Seasonal expression of reproductive axis-related neuroendocrine genes and their relation with ovarian maturation in captive yellowtail kingfish (Seriola lalandi)

The yellowtail kingfish (Seriola lalandi) is a key species for the diversification of Chilean aquaculture. While controlled reproduction is essential for reliable fish production, the physiological and molecular bases underlying its reproductive cycle remain insufficiently explored. This study aimed to assess the expression patterns of brain-expressed neuroendocrine mRNAs involved in the activation of brain-pituitary-gonad (BPG) axis throughout different year seasons and to correlate them with ovarian maturation stages in S. lalandi females under captive conditions. Reproductive stages were determined by ovarian histology and gonadosomatic index (GSI) analysis. Expression levels of GnRH1 and GnRH2 genes (gnrh1 and gnrh2) as well as melatonin (mtn1ra), dopamine (drd2a), and kisspeptin (kiss1r) receptors were quantified by real time PCR in brain samples from adult individuals. Fish were maintained in temperature- and photoperiod-controlled tanks simulating the four seasons. Histological and GSI analyses identified four distinct reproductive stages. Gene expression peaked in winter and decreased in autumn, aligning with the seasonal progression of ovarian development. These results are consistent with the expected activation of the reproductive axis during the winter months in S. lalandi. Notably, the elevated expression of drd2a in winter suggests that modulation of GnRH action on pituitary function may not rely solely on dopaminergic inhibition. Taken together, our findings indicate that S. lalandi exhibits reproductive dynamics under captivity that mirror those of wild populations, supporting its use as a reliable model for studying reproductive physiology. Moreover, its responsiveness to environmental cues under controlled conditions enables the development of experimental strategies that would be logistically unfeasible in the wild.