Floating feces: A new approach for efficient removal of solids in aquacultural management

Abstract The rapid removal of suspended solids from aquacultural systems is of utmost importance in maintaining healthy stock and system stability and in addressing environmental concerns. This research tested a new approach, successfully manipulating fecal density to the point of floatation. Fecal casts floating at the water's surface can be transported quickly to a removal device. The speed of removal minimizes opportunity for leaching, and exposure to shear forces and turbulence caused by mechanical devices and fish motion. Waste thereby persists as larger particles, which are easier to remove by traditional microscreens or skimming apparatus. Four different low-density feed additives were tested in different dosages and gradings on duplicate groups of rainbow trout, in order to appraise the effects on fecal density, and on growth and health of fish stock. The control groups received the same basal diet without additives, which resulted in fecal densities in the upper ranges expected for commercial trout diets at 1.04 g cm − 3 and 1.05 g cm − 3 for water-soaked and intestinal feces, respectively. Five of the additive diets significantly reduced the density of both intestinal and water-soaked feces, with the most effective (cork; 0.5–1 mm; 2%) leading to floating feces (4.39% to 1.00 g cm − 3 and 5.12% to 0.98 g cm − 3 for intestinal and water-soaked feces, respectively). The larger grade of cork granules performed significantly better than the smaller grade. The possibilities for reducing levels of effective cork incorporation and enhancing effects on density by other quality improvements are discussed. Feed efficiency and fish health were not impaired by the additives. It is suggested that the systematic manipulation of fecal density with low-density additives may achieve economic and ecological advances and offer a new and effective means of managing and optimizing waste output from aquaculture. The effects of floating feces on removal efficiency, leaching effects, water quality and operating costs in aquacultural systems have to be further explored.