Background: Catecholamines and cortisol are stress hormones in teleosts secreted, respectively, by the adrenal homologs, chromaffin and interrenal tissues. It is well known that the stress hormones respond to a variety of stress stimuli, induced or natural. There is a cross-talk between the stress and reproductive axis but the physiological implications are debated. It is believed that breeding activity stimulates the stress hormone axis and, if so, the stress hormone levels will be greater at peak reproductive stage comparable with the responses during stress. In the current study the hypothesis was tested.
Methods and findings: The stress hormones were measured in the head kidney of female catfish H. fossilis in different phases of the reproductive cycle (preparatory, pre-spawning, spawning, post-spawning and resting) and in fish exposed to confinement stress at various time points over 24 h duration. Catecholamines were identified and measured by gradient HPLC elution of head kidney (adrenal) samples in a C-18 reverse phased column with a fluorescence detector. Cortisol was measured using a specific ELISA kit. Epinephrine and norepinephrine levels increased significantly in gonad active phases (preparatory, pre-spawning phase and spawning phases). Epinephrine is the dominant catecholamine, about two-fold higher than NE. In contrast, dopamine and its metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) levels were higher in gonad-inactive phase (post-spawning and resting phases) and early recrudescence (preparatory phase) but lower in the pre-spawning and spawning phases. Cortisol level was low in gonad-inactive phase and early recrudescence but increased in the prespawning phase to reach the peak in the spawning phase. In the confinement stressed fish, the epinephrine level was elevated at 2 h, 4 h and 8 h with the peak rise at 4 h. The norepinephrine level registered a significant increase only at 4 h but the norepinephrine metabolite normetanephrine level decreased throughout. The dopamine level increased at 8 h with a decrease in the DOPAC level. Similarly, cortisol level increased significantly with the peak rise at 4 h.
Conclusion: Comparable changes occurred in the levels of the stress hormones epinephrine, norepinephrine and cortisol during the peak reproductive activity and during the confinement-stress and may be indicative of metabolic stress aimed at energy partitioning for reproduction and stress mitigation, respectively. Confinement stress may mimic high stocking density stress and is a critical ecological factor that needs management like water quality and diet.
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