Understanding and predicting fish performance in ponds can be relatively difficult without the prior knowledge of how water parameters influence fish behaviour.
In the last couple of years, I have observed that most farmers that operate good ponds, stocked with the right quantity of fish seeds, still recorded huge losses even though they fed their fish very well.
This is due to poor knowledge of fish water chemistry.
Fish, unlike other animals, feed and defeacate inside the same water where they live and the quality of the water inside which they live directly affects feed efficiency, rate of growth, survival and the state of health of the fish.
When water quality depreciates, consumed feed is not properly converted into body flesh. Poor growth is recorded, fish survival is affected and ultimately massive fish kills may occur.
In fish production, key water quality parameters which need to be continually monitored are temperature, dissolved oxygen, pH, and ammonia.
Due to dynamics within the ponds, these parameters could change at short notices. I desire to share my experience and observation with fish farmers concerning the various ways in which the fluctuations of these water parameters could influence fish health, fish growth and fish survival.
Dissolved Oxygen (DO)
The relevance of monitoring the level of dissolved oxygen in ponds is very important. For the African catfish, a farmer should try as much as possible to maintain dissolved oxygen levels at between 4mg/liter to saturation levels in the pond.
Gas bubble disease can happen to the fish when DO levels are consistently too high and the water is super-saturated to well above 300 per cent. When DO level is consisitently between 1.5mg/liter to 5mg/liter, fish will be alive, but feed intake will reduce.
Growth rate will also reduce and high Feed Conversion Ratios (FCR) will be recorded. When DO levels are lower than 1.5mg/liter, fish will be stressed and they will die. The periods of achieving desired weights in fish will be lengthened and ultimate loss on investment will occur.
Infact, I can categorically emphasize that with consistently low levels of DO in ponds, the use of low quality feed might even be a waste of money.
This is simply because of the fact that fish breathe in oxygen for general body metabolism. DO is needed to help breakdown any potentially harmful metabolic waste into less harmful forms, e.g ammonia (NH3) broken down into nitrites (NO2) and then into nitrates (NO3).
Temperature
Unlike man that is warm blooded, fish are cold blooded. The metabolism which occurs in their bodies is greatly influenced by the water temperature.
For the African Catfish, an acceptable temperature range is between 26ºC to 32ºC.
When water temperature in the ponds consistently stays between 16ºC and 26ºC, feed intake reduces and fish growth rate also drags tremendously. A farmer will record high FCR, and the fish will also be stressed.
Prolonged stress can open up the fish to opportunistic infections. When fish are consistently exposed to temperatures below 15ºC, fish growth will ultimately stop and death is just around the corner.
Low temperature negatively affects rates at which wastes are converted in the water. However, when water temperature is above 32ºC, the resultant effect on the African Catfish in not good at all. This is because of the fact that Oxygen is not readily soluble in very warm water. High temperature in ponds will stress the fish and eventually lead to death.
pH
pH is the level of the Hydrogen ion present in the water. For the fish in the pond, acceptable pH value is between 6.5 to 7.5. When it is below 4, fish will die due to water acidity.
I have personally experienced this and it was not in any way pleasant.
When pH is constantly between 4 to 6, fish will be alive, but, due to stress, will experience slow growth. Feed intake will be highly staggered and reduced. FCR will also be very high.
Infact, for the observant fish farmer, low pH in pond water is an indication of high CO2, (carbon dioxide) in the water.
High pH values of between 9 to 11 in pond water will also retard fish growth. Fish will ultimately die when pH levels rise above 11. Low pH aids higher proportions of ionized ammonia which is less toxic to fish. The reverse is the case with high pH in water.
There is nothing as painful as being ignorant of these facts. These water parameters play a major role in the overall business of profitable fish farming.
Making profit from fish farming really goes beyond just giving food to the fishes. Water Quality parameters must be monitored and acceptable ranges must be maintained.
Growth time of fish in ponds must be within acceptable times. Nothing is as painful as keeping fish in ponds for an unnecessary long period of time while money is being wasted on feed.
June 2014
