Abstract:
Cadmium (Cd) and Lead (Pb) are toxic metals ubiquitous in the aquatic environment, inducing reactive oxygen species that cause stress, toxicity and mortality in fish. Organic source such as allicin extracted from garlic reversed this toxicity; however, there is a dearth of information on the use of raw organic source to reverse these conditions. This study was designed to explore the potentials of raw garlic (Gc) in ameliorating the toxic effects of these metals in cultured Clarias gariepinus (Cg).
Two hundred and forty apparently healthy Cg juveniles were exposed in four triplicate groups (20 per group/10 per sex) to garlic A; 8.0g /L, B; Cd 0.03mg/L, C; Pb 0.3mg/L, and D the control in static culture for 90 days. Also four hundred and eighty randomly-selected female Cg juveniles of 20 fish each were exposed to Cadmium alone, Cadmium + Gc1 and Gc1 or Gc2 only. Cadmium was replaced with lead and cadmium + lead in other experiments. Cadmium, lead, Gc1 and Gc2 were given at 64, 126, 0.65 and 0.87 mg/L, respectively. Exposure to metals was for six-hours followed by six-hours in freshwater before 12-hours garlic treatment for two consecutive days. Clinical signs for toxicity were monitored for 120-hours. Tissue concentration of metals, oxidative stress markers, gross and histopathology of tissues were also conducted using standard methods. Data were analysed using ANOVA and DMRT at α0.05.
Group A at forty-eight hours post-exposure manifested vertical positioning in 40.0% of fish. At day 30, scanty degenerate germinal cells were observed in group B while there were no visible lesion in the testis of group A fish at day 90. At day 90 female liver Pb concentration decreased in A (91.5%), increased in B (11.4%) and C (73.5%) groups relative to control. Also Cd, Pb and their combinations groups induced 60.0 – 90.0% vertical positioning and copious mucus secretion. There was also 5.0% mortality at six-hours exposure in Cd + Pb group. At 120-hours glucose decreased in Pb + Gc2 (7.9%), Pb (36.4%) and increased in Gc2 (9.8%) groups. At 120-hours intestinal manganese level increased in Cd + Gc1 (79.4%) and decreased in Cd (58.6%) while hydrogen peroxide level in the liver decreased in Cd + Gc1 (17.3%) and increased in Cd (16.4%) groups. Malondialdehyde level in the liver decreased in Pb + Gc2 (20.0%) and increased in Pb only (8.0%) while superoxide dismutase level increased in Gc2 (7.1%) groups. Spleenic congestion, goblet cell hyperplasia, neuronal necrosis of the brain, hepatocellular necrosis, hypochromasia, poikilocytosis, and rouleux formation were observed in all groups exposed to the metal(s). The severity of these lesions decreased with garlic bath
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at 120-hours. Micronuclei were observed in Cd + Pb at six-hour post-exposure and Pb group at 120-hours.
Exposure to garlic reversed the deleterious effects of Cadmium and Lead, suggesting its efficacy in the detoxification of Cadmium and Lead toxicity in cultured fish. It is recommended that fish farmers use at least 0.65mg/l of raw garlic to reduce the lethal effects of these metals on farmed Clarias gariepinus.
Keywords: Clarias gariepinus, Reactive oxygen species, Cadmium and lead, Garlic toxicity treatment.
Word count: 498.
