The objective of this work was to evaluate the performance of the bullfrog tadpoles (Rana catesbeiana Shaw, 1802) under different photoperiods. Seven hundred and twenty animals from the same spawn were used, on the stage 25, according to Gosner (1960). The fishes were allotted to 24 polyethylene 30 L boxes, with a density of one tadpole per liter. The treatments consisted of six photoperiods [0L:24D; 8L:16D; 12L:12D; 14L:10D (natural as witnessed); 16L:8D and 24L:0D] and four replicates, using environment temperature. The experiment was developed from December 2000 to April 2001. The photoperiods were programmed using the black plastic covering the boxes, except for natural photoperiod (colorless plastic). Three timers with 21 watts fluorescent lamps, to photoperiods of 8L:16D; 16L:8D and 12L:12D, were also used. The statistical analyses were performed by a complete randomized split-plot design. The experiment was analyzed managing best regression model. Tadpoles presented length and weight gain with cubic tendency for most of the treatments, except for length for 24L:0D photoperiod, that showed quadractic tendency. For metamorphosis evaluation, statistical analyses were performed by ANOVA and Duncan test at 5% level. The best result was obtained in a 12L:12D photoperiod, as in 120 days the bullfrog tadpoles showed the greatest weight (1.80 g) and the best metamorphic rate with about 50% of the population on this process. After 120 days, the animals showed smaller weight, that characterized the complete metamorphic process. The worst result occurred in the 24L:0D photoperiod. Higher weight (2.0 g) was obtained with 4% of metamorphic rate. This result showed that the photoperiod inhibited the development of tadpoles. The following worst result was obtained for the treatment 16L:8D. The photoperiods 0L:24D, 8L:16D and the natural process showed the intermediate results.
bullfrog; growth; metamorphosis; photoperiod; Rana catesbeiana; tadpoles
