Author Description

Three technologies showed to improve productivity and sustainability of pond production: (1) C/N ratio control, (2) providing substrates for periphyton development, and (3) fish driven re-suspension. The novelty of this PhD research is to combine these technologies, with the goal to raise pond productivity above levels obtained with each one of these technologies separately, and to increase the nutrient use efficiency in ponds above levels presently achieved, further enhancing sustainability. This combined technology is further referred to as C/N controlled periphyton (C/N-CP) technology. A series of experiments (Chapter 2-6) were conducted to develop such technology. The first step (Chapter 2) evaluated if increasing C/N ratio (from 10 to 20) in combination with providing vertical substrates for periphyton development in freshwater prawn monoculture ponds can enhance overall pond productivity. The results were encouraging due to the 75% increase of production; in addition it seemed that natural foods were underutilized by freshwater prawn. Therefore, the next step (Chapter 3) was further analysis of the above mentioned experiment investigating how C/N ratio control and addition of substrates influenced the natural food communities in freshwater monoculture ponds. This study suggested further investigation on the possibility of increasing stocking density of freshwater prawn and inclusion of tilapia due to its both sediment re-suspension and periphyton grazing activity. Therefore, in thethird step (Chapter 4) increasing stocking densities of prawn (from 2 to 3 m−2) and addition of different levels of tilapia (0, 0.5 and 1individual m−2) were tested. This study concludes that both stocking densities (2 and 3 juveniles m−2) of prawn with the addition of 0.5 tilapia m−2 resulted in higher fish production, good environmental condition and economic return. In the fourth step (Chapter 5), the effects of addition of periphyton substrates and tilapia driven bioturbation wer