A pond is overstocked when the carriage capacity of such a pond cannot support healthy growth of certain number of fishes for a period of time between stocking and maturity. Maturity mentioned here is a relative term. For instance, 3 months may be the maturity period for a fish that will be sold in dry fish market (average weight of 600 grams to 900 grams) whereas it could be up to 6 months for fishes that will be sold at Abuja market (average weight of 1kg to 2.5kg). A pond that carries a particular number of fishes successfully for 3 months might not be able to support the same number of fishes for 6 months. Therefore, the concept of overstocking is best explained by making reference to the ultimate carriage capacity of a pond.
According to a 2009 study by N.A. Jamabo and R.I. Keremah, “Stocking density has a significant effect on growth, survival and food conversion.”
There are factors that may affect the carriage capacity of a pond; these factors need to be mentioned so as to determine accurately the capacity of a pond in relation to the number of fishes to be stocked:
- Surface area (pond size): The bigger the pond, the better the carriage capacity of such a pond. For example, a pond of 10m by 20m in dimension will contain and support more fishes than a pond of 5m by 7m, all things being equal.
- Pond depth: Shallow ponds may not really support much fishes in terms of tonnage produced at the end of the farming season, whereas a deep pond of the same surface area will definitely support more fishes as a result of increase in volume of water.
- Season: Ponds are constantly refreshed during the wet/rainy season as a result of direct rainfall into the surface area of the pond and also increase in groundwater coming up into the pond. (Note: this is not applicable to concrete ponds and other containers.)
Refreshed water is rich in oxygen and low in pollution hence carriage capacity of the pond is increased.
- Fish species: Some catfish species possess large body mass that occupy relatively bigger space as against some with smaller body mass and better weight. In catfish farming business, weight is better than large body structure since value of sales is subject to weight.
I recommend between 8 and 12 fishes per square meter, depending on the depth of your pond. However, under a very special condition where there is sufficient water, the theory of 8 to 12 fishes per square meter of water might not necessarily be a standard. The carriage capacity of ponds is increased by at least twice under a flow-through system of ponds. In fact, under this system a pond produces more fish tonnage in relation to the volume of water in such a pond.