Effects of dissolved oxygen concentration and stocking density on the growth, energy budget and body composition of juvenile Japanese flounder, Paralichthys olivaceus (Temminck et Schlegel)

An energetic method was used to investigate the effects of stocking density and dissolved oxygen (DO) concentration on the growth of juvenile Paralichthys olivaceus. Fish, with initial weights of 14 +/- 2.1 g, were exposed to a normal and a high DO of 5.5 +/- 0.5 and 14 +/- 2 mg L-1, as well as four stocking densities per DO concentration (100, 200, 300 and 400 ind m-2 for the normal DO and 200, 400, 600 and 800 ind m-2 for the high DO). The feed efficiency (FEW) decreased significantly with increasing stocking density and increased significantly with increasing DO concentration. The maximum weight was achieved at 400 ind m-2 under a high DO depending on our rearing conditions. The stocking density and DO concentration change energy ingestion and its allocation for respiration, growth and excretion lost in nitrogen excretion, but do not affect the energy loss through faeces. The results of the body composition of fish indicated that the stocking density and DO concentration had no significant effects on the moisture, lipid content and gross energy, but are affected by the same. Energetic analysis demonstrated that high DO concentrations could alleviate the growth depression caused by high stocking densities, decrease energy loss in respiration and nitrogen excretion and increase the energy proportion allocated to growth.