Variation of Photoperiod Regime during the American Bullfrog Tadpole Stage: Influence on Growth and Metamorphosis

In culture of the American bullfrog Lithobates catesbeiana, photoperiod is a crucial factor affecting productivity success. Here, the objective was to determine the effect of three photoperiods (high light [HL] = 12 h light [L] : 12 h dark [D]; medium light [ML] = 10 h L : 14 h D; low light [LL] = 8 h L : 16 h D) with different application times on the performance of bullfrog tadpoles. Tadpoles at Gosner stage 25 were subjected to seven different treatments: the HL photoperiod for 90 d (HL90; control); ML for 45 d followed by HL for 45 d (ML45–HL45); LL for 45 d followed by HL for 45 d (LL45–HL45); ML for 60 d followed by HL for 30 d (ML60–HL30); LL for 60 d followed by HL for 30 d (LL60–HL30); LL for 30 d followed by ML and HL, each for 30 d (LL30–ML30–HL30); and ML for 30 d followed by LL and HL, each for 30 d (ML30–LL30–HL30). Response variables included growth, survival rate, feed conversion ratio, protein efficiency ratio, and metamorphosis rate. Likewise, the concentrations of thyroid hormones were established as explanatory variables. The results suggested that by implementing the ML60–HL30 treatment, a higher productive performance was obtained (growth [mean ± SD] = 7,318 ± 0.01 g; survival = 89.33 ± 1.7%; metamorphosis rate = 92.7 ± 1.1%) in relation to HL90 (growth = 7,027 ± 0.02 g; survival = 81.67 ± 2.05%; metamorphosis rate = 90.4 ± 1.7%). The information allows consideration of changes in bullfrog culture, establishing management plans inherent to the exposure times of the different photoperiods in order to obtain the highest performance.