Growth and survival of post-larvae of sole ( Solea senegalensis) in net cages at the bottom of earthen ponds

Abstract

The growth of 1 month old juvenile sole, Solea senegalensis, was monitored 6 months in net cages placed at the bottom of earthen ponds in commercial fish farms in the Tagus and Sado estuaries (Portugal). The post-larvae were stocked at a density of 50/m 2. Cages of two different sizes (2 and 6 m 2) were used to protect the post-larvae from predators and to facilitate the monitoring of fish growth and survival over time without significant changes in environmental pond conditions. The specific growth rates ranged from 1.30% in 7 month juveniles to 3.18% per day in 2 month old juveniles. The survival rates presented some variability (65% ± 26%), sometimes as much as 90% or 99%. After 7 months sole juveniles attained an average length of 11.78 ± 2.26 cm and an estimated weight of 13.98 g. Sole of this weight are tolerant to abrupt changes in environmental conditions (temperature and water turbidity) and can escape from predators. The cages used proved to be very effective in preventing natural predation in the ponds and, at the same time, allowed the development of natural prey suitable for sole juveniles. These results show that it is possible to raise 1 month old sole, in cages set in earthen ponds, fed upon natural prey, thus overcoming one of the main constraints of the life cycle of this species: survival of post-larvae.