Effects of photoperiod and temperature on kisspeptin1 (kiss1) expression in the gonads of Clarias batrachus.

Photo-thermal regulation of reproduction in seasonally breeding vertebrates, including teleost fishes, is established. The photo-thermal cues are relayed to the higher brain centers, where from command, neurosecretions are released to the hypothalamus to activate the hypothalamo-pituitary–gonadal axis to secrete GnRH-FSH/LH-sex steroids in general. GnRH being a pivotal regulator of reproduction, plenty of studies have been carried out to investigate the regulators of GnRH secretion. Kiss is the recently established upstream regulator of GnRH. However, studies on the regulation of kiss are highly ambiguous in vertebrates, including fishes. Therefore, attempts were made to examine the role of photoperiod and temperature in the regulation of kiss1 expression in the gonad during the late-quiescence phase of the reproductive cycle of the catfish, Clarias batrachus, employing the techniques like histology, immunohistochemistry, and enzyme-linked immunosorbent assay (ELISA) along with analysis of data through analysis of variance (ANOVA) followed by a post hoc test and Duncan's multiple range test at P < 0.05 for comparisons amongst different groups. The study reveals that long photoperiod and high temperature stimulate the expression of kiss1 significantly (P < 0.05), while short photoperiod and low temperature suppress its expression in fish gonads (P < 0.05). Photoperiod and temperature were almost equally effective in regulating the kiss1 expression, but when long photoperiod and temperature are given in combination, their stimulatory role in kiss1 expression is amplified significantly (P < 0.05). The long photoperiod and high temperature also increase the steroid levels in gonads (P < 0.05) and stimulate gametogenesis. [ABSTRACT FROM AUTHOR]