Improper Salinity

IMPROPER SALINITY

  • Salinity is the amount (mass) of all ions in water and is most commonly expressed as parts of ions per thousand part water (abbreviated as ppt or º/ºº). Freshwater has less than 0.5 ppt salinity, while natural, full strength seawater ranges from 30 to 40 ppt salinity. Between these two extreme are various concentrations of brackish (estuarine) water, including oligohaline, mesohaline and polyhaline. As with other water quality variables, salinity tolerance of fish varies (i.e., with age, environment).

Diagnosis of improper salinity

  • Salinity is difficult to measure directly but can be measured indirectly in several ways, including conductivity, chlorinity, refractive index, or specific gravity. Salinity can be measured least expensively by using a hydrometer, which measures specific gravity. However, this method is cumbersome when compared with refractometry and needs a relatively large volume of water (usually atleast 50 ml). If salinity is to be measured frequently, it is easiest to use a handheld refractometer or electronic meter.

Treatment of improper salinity

  • Abnormally high or low salinity places an osmotic stress on the fish and should be corrected as soon as possible with appropriate addition of salt or freshwater. It is generally recommended that the salinity be changed not more than 1 ppt/hour. For estuarine fish, salinity should not be adjusted more than 10 ppt in a few hours. As with other water quality variables, rapid changes are less tolerated.
  • Salt is also a useful prophylactic and can be added to freshwater aquaria to reduce prevalence of many infectious diseases, many of which are inhibited by even low salt concentrations.
Last modified: Friday, 16 September 2011, 11:54 AM