Evaluation of Two Densities for Holding Live Food Fish in a Small Recirculating Aquaculture System

Abstract

Small recirculating aquaculture systems (RASs) are used to market live food fish, particularly in certain ethnic markets. We evaluated fish performance, water quality, and physiology of Channel Catfish (CCF) Ictalurus punctatus and Largemouth Bass (LMB) Micropterus salmoides that were harvested from ponds, transported, and held live at two stocking densities in a small RAS. One trial was conducted for each species, with two treatments (20 and 40 kg/m3) in each trial. Trials were conducted in individual RASs without feed during a holding period of 8 d. Water quality for each holding tank was measured at stocking and daily thereafter (24, 48, 72, 96, 120, 144, 168, and 192 h). Blood samples were obtained from fish to evaluate physiological response. Both CCF and LMB survived well in the system, with no mortality in either treatment. Average weight loss across both trials at a temperature of 15°C was 3.1% for CCF and 4.8% for LMB. Total ammonia nitrogen (TAN), un‐ionized ammonia (UIA), nitrite, and nitrate increased significantly over time in both trials. Mean water pH was significantly lower and mean TAN and UIA were significantly higher in the 40‐kg/m3 treatment for both trials. Blood glucose rose significantly after harvest and returned to a resting state during the holding period in both species. Blood sodium, potassium, and chloride also returned to a resting state within 24–72 h in the holding system. Estimated accumulation of TAN was 35.6 mg kg fish−1·d−1 for CCF and 21.6 mg kg fish−1·d−1 for LMB. Although the RAS biofilter was unable to convert ammonia to nitrate at the rate it was produced, the holding systems performed adequately at the densities evaluated. These trials provide data in support of the common practice of holding food‐size CCF and LMB at densities of 40 kg/m3 or less over a period of 8 d in a small RAS.