In Ghana, farmers growing fish in ponds and tanks often choose to exchange water to supply additional oxygen and remove fish wastes. However, water does not contain much oxygen (about 0.0008%) whereas air contains 20.9% oxygen. Therefore, fish farmers in other parts of the world have realized that aeration is a much more effective means to supply oxygen, compared to water exchange. However, at some point, water exchange is necessary to remove metabolites such as ammonia. A series of trials was run on a private farm to demonstrate to the farm and to others the trade-offs between aeration and water exchange. Each of 20 outdoor tanks containing 1 cubic meter of water were stocked with 1000 tilapia fry of 0.3 grams. Five treatments of 4 replicates each were run. The treatments were as listed in the table and figure below. Aeration was turned off during the day for treatments 1, 3 and 5. Fish were fed 3 time per day to satiation. Twice daily measures of dissolved oxygen and temperature were made on most days, whereas pH and total ammonia were measured twice weekly.
Total daily feed input reached 60g per cubic meter water volume, which is about 6 times the recommendation for static water non-aerated tilapia ponds. Fish growth was superior in all of the aerated treatments, compared to the non-aerated. Morning dissolved oxygen was much lower in the non-aerated treatments and, in the latter part of the trial, was frequently below 1mg/l. Total ammonia was not different between treatments.