UNDERSTANDING THE WATER QUALITY PARAMETERS FOR YOUR FISH

To a large extent, the quality of the water determines the success or failure of a fish farming operation. Fish carries out all bodily functions in water; they feed, excrete, reproduce, respire, and take in and lose salt.

Water quality in aquaculture describes the hospitality of a water body for the cultivation of desirable aquatic species. The quality of the water varies by species and needs to be monitored to ensure growth and survival. The quality of the water in the production systems can have a significant impact on the health of the organism and on the costs of bringing the product onto the market.

It is however important for fish farmers to know the various water parameter and level which is best suitable for their species.

The most important physical and chemical water quality parameters comprise of temperature, turbidity (light penetration), pH, salinity (salt level), dissolve oxygen, chlorine, and conductivity

TEMPERATURE

Temperature control is very important for fish welfare since it can affect their behavior, feeding, growth, and reproduction. Temperature is defined as the degree of warmth or coldness in a living organism, whether in water or on land. Since fish is a cold-blooded animal, its body temperature changes depending on the environment that affects its metabolism and physiology and ultimately affects production.

It should be noted that each species has optimal temperature for growth; catfish and tilapia are the species mostly cultured in Nigeria, so this article will be focusing on the level of each parameter needed for growth. Temperature is measure in °C or °F. The optimal temperature range for catfish and tilapia is between 75-95°F (23-35°C), excessively cool temperature in catfish and tilapia can result in mortality. To maintain the required temperature in your pond, you can result in planting shady trees around your ponds during hot weather and also make use of mechanical aerators.

TURBIDITY

Water turbidity refers to the volume of fluid suspended, which interferes with the light penetration in the water column thereby limiting photosynthesis.

Water turbidity is caused by the presence of mineral, humus, and plankton particle; Mineral and humus turbidity reduces the amount of light entering the water. Light penetrates only a short distance in highly turbid waters, and photosynthesis is reduced. Oxygen production during the day is relatively small. Both the growth of fish and their natural food organisms can be severely affected. Also, high mineral turbidity can directly affect fish by damaging their breathing organs, reducing their growth rate, or preventing their reproduction. There are however several ways to control turbidly in your pond;

• To control mineral turbidity, farmers’ may apply organic matter spread across the pond at a rate of 20 kg/100m2; this process may require two or more treatments
• Alum (aluminum sulfate) or gypsum (magnesium sulfate), at a rate of 1 to 3 kg/100 m2, this should be first tested for a small area.
• To control plankton turbidity, farmers’ should make sure the pond is properly limed and fertilized and also make use of water filters.

pH (ALKALINITY AND ACIDITY)

pH or the concentrations of hydrogen ions (H+) present in pond water is a measure of acidity or alkalinity i.e the number of hydrogen ions (H+) in water will determine whether this is acidic or basic. Fish have an average blood pH of 7.4, a slight deviation from this value, generally between 7.0 and 8.5 is more optimal and conducive to fish life. To reduce pH in a pond, add gypsum (CaSO4) or organic matter (cow dung, poultry dropping, etc.), also to adjust low pH level, use quicklime (CaO).

SALINITY

Salinity plays a significant role in the development of cultured species through osmoregulation of body minerals from those of the surrounding water. Salinity is a major driving factor affecting the density and growth of the population of aquatic organisms. In general, freshwater pond species live best in pond water containing less than 3,000 ppm salinity, but many common pond species will live in up to 10,000 ppm salinity, otherwise, the habitat would become too saline to thrive. The optimum salinity range in aquaculture ponds should be maintained for better survival and growth.

DISSOLVED OXYGEN

Like humans, fish require oxygen to function. It is one of the most important parameters in aquaculture. The amount of oxygen the fish consumes depends on its size, the rate of feeding, the level of activity, and the temperature. Small fish consume more oxygen per mass than large fish; this is because of their higher metabolic rate. Depletion of oxygen in water contributes to inadequate fish feeding, malnutrition, decreased growth, and further fish mortality, either directly or indirectly. For average or good production in fish ponds, dissolved oxygen should be above 5.0 ppm; most pond water can hold approximately 10 to 12 mg / L of oxygen.

CHLORINE

Chlorine (Cl-) is a gas that is added to water as a disinfectant to control harmful bacteria and chloride is the same element found in the form of salt, both of which have dramatically different chemical properties. Chloride is a common component of most waters and is useful for fish to maintain their osmotic balance. The desirable range of chlorides for commercial catfish production is greater than 60 mg L-1and this is often ten times higher than nitrite. The ratio of chloride to nitrite in a pond should be 10:1, this reduces nitrite poisoning as catfish are susceptible to “brown blood” disease (due to excess nitrite in the water). However, the chloride content of water also depends on the level of salinity.

CONDUCTIVITY

Conductivity is a measure of the ability of a solution, such as water in a stream, to pass an electrical current. This is an indicator of the concentration of electrolyte ions dissolved in the water. It does not identify the specific ions in the water. However, a significant increase in conductivity may be an indicator that pollutant discharges have entered the water. Ideally, freshwater streams should have a conductivity of between 150 and 500 μS / cm to support the culture of certain species.

It is important to establish a standardized protocol for water quality testing for your specific situation. Know the tolerance range for your crop species, establish critical levels, and be prepared to act when an issue arises.