This paper elucidates the phytoremediation potential of water hyacinth and water lettuce on the reduction of wastewater toxicity. Acute toxicity tests were performed in an aquarium with a population of Sarotherodon melanotheron, contaminated by different concentrations of wastewaters before and after phytoremediation with Eichhornia crassipes and Pistia stratiotes. Lethal concentrations (LC50) of the fish's population obtained during 24 hours of exposures were determined. COD, BOD, ammonium, TKN and PO4(3-) concentrations in wastewaters were of 1850.29, 973.33, 38.34, 61.49 and 39.23 mg L(-1), respectively, for each plant. Phytoremediation reduced 58.87% of ammonium content, 50.04% of PO4(3-), 82.45% of COD and 84.91% of BOD. After 15 days of the experiment, metal contents in treated wastewaters decreased from 6.65 to 97.56% for water hyacinth and 3.51 to 93.51% for water lettuce tanks. Toxicity tests showed that the mortality of fish exposed increased with increase in concentration of pollutants in wastewaters and the time of exposure. Therefore, the highest value of LC50 was recorded for fish subjected to 3 hours of exposure (16.37%). The lowest rate was obtained after an exposure of 20 to 24 hours (5.85%). After phytoremediation, the effluents purified by Eichhornia crassipes can maintain the fish life beyond 24 hours of exposure.
The Ebrié lagoon undergoes numerous disturbances of anthropic origin manifesting since these last decennis by a massive and sudden mortality of the ichthyological populations. In order to measure the impact of these disturbances, length-weight relationship was estimated for the main ichthyologic species in the lagoon Ebrié. The specimens were collected from 457 identification, each sample was weighed to the gram and measured to average millimeter. For this study, 15 species belonging to 11 families were selected because of their presence during the sample period. The length-weight regressions were significant with a coefficient of determination (r²) ranging from 0.717 (Ethmalosa fimbriata) to 0.923 (Gerres eucinostomus). The allometry coefficient b is ranged from 2.36 for Tylochromis jentinki to 3.12 for Liza falcipinnis. The majority of the regression coefficient of the captured species (66.67%) was lower than 3. The size frequency distribution showed that 92% of the captured species are small in size with a minimum size of 30 mm for Gerres nigri and a maximum of 370 mm for Chrysichthys spp.
Investigations are underway in the Centre de Recherches Océanologiques d'Abidjan (Côte d'Ivoire) to find whether the catfish (Heterobranchus bidorsalis) could be an interesting aquaculture species. Within this framework a 28-day aquarium culture feeding trial was conducted to investigate the effects of three diets (Artemia salina nauplii, beef brain enriched with vitamins, and a compound food) on the growth and survival rates in 2-day post hatch H. bidorsalis. The feeding experiments started after the yolk sac of the larvae was absorbed (initial mean weight = 2.03±0.38 mg). Larvae fed Artemia nauplii had a higher growth rate (final mean weight = 708.60±411.61 mg] than those fed beef brain (381.81±118.88 mg) or compound food (102.72±48.09 mg). Conversely, the beef brain diet yielded a better survival rate (70.47±9.48%) than the Artemia nauplii (38.72±7.74%) or the compound diet (5.37±2.24%). Thus, beef brain can be used as a starter food for larval rearing of H. bidorsalis.
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