Natural vs laboratory conditions on the reproductive biology of common snook Centropomus undecimalis (Bloch, 1792)

As reproduction represents one of the main obstacles for common snook aquaculture, crucial aspects such as the effect of captivity need to be addressed. The aim of this study was to evaluate this effect under estuarine and sea water conditions on the common snook reproductive cycle by means of histological analysis and the assessment of sperm quality, sex hormones (testosterone, T and estradiol, E2) and calcium concentration in plasma. Results showed little effect of estuarine captivity as most fish gonads were observed in maturing and mature stages of development. These cellular observations coincided with T, E2 and calcium concentrations. T and E2 levels were higher than those previously reported for maturing and mature common snook (0.27 +/- 0.06-1.16 +/- 0.15 ng ml(-1) and 0.16 +/- 0.02-0.40 +/- 0.06 ng ml(-1) respectively). Peaks in calcium levels coincided with the peaks in salinity recorded for the two locations in April, August and September, while highest E2 concentrations were observed in the last two months. A drop in T under sea water conditions contrasted with the steady high levels observed under estuarine conditions. No differences were found between the two locations regarding sperm quality. Sea water conditions, however, had a positive effect on viability, morphology and motility index. Taking all the above into account, although common snook plasticity allows the species to be maintained in brackish or sea water conditions, our results suggest that broodstock should be kept above 35 ppt to ensure the best outcome in their reproductive cycle.