Annex 2 Periphyton

Rich periphyton communities boost fish production. The distribution of periphytic fauna shows differences with regard to quantum and seasonal succession. Periphyton supported aquaculture systems offer the possibility of increasing both primary production and food availability for fish; especially those low in the food chain. The culture of milkfish (Chanos chanos), a very popular cultured species in Indonesia, Philippines and Taiwan Province of China, is mainly based on periphytic “lab lab” as food, the production of which is enhanced by organic and inorganic fertilization (Juliano, 1985).

The “acadjas” of West Africa (Welcomme, 1972), the brush parks of Sri Lanka (Senanayake, 1981) and the “Katha” fisheries of Bangladesh and India (Wahab and Kibria, 1994) are well-known examples of periphyton-based aquaculture systems.
Dempster, Beveridge and Baird (1993) have reported that Nile tilapia graze more efficiently on periphyton substrates than on micro-particles in the water column. Algal biomass is also higher in periphyton systems. Bhaumik et al. (2005) have reported that richness of periphytic structure in closed wetlands results in higher fish production (1 570 kg/ha/year) compared to open system (384 kg/ha/year). Lagoons provided with substrates for periphyton, supports eight times higher algal biomass compared to the surrounding lagoons (Konan-Brou and Guiral, 1994).

A range of substrate-supported aquaculture systems (Table 1) have been developed to reduce the cost of feeding fish (Azim et al., 2002a, 2002b; Keshavanath et al., 2002; Garg, 2005). In these systems additional substrates are provided for the growth of periphyton, which has positive effects on fish production. The association of microorganisms, algae and planktonic organisms attached as periphyton serve as food for fish and also act as an in situ water purifier ensuring better living conditions. Wahab et al. (1999) have reported 1.8 times higher production of carp kalbaush (Labeo calbasu) in ponds provided with scrap bamboo as substrate than from ponds without substrate. Similar results were also observed with rohu (Labeo rohita) (Azim et al., 2001), Mahseer (Tor khurdee) (Keshavanath et al., 2001) and milkfish (Chanos chanos) (Jana et al., 2006). Fish yield is linearly correlated with substrate area (Azim et al., 2004). Garg (2005) has reported that grey mullet (Mugil cephalus), milkfish (Chanos chanos), pearlspot (Etroplus suratensis) and Nile tilapia (O. niloticus) are suitable species for periphyton-based brackish water culture systems. Survival and growth of these four fish were higher in substrate-supported periphyton-based culture systems compared to the systems without substrate. The provision of additional substrates in fish culture ponds reduce the use of artificial feed, especially those species that thrive low in the food web.

Table 1
Various substrates used in periphyton-based culture system