Economic impacts of ponds management on water quality and growth performance of fish in polyculture

The present study was conducted to evaluate the economics of the fish farms management under different systems and different water sources and its impact on the growth performance of fish in polyculture.The study was conducted in two fish farms in the provinces of Kafr El-Sheikh, Ismailia and Port Said, four earthen ponds in each fish farm two feddans for each pond. The ponds were cultivated by Nile tilapia and mullet with an average weight of 2; 30 g for tilapia and mullet, respectively. The first fish farm was fertilized by organic and mineral fertilizers only during the first three months and then the artificial feed was added until harvest. In the second fish farm used in artificial feed 25% Protein only during the whole season. Water samples were taken monthly to measure water quality parameters and phytoplankton and zooplankton abundance. Also, fish samples were taken monthly to calculate growth rates.
Significantly increase in nitrogen compounds (NH₄, NH₃, NO₂, NO₃), dissolved phosphorus and chlorophyll "a" in the fertilization fish farms led to increased phytoplankton and zooplankton.  
The results revealed significant increase in tilapia survival rate than mullet and significant increase in daily growth rate in tilapia than mullet in each fish pond under different pond managements. The daily growth rate significantly increased in feed system ponds than fertilizers system. Significantly increase of total fish production per Fadden on Shader Azzam and after Kafr El-Sheikh fish ponds in each pond managements.  Significantly increase of total fish production per Fadden on Shader Azzam and after the Kafr el-Sheikh fish ponds under feeding systems and the same trends in fertilizers systems.
Significantly increase Dabbashi, Super, Grad1 in tilapia production in feed systems than fertilizers.  The cost of feed per feddan were 44.99, 79.4, 44.65, 78.78, 45.97 and 76.53% of total operating costs in KM; KF; IF; IM; PM and PF fish farm respectively. The total returns of fish were 22780, 40930, 23630, 39030, 22730 and 35930L.E in the same fish farms respectively.The study indicated that fertilization reduces the cost of production, but artificial feed must be used with fertilization in the last two months of the season.