Settling characteristics of solids settled in a recirculating system for California halibut (Paralichthys californicus) culture

The settling velocity of solids settled within California halibut (Paralichthys californicus) culture vessels was determined in the present study. Data were gathered for fish between 0.17 and 108 g wet mass. Three commercial diets were used in this study: Nippai “Ambrose 600”® for fish from 0.17 to 0.7 g; BioKyowa 1000® for fish from 1.5 to 3.0 g; BioKyowa 2000® for fish from 6 to 40 g; EWOS 2® for fish from 10 to 20 g; and EWOS 3® for fish from 35 to 110 g. A top-loading settling column was used to characterize the settling properties of the solids. Settling velocities were found to vary among feeds used regardless of fish size. Average settling velocities were 1.7 cm/s for Nippai™ 600, 2.2 cm/s for BioKyowa™ 1000, 4.4 cm/s for BioKyowa™ 2000, 1.7 cm/s for EWOS™ 2, and 2.0 cm/s for EWOS 3. The measurements indicate that solids produced by feeding fish with BioKyowa™ pellets had the fastest settling velocity among the diets tested. The settling velocity curves obtained in this research contain valuable information that can be used to select appropriate devices for the removal of solids.