is at the verge of extinction and has been listed as critically endangered species by the International Union for Conservation of Nature (IUCN), primarily due to overfishing. Using 632 bp of partial mitochondrial cytochrome oxidase subu- nit I (COI) sequences from 115 samples, this work aims to assess the population genetic status and demographic history of this species to better manage and advance its conservation. The analysis of molecular variance (AMOVA) revealed a low and non- significant genetic differentiation index across the populations under study (ΦST = 0.003, p = 0.278), indicating a lack of popu- lation genetic structure. Phylogenetic analysis, grouped together all COI haplotypes of O. karongae from the six sampled sites. Nonetheless, the results showed signs of population expansion from a historic bottleneck, consistent with most data from the Western Indian Ocean Fauna. The findings from this study could be used to improve management and conservation strategies for critically endangered O. karongae in Lake Nyasa.
Population expansion but limited gene flow in kuhl's blue-spotted maskray along the Tanzanian coast
(2024) Nehemia, Alex; Shabani, Maulidi; Malisa, Allen Lewis
The blue-spotted maskray Neotrygon kuhlii (Müller & Henle, 1841) is a member of the Dasyatidae family of stingrays which grows slowly. Members of this group mature late and have a low fecundity rate. The ICUN Red List of Threatened Species lists N. kuhlii species as data deficient (DD) because information on its ecology and life history is not readily available. The purpose of this study was to determine the genetic diversity, demographic history and population structure of N. kuhlii, all of which are critical information for efforts aimed at conserving the species. The investigation was carried out along Tanzania's coastline using 595 base pairs of partial mitochondrial cytochrome oxidase subunit I (COI) sequence. The haplotype diversity ranged between 0.37 and 0.70 and nucleotide diversity between 0.11% and 0.50%. The findings show that samples from Unguja had higher mean molecular diversity indices than those from other sampling sites. Nonetheless, samples from Mafia and Unguja were found to have the largest effective population size. Genetic variations were found between the subpopulations under study, suggesting limited genetic connectivity among the studied subpopulations. The COI sequences of N. kuhlii from most subpopulations studied showed signs of past population expansion, which are typical for most Western Indian Ocean (WIO) fauna. The findings highlight the need for enhanced management and conservation strategies for N. kuhlii and other coastal stingray species in Tanzania, particularly in areas where sampling sites showed low levels of genetic diversity and effective population size.
Population Genetic Structure and Demographic History of Opsaridium microcephulum along Lake Nyasa
(University of Dar es Salaam, 2023) Nehemia, Alex; Mwakalesi, Alinanuswe J.
The Sanjika, Opsaridium microcephalum is among the fish species that serve as a major source of proteins and income to people along Lake Nyasa. However, the information on its genetic diversity and structure particularly in the Tanzania part of the Lake is limited. Therefore, the assessment of the genetic diversity and structure of O.microcephalum along the Lake Nyasa part of Tanzania was conducted in the current study using a fragment of the mitochondrial COI gene from 92 individuals of O. microcephalum. The findings showed that an average haplotype diversity and average nucleotide diversity were 0.8065 ± 0.0314 and 0.002380 ± 0.001640, respectively. The molecular Variance (AMOVA) indicated significant genetic variations among the subpopulations studied (Overall Φst = 0.31560, p < 0.001). The lowest haplotype diversity was recorded at Manda and the highest haplotype diversity was recorded at Buloma. The lowest nucleotide diversity was recorded at Manda and the highest was recorded at Lupingu. The differences in genetic diversity can be a possible indicator of different localised evolutionary forces that require attention to conservationists for the sustainable management of O. microcephalum.
Reduced genetic diversity and alteration of gene flow in a fiddler crab due to mangrove degradation
(PLOS, 2017) Nehemia, Alex; Kochzius, Marc
The fiddler crab Austruca occidentalis is a dominant species in mangrove forests along the East African coast. It enhances soil aeration and, through its engineering activities, makes oth- erwise-inaccessible food available for other marine organisms. Despite its importance, the hab- itat of A. occidentalis is threatened by human activities. Clearing the mangroves for salt farming and selective logging of mangroves trees continue to jeopardise mangrove ecosystems in the Western Indian Ocean. This study aims to use partial mitochondrial COI gene sequences and nuclear microsatellites to determine whether salt farming activities in mangroves have a nega- tive impact on the genetic diversity and gene flow of A. occidentalis collected along the Tanza- nia coast. The level of genetic diversity for both mitochondrial DNA and nuclear microsatellites are relatively lower in samples from salt ponds compared to natural mangrove sites. Analysis of molecular variance (AMOVA) among all populations showed low but significant differentia- tion (COI: F st = 0.022, P < 0.05; microsatellites: F st = 0.022, P < 0.001). A hierarchical AMOVA indicates lower but significant genetic differentiation among populations from salt ponds and natural mangroves sites (COI: F ct = 0.033, P < 0.05; microsatellites: F ct = 0.018, P = < 0.01). These results indicate that salt farming has a significant negative impact on the genetic diver- sity of A. occidentalis. Since higher genetic diversity contributes to a stable population, restoring the cleared habitats might be the most effective measures for the conservation of genetic diver- sity and hence adaptive potential to environmental change in this species.
Survival and growth of tilapia zillii and oreochromis urolepis urolepis (Order perciformes; Family cichlidae) in seawater
(Western Indian Ocean J. Mar. Sci, 2014) Nehemia, Alex; Mmochi, Aviti; Mtolera, Matern
The potential for Tilapia zillii and Oreochromis urolepis urolepis culture in seawater was evaluated by determining their survival and growth in seawater at 35‰. Fingerlings were collected from Pangani River using seine nets and reared in 1 m 3 concrete ponds after acclimatization from salinity of 2‰ to 35‰. Fingerlings were also reared in freshwater as controls. Fingerlings were fed twice daily using commercial fish feeds (White Rose floating pellets), initially at a rate of 5% of their total body weight (TBW) and 10% of their TBW after two weeks. Their growth rate (length and weight) was recorded weekly except controls for handling, their growth being recorded at the beginning and end of the experiment. The average weight gain (g.week -1 ), percentage weights gain (week -1 ) and specific growth rate (SGR, %.day -1 ) were determined in freshwater and seawater. There was no significance difference (p >0.05) in the SGR between the two species in seawater. The survival rates of O. urolepis urolepis were 100% in freshwater and seawater and 89% and 96% respectively for T. zillii. This study showed that T. zillii and O. urolepis urolepis can survive and grow in seawater but the former is a better candidate for mariculture.
The current population genetic status of oreochromis niloticus (linnaeus, 1758) along the malagarasi river, Tanzania
(Elsevier, 2024) Nehemia, Alex; Umbayda, Tlehema
In East African countries, the O. niloticus species is the second most important fish species in terms of economic significance. However, localized overfishing, habitat degradation, and hybridization have resulted in pop ulations’ decline that poses a threat to this species in this area. This study assessed the genetic diversity, pop ulation structure, demographic history, and effective population size of this species along the Malagarasi River. Comparisons were made between the population genetic structure and demographic history of populations of this species from Malagarasi River and other sites in the East Africa (EA) region. The study used COI gene se quences isolated from O. niloticus species collected along the Malagarasi River and COI gene sequences of this species from other sites in the EA region. The populations of O. niloticus from the Moyowosi had the highest haplotype diversity (0.80 ± 0.06) and nucleotide diversity (0.72 ± 0.41 %). At Ilagala, the lowest haplotype diversity (0.44 ± 0.13) and nucleotide diversity (0.16 ± 0.13 %) were found. Fixation index (Fst value) analysis resulted into significant genetic difference among the populations along Malagarasi River (Fst = 0.08419, P < 0.01). The Fst values and minimum spanning haplotype network revealed genetic break between population of O. niloticus from the Malagarasi River and other sites of the EA region. In order to ensure the sustainable exploitation of O. niloticus and other threatened fish species along the Malagarasi River, these findings urge for strengthening the implementation of fisheries laws, particularly in areas where samples exhibit low genetic diversity.