Unexpected lower testosterone in faster growing farmed saltwater crocodile (Crocodylus porosus) hatchlings

• We measured testosterone and estradiol in farmed crocodiles over three samplings.
• First ever reporting of plasma sex steroid levels in saltwater crocodiles.
• Baseline corticosterone had no effect on sex steroids.
• Testosterone levels were higher in slower growing individuals.
• Results should provide foundation for future behavioral and physiological research.

Agricultural production of the saltwater crocodile (Crocodylus porosus) is an emergent industry in northern Australia with many of the factors affecting production remaining unknown. In this study, we sought to expand upon our previous findings of reference corticosterone and immune function by reporting baseline sex hormone levels [testosterone (TEST) and estradiol (ESTR)] and their association with growth. This was achieved by sampling 253 hatchling crocodiles repeatedly at 3, 6, and 9 months of age. Sampling age had a significant effect on both TEST (p < 0.001) and ESTR (p < 0.001) suggesting climatic/abiotic factors have an influence even in prepubescent crocodiles. Stress, as measured by plasma corticosterone, had no detectable effect on plasma ESTR or TEST levels. Unexpectedly however, TEST was higher in slower-growing crocodiles, which is contrary to what has been reported for the American alligator. ESTR was not associated with growth.