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Item Comparison of different aerogels derived from Eichhornia crassipes for efficient oil removal from water(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Darshani, U. G. N. P.; Manage, P. M.; Idroos, F.S.Oil-related water pollution originates from various sources, including industrial discharge, accidental oil spills, road runoff, etc. In recent years, it has become one of the most severe global challenges due to its detrimental effects on the environment and the economy. Typical oil clean-up techniques from water are categorized as physical/mechanical, chemical, biological, and physiochemical methods. These conventional methods have several limitations such as being labour intensive, high cost, timeconsuming and less effective for some oil types. The current study aimed to synthesize environmentally friendly and hydrophobic aerogels with low density, high porosity, high oil absorption capacity, rapid oil absorption rates, and enhanced reusability by using Eichhornia crassipes (Water hyacinth-WH), an aquatic invasive plant as the raw material. Aerogel is a special sponge-like porous sorbent material with excellent physiochemical properties enabling effective adsorption of oil. In this study, aerogels were prepared in two forms: WH cellulose-based aerogel and WH biochar-based aerogel. Both aerogels were produced using the same method, including alkaline/H2O2 pre-treatment, crosslinking with Polyvinyl Alcohol (PVA), freeze-drying, and finally silanization with Methyltrimethoxysilane (MTMS) to produce hydrophobic aerogels. Among these 2 aerogels, WH biochar-based aerogel showed the highest oil adsorption capacity (19.10 ± 0.35 g g-1) and the highest oil adsorption rate (3.82 ± 0.07 g s-1), while 16.31 ± 0.69 g g-1 of oil adsorption capacity of cellulose-based aerogel for different oils including crude oil, gasoline, diesel, etc. High adsorption capacity allows the sorbents to hold more oil, reducing the frequency of replacement or regeneration needed and high adsorption rate ensures rapid response to oil spills, minimizing the duration of environmental exposure and potential damage. Moreover, this biochar-based aerogel showed the lowest density (0.30 ± 0.01 g cm-3), highest porosity (80.78±0.82%) and excellent reusability. Low density, high porosity, and high reusability are essential for oil sorbents as they ensure lightweight handling, increased oil adsorption capacity, and cost-effective, sustainable operation. Furthermore, the physicochemical properties of the developed aerogels, including chemical structure and surface morphology were thoroughly characterized using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). The findings revealed that the aerogels exhibited a complex, interconnected three-dimensional pore structure consisting of multiple layers. These pores were connected by flexible sheets and contained a large number of macro and micro pores throughout the aerogels. Additionally, various functional groups such as alcohol (-OH), alkane (C-H), carboxylic group (R-COOH), ether (R-O-R), aromatic, etc., were observed distributed on the surface of the aerogel. Together with these properties, both aerogels are suitable for oil clean-up applications, while biochar-based aerogel exhibited superior performances in addressing oil pollution challenges. Therefore, the present study proposes a low-cost, sustainable, green method for the effective utilization of aquatic invasive plants for oil clean-up approaches.Item Biovalorization of agro-food wastes for the production of melanin pigment via a submerged fermentation process using Aspergillus niger: as a sustainable approach(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Rasna, N. F.; Jayathilake, K. M. P. I.; Manage, P. M.; Idroos, F. S.Biovalorization harnesses biological processes to convert waste materials into value added products, encouraging sustainability and resource efficiency. The current study aims to explore and optimize a sustainable method for the production of melanin pigment through the submerged fermentation (SMF) process by utilizing banana peel waste, affected Sesbania grandiflora leaves and stem wastes, and used tea dust waste using Aspergillus niger. The pH, moisture content, total organic carbon, and total ash contents of collected food wastes were measured using standard methods. Fungal cultures were incubated under the submerged fermentation process, at 25 °C with an agitation speed of 160 rpm for 14 days. Subsequently, the fungal-produced pigment was extracted using 1.0 mol/L KOH and subsequently characterized using physicochemical tests with water, organic solvents, alkaline and acidic solutions, and an oxidizing-reducing agent. Further, the pigment was confirmed based on ultraviolet-visible spectroscopic analysis and Fourier-transform infrared spectroscopic (FTIR) analysis. The extracted pigment was tested for toxicity, antibacterial, and antioxidant properties to the determination of the distinctive characteristics and quality of the extracted pigment, hence enabling their industrial use. The pigment yield from banana, Sesbania, and tea wastes were 597.2 ± 21.5 mg/L, 395.4 ± 39.1 mg/L, and 135 ± 12.9 mg/L, respectively. Compared to the control setup, a significant difference (p < 0.05) was observed between the pigment yields produced by A. niger when utilizing different types of food waste. In the physico-chemical analysis, the blackish brown colour of the pigment served as primary evidence for melanin. The pigment was insoluble in water and organic solvents (acetone, chloroform, ethanol, and sodium acetate), but it was readily soluble in KOH and NaOH, precipitated with HCl, and decolorized with H₂O₂. The UV-Vis spectrum indicated that the pigment possessed a λmax around 213–216 nm. The FTIR spectrum showed broad bands around 3000– 3500 cm⁻¹ (OH), 2924.7 and 1032.6 cm⁻¹ (saturated carbon and C-O), 2830–2930 cm⁻¹ (CH2 and CH3), 1500–1650 cm⁻¹ (aromatic C=C or C=O), 1320 and 1390 cm⁻¹ (C-N), and 1210–1230 cm⁻¹ (C-OH). The extracted pigment exhibited low toxicity to mung beans (4.4–6.7%) compared to the positive control (100% extraction solvent). In the antibacterial activity assay, inhibition zones ranged from 2.1 ± 0.1 to 2.6 ± 0.1 cm for Staphylococcus aureus and 2.1 ± 0.1 to 2.5 ± 0.1 cm for Escherichia coli. The antioxidant assay demonstrated an increase in the percentage of DPPH inhibition with increasing pigment concentration, suggesting the pigment's ability to scavenge free radicals. This study proposes a sustainable approach for the production of fungal-based pigment (melanin) through a submerged fermentation process utilizing agro-food wastes with Aspergillus niger strain, which was not documented in previous studies.Item Development and characterization of biodegradable nanocomposite membrane using chitosan and green ZnO nanoparticles(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Ginige, G. C. C.; Manage, P. M.; Idroos, F. S.In response to the growing demand for sustainable industrial materials, this study focuses on the development and characterization of novel Chitosan/green ZnO nanocomposite membranes. This study aims to create inexpensive, non-toxic, and biodegradable materials using sustainable sources. Chitosan, extracted from shrimp shells, was combined with ZnO nanoparticles synthesized through a green approach utilizing the invasive plant Hydrilla verticillata. Chitosan was extracted from shrimp shells, following a series of processes: demineralization using 4% HCl, deproteinization with 5% NaOH, and deacetylation with 70% NaOH, achieving a 61% yield and a moderate degree of deacetylation (DDA%) of 70.83%. The green synthesis of ZnO nanoparticles was carried out using an aqueous extract of the invasive plant Hydrilla verticillata, resulting in a yield of 67.5%. Four types of membranes were fabricated via a solution-cast method, incorporating varying ZnO nanoparticle content (0.0, 0.2, 0.5, and 0.8 g) into a fixed amount of chitosan (1.0 g). The transparency of the membranes decreased, and their color changed from off-white to light brown with increasing ZnO content. Characterization techniques, including XRD, FTIR, SEM, and EDS, were employed. XRD spectra confirmed the crystalline nature of both pure chitosan and CS/ZnO nanocomposite membranes. The presence of characteristic ZnO peaks indicated successful nanocomposite formation. The average crystalline size of ZnO NPs was calculated as 27.49 nm. FTIR spectra revealed the presence of functional groups in chitosan and confirmed the incorporation of ZnO NPs within the nanocomposite membranes. SEM images showed a random pore structure on the pure chitosan membrane surface, while these pores were masked by ZnO NPs in the nanocomposite membranes. EDS results confirmed the presence of expected elements (C, O, N, and Zn) in the nanocomposite membranes. The study demonstrates that these novel nanocomposite membranes, derived from sustainable materials, hold promise for various industrial applications due to their unique combination of biodegradability, non-toxicity, and potential for tailored properties through variations in ZnO NP content.Item Isolation, characterization, and application of phosphate-solubilizing fungi as a biofertilizer for plant growth promotion(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Jayathilake, K. M. P. I.; Manage, P. M.; Idroos, F. S.Plants require major nutrients such as nitrogen and phosphorus for their optimal growth. Phosphorus is an essential macronutrient, yet its availability in soil is often limited due to its insoluble form. Soil microbes can convert insoluble phosphate into soluble phosphate through various mechanisms. Phosphate-solubilizing fungi (PSF) play a vital role in this process, contributing to the phosphorus requirements of plants. Hence, the present study aimed to isolate, characterize, and utilize PSF as a biofertilizer. The PSF strains were isolated from compost soil in Karadiyana (6°48′ 51.8′′ N, 79° 54′ 17.0′′ E) using Pikovskaya's agar (PVK) medium. The phosphate solubilizing index (PSI) was determined by observing halo zone formation after a 7-day incubation period. Phosphate solubilizing efficiency was assessed using PVK broth supplemented with 0.5% tricalcium phosphate following 7 days of incubation at 160 rpm (28 oC). The isolated fungal strains were introduced to a developed potting medium containing compost, coir dust, and soil in a 1:1:1 ratio. Mung bean (Vigna radiata) was selected as the experimental plant. Plant growth parameters (shoot length, root length, wet weight, and dry weight) were measured to determine the effect of the isolated fungal strains. These parameters were recorded after 30 days. Genotypic identification of the isolated strains was performed using the Internal Transcribed Spacer (ITS) region. The strains were confirmed as Fusarium proliferatum, Aspergillus niger, and Aspergillus flavus. A. niger demonstrated the highest phosphate solubilizing efficiency (296.8 ± 0.2 μg/mL) after 6 days of incubation, with a PSI of 2.15 ± 0.1. Fungi-inoculated pots showed a significant increase in shoot length, root length, wet weight, and dry weight compared to the control (n = 9, p < 0.05). Potting media inoculated with A. niger showed the best results, with the highest root length (11.8 ± 0.5 cm), shoot length (16.7 ± 0.5 cm), wet weight (0.6381 ± 0.03 g), and dry weight (0.1060 ± 0.02 g) was recorded. This study suggests that the potting media containing F. proliferatum, A. niger, and A. flavus exhibited significant roles in phosphate solubilization and plant growth promotion, indicating their potential to be used as an effective biofertilizers.Item Isolation and characterization of nitrogen-fixing bacteria from compost soil and their impact on nitrogen uptake and plant growth(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Jayathilake, K. M. P. I.; Manage, P. M.; Idroos, F. S.Nitrogen-fixing bacteria play a critical role in sustainable agriculture by enhancing soil nitrogen availability, reducing the need for synthetic fertilizers, and promoting plant growth. This study aimed to isolate and characterize nitrogen-fixing bacterial (NFB) strains from compost soil and evaluate their potential to improve nitrogen uptake and plant growth. NFB strains were isolated from compost soil in Karadiyana (6°48′ 51.8′′ N, 79° 54′ 17.0′′ E) using an Ashby medium. The molecular level identification of each isolate was carried out using the 16S rRNA gene region. The production ability of ammonia, nitrate, and nitrite was determined after 7 days of incubation in Ashby broth medium inoculated with each isolated strain. The effect of isolated NFB strains on plant growth was determined using a pot experiment. The isolated nitrogen-fixing bacteria (NFB) strains were introduced to the developed potting media prepared with compost, coir dust, and soil in a 1:1:1 ratio, with mung bean (Vigna radiata) selected as the experimental plant. Control potting media was prepared without the inoculation of NFB strains. Shoot length, root length, wet weight, and dry weight of the grown plants were measured after 30 days of the seed germination period as growth parameters to determine the effect of the isolated NFB strains. The molecular level identification confirmed that the isolated strains were Microbacterium aquimaris (CTD16), Bacillus xiamenensis (MCCC 1A00008), Bacillus aerophilus (XA5-12), Bacillus subtilis (NCIB 3610), Bacillus cereus (CCM 2010), Bacillus subtilis (BHU7), and Bacillus aerius (24K). The highest ammonia (1.6 ± 0.5 mg/L) and nitrate (1.08 ± 0.04 mg/L) production were recorded in Ashby broth media inoculated with B. cereus after 7 days of incubation. Pots inoculated with NFB strains showed a significant increase in measured growth parameters compared to the control (n = 9, p < 0.05). Potting media inoculated with B. cereus strain CCM 2010 showed the best results, with the highest root length (11.3 ± 1.1 cm) and shoot length (17.5 ± 0.5 cm), wet weight (0.6898 ± 0.1 g), and dry weight (0.1015 ± 0.01 g) recorded. The study demonstrated that all isolated Bacillus spp. and Microbacterium aquimaris exhibited significant roles in nitrogen fixation. These findings indicate their potential as effective biofertilizers, contributing to enhanced nitrogen availability and improved plant health.Item Prevalence of antibiotic resistance in surface water, ground water and sediment in the transition zone of the Kelani River basin, Sri Lanka(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Meddage, A. K. M. M. K.; Liyanage, G. Y.; Idroos, F. S.; Manage, P. M.Antibiotics are mainly used to treat and prevent diseases in humans and animals, and they also serve as growth promoters and feed efficiency enhancers in agriculture and animal husbandry. However, antibiotic-resistant bacteria (ARB) have emerged as a result of antibiotic overuse and misuse. The prevalence of ARB becomes more critical, particularly for rivers that fulfil urban drinking water demand. Furthermore, the ARB poses a significant threat to human health by potentially treatments ineffective and leading to the spread of untreatable infections. This study aims to screen the presence of ARB against selected antibiotics such as Ciprofloxacin (CIP), Cefuroxime (CXM), Cloxacillin (CLOX), Amoxicillin (AMX), Co-Amoxiclav (CO-AMX); Tetracycline (TC); Azithromycin (AZT), Erythromycin (ERM); Sulfamethoxazole (SMX) and Gentamycin (GEN) in the transition zone of Kelani River Basin, Sri Lanka. Samples were collected during the first inter-monsoon season in March 2024. Twenty-five water samples (groundwater - 07; surface water - 18) and 12 sediment samples were subjected to determine Total Viable Count (TVC) and ARB using the standard pour plate method at 60 mg/L of antibiotic. The TVC of bacteria ranges between 0.2 × 102 – 4.0 × 102 CFU/mL in collected surface water samples, whereas 0.2 × 102 – 2.2 × 102 CFU/mL, and 0.6 × 102 – 1.2 × 102 CFU/mL for groundwater and sediments, respectively. The resistance bacteria percentage against CXM (16.55%), CLOX (15.82%), AMX (13.98%), AUG (12.90%), SMX (10.46%), GEN (10.22%), ERY (8.76%), AZT (6.60%), CIP (2.68%), and TET (2.19%). According to the obtained results, CXM and CLOX showed the highest resistance, indicating bacterial adaptation in both sediment and water. However, TET and CIP exhibited the lowest resistance rates, suggesting they remain effective options. Moderate resistance was observed for SMX and GEN, highlighting the need for cautious use to prevent further resistance. These findings highlight the notable presence of antibiotic-resistant bacteria in environmental samples. Moreover, the results revealed that a thorough investigation into the presence and spread of antibiotic resistance throughout the Kelani River Basin is urgently required.Item Determination of combined acute toxic effects of well water hardness and fluoride using the embryos of Danio rerio (zebrafish)(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Imanthi, K. P. A.; Wanigasuriya, J. K. P.; Perera, P. P. R.; Jayasundara, N.; Manage, P. M.Water hardness is expressed as the concentration of dissolved minerals, mainly calcium and magnesium which are naturally present in both ground and surface water sources. Water hardness and fluoride levels in drinking water have significant impacts on human health. The synergistic effect of total hardness and fluoride is considered to be one of the major hypotheses for Chronic Kidney Disease of unknown etiology (CKDu) in Sri Lanka. The kidney accumulates more fluoride than other soft tissues, which may contribute to the origin and progression of kidney disease. Water hardness can affect early development as it alters the availability of essential ions for physiological processes. This study was conducted to evaluate the total hardness and fluoride levels in well water from Agunukolapelassa and determine the acute toxic effect of different hardness and fluoride combinations on embryonic development using zebrafish. Thirty well water samples were collected randomly. Highest total hardness was measured as 158.67 ± 0.05 mg/L (H1) and lowest was 16.00 ± 0.10 mg/L (H2) while fluoride was ranged between 1.93 ± 0.00 mg/L (F1) to 0.16 ± 0.00 mg/L (F2). Four different solutions were prepared by combining the above concentrations solution 1 (H1, F1), solution 2 (H1, F2), solution 3 (H2, F1), and solution 4 (H2, F2). Hardness solutions were synthetically prepared using MgCl2 and CaCl2, fluoride solutions were prepared using NaF. Distilled water was used as the control. Zebrafish embryos after 2 hours of post fertilization (hpf) were exposed to different solutions, thirty per each and triplicated. Mortality, hatching rates, heart rates and morphological abnormalities were observed using a light microscope (10×4) until 96 hpf. The highest mortality, 27.8% was recorded in solution 1 and others were 15.5%, 20.0% and 8.8% respectively. The hatching rate was recorded after 54 hpf and it was 3.3%, 16.6%, 11.1% and 22.2% for each solution. Heart rate was lowest in solution 1 as 84 beats per minute (bpm) and highest in solution 4 as 100 bpm. Subsequently, control showed 0% mortality, 80% hatching rate and 140 bpm heart rate at the same time. Around 40% of embryos showed morphological abnormalities such as yolk sack oedema and bent body axis in solutions 1 and 3. Oedema in belly region indicates the damaged pronephros, which alters the kidney function in embryos. Results emphasize the adverse developmental effects of total hardness and fluoride combinations on embryos as it increases mortality, reduces hatching rate and heart rate. Especially higher levels of fluoride induce having physical deformities, organ damages and reduce blood flow in embryos. These effects on early development can reduce embryonic viability, organ functioning and survival in the natural environment.Item Quality index assessment for compost derived from municipal solid waste using novel bacterial consortia(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Wijerathna, P. A. K. C.; Udayagee, K. P. P.; Idroos, F. S.; Manage, P. M.Composting is one of the integral components of the global circular bio-economy platform. Traditional composting requires a prolonged time, and the inoculation of efficient bacterial consortia is a novel technique to enhance the composting rate. Further, assessing compost quality is crucial because the application of immature compost can cause phyto-toxicity, damage the natural ecological balance and disrupt soil structure. The present study focused on the quality assessment of compost produced by five novel microbial consortia (C1–C5) using indexing methods; Clean Index (CI), Fertilizing Index (FI), Germination Index (GI) and Vigor Index (VI). The experiment was conducted using an organic fraction of Municipal Solid Waste (MSW); composed bins made out of concrete were filled with 90 kg of MSW and 2% of v/w each broth consortia were separately inoculated. The experiment was conducted in an open environment, and all the treatments were triplicated. A control treatment with three replicates was used without the addition of any broth consortia. The bins were closely monitored over 30 days for the composting parameters including the pH, conductivity, bulk density and the compost analysis was done following the standard methods. The FI was determined based on the characterization results of the final compost and the CI was determined based on the analyzed heavy metals Cd, Zn, Cr, Pb and Cu analysis carried out using the ICP-OES technique following the acid digestion. The GI and VI were determined using healthy and mature green gram (Vigna radiate) seeds and data were statistically analyzed using Tukey’s test. The FI and CI were calculated using a weighting scale of heavy metals based on their toxicity and the GI and VI were calculated based on the seed germination and their radical lengths. Based on the results, the FI, CI, GI and VI values were significantly different (p < 0.05) and ranged from 3.0–4.5 and 4.0–5.0, 72.4–110.2 % and 364.8–551.0 respectively. Further, the greatest FI, CI, GI and VI values were recorded in the C5 compost, which inoculated the consortium which comprises Bacillus haynesii (PP391133), Bacillus amyloliquefaciens (PP391056) and Bacillus safensis (PP391033) strains. Consequently, the compost produced by the C5 consortium was categorized into the compost quality “A” category indicating its high quality and fertilizing potential. In contrast, the control compost belonged to the compost quality “D” category indicating the lowest quality. Thus, the results evidenced the potential applicability of the C5 consortium to produce good quality compost as a sustainable waste management approach.Item Isolation and characterization of native phosphate-solubilizing microorganisms from Eppawala rock phosphate and associated soil(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Rathnapriya, R. H. K. G.; Wijerathna, P. A. K. C.; Manage, P. M.Phosphorus is a crucial macronutrient in plant growth and development. The lower bioavailability of phosphorus in agricultural lands causes phosphorus deficiency in plants leading to plant growth retardation. As a remedy, rock phosphate is incorporated into phosphorus fertilizers. However, the direct application of rock phosphate as a phosphorus fertilizer is not recommended due to its lower solubility. Hence, the focus of the present study was to isolate and characterize the phosphatesolubilizing microorganisms as a cost-effective greener solution to solubilize insoluble rock phosphate. In the present study, phosphate-solubilizing microorganisms were isolated from rock phosphate and associated soil from the Eppawala rock phosphate deposit in Anuradhapura, Sri Lanka. The Pikovskaya's medium was used for the isolation of microorganisms and their ability to solubilize Eppawla rock phosphate was evaluated using phosphate solubilizing index. The quantification of available phosphate was carried out using the molybdenum blue spectrophotometric method with three replicates and the most efficient isolates were subjected to 16S rRNA and ITS molecular identifications. Statistical analysis was conducted using two-way ANOVA in Minitab, followed by Tukey's pairwise comparison test to identify significant differences between treatments at a 0.05 significance level. Based on the results, fifteen bacterial isolates and one fungal isolate were identified as phosphate-solubilizing microorganisms, with phosphate-solubilizing indexes ranging from 2.12 ± 0.03 to 3.00 ± 0.02. When available phosphorus levels were quantified, four isolates with the highest significant (p < 0.05) available phosphorus concentrations; 36.15 ± 0.64 mg L⁻¹, 33.39 ± 0.53 mg L⁻¹, 29.27 ± 0.65 mg L⁻¹ and 28.87 ± 0.27 mg L⁻¹, were identified. They were identified as Pseudomonas monteilii, Aspergillus niger, Paraburkholderia bannensis, and Burkholderia vietnamiensis respectively. Their phosphate solubilizing indexes were recorded as 2.50 ± 0.05, 2.12 ± 0.03, 3.00 ± 0.02, and 2.33 ± 0.03, respectively. Additionally, a significant reduction (p < 0.05) in the pH in media compared to the control suggests the production of organic acids, a key mechanism used by microorganisms for solubilizing insoluble phosphate. This study confirms the potential of native phosphate-solubilizing microorganisms to solubilize Eppawala rock phosphate, demonstrating its effectiveness as a cost-efficient and environmentally friendly phosphorus source. The results provide key insights into the development of biofertilizers, contributing to sustainable agricultural practices.Item Effect of storage temperature and time on histamine concentration in commercially available fresh fish in Sri Lanka(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Perera, K. B. S. M. H.; Liyanage, G. Y.; Manage, P. M.People consume fish in order to fulfil their protein requirements. As fish contain high protein and amino acid levels and are susceptible to enzymatic and bacterial processes that result in the formation of biogenic amines like histamine, can lead to histamine fish poisoning. Histamine is a heat-stable compound, resistant to thermal processing and improper storage conditions can elevate its levels in foods. This study evaluated the effect of storage temperature and time on histamine concentration in commercially available fresh fish. Four species of fresh fish (n = 20 each) were examined: frigate tuna (Auxis thazard), Indian scad (Decapterus russelli), skipjack tuna (Katsuwonus pelamis), and mackerel tuna (Euthynnus affinis). Histamine quantification was performed using HPLC-DAD system with a mobile phase consisting of 85% of phosphate buffer and 15% acetonitrile. Fish muscle samples were kept at 27 ℃, 32 ℃, and 37 ℃, and histamine concentrations were measured at these specific temperatures. Study results indicated that, histamine concentration increased with storage temperature. At 37 ℃ all species showed the highest histamine concentrations: frigate tuna (17.99 ± 0.93 mg/kg), Indian scad (14.59 ± 0.97 mg/kg), skipjack tuna (38.92 ± 2.55 mg/kg), and mackerel tuna (32.80 ± 1.37 mg/kg) compared to the histamine concentrations at 27 ℃: 13.05 ± 1.06 mg/kg, 12.82 ± 0.88 mg/kg, 28.72 ± 1.93 mg/kg, and 24.37 ± 0.86 mg/kg respectively. Further, fish muscle samples were kept at 4 ℃ for three consecutive days with samples taken at 24 hours, 48 hours, and 72 hours. The initial histamine concentrations, in frigate tuna, Indian scad, skipjack tuna, and mackerel tuna were 12.91 ± 0.27 mg/kg, 13.99 ± 0.01 mg/kg, 27.17 ± 0.63 mg/kg, and 24.91 ± 0.16 mg/kg respectively. However, after 72 hours, the highest histamine concentration was recorded as 15.24 ± 0.32 mg/kg, 14.49 ± 0.29 mg/kg, 29.31 ± 1.12 mg/kg, and 26.41 ± 0.59 mg/kg respectively in all species, indicating that the histamine concentration has increased with storage time duration. The regression analysis indicated that storage temperature and time had a significant effect on histamine concentration for frigate tuna, skipjack tuna, and mackerel tuna (p < 0.05), but not in Indian scad. This study concludes that histamine concentration increases with the temperature, so it is necessary to store fresh fish at lower temperatures, to prevent bacterial growth and histamine production. This study recommends consuming freshly caught fish without prolonged storage, even in refrigerators.