Growing algae in wastewater ponds such as abattoir or hatchery wastewater could be an option if lagoons are used at hatcheries to dispose wastewater. The wastewater is managed through a series of ponds to produce algae, zooplankton, ornamental fish and cleaner water that is suitable for irrigation. (Note that the ornamental fish industry is a mutli-billion dollar industry worldwide with high demand for various fish species). However, good management and design of ponds are required to optimise ornamental fish production. Fresh water molluscs are potential species to introduce into the ponds to filter the waste water and improve algal and zooplankton growth. The zooplankton and micro-algae are grazed by the fish. Management of nutrients in ponds (particularly P levels) is critical if pond production is to be optimised.