Tilapia Topic, Aquaculture Environment, Salinity

Salinity is the amount of Salt in the water.

Tilapia (specifically O. mossambicus ) can tolerate of a wide range of salinity from 0 to 100 parts per thousand (ppt). However, rapid or abrupt transfer of tilapia from freshwater (0 ppt) into water of a salinity of 20 ppt or more can result in fish mortality. On the other hand most strains of tilapia grown in Hawaii can tolerate acute transfer from saltwater (32 ppt) into freshwater (0 ppt). Culturists are advised to use a salinity and temperature acclimation schedule (see the section on salt in the treatment module) whenever tilapia are changed from one environment into another.

For tilapia cultured in Hawaii, relationships can be assessed between salinity and two water quality factors or infection by three ectoparasites.

Temperature - If O. mossambicus is cultured in water of 20 ppt or higher salinity and the temperature is within the range of 23-26'C, growth rate of the fish may be reduced. However, this effect may disappear if rearing temperature is between 27-30'C.

Nitrite - Chloride anions compete with nitrite anions for transport across the gills, thus chloride anions in the culture water will reduce the potential for nitrite toxicosis in cultured fish including tilapia.

Nitrite toxicosis of tilapia is reduced when salinity is ò 1 ppt.

Ectoparasites - Certain ectoparasites that affect tilapia in Hawaii do not occur in freshwater. These relationships are given below:

• Caligus sp. and Amyloodinium sp. infections should not be found on tilapia raised in water of salinity < 3 ppt.
• Neobenedenia melenia infection should not be found on tilapia cultured in water of salinity < 10 ppt.

  .