Effect of photosynthesis on Nile tilapia culture water's alkalinity

The physical and chemical characteristics of the culture water affect strongly the growth, reproduction, health and survival of fish. The present work was designed to evaluate the effects of the photosynthetic activity on the Nile Tilapia Oreochromis niloticus culture water's total alkalinity. There were eighteen 25-L polyethylene aquaria equally distributed in two culture systems (indoor and outdoor). At the setup fifteen 0.52 +/- 0.06 g juveniles were stocked in each indoor and outdoor aquarium. The indoor and outdoor aquaria were the control and experimental group, respectively, with 9 replicates each. Fish were maintained into the aquaria for 6 weeks. Every week water samples from each aquarium were collected to determine their total alkalinity and pH. These results were submitted to ANOVA for completely random experiments at 5% level of significance. The average water pH in aquaria without and with phytoplankton were 7.32 +/- 0.39 and 8.45 +/- 0.40, respectively. These results were significantly different between them (P<0.001). The total alkalinity of the water averaged 50.49 +/- 6.07 and 63.52 +/- 2.12 mg L-1 CaCO3 for the indoor and outdoor systems, respectively. These results were also significantly different between them (P<0.001).