The effect of periphyton substrate density on production in freshwater polyculture ponds

The present research investigated the optimum surface area of periphyton substrate in earthen ponds stocked with a pre-optimized density and ratio of the Indian major carps, catla (Catla catla), rohu (Labeo rohita) and kalbaush (Labeo calbasu) to support enhanced fish production. Four treatments in triplicate were tried: no substrate (control), bamboo submerged substrate equal to 50% (treatment S-50), 75% (S-75) and 100% of the pond surface area (S-100). Water temperature ranged between 17 and 28 degreesC, which is relatively low for tropical fish culture. Secchi disc depth and total ammonia concentrations were higher in control treatment than in substrate treatments. The average dissolved oxygen concentrations were higher than 5 mgl(-1) in all treatment ponds and never fell below critical levels. More phytoplankton cells were found in ponds without substrates. Periphyton dry matter per surface area was lower in treatment S-50. About 32 genera of algae and 10 genera of zooplankton were identified from periphytic mats. Net yields of catla in all substrate treatments were higher than in control treatment, but the yields did not vary significantly among three substrate densities. Net yield of rohu in treatment S-100 was higher than in treatment S-50 and control, but not different from treatment S-75. Kalbaush yield in treatment S-100 was higher than in the other treatments. The combined net yield of the three species was higher in treatment S-100 than in the control and treatment S-50, but was not different from treatment S-75. It was found that combined net fish yields were linearly correlated (R-2 = 0.93) with substrate density. The added substrate density equal to 50%, 75% and 100% of the pond surface areaincreased production by 114%, 168% and 209%, respectively, compared to the control. It was concluded that any amount of substrate area installed in the ponds up to 100% of the pond surface area will increase production. (C) 2004 Elsevier B.V. All rights reserved.