Effects of substrate addition and supplemental feeding on plankton composition and production in tilapia (Oreochromis niloticus) and freshwater prawn (Macrobrachium rosenbergii) polyculture M.S. Uddin a , M.E. Azim b , M.A. Wahab a , M.C.J. Verdegem c, ⁎ a Department of Fisheries Management, Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh b Department of Physical and Environmental Sciences, University of Toronto, 1265 Military Trail, Toronto, Ontario, Canada M1C1A4 c Fish culture and Fisheries Group, Department of Animal Sciences, Wageningen University, P.O Box 338, 6700 AH Wageningen, The Netherlands abstract article info Article history: Received 4 March 2009 Received in revised form 15 September 2009 Accepted 18 September 2009 Keywords: Periphyton Tilapia Freshwater prawn Polyculture Substrates Net return This study investigated the effects of substrates and supplemental feeding on growth and production of tilapia (Oreochromis niloticus) and freshwater prawn (Macrobrachium rosenbergii) in a polyculture system. On actual farms, four treatments were evaluated in triplicate: substrate plus feed (herein called treatment SF), no substrate plus feed (S 0 F), substrate plus no feed (SF 0 ) and no feed and substrate (control). All ponds were stocked with tilapia and freshwater prawn juveniles at a stocking density of 30,000 ha -1 with the ratio of 75% tilapia and 25% freshwater prawn. In the substrate-based system bamboo poles provided 60% additional surface area (compared to pond surface area) for periphyton growth. A commercial 25% protein diet fed at 2–3% tilapia body weight per day was applied. The feed conversion ratio (FCR) of tilapia was significantly higher in the treatment with substrate and feeding (SF) than in the treatment with only feeding (S 0 F). The combined net yields varied significantly (P < 0.05) among four treatments and productions were 59, 48 and 47% higher in ponds with substrate and feed (SF), feed alone (S 0 F) and substrate alone (SF 0 ), respectively, compared to the control. The combined net yields of tilapia and prawn in the treatments S 0 F and SF 0 were similar (P > 0.05). 29 genera of algae and 9 genera of zooplankton were identified from pond water and it showed significant (P < 0.05) differences for Chlorophyceae, Bacillariophyceae and Cyanophy- ceae in the treatment SF compared to the control. There were no significant (P > 0.05) differences for periphyton biomass in terms of ash free dry matter (AFDM), chlorophyll a and phaeophytin a in substrate- based systems. The net profit margin was highest in treatment SF 0 (57%) followed by SF (51%), S 0 F (50%) and the control (24%). © 2009 Elsevier B.V. All rights reserved. 1. Introduction Global aquaculture places a lot of pressure on fishmeal and fish oil resources, mainly through the use of formulated feeds (Naylor et al., 1998). Farming carnivorous species requires 2–4 kg of wild fish per kg production, while for carp and tilapia 0.1–0.4 kg wild fishes are used (Tacon and Metian, 2008). In response to a growing consumer appre- ciation, Nile tilapia (Oreochromis niloticus) is becoming quickly an important pond fish in Bangladesh. Concurrently, in Bangladesh there is a tendency towards intensification of pond aquaculture through the use of formulated feeds. Freshwater prawn (Macrobrachium rosenbergii) is also a popular species in Bangladesh for its taste, growth and high international and domestic market value. The farmers are very interested to culture freshwater prawns because the potential profits are higher than for other types of culture. Many trials have demonstrated that fish production from ponds provided with substrate for periphyton is higher than from substrate- free ponds (Azim et al., 2001b; Hem and Avit, 1994; Keshavanath et al., 2004; Uddin et al., 2007a; Wahab et al., 1999). Also Nile tilapia production increased when substrates for periphyton were added to ponds (Dempster et al., 1993; Keshavanath et al., 2004; Uddin et al., 2007a). Substrate-based systems tested with freshwater prawn have also shown encouraging results (Tidwell et al., 1998). However, the role of supplementary feeds in semi-intensive polyculture systems is not straightforward as there are complex interactions among natural food organisms, supplementary feeding practices, environmental parameters and species (Azim, 2001). From environmental and eco- nomic points of view, possible options to make aquaculture systems more resource efficient are worth investigating. In recent years, a series of experiments has been conducted to develop a substrate- based tilapia–prawn polyculture system in Bangladesh. Trials have demonstrated that tilapia and prawn production from substrate- Aquaculture 297 (2009) 99–105 ⁎ Corresponding author. Tel.: + 31 317 484584; fax: + 31 317 483937. E-mail address: marc.verdegem@wur.nl (M.C.J. Verdegem). 0044-8486/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2009.09.016 Contents lists available at ScienceDirect Aquaculture journal homepage: www.elsevier.com/locate/aqua-online