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Hydraulic–oxygenation and nutrient–ionic axes structure fish assemblages in a tropical river: a pre-impoundment baseline from the Lower Gurara River, Nigeria

2026-06-29T00:00:00Z

Title: Hydraulic–oxygenation and nutrient–ionic axes structure fish assemblages in a tropical river: a pre-impoundment baseline from the Lower Gurara River, Nigeria Authors: Abubakar, Danasabe S; Meye, Jacob A.; Ayanwale, Adesola V.; Auta, Yohanna I.; Ukubuiwe, Azubuike C.; Arimoro, Francis O. Abstract: This study establishes a comprehensive pre-impoundment ecological baseline for the Lower Gurara River, quantifying how physicochemical gradients structure fish assemblages across spatial and seasonal scales in advance of hydropower regulation. The assemblage comprised 3,831 individuals representing 15 species and 11 families, reflecting a typical West African tropical river community. Multivariate analyses identified two dominant environmental axes: a “hydraulic–oxygenation axis” associated with coarse substrates, high turbulence, and elevated dissolved oxygen in upstream reaches, and a “nutrient–ionic axis” that intensified progressively downstream with increasing conductivity, sulphate, and phosphate. These gradients corresponded closely with observed community patterns. Rheophilic and benthic foraging taxa were most abundant at well-oxygenated upstream stations (S1–S2), whereas generalist and disturbance-tolerant species dominated depositional, nutrient-enriched downstream habitats (S3–S4). Species richness remained constant across stations, but evenness declined and dominance increased downstream, indicating an altered assemblage structure rather than compositional turnover. Seasonal patterns showed strong wetseason increases in abundance driven by flood-pulse connectivity, while α-diversity metrics remained comparatively stable, consistent with hydrology-mediated dynamics in tropical rivers. Interannual increases in total abundance from 2021 to 2022 reflected regional hydroclimatic variability, particularly sensitivity of low flows and flood extent. Collectively, these results demonstrate that linked hydraulic–oxygenation and nutrient– ionic gradients offer a robust, mechanistic framework for interpreting fish assemblage responses. The baseline also identifies key sentinel stations, S2 for aeration sensitivity and S4 for enrichment, and thermal change, and supports the development of threshold-based monitoring dashboards to guide adaptive management following impoundment. This dataset provides a defensible reference condition crucial for safeguarding ecological integrity during and after hydropower development on the Lower Gurara River. Description: AUTHOR CONTRIBUTION F.O. Arimoro conceptualized the study alongside D.S. Abubukar, while F.O. Arimoro, D.S. Abubukar, Y.I. Auta, and A.V. Ayanwale were responsible for designing the field methodology and fish surveys. D.S. Abubukar and Y.I. Auta co-conceptualized the study, coordinated field logistics, and wrote the initial draft of the manuscript. F.O. Arimoro also served as the academic supervisor, providing oversight throughout the research process, including study design, methodological refinement, and critical review of the manuscript. All authors contributed to data interpretation, manuscript revisions, and approved the final version.

Growth performance and proximate composition of Clarias gariepinus (Burchell, 1822) fingerlings fed varying inclusion levels of ripe banana (Musa Sapientum) peel

2022-09-22T00:00:00Z

Title: Growth performance and proximate composition of Clarias gariepinus (Burchell, 1822) fingerlings fed varying inclusion levels of ripe banana (Musa Sapientum) peel Authors: Samuel, Patrick Ozovehe; Ogere, Isreal Onimisi Abstract: The cost of fish feed is of great concern in fish farming. The growth performance and proximate composition of Clarias gariepinus fingerlings fed varying inclusion levels of ripe banana peels as a possibility of replacing soybean as a component of the fish feed were evaluated for a period of 12 weeks. 250 C. gariepinus fingerlings were acclimated for 2weeks and fed to satiation morning and evening. Five isocaloric and nitrogenous diets were prepared from ripe bananapeel thus: 0% (Control), 25% (T25), 50% (T50), 75% (T75) and 100% (T100) inclusion levels to replace equal weights of soybean, respectively. Some growth parameters such as standard length (SL), total length (TL) and weight weredetermined on weekly basis. The proximate compositions of the fish in each treatment and control were determined at the end of the experiment. The data generated were subjected to one way analysis of variance and considered significant at P≤0.05. From the results; the weight, SL and TL mean values measured in the control were significantly higher than other treatments in most of the weeks of the experiment. The highest weight in the control was 52.43±10.80g while the highest amongst other treatments was 30.67±6.69g obtained in T75 at the end of the 12 weeks. The ash content, crude fibre and fat contents were mostly significantly in T75 and T100. The highest moisture content (12.88±0.74%) was also obtained in T100. The crude protein content was significantly higher in the control than other treatments with 68.69±0.35% at the end of the 12th week. The results of this research has shown that banana peel can be included up to 75% level of inclusion as possible replacement for soybean in fish meal production and therefore, capable of reducing the cost of fish production incurred by farmer. For optimal performance, the crude protein content should be improved upon by inclusion of other cheap protein sources.

Impacts of Vitamin E on Some Growth, Haematological, Antioxidant Activities and Proximate Compositions of Clarias Gariepinus (Burchell, 1822) Under Laboratory Conditions

2026-05-23T00:00:00Z

Title: Impacts of Vitamin E on Some Growth, Haematological, Antioxidant Activities and Proximate Compositions of Clarias Gariepinus (Burchell, 1822) Under Laboratory Conditions Authors: Samuel, Patrick Ozovehe; Garba, Hajara; Ahmed, Ramatu Nakordi Abstract: The assessment of the impacts of vitamin E on the growth, haematological parameters, proximate compositions, and production levels of reduced glutathione (GSH) and Malondialdehyde (MDA) of Clarias gariepinus (Burchell, 1822) fi ngerlings was evaluated for a period of twelve (12) weeks. A total of 300 fi sh were acclimated for two weeks, during which they were fed twice daily. These were then distributed into four treatments and replicates, including a control. Vitamin E was administered as 350mg/L for T1 , 450mg/L for T2, and 600mg/L for T3 . Measurements were made from each trough randomly bi-weekly for the duration of the research. These measurements include total length (TL), standard length (SL), and body weight. The specifi c growth rate (SGR), percentage total weight gain (%TWG), condition factor (CF), and Hepatosomatic Index (%HSI) were also calculated. Blood collection was also made from three randomly selected samples at the end of the experiment. These blood samples were analysed for full blood count following standard procedures. 3 samples were also randomly selected, and the liver, kidney, and gills were excised; homogenized in phosphate buff er, and then assayed for GSH and MDA. 2 samples of the fi sh were also processed for proximate composition analyses. The data generated were subjected to one-way analyses of variance at P<0.05 level of signifi cance. The results indicated that monocyte and neutrophil counts were signifi cantly diff erent in T2 and T3 , respectively. The red blood cells, white blood cells, haematocrit, and blood platelet counts were not signifi cantly diff erent. The SL mean values increased with an increase in Vitamin E concentration, and the maximum value was obtained in T3 at the end of the 12th week. At later stages of the research, the TL also increased with an increase in Vitamin E concentration and peaked in T3 with a mean value of 18.17cm. Likewise, the highest weight value was also obtained in T3 . The peak SGR, %HSI, and %TWG were also obtained in T3, while the maximum CF was obtained in T1 . The highest protein content (20.58±0.26%) was obtained in T3. The moisture content decreased with an increase in the concentration of the vitamin. The GSH production levels in the liver, kidney, and gills increased with an increase in the concentration of the vitamin, and the T3 mean values were signifi cantly higher than those of other treatments, including the control. The MDA production levels, however, decreased with an increase in vitamin E concentration. The results in this research have displayed positive impacts of the addition of vitamin E in terms of physical and physiological features of C. gariepinus and can therefore serve as an invaluable addition in fi sh farming.

Aflatoxin B1 Contamination and Dietary Risk Assessment in Commonly Consumed Smoke Dried Fish Species in Minna, Niger State, Nigeria

2026-06-10T00:00:00Z

Title: Aflatoxin B1 Contamination and Dietary Risk Assessment in Commonly Consumed Smoke Dried Fish Species in Minna, Niger State, Nigeria Authors: Raji, E. D; Samuel, Patrick Ozovehe; Adama, S. B.; Salihu, F. Abstract: The contamination of smoke-dried fish with Aflatoxin B1 (AFB1) poses a significant yet under investigated food safety threat in Nigeria. This study assessed the levels of AFB1 and evaluated the associated dietary risk among consumers of commonly consumed smoke-dried fish species in Minna, Niger State. A total of 24 smoke-dried fish samples comprising Clarias gariepinus, Protopterus annectens, Gymnarchus niloticus, and Synodontis membranaceus were collected from three major markets in Minna metropolis: Kure, Mobil, and Kasuwa-Gwari between July and August 2025. AFB1 was quantified using a validated indirect Enzyme-Linked Immunosorbent Assay (ELISA). Dietary risk was evaluated deterministically and probabilistically using the Estimated Daily Intake (EDI) and Margin of Exposure (MOE) methods, with consumption data derived from a structured survey of 84 respondents. The results indicated that AFB1 was detected in all 24 samples (100% prevalence), with concentrations ranging from 0.38 to 6.05 µg/kg (overall mean: 2.95 µg/kg). Clarias gariepinus recorded the highest mean AFB1 concentration (5.42 ± 0.47 µg/kg), while Synodontis membranaceus had the lowest (0.69 ± 0.27 µg/kg). Market level differences were not statistically significant. The deterministic MOE was 27.78, and the Monte Carlo-simulated median MOE was 35.47, both substantially below the regulatory concern threshold of 10,000 for genotoxic carcinogens. Furthermore, 88.3% of simulated population-level MOE values fell below 100, indicating a high probability of public health concern. These findings demonstrate widespread AFB1 contamination across fish species and market locations in Minna and signal an elevated carcinogenic risk for regular consumers. Urgent regulatory intervention, improved smoke-drying practices, proper storage and routine surveillance are recommended.