World Aquaculture 53 Table 1. Growth of Pacu variables at culture for A, B, C and D densities. Density A (1 ind/m2) B (0.5 ind/m2) C (0.3 ind/m2) D (<0.3 ind/m2) Initial mean weight (g) 0.25 0.25 0.25 0.25 Final mean weight (g) 560.2 753.7 953.0 1374.2 Days of culture 495 495 495 495 Number of ponds 10 11 8 6 Mean growth (g) 559.8 753.5 952.8 1374.0 Daily mean growth (g/day) 1.13 1.52 1.92 2.77 Specific growth rate1 1.56 1.62 1.66 1.74 Initial feeding rate (%) 10 10 10 10 Final feeding rate (%)2 < 2 < 2 < 2 < 2 Mean FCR3 1.45 1.56 1.75 2.70 Survival rate (%) 97.5 99.7 99.1 43.8 Mean Production (kg/ha) 6071 4170 3027 2890 1Specific growthrRate = (ln fW – ln iW) x 100 / t = %percent/day 2Means determined at crop for each density. Range 0.75-1.5 percent. 3Feed conversion ratio (FCR) = Feed offered/mean weight gain weight was 753.7 g (ranging from 597.3 to 950.3 g). The average FCR was placed in 1.56 (ranging from 1.40 to 1.78). Density C (0.3 fish/m2): Results from eight out of 12, 300 and 500 m2 ponds were considered. Final average weight was 953.0 g (ranging from 807.9 to 1,195.2 g). Final FCR was 1.75 (ranging from 2.03 to 1.45). Density D (less than 0.3 fish/m2): Results from six, 300 and 500 m2 ponds were evaluated. Ponds were stocked at 1.0, 0.5 and 0.3/ m2. High mortality rates were during the first sampling. Larval mortality was probably a result of bird predation. Average mortality at final harvest across in the D group was 0.21 fish/m2 (ranging from 0.3 to 0.12 fish/m2). In those 6 ponds there was a food oversupply that could be clearly seen in the FCR values. Final average weight was 1.37 g (ranging from 1.14g to 1.72 g). Average FCR was 2.70 (ranging from 2.02 to 4.10). In February 2001, average weight for the four densities were significantly different. Density A was 447.7 g, density B was 565.0 g, density C was 692.6 g and density D was 1,917.5 g. Differences among weights became clearer as time went by. This made us think that the fish in density A ponds were nearly reaching their maximum carrying capacity. According to Bernardino et al. (1998) that would be in the range of 500-600 g/m2. At final harvest, the density A ponds showed 607.0 g/m2 carrying capacity while B density units were 417.0 g/m2. Both showed daily weight gains of less than 3.0 g while the carrying capacity of densities C and D ponds was around 300 g/day, with growth of 4.5-5.1 g/ day (Table 1). Our data differed from those of Jacobo et al. (1992) and Roux and Bechara (1998) because in the present study lower densities showed higher weight gains. Results from the present study were similar to those of Silva et al. (1997), working with pacu in Ceará, Brazil, without a clear winter season. Fish were grown at two densities for more than a year on a low protein ration (22 percent). Differences among the studies mentioned are shown in Table 2. Survival Survival was high in densities A, B and C, ranging between 97.5 and 99.7 percent. Survival in the six density D ponds at final harvest was 43.8 percent. There were no significant mortalities from diseases or parasites. Fig. 5. Pacu final weight at different stock density. Fig. 6. Growth for Pacu at different culture densities (A,B,C and D).
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