Effects of Substrate Amount and Orientation on Production and Population Structure of Freshwater Prawns Macrobrachium rosenbergii in Ponds

Abstract.— Previous studies have demonstrated a direct linear relationship between freshwater prawn Mucrobrachium rosenbergii production intensity (kg/ha) and amount of added substrate. However, increases greater than 80% have not been practicable with multiple layers of substrate installed in horizontal orientation. Vertical orientation could allow higher inclusion rates, but might not be useable by prawns which had recently molted. This study compared the effectiveness of substrate (in the form of polyethylene fencing) oriented horizontally or vertically, and evaluated the impact of increasing amounts of vertical substrate (0, 50, and 100%) on prawn production. Juvenile prawns (0.2 ± 0.1 g) were stocked into 12 0.04-ha ponds at 65,000/ ha. Ponds were randomly assigned one of four treatments with three replicate ponds per treatment: 1) controls containing no substrate, 2) 50% increase in horizontal orientation, 3) 50% increase in vertical orientation, or 4) 100% increase in vertical orientation. After 106 d, orientation of substrate (horizontal or vertical) had no significant ( P > 0.05) impact on prawn survival, production, or population structure. In ponds with different amounts of vertical substrate, average weight (42 9). survival (89%). and feed conversion ratio (2.7) were not significantly different ( P > 0.05) among treatments. However, total yield (kg/ha) was significantly greater ( P > 0.05) in ponds with 100% increase in surface area (2,653 kg/ha) than in control ponds (2,140 kg/ha). Ponds with a 50% increase in surface area had yields (2,452 kg/ha) that were not significantly different ( P > 0.05) from control ponds or ponds with a 100% increase. These data indicate that orientation does not impact substrate effectiveness in ponds and that increasing amounts of added substrate continue to increase prawn production up to at least an increase of 100% in available surface area.