Just as fish need good water quality conditions to thrive, they also need an abundant supply of food to grow. We can provide food for our fish in two different ways: We can give them “artificial” feeds that are prepared either commercially or at home, or we can ensure that they have an abundance of natural foods by using fertilizers to increase pond productivity. In either case, it is important to try to provide them with a diet that is nutritionally complete.
This section focuses on fertilizing ponds to enhance their natural fertility and productivity. Fish ponds in red and lateritic soil zones exhibit low availability of phosphorus (P), resulting in restricted accumulation of various fish food organisms and, thereby, lesser fish production.
Primary Nutrients in Agriculture and Aquaculture
In both agriculture and aquaculture certain nutrients are of key importance for plant growth. The nutrients that most often limit the growth of plants (through their absence) in agriculture (land crop production) are nitrogen (N), phosphorus (P), and potassium (K). This is why many commercial (inorganic) fertilizers are sold as “complete” N-P-K fertilizers. The different levels of N, P, and K present in a particular product indicate a mixture that is considered appropriate for a particular crop in a particular region.
In aquaculture (especially for Tilapia ponds) we are interested in plant growth because in many cases we wish to maintain a high population density (a “bloom”) of phytoplankton in the pond as the basis for the natural food chain. Phytoplanktons are the microscopic plants suspended throughout the water in a pond. There are many kinds of phytoplankton, but it is the green and blue-green phytoplankton that are most common, and that give ponds their “green water” appearance when present in great numbers.
Pond water that is very green indicates a high population of phytoplankton, which in turn indicates that the nutrients needed by phytoplankton for growth and reproduction are sufficiently present; in other words, such a pond would be considered to be highly fertile. Conversely, a pond with very clear water is indicative of low fertility; such a pond will have a relatively poor supply of natural foods in it.
- N (nitrogen)
- P (phosphorus)
- K (potassium)
How do we add fertilizers to the pond?
Apply organic fertilizers to the pond before filling it with water. Never fertilize a pond if it is full of weeds. Pull them out first then fertilize afterwards. Shallow waters promote weed growth. Keep pond sides trimmed so the grasses on the pond dikes do not spread out into the pond.
- Determine which organic fertilizers are readily and cheaply available. The most common examples of organic fertilizers are animal manures (e.g., from cattle, poultry, donkeys, rabbits, sheep, goats) and decaying plant matter, such as cut grasses.
- Apply available animal manure to the fish pond at a rate of 50 g of dry matter per m2 per week. This is equivalent to 5 kg/100m2/week.
Apply the manure to your pond in one of the following ways:
- Spread dry manure on the pond floor before filling with water.
- Spread (broadcast) dry manure on water surface periodically.
- Place dry manure in a crib in a corner or along the side of the pond.
- Set sacks filled with manure to float within the pond and shake them daily to allow nutrients to leach out and enhance water fertility .
- Construct poultry houses or pig pens above or adjacent to ponds to facilitate easy movement of the manure
Regulating water flow into the pond
- If water flows through the pond continuously, the temperature will be lower and nutrients will not accumulate. This is good for trout production but very bad for tilapia, catfish and fairly bad for carp production. Water flowing into the pond brings in silt and can bring in chemical residue from pesticides. Tilapia, carps and catfish do best at high water temperatures. Keeping the temperature of the water low will make them grow slower.
- Reducing the water flow into ponds will reduce silt loads and lessen the risk of chemical contamination. Tilapia and catfish feed on the phytoplankton that the fertilizers encourage to grow. Washing this food out of the pond is a waste.
- Water should be screened before it enters the pond. This can be achieved by having the water enter the pond through PVC or a bamboo pipe and tying a feed sack to the end entering the pond. If you do not screen your water, you may get some wild fish, some predators or other unwanted insects and snails into your pond.