Performance of grass carp (Ctenopharyngodon idella) using peruvian watergrass (Luziola peruviana) as main food source

Abstract

For irrigated rice are built pond for water storage, which, over time, are colonized by aquatic macrophytes that reduce the capacity of the retention of the water and increase the loss by evapotranspiration. The objective of this study was to evaluate the performance of grass carp (Ctenopharyngodon idella) feeding with Luziola peruviana (Peruvian watergrass), the dominant species in shallow ponds in Rio Grande do Sul. The production of the herbivorous grass carp during four years allowed assessing the variation of the conditions that exist in an extensive system of creation. The introduction of fish has always occurred in October with the harvesting in April of the following year. The pond has area of 7.62 ha of water surface and maximum depth of 1.24 m. The biomass of L. peruviana was estimated by the method of square plots of 0.25 m² at 15 points randomly distributed in the pond. The grazed areas were measured each year before the introduction of the fish and after the harvesting. The fish consume the stems and leaves, that representing a biomass of 9,852 kg DM ha^-1. The grass carp had a good performance, since it obtained a mean weight gain of 1.0 kg fish^-1 after 180 days, specific growth rate of 0.74 g day^-1 and feed conversion ratio of 43 kg DM kg^-1 fish. The initial biomass of 93 kg ha^-1 of grass carp, using juveniles of 320 g of weight, was adequate for a good performance of the fish, and for the efficient control of the macrophyte L. peruviana.