Optimal stocking density of juvenile Atlantic cod (Gadus morhua L.) reared in a land-based farm

The effects of stocking density on the productivity in a juvenile cod farm were studied in a flow-through system for fish weighing initially 44 g. The fish densities increased throughout the experiment from 4 to 21, 11 to 54 and 22 to 95 kg/m3. Growth rates were negatively affected at densities above 50 kg/m3 and at the end of the experiment the mean weights were 242, 221 and 205 g at low, medium and high densities, respectively. The average cumulative mortalities increased with density and were 1.8, 4.2 and 7.3% of initial number of fish at low, medium and high densities, respectively. Antibiotics were administered twice at high, once at medium and never at low density. The average feed conversion ratios were 0.81, 0.91 and 1.02 at low, medium and high densities, respectively. The average biomass increase was 16.8, 42.7 and 72.8 kg/m3 at low, medium and high densities. A simple economic analysis indicates a parabolic relationship between profit and density with optimal density at the peak of the curve. Given reasonable assumptions about production costs in a land-based farm, the break-even density is 35 kg/m3 and the optimal final density is 95 kg/m3. Changes in fixed costs, such as financial costs and salaries, have no effects on the optimal final density whereas changes in variable costs, such as feed and juvenile costs, directly affect the optimal final density.

► A lab study of stocking density, growth rate, survival and FCR of juvenile cod.
► A model to estimate profit and optimal stocking density in a land-based farm.
► For base-line assumptions about production costs the optimal density is 95 kg/m3.