Stephanie Grodeska | 11/2/2016 8:43:38 PM
Cocahoe minnows are an estuarine species. This means that they typically live in water that has varying amount of salt. How salty the water is, or the salinity, can be measured several different ways. The most common is parts per thousand (ppt or percent) or how many salt ions there are for every thousand water molecules. Salinity can also be measured in grams of salt per liter of solution (g/L). Cocahoe minnows can tolerate a wide range of salinities for at least short time periods. However, they do best in water between 5-15 ppt. When raising cocahoe minnows, or any other fish, it is important to take into consideration what kind of salt to use to maintain salinity. The most common forms of salt, such as road salt and rock salt contain only sodium chloride. Seawater, however, contains many other ions that are necessary for the survival of the fish. These ions include, but are not limited to, calcium, potassium, magnesium and sulfate in addition to sodium and chloride. All of these components play an important role in raising healthy fish.
Kinds of Salts
Salt comes with many names and in many forms; however much of
it means the same thing. The following table will help navigate the
wide world of salt.
What Kind of Salt to Use
The kind of salt to use depends on the source of the water. It is
important to get the water tested for ionic content; Louisiana State
University Department of Agricultural Chemistry charges about $15 to
test a water sample. There are also private companies that will test water
samples usually for a fee. When using dechlorinated water from a tap
or hose it will most likely require a marine salt. When using natural
water from a bayou, estuary or pond, many of the additional ions may
be present. If the water has most of the required ions, a cheaper salt,
like rock salt, may be adequate or it may need to be supplemented with
only a single missing ion like potassium. Rock salt is typically much
less expensive than marine salt especially when using large quantities.
For this reason it is best to use rock salt due to cost. However, it does not contain potassium, magnesium, and calcium, which are very important ions
that cocahoes need to survive. Never use table salt. The iodine and additives it
contains can be harmful to fish and invertebrates.
How Much Salt to Use
The amount of salt needed depends on the salinity of the water source and the
desired end salinity. Most marine salts will have directions to make full strength
seawater, about 30 ppt. Cocahoe minnows can be raised at a lower salinity. As
a rough guide, about 1 lb. of salt per 10 gallons of freshwater will yield about 12
ppt, an ideal salinity for raising cocahoes. However, this can vary depending on
the water and type of salt used, and every culture situation should be assessed
independently. A salinity-measuring instrument (Figure 3) will be needed to
check salinity not just while mixing
the water but also periodically after
the system has been established as
evaporation will raise the salinity.
There are several different types of
instruments to measure salinity that
range from the fairly inexpensive
hydrometer, to a slightly more expensive refractometer, to the several
thousand dollar electric water quality meters that can measure
salinity, dissolved oxygen, pH, temperature, depth, etc. In most cases,
a hydrometer or refractometer will be more than sufficient. Do not
mix the startup water while the fish are in it as the rapid change in salinity can cause shock. Make sure salinity is
at the right level before adding water to livestock.