STRESS RESPONSIVENESS OF THE PITUITARY-INTERRENAL AXIS DURING EARLY-LIFE STAGES OF COMMON CARP (CYPRINUS-CARPIO)

Whole-body levels of ACTH, alpha-MSH and cortisol in eggs and larvae o f the common carp (Cyprinus carpio) were determined periodically up un til 168 h after fertilisation. ACTH, alpha-MSH and cortisol immunoreac tivity was detected in unfertilised eggs, and endogenous production of ACTH and alpha-MSH was observed 24 h after fertilisation and that of cortisol 36 h after fertilisation. ACTH immunoreactivity reached peak levels before hatching (56-72 h after fertilisation) and remained rela tively stable thereafter, while alpha-MSH immunoreactivity started to increase after hatching. At 36 h after fertilisation, whole-body corti sol levels increased rapidly reaching peak levels at the end of hatchi ng (72 h after fertilisation), remaining stable until the end of the e xperiment. From 50 h after fertilisation onwards, embryos and larvae i ncreased their whole-body cortisol levels when subjected to handling ( mechanical pressure during egg stage or netting during the larval stag e). It is concluded that the pituitary-interrenal axis in carp is full y functional at the time of hatching. No indications of a stress non-r esponsive period after hatching were observed. To characterise ACTH an d alpha-MSH immunoreactivities in carp larvae, whole-body homogenates were analysed by HPLC, with pituitary homogenates of adult carp servin g as a reference. ACTH and alpha-MSH immunoreactivity in carp larvae h omogenates consisted of three and two products respectively. HPLC of a dult carp pituitaries revealed the presence of two ACTH immunoreactive products, which may represent a phosphorylated and a non-phosphorylat ed ACTH variant, while the three alpha-MSH peaks most likely represent des-acetylated, mono-acetylated and di-acetylated alpha-MSH, the latt er being the predominant form. In carp larvae, however, one of the ACT H immunoreactive products co-eluted with the non-phosphorylated ACTH, while the two alpha-MSH products identified co-eluted with des-acetyla ted and mono-acetylated alpha-MSH, indicating that POMC processing at this stage of development is different from prohormone processing in a dult fish.