Annual changes in brain concentration of arginine vasotocin and isotocin correspond with phases of reproductive cycle in round goby, Neogobius melanostomus

Abstract

Reproductive cycle of seasonally breeding fish is synchronized with changes of photoperiod and temperature in environment. We hypothesize that arginine vasotocin (AVT) and isotocin (IT) are involved in timing and synchronization of seasonal reproductive activity in the round goby (Neogobius melanostomus). To verify this hypothesis, we examined the annual profiles of brain AVT and IT in round goby males and females in relation to their reproductive cycle. Wild round gobies were exposed to annual environmental changes in their natural habitats from where they were sampled monthly over a year. AVT and IT were measured using HPLC with fluorescence detection preceded by solid-phase extraction. This study shows seasonal variations in brain AVT and IT levels. Profiles of changes were similar in males and females: the peak of AVT was observed before spawning in March-April, whereas that of IT during spawning in May–June. Furthermore, the lowest AVT level was noted out of breeding season from November to January, while the level of IT decreased immediately at the end of the spawning. The results show that high AVT levels correlate with pre-spawning period whereas the highest IT levels correspond to spawning. A significant decline in AVT and IT in non-spawning season coincided with the quiescent phase of gametogenesis in both sexes.

• Circadian rhythmicity
• fish
• gametogenesis
• neurohypophyseal peptides
• photoperiod
• reproductive cycle
• spawning
• temperature
• time-keeping system

ACKNOWLEDGEMENTS

The authors would like to thank Dr. Katarzyna Smolarz from the Institute of Oceanography, University of Gdańsk, Gdynia, Poland for the opportunity to take pictures of histological slides.

DECLARATION OF INTEREST

This study was financially supported by the National Science Centre grant no. N N304 260740 and Institute of Oceanology of the Polish Academy of Sciences (statutory research task IV.2.1 to E. Sokołowska). The authors report no conflicts of interests. The authors alone are responsible for the content and writing of this article.