There is a limit to the number of fishes your pond can contain per time. The maximum weight of fishes a pond can contain successfully without crisis is referred to as the “carriage capacity” of pond in this text. In the time past, there have been series of questions related to number of fishes a given size of pond can carry for a particular period of time. Answers given to these questions are not specific. Experience has taught me that carriage capacity of a pond is a factor of water management technique adopted in a farm. In other words, re-circulatory system of water management can accommodate higher number of fishes per square meter than a pond system. Even in a pond system, there are factors that affect the appropriate stocking density of two different ponds of the same size and depth in different location. Soil quality has a great impact on water quality which is an important factor in determining pond capacity.
Also the flow rate of ground water has a lot to do with number of fishes to be stocked. Probably you have read from that a meter square of water in a pond system should have between five to six fishes, I tell you some of the factors mentioned above must be taken into consideration to determine the actual number of fishes to be stocked in your pond. Experience teaches better than stories. A catfish farmer can determine the actual capacity of his ponds after one or two seasons of observation. To help farmers reach a logical conclusion on this matter, I recommend a number of indicators that will let you know when your ponds reach their carriage limit.
Maximum Carriage Capacity Indicators
Response to feed reduces drastically as soon as your pond reaches its carriage limit. This is due to the fact that water environment condition will no longer be conducive for healthy growth. At this point in time, fishes only feed to survive and not to grow. Any further effort to improve their feeding rate without improving environmental condition will be effort in futility. More feed will result in more pollution and ultimately an economic waste. In case you overstocked your pond with intention to share some of the fishes into other ponds at a later time, you must think of sharing them as soon as you notice persistent drop in their feed consumption. However the best option is to sell off your grow-out fishes after you notice drop in their feeding habit in spite of your effort to improve their water environment.
Feed Conversion Ratio becomes lower due to overcrowding. It is a normal practice in catfish farming to measure some sample fishes regularly so as to monitor the growth of the general stock through sampling. This will help farmer to monitor closely how well his stock convert feed to flesh. From experience, depending on the quality of floating feed in use, a farmer can get as much as one to one feed conversion ratio. And in a worst case scenario, feed conversion ratio could drop to as low as one point three to one. The same in locally pelletized feed, the quality of feed formulation and water management has a lot to do with conversion ratio.
However, due to restlessness in catfish, I don’t always recommend sample weighing. A catfish farmer can observe the progress in growth of his fishes without sampling the fishes but through mere observation of third party farmer who visit weekly. When the growth becomes less obvious it could be that your pond capacity can no longer support their healthy growth further.
Depletion in the Dissolved Water Oxygen is a sign of overcrowding especially in pond system. The dissolved oxygen in water is overused and fishes look for an alternative way of surviving through atmospheric oxygen. The alternative way of breathing will cost a level of energy lost which will slow down their growth. The users of pond system should note that depleted water oxygen is a sign that your pond has reached its elastic limit in terms of carriage capacity.
Water Temperature increases significantly as pond carriage capacity reach its elastic limit. The heat generated through activities of fishes becomes intense as density of your fishes increase due to growth. It will get to a time when water temperature becomes unbearable for normal fish activities except if there is an external coolant which is not always available in a pond system. Most of the time, your fish will not die due to an increase in water temperature but they will only live to merely survive the harsh environment. I will recommend the use of a simple thermometer to monitor the progress of your water temperature. Take a precise action when temperature becomes abnormal.
Constant Mortalities occur regularly when resources meant for survival of fishes in pond becomes depleted. The weak ones will feel the effect of this shortage most. Increase in ammonia gas in water could trigger some infection which will spread rapidly because of huge density of fishes in the pond. Most of the time, mortality re-occur after treatments and more fishes have to die to ensure balance and stability in the pond. Once your pond reaches its maximum carriage capacity, mortality becomes a common occurrence.
Water Color changes from lemon green to grey or blackish at a given rate of water inflow. The environment will be too harsh for plants that give pigment to water in the pond to survive. Also, the rate of pollution increases as density of fishes grows leading to change in water color. As a matter of fact, water color is one of the ways you can use to assess the well-being of your stock. When water color changes constantly in spite of water in flow, it might be the result of increase in activities of your stocks.
Other indicators are internal attacks among fishes, restriction in movement of stock, too busy water surface, intensive competition for feed and regular restlessness.