One of the frequently asked questions in catfish farming is that of how to know the number of catfish to be stocked in a pond or container. I have answered this question through my article on carriage capacity of pond.
Like I said in some of my previous writeups, calculation of stocking density depends so much on a number of variables. Pond type is an important variable that must be given priority in calculating capacity of pond in relationship to stocking/harvest ratio. Other vital variables include; availability of water source and volume, water management techniques to be adopted, desired size/volume expected at harvest, groundwater capacity in earthen pond, feed type to be used, estimated mortality rate based on previous experience or average mortality rate in your environment and numerous other variables.
Recently, a friend sent a writeup on how to calculate stocking density in catfish to me. I wish to share this piece of information with you. Although the research was done in the USA, we can still make use of the recommendations with little or no adjustment to suit our tropical environment and African catfish that we culture in our region. The calculation was done on static water pond with depth not specified. However, the volume of water must be known and I do hope we can all calculate water volume in any form of container based on our knowledge of elementary mathematics. Good! Another important thing you must predetermine before calculation begins is target size at harvest as well as expected mortality rate — usually between 5-10 percent. Generally, according to the recommendation of the research, a static pond system has maximum stocking capacity of 1.8kg of fish per meter square. Arithmetically, the calculation is simple: 2000 meter square of static pond water can carry 3,600kg of catfish.
There is more to the above calculation because we still don’t know the number of fishes to stock. Assuming your static pond water volume is 2000 meter square and you intend to produce average size of 900 grams of catfish at end of culturing season with an average mortality rate of 5 percent, and then calculation can be done thus:
2000 meter square of water volume multiplied by 1.8 divided by 900 gram plus 5 percent expected mortality rate i.e. (2000m2 x 1.8kg/900g) + 5% (2000m2 x 1.8kg/900g)
(3600/0.9) + 5%
4000+ 5% of 4000
4000+ 200 = 4200 juvenile
Note: The above calculation is recommended for a mono-culture system of catfish farming and to maintain water quality, each fish should not be fed above 20 g.
The above calculation might not be 100 percent applicable in tropical catfish farming system but can be used as basis upon which stocking density can be calculated with due consideration to other unique factors in our environment. It must also be noted that stocking capacity of pond can increase significantly if external source of water is introduced to a static pond. The increase in the level of dissolved oxygen in pond water can help increase the level of stocking density as waste is removed from pond either through flow through system or re-circulatory system.