Assessment of Hydroponically Grown Macrophytes for Their Suitability as Fish Feed

Water hyacinth, water lettuce and parrot's feather plants were examined for their ability to remove nutrients from aquaculture wastewater at two retention times. During the experiment, the aquatic plants grew rapidly in the hydroponics system and appeared healthy with green color. At hydraulic retention times (HRTs) of 6 and 12 days, the average water hyacinth, water lettuce and parrot's feather yields were 83, 51 and 51 g (dm) m^-2 and 49, 29 and 22 g (dm) m^-2, respectively. The aquatic plants were able to significantly reduce the pollution load of the aquaculture wastewater. The TS, COD, NH₄⁺-N, NO₂^--N, NO₃^--N and PO₄^3--P reductions ranged from 21.4 to 48.0%, from 71.1 to 89.5%, from 55.9 to 76.0%, from 49.6 to 90.6%, from 34.5 to 54.4% and from 64.5 to 76.8%, respectively. Generally, the reductions increased with longer retention times and were highest in compartments containing water hyacinth followed by compartments containing water lettuce and parrot's feather. The nutritive value of the three wastewater grown plants was assessed to determine the suitability of using the plants as a component in fish feed. The three wastewater grown plants did not contain sufficient amounts of protein and fat to meet the dietary requirements of fish and shellfish. They also contained high concentrations of K, Cu, Fe, Mn, Se and Zn, which can lead to reduced feed intake, weight gain and growth rates in fish and shellfish.