Stephanie Grodeska | 11/2/2016 9:03:48 PM
Water quality may be the most important factor in cocahoe minnow production. This fact sheet introduces parameters that must be taken into consideration when raising fish. A number of factors must be managed properly to ensure good survival and health of fish.
Dissolved Oxygen (DO)
Dissolved oxygen is the most important factor to successfully maintain live
bait. DO is often measured in parts per million (ppm) or milligrams per liter
(mg/L), and the ideal range for live fish is 6 to 10 ppm of oxygen. At no time
should oxygen be allowed to fall below 4 ppm.
DO problems may be chronic or acute. The most common chronic DO
problems are caused by (1) overloading systems with too many fish and (2)
warm, stagnant water. In addition, overfeeding, and uneaten feed can cause
ongoing oxygen problems. The first sign of oxygen-related stress is usually
an abrupt lack of activity, followed shortly by minnows crowding up at the
surface and gulping for air or congregating near a
water inlet or air stone.
DO problems can usually be corrected by reducing the number of minnows per gallon
of water (to about 1 pound of fish per 10 gallons of water). Other methods to improve
oxygen levels include pumping tank water through spray nozzles, but avoid creating
strong currents that can damage or exhaust fish. Some facilities use electric agitators
to maintain sufficient levels of oxygen, but again care should be taken to avoid creating
excessive currents that can damage or exhaust live bait. Low-pressure air pumps and
air stones can also be used to aerate tanks. An alternative in some situations is to use a
low flow of compressed oxygen through an air stone; however, care should be taken not
to super saturate DO from an oxygen bottle.
Chlorine or chloramine is added by water companies to tap water to remove
bacteria. Even very low concentrations of chlorine or chloramine can cause
damage to the gills of minnows. Chlorine or chloramine in tap water can be
removed by adding commercially available products such as sodium thiosulfate,
or chlorine can be removed by aerating the water overnight.
Cocahoe minnows can tolerate a wide range of temperatures but cannot
tolerate sudden temperature changes. The ideal temperature range for most
bait holding systems is usually between 60 o
F and 80 °F. Avoid direct sunlight
on systems during most of the year to minimize unwanted heating (Figure
3). Under some limited circumstances, indoor fans can be directed across the
surface of holding tanks to provide for evaporative cooling.
Ideally, baitfish systems that rely on biological filters should have water with
alkalinity ranging from 100 to 250 ppm. In most instances, higher alkalinity
will not cause problems, but lower levels may reduce the ability of biofilters to break down ammonia into less toxic products. Alkalinity is a measure of carbonate and bicarbonate in water, and
baking soda (sodium bicarbonate) can be added to water as needed
to maintain alkalinity levels at or above 100 ppm. Alkalinity also
provides a buffer against acidification of water due to CO2
(really carbonic acid in equilibrium)
pH is a measure of the acidity of water. Normal levels are in the range of 7.5 to 9 pH units. pH can usually be
maintained at acceptable levels as long as alkalinity is above 100 ppm. Moving live bait from a system where pH
has already reached low levels into fresh water with a higher pH can cause stress and occasionally result in death.
Total Ammonia Nitrogen (TAN) is given off as a waste product by the minnows, and therefore, can build up from
overfeeding or overcrowding. As it builds up, it can become toxic to the fish. Bacteria break down ammonia to less
toxic nitrite. Further breakdown results in the less toxic stable form of nitrate. Ammonia needs to be monitored to
prevent mortality. The safe range of TAN decreases with higher pH and
temperature, but generally should be less than 1.00 ppm.
Nitrites are the less toxic product of broken down ammonia. While nitrites
are considered relatively toxic in freshwater systems, they have a much
less detrimental effect in saline water. As long as cocahoes are raised in
their optimal salinity, between 5-15 ppt, nitrites should have a minimal
effect on fish health unless the system has a severe nitrite problem. For
best results nitrite levels should try to be kept below 10 ppm.
A number of commonly used household products can be toxic to live bait.
These include insecticides, insect repellents, and common cleaning solutions used on windows, floors or other
surfaces. Additionally, certain paints and metal fixtures used in holding systems can be toxic to live bait as well.
Plumbing in fish holding systems should be done with PVC and not copper. Holding tanks made of concrete or
block can release alkalis into the water for some time unless treated. The easiest approach is to fill a new concrete
tank with water and add 1 pint of vinegar for every 50 gallons of water. Leave this solution in the tank for 4 or 5
days, drain, and repeat. Similarly, galvanized tanks can release zinc, which is toxic. Galvanized tanks should be
coated with waterproof epoxy paint or other nontoxic coatings. Care should be taken whenever applying coatings
to allow for sufficient curing time and flushing of any unwanted residues prior to putting holding tanks into use.
See Salinity Fact Sheet.