An assessment of selected wetland plant materials' potential for periphyton production in finger ponds in Uganda

Abstract

The use of periphyton in seasonal wetland fish ponds (Fingerponds) was considered in this study, in lieu of the observation that South East countries such as Bangladesh and India are successfully practicing traditional fish production based on periphyton. Periphyton-based systems have been observed to provide affordable inputs for resource-poor farmers for semi-intensive aquacultural production. The study took place between August and November 2003 in fingerponds located in the Gaba wetland, within the lake Victoria catchment area, in Uganda, with the objective of assessing temporal changes in the periphyton community that developed on wetland plant materials used as substrates for their attachment; and how the substrates impacted on the fingerpond water quality, as an initial step in determining the viability of periphyton-based aquacultural production systems in Uganda. Locally available wetland plant materials namely: Cyperus papyrus L. (papyrus), phragmites mauritaianus Kunth. (Phragmites), Raphia farinifera (Raphia) and Oreobambos sp – Bamboo; woven into 1 x 1 m mats (plant frames/substrates); installed in fingerponds (24 x 8 m) covering an area equivalent to 28-33% of the total pond surface area, were utilized. The periphyton community’s biomass, abundance and composition were determined and pond water quality parameters monitored over two six-week experimental periods. Mean periphyton biomass as ash free dry matter (AFDM, gm-2) was highest for bamboo at 4.98, followed by 3.55 for phragmites , and 0.22 for Raphia and Papyrus. All the substrates exhibited potential to generate periphyton albeit of different quality and quantity. A total of eight Phyla namely: Algae (Bacillariophyta, Cyanophyta, Euglenophyta); and sessile Zooplankton (Arthropoda – (Crustaceans), and Rotifera); Fungi, and Protozoa, represented by 54 genera colonized the substrates; a good number of which are known to be potential fish feed for locally available fish species. The most common genera were from Phylum Chlorophyta (green algae) followed by Arthropoda (Crustaceans). The periphyton community exhibited dynamism in proportions of algae; zooplankton and others. Periphyton on Raphia developed and died-off very rapidly. Phragmites and Bamboo had the most stable periphyton communities and highest durability. Papyrus had the most diverse periphytic community, exhibiting the most systematic increase in biomass with time however, the tendency to be mainly colonized by Cyanophyta over time, and its rapid degradation made it the least desirable substrate. The substrates did into significantly affect the fingerponds’, water quality for the duration of the experiment. Bamboo and phragmites exhibited the best performance in terms of quality and quantity of periphyton; and durability of the substrate, however, all four substrate have potential for supporting periphyton-based aquacultural production in this area, thereby enhancing resource-poor farmers’ wise use of wetlands to improve their livelihoods.