Plasma cortisol is the most commonly used indicator of stress in fish but, as the blood sampling procedure itself can be a source of stress, it would be helpful to measure cortisol using less invasive matrices. It is also necessary to find alternative matrices as stress indicators in dead fish in which blood sampling is impossible. In the present study, we investigated transport stress in three aquaculture species, European sea bass (Dicentrarchus labrax L.), common carp (Cyprinus carpio L.) and rainbow trout (Oncorhynchus mykiss Walbaum), by cortisol determination (radioimmunoassay) in plasma and other matrices (skin mucus, gut content, lateral muscle and caudal fin). Cortisol significantly increased after transport in all species and matrices, except in the sea bass gut content, where it remained unchanged. The three species responded to transport stress by producing different cortisol levels. In conclusion, the significant correlation found between plasma cortisol and most of the other matrices opens up the possibility of using them to evaluate stress in fish: mucus sampling is a less invasive method than blood sampling, and in addition to muscle and fin sampling, it can be used in postmortem fish.

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In general little is known about hormones and the ontogeny of the stress response in the early developmental stages of chondrostean fishes and in particular of white sturgeon (Acipenser transmontanus, Richardson 1836). In this study, we measured for the first time cortisol and sex steroids (testosterone and estradiol) in eggs, larvae, post-larvae,\ud and fry of white sturgeon by radioimmunoassay (RIA), to elucidate some endocrine aspects of its development. The cortisol, testosterone, and 17b-estradiol of maternal origin found in unfertilized eggs of white sturgeon probably regulate both growth and development of the\ud embryo. Cortisol decreased after fertilization, whereas testosterone and 17b-estradiol did not significantly change. During the late stages of embryo development and immediately after hatching, endogenous production of cortisol and sexual steroids, respectively, occurred. Sex steroids may be physiological inducers of gonad sex differentiation in sturgeon. All steroids showed an increase 10 days post-hatch (dph), near the transition\ud from an endogenous to an exogenous energy source. Cortisol maintained the same basal levels even after metamorphosis, whereas testosterone and 17b-estradiol declined significantly in post-larvae at 35 and 45 days post-hatch. In addition, to evaluate the ontogeny of\ud a functional hypothalamic-pituitary-interrenal (HPI) axis, larvae and fry were submitted to acute stress. The HPI axis did not seem to be functional on the first day post-hatch, but\ud became so from the third day post-hatch onward

Stress indicators (plasma cortisol, glucose and lactate) were evaluated in sea bass Dicentrarchus labrax submitted to different pre-slaughter conditions, and cortisol levels in plasma were found to correlate with those detected in mucus, gut contents and muscle. The results demonstrate new possibilities for monitoring stress status in fishes in which blood sampling is difficult or impossible.

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