Growth curve comparison of native fish cachara (Pseudoplatystoma reticulatum) and cachapinta hybrid (P. reticulatum x Pseudoplatystoma corruscans)

This study was undertaken to compare the growth curves of native fish cachara (Pseudoplatystoma reticulatum) and of the cachapinta hybrid (P. reticulatum x Pseudoplatystoma corruscans), both reared in net cages. The experiment was carried out for 216 days in net cages that were placed in a 24-ha dam, in a completely randomized experimental design with two treatments (cachara and the cachapinta hybrid) and three replicates, totaling six experimental units (13.5-m(3) net cages). The average weights of the fish at the start of the experiment were 75.00 +/- 0.004 g (cachara) and 85.00 +/- 0.006 g (hybrid). An exponential model was chosen to analyze the growth curve of the morphometric traits in each genetic group. The likelihood ratio test was used to compare the growth curves, where the equality of the A (initial size) and (K growth rate) parameters was checked. There was no difference between the growth curves (similar A and K parameters) between cachara and the cachapinta hybrid for weight, standard length, body height, body width, or head length. For head length, the A parameter (1.7416 cm) was lower (P < .05) and the K parameter (0.00499 cm) was higher (P < .05) in cachara than in the hybrid (A: 1.9445 cm; K: 0.00441 cm/day). For body length, only the A parameter (6.4970 cm) was higher (P < .05) in the cachara (A: 6.0033 cm). In conclusion, the growth curve of the cachapinta hybrid is similar to that of cachara for weight and most of the morphometric traits, demonstrating that the hybrid does not have superior growth characteristics in this low density net setting.