Larval and juvenile rearing of common sole (Solea solea L.) in the Northern Adriatic (Italy)

Abstract Research on the rearing cycle of the common sole, Solea solea , was done at an experimental hatchery in the Lagoon of Venice (Italy). The aim was to develop rearing schedules suitable for market production and document any technical problems. Larval metamorphosis studied on 9 groups of larvae reared at 18 °C demonstrated high temporal variability. Caudal metamorphosis and eye migration occurred between 9 days after hatching (DAH) and 24 DAH, and between 13 DAH and 25 DAH, respectively. A larval rearing schedule based on live-food feeding was set at 18–19 °C, which achieved an average survival rate of 40% at 28 DAH. Three weaning trials comparing two commercial feeds were carried out on larvae about 30 DAH. One of these feeds was sufficient in itself to complete juvenile weaning, reaching average survival rates of 85%, which are comparable to those obtained in the control groups fed with live Artemia . Average survival rates of 43% were obtained with the second commercial feed. Both commercial feeds enabled superior juvenile growth on average to that in the control groups. An on-growing trial in extensive conditions was done in an earthen pond of 370 m 2 , stocking juveniles with an average weight of 3.6 g at a density of 1.5 juveniles/m 2 . The trial started in mid-September and lasted until the following August, when it was stopped because of high mortality due to viral encephalopathy and retinopathy infections. Growth was negligible during winter and began again in spring, reaching the maximum incremental rate between May and June, at temperatures of between 20 and 25 °C. The specific growth rate never exceeded a daily value of 2%, while the average final size reached after 10 months rearing was 12 g. A double replicate trial of intensive rearing was carried out starting with soles of 7 g, reared at a density of 150 juveniles/m 2 in circular fibreglass tanks of 10 m 2 surface. This trial was also stopped during the following summer because of the considerable mortality due to viral infection. The soles had reached an average size of 54 g in August, after 300-day rearing. Sole can be bred and reared with good efficiency related to its survival rate, but the results of the growth trials, both intensive and extensive, do not allow conclusions to be made on the growth performance in the experimented conditions. The health problems compromised the growth trials towards the middle of the favourable growing season. The trials highlight both the high susceptibility of sole to viral encephalopathy and retinopathy infections, and the scarce tolerance of this species to temperatures of above 25 °C, which caused the onset of frequent bacterial infections.