Efeito da cor do tanque sobre o desempenho, metamorfose, coloração da pele e parâmetros bioquímicos de girinos de rã-touro americana (Aquarana catesbeiana)

Abstract

Research that investigates the impact of structural environmental enrichment on performance and welfare in captive animals is necessary to provide more ethical environments for animal production that promote welfare aligned with productive potential. In frog farming, the materials and structures used for tadpole rearing vary in color, often influencing costs and initial investment, with blue, white, and black being the most common. Due to its ability to distinguish colors, the American bullfrog (Aquarana catesbeiana) may show preferences for specific environments, which can affect comfort and development. Therefore, it is important to investigate the impact of environmental color on bullfrog development to assist in decision-making regarding production structure design. This study aimed to investigate the impact of environmental color on the growth performance, batch uniformity, metamorphosis time, and biochemical body parameters of bullfrog tadpoles. Six hundred tadpoles (0.94 ± 0.11 g – Gosner stage 25) were randomly distributed into 15 tanks (40 L; 1 tadpole L⁻¹) in a water recirculation system, with five replicates per color: blue, white, and black. Biometric evaluations were performed every 14 days. The animals were also assessed at the metamorphic climax and at the end of metamorphosis for growth performance, uniformity, and skin pigmentation. After completing metamorphosis, 24 individuals per treatment were randomly collected and euthanized, twelve were used for whole-body biochemical analyses and twelve for biological index determination. Tadpoles reared in blue and black tanks reached the metamorphic climax faster (median times of 81 and 80 days, respectively) and completed metamorphosis in a shorter period (97 and 96 days, respectively) compared to those reared in white tanks (85 days for climax and 104 days for completion). The time to complete the metamorphic climax was slightly longer in black tanks (13 days) than in blue and white tanks (12 days). According to regression analysis, there was a significant interaction between time and treatments for growth performance, with a greater increase over time in the final weight of tadpoles reared in blue tanks compared to those in white and black tanks. Significant interactions between days and treatment were also observed for weight gain, length, length gain, and protein efficiency ratio, showing improved performance for tadpoles in blue tanks compared to those in white tanks. The specific growth rate was about 1% lower in white tanks compared to blue ones. Feed conversion ratio increased over time with a significant interaction between time and rearing in white tanks, resulting in poorer feed conversion in that treatment. Tank color also influenced batch uniformity. Tadpoles reared in blue and black tanks showed lower weight variance than those in white tanks at 14 days (blue: 0.29, black: 0.27, white: 0.42), 42 days (blue: 7.58, black: 6.56, white: 9.47), 56 days (blue: 10.35, black: 8.40, white: 14.69), and 70 days (blue: 9.26, black: 8.45, white: 12.93). At 98 days, weight variance of tadpoles in black tanks (8.53) did not differ from those in white tanks (8.62), but both differed significantly from those in blue tanks (4.95). Skin pigmentation at the metamorphic climax and post-metamorphosis was also affected by tank color. Colorimetric analysis of skin L*a*b* coordinates showed lighter tones in tadpoles reared in white tanks compared to those in blue and black tanks. The mean of growth performance (body length, body weight, and weight uniformity of metamorphic climax tadpoles and newly metamorphosed froglets), and the mean of whole-body biochemistry parameters of newly metamorphosed froglets, were not affected by tank color. Therefore, considering homogeneity of growth performance and time to complete the metamorphosis, blue tanks represent the best choice for rearing American bullfrog tadpoles.