a) Optimal Temperature:
Various species and strains of tilapia differ in tolerance to low temperatures, but growth is poor at water temperatures below 16OC and death occurs from temperatures below 12OC.Most will not feed or grow at water temperatures below 15oC and will not spawn below 20OC. The normal water temperature should be between 20 to 30oC. Higher temperatures will result to fish death.
b) Optimal Dissolved Oxygen (DO):
Tilapias are able to tolerate low levels of dissolved oxygen. Usually, well fertilized ponds will have low levels of oxygen early in the morning. Night activities are dominated by respiration and decomposition which reduce DO. Larger fish are less tolerant than juveniles. This could be due to the difference in their metabolic demand. The optimal DO for tilapia culture is 4 mg/litre (50%) and should not go below 2.3 mg/litre.
All tilapia are tolerant to brackish water. The Nile tilapia is the least saline tolerant of the commercially important species, but grows well at salinities of up to 15 ppt. The Blue tilapia grows well in brackish water up to 20 ppt salinity, and the Mozambique tilapia grows well at salinities near or at full strength seawater.
pH refers to hydrogen ion concentration levels. Tilapia can survive in pH ranging from 5 to 10 but do best in a pH range of 6 to 9.
Massive tilapia mortality will occur within a few days when the fish are suddenly exposed to water with unionized ammonia concentrations greater than 2 mg/L. Prolonged exposure (several weeks) to un-ionized ammonia concentration greater than 1 mg/L causes deaths, especially among fry and juveniles in water with low DO concentration.
Nitrite is toxic to many fish and chloride ions reduce the toxicity. Tilapias are more tolerant to nitrite than many cultured freshwater fish. In general, for freshwater culture the nitrite concentration should be kept below 27 mg/L.