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Rising atmospheric carbon dioxide (CO2) concentrations over the past two centuries have led to greater CO2 uptake by the oceans; raising concern over the current and future effects it may have on world climates. Certain changes are already evident but the impact of these changes on marine and coastal living resources is only poorly understood at this stage, particularly in sub-Saharan Africa. This study assessed seasonal dissolved carbon dioxide and pH of fresh and marine aquatic systems in Nigeria. Dissolved CO2 was non-significantly (p=0.07) higher in freshwater during the wet season (20±7ppm) compared to dry season (15 ± 1ppm), while in the marine system, dissolved CO2 level was significantly (p=0.02) higher (42±6ppm) during the dry season compared to the rainy season (31±5ppm). Mean pH values was significantly higher (p=0.003 and 0.05) in freshwater (6.8±0.8 and 6.9±0.2ppm) relative to marine (6.2±0.2 and 6.5±0.3ppm) during wet and dry seasons, respectively. The pH values were generally at the borderline of the acidic limit of the recommended pH values for aquaculture (6.5-9) during the two seasons. Rising atmospheric carbon dioxide (CO2) concentrations over the past two centuries have led to a greater CO2 uptake by the oceans, acidification and consequently, saturation, thereby affecting the ocean’s continued ability to store CO2. This study therefore provides preliminary information on seasonal changes in CO2 and pH of fresh and marine systems in Nigeria; and their potential impacts on global climate and aquatic ecosystems.Keywords: Acidification, Aquatic system, Carbon dioxide, Climate change, Fresh water, Marine water

Tetracycline is a broad-spectrum antibiotic used extensively to treat infections in both man and animals, however, its abuse could contribute to the emergence of antibioticresistant micro-organisms. This study was conducted to determine the tetracycline residue in Clarias gariepinus from selected fish farms and markets in Ibadan. Pre-tested structured questionnaire was administered to 116 consenting farmers to obtain information on antibiotic usage amongst others in five LGAs of Oyo State. Ten fish farms and two major markets (Sabo and Bodija) were purposively selected based on generated data. One hundred fresh fish, twenty (20) smoked catfish and water samples were tested for tetracycline residue using Elisa Test Kit (Rayto® SF-510). Tetracycline usage was (69%) compared with erythromycin (25%), enrofloxacin (22.4%), penicillin (25%), sulfamethazole (12.1%) and virginiomycin (6%). Tetracycline residues were detected in both fresh and smoked fish samples. Tetracycline residue was not detectable in 8:3 (16%:30%) samples; 10:5 (20%:50%) samples which had values below Maximum Residue Limit (MRL) of (200ng/ g) in fish muscle, while the remaining 32:2 (64%:20%) samples had values above MRL respectively. The mean residue level of the detectable tetracyclines (236ng/g) was higher than the recommended MRL (200ng/g) in fish muscle. It is therefore established that tetracycline was being used indiscriminately in fish ponds in the area. It is imperative that farmers should be enlightened on proper usage of antibiotics based on prescription and the need to observe withdrawal periods before fish harvesting. Veterinarian and Public Health officers should pay closer attention to ensuring that good management practice and hazard analysis critical control points are maintained in fish production and distribution chain.Keywords: Antibiotic, Elisa Test kit, Maximum residue limit, Withdrawal periods

Changes in Clarias gariepinus' blood cells were investigated after 96-h of exposure to lead. Ninety (90) Clarias gariepinus with average weight of 262.2g and average length of 30.8 were divided into 5 groups (A-E) at six (6) fish per group and in triplicates after being acclimatized for 14 days. They were then exposed to various concentrations (0, 25, 50, 100 and 200 mg/l) of lead nitrate. The packed cell volume (PCV) of the treatments decreased significantly relative to that of the control, while their platelet counts increased compared with the control. There was also a reduction in the RBC of treatments. Other blood parameters did not vary significantly in comparison to the control group, but it is worth noting that the mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH) and mean corpuscular haemoglobin concentration (MCHC) increased considerably in all treatments compared to the control. These alterations have been attributed to direct or feedback responses of structural damage to RBC membranes resulting in haemolysis and impairment in haemoglobin synthesis, stress related release of RBCs from the spleen and hypoxia, which was induced by exposure to lead. This study therefore gives an insight into toxic effect of lead on fish.

Clarias gariepinus (Burchell, 1822) of mean weight 320±11.2 g and total length 60.0±1.0 cm were exposed to nitrite (0.2 mg/l NO2) for 48 h at 27 and 35°C in order to investigate the effects of nitrite poisoning at these water temperatures. The effects of nitrite exposure on fish was assessed on selected haematological and biochemical indicators of the blood. The test was performed in a semi-static assay for 48 h. Fish were kept in thermostart –controlled water baths each containing 15 L of test solution. Four groups each containing 8 specimens of 3 month old C. gariepinus were exposed to nitrite at the different water temperatures. Nitrite exposed fish showed lower haematocrit value (PCV) at both experimental temperatures compared with controls. Significantly higher PCV values were recorded in fish with nitrite at 27°C (36.67±0.57%) when compared with fish at 35°C (33.33±0.57%). A significant difference was also recorded for haemoglobin level and the erythrocyte counts. Leucocyte count in fish with nitrite at 270 C was significantly higher (P