Abstract

Water hyacinth [Eichhornia crassipes (Mart.) Solms] was used in an attempt to control phytoplankton abundance through nutrient and sunlight competition to increase oxygen levels in warm w ponds without the need of water exchange or aeration. Measurements of phytoplankton densities, water quality, and fish production were compared among ponds with hyacinth covers of 0, 5, and 25 % over the six months of the study. Male tilapia [Oreochromis niloticus (Trewavas)], average weight 28 g, were stocked at a density of 3/m2. Regression analysis indicated a signifie in chlorophyll-a concentrations in ponds with 0, 5, 10, and 15 % cover over time, chlorophyll-a concentrations in ponds with 20 and 25 % cover did not significantly change. Average ch concentrations were negatively correlated but did not significantly decrease with increasing plant cover. Weekly average oxygen levels decreased significantly in all ponds over time, but concentrations were not significantly different among them. Total ammonia concentrations significantly increased over time in the 0 % cover pond. Total pond production did not significantly increasing plant cover, but increasing plant cover resulted in significantly greater production of larger fish (25-27 cm total length). The results suggest that to partially cover the area of a warm water production pond with water hyacinths may improve the water quality of the pond and in turn have beneficial effects on the fish production.

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