Photo-thermal manipulations induce captive maturation and spawning in endangered golden mahseer (Tor putitora): A silver-lining in the strangled conservation efforts of decades

Present study was undertaken to explore the possibilities of inducing maturity and spawning of T. putitora under captivity through manipulation of environmental cues i.e. photoperiod and temperature. In experiment I, adult T. putitora were subjected to three photoperiod (8L:16D, 12L:12D and 16L:12D) regimes for 100 days. In females, darker photoperiod (8L:16D) significantly decreased the plasma estradiol levels compared to 12L:12D and 16L:8D photoperiods. Plasma 17α, 20β-diOH-P was significantly (p < .05) changed both in females as well as males due to different photoperiods. Highest level was observed at 12L:12D in females and 16L:8D in males whereas the lowest level was found in 8L:16D. There was no significant effect of photoperiod on plasma 11-ketotestosterone (11-KT) levels and gonado-somatic index (GSI) of both males and females. In experiment II, effect of temperature (ambient, 21.2 ± 1.4 °C and elevated, 23.7 ± 1.3 °C; Mean ± SD) on inducing maturity under captive conditions was explored. The level of 17β-estradiol and 17α, 20β-diOH-P was significantly increased in females kept at elevated temperature compared to its ambient counterpart. Correspondingly, GSI of females increased 6-fold at elevated temperature. In fact in the ovary of females reared at elevated temperature, oocytes were in vitellogenic and maturing stage, whereas it was only in cortical alveolar stages in the fishes kept at ambient temperature. On the other hand, there was no marked change found in testicular histology. However, there was presence of some macrophage aggregations on the efferent duct region of testes at elevated temperature. No significant (p > .05) effect of temperature was observed on plasma levels of 11-KT of both sexes. Experiment III was meant to explore the possibility of achieving captive spawning by simulating natural spawning ground using a gravel bed bio-filter. Natural spawning occurred after four months of rearing in the simulated facility. Subsequently, fishes further spawned seven times in a period of 4 months on an interval of 15–20 days. Overall, our results suggested that captive maturity and spawning of golden mahseer can be achieved by manipulating the environmental cues. The results solved the prevailing decadal issue of captive maturation of golden mahseer which otherwise has been a major bottleneck for its wide spread rehabilitation and conservation programmes.