Channel catfish were cultured for 177 days in circular tanks containing 1.6 m3 of water at combinations of five stocking densities (90–720 fish/m3) and five water exchange rates (2.0–0.5 h per exchange). Net yield increased as stocking density increased up to 540 fish/m3 then declined at higher densities. Mean fish weight, feed conversion efficiency and survival all declined as stocking density increased.
Water exchange rates of 1.5 h or greater achieved similar results at stocking densities of 180 and 360 fish/m3. However, at a density of 540 fish/m3 a faster exchange rate resulted in increased growth, feed conversion efficiency and survival. At 2.0 h per exchange, these parameters were depressed at 180 and 360 fish/m3.
The following predictive equations (P = 0.01) were formulated from the data, where x1 represents the stocking density and x2 the exchange rate.
Net yield:
Y1= −64.785 + 0.52x1+ 121.977x2− 2.25 × 10−5x12− 43.989x22− 0.0104x1x2.">Y1= −64.785 + 0.52x1+ 121.977x2− 2.25 × 10−5x12− 43.989x22− 0.0104x1x2.
Mean fish weight:
Y2= 26.649 − 0.346x1× 246.384x2− 97.55x22.">Y2= 26.649 − 0.346x1× 246.384x2− 97.55x22.
Feed conversion efficiency:
Y3= 1.799 − 9.673 × 10−4x1+ 0.464x22.">Y3= 1.799 − 9.673 × 10−4x1+ 0.464x22.
The maximum predicted net yield of 93.1 kg occurs at a stocking density of 399 fish/m3 and 0.91 h per exchange.
