| Prawns (Panaeus japonicus) were rearing during more than nine months in experimental closed circuit tanks. In such systems the nitrite appearance is related to the normal nitrification process and to oxygen deficiency. Above a given level, nitrite causes the death of prawns. The soluble oxygen concentration and, thus, nitrite level in the water appears as the main factor for a successful development of prawns in closed circuit tanks. In these conditions, the growth rate of the prawns is relatively low (9g/per individual in seven months). Never theless, such a system allows a load of some 600 g prawns per m2. |
