Steroidogenic landscape and pronounced inter-female variability in Murray cod (Maccullochella peelii): Implications...

In this study, we investigated the role of steroid hormones in regulating oocyte maturation in farmed Murray cod (Maccullochella peelii) under targeted photothermal manipulation. The plasma levels of nine steroid hormones were quantified across two photothermal regimes (advanced vs. control), which differed in initiation timing by one-month, using liquid chromatography coupled with triple quadrupole mass spectrometry (LC-TQMS). We found that 17α,20β-dihydroxy-4-pregnen-3-one (DHP) was a key maturation-inducing steroid (MIS), showing an eightfold increase (P < 0.001) following human chorionic gonadotropin (hCG) administration. The advanced photothermal regime successfully induced non-seasonal oocyte maturation, achieving a hatching success (27 ± 22%) comparable to that of the control group (37 ± 34%; P > 0.05). Consistent with this similar hatching success, there was no significant difference in the profiles of measured steroid hormones between the two groups, indicating that photothermal manipulation maintained overall steroidogenic homeostasis. In both groups, significant inter-female variability of steroid profiles (coefficient of variation: 41-256%) was observed, suggesting marked oocyte developmental asynchrony independent of environmental treatment. While targeted photothermal cues can effectively induce oocyte maturation without disrupting steroidogenic homeostasis, their successful translation into aquaculture depends on precision broodstock management addressing marked inter-female variability in steroid profiles.