PhD Thesis

Morphometric and Molecular Characterization of Mosquito Species from Different Larval Habitats in Gulshan Thana, Dhaka

2026-03-02T00:00:00Z

Morphometric and Molecular Characterization of Mosquito Species from Different Larval Habitats in Gulshan Thana, Dhaka Noor-E Jannat, Khandaker This comprehensive study, conducted in Gulshan Thana, Dhaka, investigated mosquito diversity, larval habitat characteristics, and cryptic species identification using an integrated approach combining wing morphometrics and molecular analysis. Larval habitats were systematically surveyed across natural and artificial breeding sites during pre-, peak-, and post-monsoon seasons over three consecutive years using a stratified random sampling design. GPS-referenced data analyzed in ArcGIS Pro revealed high-density breeding zones through kernel density and hotspot analyses. A total of 36 mosquito species across eight genera were identified, including 11 new records for Bangladesh: Aedes (Ae.) aegypti aegypti, Ae. aegypti var. luciensis, Ae. flavopictus, Culex (Cx.) annulirostris, Cx. pipiens, Cx. pipiens f. pipiens, Cx. pipiens f. molestus, Cx. pipiens pallens, Cx. pseudosinensis, Lutzia (Lt.) chiangmaiensis, and Ochlerotatus sp. The Breteau Index comparison between Ae. aegypti and Ae. albopictus was significant (U = 109.5, p = 0.032), peaking in September, with Korail slum identified as a year-round hotspot for Ae. aegypti. Habitat preferences varied, with Culex preferring drains (16.83%) and Aedes favoring water filter pots (27.07%). Morphometric analysis of wing landmarks (CVA and PCA) revealed significant interspecific variations in size and shape (p < 0.0001). Molecular characterization using COI and rRNA markers produced 33 COI and four ribosomal sequences, with an average length of 662.91 base pair. Genetic divergence among six mosquito genera was evaluated using the Kimura 2-parameter model, revealing an average pairwise distance of 21.62%. A Neighbor-Joining (NJ) tree was constructed with 1,000 bootstrap replicates using MEGA 11, to evaluate the robustness of the inferred clades. The Kruskal-Wallis test confirmed significant intergeneric variation (H = 33.14, p = 3.54 × 10⁻⁶). A median-joining network of 20 COI haplotypes revealed high intraspecific genetic diversity (HD = 1.000 ± 0.016; π = 0.11723 ± 0.00855). Notably, Ae. aegypti showed clear divergence from its cryptic subspecies: Ae. aegypti aegypti (distance: 0.21) and Ae. aegypti var. luciensis (distance: 2.15), with 2.30% divergence. The detection of geographically isolated taxa such as Cx. pipiens pallens and Ae. aegypti var. luciensis highlights ongoing ecological range expansion among invasive disease vectors. This thesis is submitted for the degree of Doctor of Philosophy.

Genetic Diversity, Phylogenetic Relationship and Status of Shrimps (Crustacea:Decapoda) of Bangladesh

2025-11-05T00:00:00Z

Genetic Diversity, Phylogenetic Relationship and Status of Shrimps (Crustacea:Decapoda) of Bangladesh Datta, Sujan Kumar Shrimp, a popular and delicious food item worldwide, holds significant commercial and food value, providing a vital source of protein and contributing to a multi-billion-dollar industry in both wild-caught and farmed varieties. Belonging to the order Decapoda, shrimp play a vital role in both marine and freshwater ecosystems. However, a comprehensive, systematic taxonomic study, especially in molecular taxonomy, has not been conducted for these species in Bangladesh. To address this gap, the present study aimed to explore the genetic diversity, phylogenetic relationships, and status of shrimp species found in Bangladesh. An integrative taxonomic approach was used, combining morphological examination, DNA barcoding, and molecular species delimitation to provide a broad understanding of the systematics of shrimps in the region. Specimens were initially identified morphologically, followed by molecular analysis using two genetic markers: the mitochondrial cytochrome c oxidase I (COI) gene and the 16S ribosomal RNA (16S rRNA) gene. 50 shrimp species, representing six families and 16 genera, were morphologically identified, and 38 species and two genera were further confirmed through molecular analysis. A total of 127 sequences were generated, comprising of 55 COI and 72 16S rRNA sequences. Sequence analysis revealed 136 conserved, 561 variable, and 321 parsimony-informative sites for the COI gene, and 101 conserved, 583 variable, and 372 parsimony-informative sites for the 16S rRNA gene. The average GC content was 40.87% for COI and 33.49% for 16S rRNA. Genetic divergence was assessed with mean distances of 1.18 ± 0.02%, 23.53 ± 0.08%, and 28.29 ± 0.05% within species, genus, and family for the COI gene. For the 16S rRNA gene, the corresponding values were 2.94 ± 0.09%, 13.91 ± 0.06%, and 25.26 ± 0.04%. Notably, the mean interspecific genetic distance for COI was 34 times greater than the intraspecific distance, while for 16S rRNA, it was 15 times greater, with barcode gaps of 38.54% and 40.91% for the two markers, respectively. Phylogenetic trees based on the Neighbor-Joining (NJ) method were generated for each gene marker to explore the phylogenetic relationships among the identified species. Additionally, 11 species were newly recorded from Bangladesh, marking their first geographic occurrence in the region. This is the first comprehensive study combining morpho-taxonomy, molecular analysis, and phylogenetic relationships of shrimps from Bangladesh. The study underscores the need for effective conservation strategies and sustainable management practices to preserve the rich shrimp diversity in Bangladesh, as revealed by the molecular and phylogenetic findings. The results not only enhance our understanding of shrimp biodiversity in Bangladesh but also lay a foundation for future research on the ecological and evolutionary dynamics of these crucial aquatic organisms. This thesis is submitted for the degree of Doctor of Philosophy.

Trichodinid ciliates (Ciliophora: Trichodinidae) of selected freshwater fishes of Hakaluki Haor, Bangladesh

2025-11-05T00:00:00Z

Trichodinid ciliates (Ciliophora: Trichodinidae) of selected freshwater fishes of Hakaluki Haor, Bangladesh Ahasan Habib, Md. Moin Uddin This dissertation presents a comprehensive study on the occurrence of trichodinid ciliates parasitizing freshwater fishes from Hakaluki Haor, Sylhet, Bangladesh, conducted between April 2018 and March 2022. A total of 44 host fish species, belonging to 8 orders, 18 families, and 32 genera, were examined; among them, 16 species were infested with trichodinid ciliates. Altogether, 29 species of trichodinid ciliates were identified belonging to three genera: Trichodina Ehrenberg, 1830; Trichodinella (Raabe, 1950) Šrámek-Hušek, 1953; and Tripartiella Lom, 1959. Twenty-four species of Trichodina were identified, of which 22 are redescribed, viz., T. acuta, T. ahmedi, T. anabasi, T. cancilae, T. caspialosae, T. cobitis, T. cubanensis, T. domerguei, T. glossogobae, T. gulshae, T. hafizuddini, T. heterodentata, T. hoffmani, T. japonica, T. kupermani, T. modesta, T. molae, T. nigra, T. notopterusi, T. ovonucleata, T. siluri and T. sylhetensis. Two species of Trichodina are described and new to science, viz., Trichodina sp. 1 n. sp. and sp. 2 n. sp. Two species of Trichodinella, viz., Trichodinella epizootica and Trichodinella sunderbanensis, were recorded, along with three species of Tripartiella, viz., Tripartiella bulbosa, Tripartiella copiosa, and Tripartiella obtusa. Among the 29 species, eight (T. ahmedi, T. cubanensis, T. caspialosae, T. glossogobae, T. kupermani, T. notopterusi, T. ovonucleata, and Trichodinella sunderbanensis) are recorded for the first time from Bangladesh. Taxonomic identification followed the protocols of Lom (1958), Wellborn (1967), Arthur and Lom (1984), and Van As and Basson (1989, 1992). All species descriptions were based on dry silver nitrate impregnated specimens following Klein (1958). Photomicrographs captured at 1000× magnification, detailed morphometric data for each trichodinid species, and diagrammatic illustrations of denticles for selected taxa are included. Observations on host specificity, distribution patterns, and seasonal incidence of infection contribute valuable insights into the diversity and ecology of trichodinid ciliates in freshwater ecosystems of Hakaluki Haor. This study significantly enhances knowledge of trichodinid diversity, distribution, and ecological interactions in Bangladesh, providing essential baseline data for future parasitological research and management strategies. This thesis is submitted for the degree of Doctor of Philosophy.

Parasitic infestation on coral associated fishes of saint Martin`s Island, Bay of Bengal: Molecular, histopathological and heavy metal analysis

2025-11-05T00:00:00Z

Parasitic infestation on coral associated fishes of saint Martin`s Island, Bay of Bengal: Molecular, histopathological and heavy metal analysis Sehrin, Subrina The current study was conducted in order to observe the parasite communities and their characteristics, assemblage, prevalence, intensity, and dominance, their effects on fish, contamination from heavy metals in sediment, water, fish, and parasites from Saint Martin’s Island, in the Bay of Bengal, and evaluate bioaccumulation and the hazards to human health. A sum of 259 reef fishes under 4 families were autopsied during October to March in the years 2019 to 2022, of which 65 fishes were infected with 539 (153 metazoan ectoparasites and 386 endoparasites) parasites. In case of metazoan ectoparasites, prevalence (17.14%) was highest in Terapontidae but intensity was highest in Lutjanidae (6.8±8.15), whereas, for endoparasites, both prevalence (25%) and intensity (19.64±35.07) were highest in Sciaenidae. The analysis of species richness revealed that the ectoparasites demonstrated higher species richness than endoparasites within each family. Among the four fish families, female Terapontidae fish showed higher ectoparasite prevalence than male fish. However, in all four fish families the prevalence of endoparasites was higher in female fish compared to male fish. In endoparasites, only fishes of the Serranidae family showed a significant difference (χ 2 =10.434, p<0.05). Gill and body cavity became the most favourable sites for crustacean parasites [prevalence (12.74%), intensity (3.88±6.55)] and helminth parasites [prevalence (7.69%), intensity (15.7±33.44)] respectively. A strong positive association between host length and prevalence was found in Lutjinidae (rs =0.90, P = 0.04 at p<0.05) and Serranidae (rs =1, P = 0.002 at p<0.01) fish families according to Spearman rank correlation analysis. On the other hand the relationship between host weight and prevalence was inverse but not statistically significant (rs= -0.56, P = 0.32; rs= -0.35, P = 0.55) in Lutjanidae and Serranidae fish families, respectively. A total of 15 metazoan ectoparasites species and 8 endoparasites species were identified, belonging to isopoda, copepod, monogenea and nematoda. Copepod Lernanthropus otolithi showed comparatively highest prevalence (3.86%) among other ectoparasites, whereas isopod Argathona macronema showed the highest intensity (18±0.00) among others. Gonad infecting nematode Philometra cephalopholidis showed the comparative highest prevalence (3.47%) among other nematodes and Hysterothylacium thalassini showed the highest intensity (29.25±50.88). Hysterothylacium thalassini was the highest dominant species. Five classes of dominance were distinguished based on the dominance coefficient value and the most common class of dominance was subrecedents (14 species). Length-weight relationship between uninfected and infected fish demonstrates that both groups maintained the same general body shape and showed no significant differences due to infection status and b-values were less than 3 in all cases except for infected Terpontidae (b=3.07). The condition factor results indicated that fish from all four families were in good condition (K>1.5), with the Serranidae family performing the best (K>2). We identified four parasites through DNA barcode, of which three are up to species and one up to genus. Thymine (T/U) exhibited the highest proportion, ranging from 39.87% to 41.64%, while cytosine (C) showed the lowest content, varying between 14.29% and 15.84% across the four species. The intra-species genetic distances were low, ranging from 0.00351 to 0.02177. The low K2P distance between H. thalassini and P. decipiens implies a close evolutionary connection. The species Hysterothylacium thalassini is clustered together in a strongly supported monophyletic clade, with multiple sequences from different sources (DUZM and NCBI). Pseudoterranova decipiens forms a separate clade with two closely related sequences. Philometra sp. is positioned as a distinct branch, separating it from the other taxa. Lernanthropus otolitii forms the most divergent group in the tree, positioned as like as an outgroup relative to the other species. We employed several significant pollution indicators to evaluate ecological quality. The following heavy metals were measured in samples taken from five locations throughout the Island using atomic absorption spectrometry (AAS): Fe, Co, Pb, Cu, Mn, Ni, Zn, Cr and Cd. The results showed that Fe, Pb, Cu, Mn, Co, and Ni were the heavy metals with the lowest mean amounts in the water. The water’s mean lead content was higher than recommended levels, although the heavy metal pollution index indicated low to medium contamination levels. Cu and Fe (r = 0.910, p<0.05) revealed a significant positive correlation, according to Pearson's correlation study. Fe > Zn > Cr > Pb > Cd was the directive of concentrations in sediment, with Pb concentrations exceeding acceptable standards and a high pollution level for Cr according to geo-accumulation index. Cd and Zn (r = 0.935), Pb and Fe (r = 0.938), and Cd and Cr (r = 0.935) all showed significant correlations at p<0.05, with Zn and Cd showing a perfect connection (r = 1.000, p<0.01). According to the ecological risk measure and contamination variables, there was low to moderate sediment pollution. Fish and parasite muscle heavy metal concentrations were ranked as Fe>Pb>Zn>Cr>Cd and Fe>Zn>Pb>Cr>Cd, respectively, with Cr and Pb levels in fish muscle exceeding regulatory limits. The highest bioaccumulation was observed in fish, Terapon jerbua, and the parasite, Philometra cephalopholidis, with Fe and Cd have a higher propensity to bioaccumulate in parasites than fish. The target hazard quotient indicated significant possible health concerns from consuming Cr, Fe, and Pb-exposed fish, while the target cancer risk analysis revealed significant hazards of carcinogenesis linked to Cd and Cr. Overall, the study concluded that the nematode parasite is a suitable indicator of pollution from heavy metals. We also detected the histopathological alterations in fish tissues and found that some major changes occurred due to parasitic infestation in the stomach, intestine, liver, and gonadal tissue. Both the infected fish stomach and intestine showed haemorrhage, vacuolation, damage to microvilli, sub-mucosal breakage, breakage of microvilli, shrinkage of tissue and parasite attachment. Necrosis in the hepatocytes, haemosiderotic nodules, vacuolation, extensive vacuolar degeneration, hemorrhage, hepatocytes degeneration, blood vessels congestion, edema and focal necrosis were discovered in the infected liver. Infected ovary showed ovarian follicle degeneration, yellowish-brown pigment accumulate encircled by cells that resemble fibroblasts, breakdown of vitelline envelope, oocyte necrosis and ovarian follicle rupture. This thesis is submitted for the degree of Doctor of Philosophy.