Plankton Composition and Abundance in Semi Intensive Aquaculture Pond and their Preference by Nile tilapia

Plankton is major food item for Nile tilapia and their availability is one of the most important factors affecting its growth performance in an extensive and semi-intensive pond-based culture systems. Thus, this study aimed to examine plankton composition, abundance, and feeding preference by Nile tilapia reared under a semi-intensive pond-based production system. The experiment was carried out using ponds (10mx15mx1.7m size) fertilized with chicken manure at the rate of 100g/m2/week. Nile tilapia with 7.8g average body weight was stocked at a density of 2 fish/m2. Examination of plankton from both pond water and stomach samples of fish was done using qualitative assessment methods. The results showed that a total of 20 phytoplankton groups were identified following standard identification key. These include four types of Blue-green algae (Cyanophyceae), seven types of Green algae (Chlorophyceae), six Diatoms (Bacillariophyceae), one type of Dinophyceae, and two types of Euglenophyceae. Among the phytoplankton groups, Chlorophyceae was the dominant group with 56% followed by Bacillariophyceae (23%), Cyanophyceae (17%), and Euglenophyceae (3%) while the least was Dinophyceae (1%). The most frequently observed algal genus was Scenedesmus. In addition, three Zooplankton groups namely Copepods (43%), Rotifers (31%) and Cladocerans (26%) were also identified. The result indicated that, the most preferred planktonic groups used by Nile tilapia was green algae, particularly Chlorophyceae followed by Copepoda and Rotifers. The level of chlorophyll `a` was 62.3±2.0 μg/l concentration. The different water quality parameters together with the availability of different plankton were optimal for the growth of Nile tilapia which resulted in a 0.45 specific growth rate. In conclusion, Nile tilapia exhibit preference for green algae, blue-green algae from phytoplankton, and Copepods from zooplankton groups than other groups of plankton.