Alternative species for traditional carp polyculture in southern South America: Initial growing period

Fish polyculture is practiced aiming to increase productivity. Complementary species can increase the maximum standing crop of a pond by allowing a wider range of available foods and ecological niches. The present work was conducted in an attempt to identify the better species ratio and the introduction of jundia (Rhamdia quelen) and Nile tilapia (Oreochromis niloticus) in the traditional fish polyculture practiced in South Brazil. The experiment was conducted over 86 days, in nine 250 m2 earthen ponds (1.2 m deep), and comprised the initial growing period of fish. As control, one pond was stocked with a species ratio usually employed in the region: 35% common carp, Cyprinus carpio (CC), 35% grass carp, Ctenopharyngodon idella (GC), 15% silver carp, Hypophtalmichthys molitrix (SC) and 15% bighead carp, Aristichthys nobilis (BC) with a density of 2875 fish/ha. Treatment I consisted of two ponds stocked with the same species ratio, but with a density of 5750 fish/ha; this fish density was also used in the remaining treatments. Treatment II consisted of two ponds with 20% CC, 30% GC, 10% SC, 20% BC and 20% jundia (JN). Treatment III consisted of two ponds with 35% GC, 5% SC, 10% BC, 20% JN and 30% Nile tilapia (NT). Treatment IV consisted of two ponds with 15% CC, 30% GC, 5% SC, 10% BC, 20% JN and 20% NT. All water quality parameters evaluated were within acceptable limits for fish culture in pond water. No significant correlation was found between species rate and the water quality parameters. The final weight of different species, in different treatments, showed statistical differences. Considering growth parameters, the best result was obtained in treatment IV. A complete exclusion of the CC in treatment III had no advantage over the other treatments; however, the reduction of CC percentage from 35% to 15% allowed the introduction of JN, with positive effects. In addition, the introduction of JN in the polycultures tested had no effect over the other species. Nile tilapia grew better in treatment III with no CC, but CC had a better performance in the presence of NT. Based on the data presented herein, the most promising polyculture ratio for initial growing season seems to be that used in treatment IV. The reduction of the CC ratio and the introduction of NT and JN had positive effects in all growth parameters evaluated.