Salinity tolerance and nursing performance under different densities in spotted scat Scatophagus argus Linnaeus, 1766

Spotted scat Scatophagus argus is a euryhaline species generally nursed in brackish water and shipped to freshwater ponds or sea cages of local farms in Thailand. To find the best practice for this process in terms of survival and cost, we conducted two culture experiments. In experiment 1, spotted scat fries (up to 6.72 +/- 2.15 g) were divided into 5 size classes (S1-S5), and their survival rates were determined after 4 patterns of salinity changes [from 0 to 30 parts per thousand (ppt), from 0 to 15 ppt, and vice versa]. The survival rates were not significantly different between groups when fries were transferred from or to 15 ppt water. However, smaller fries (S1-S3) presented lower survival rates than larger fries (S4 and S5) when transferred from 0 to 30 ppt. In experiment 2, fries (0.21 +/- 0.05 g) were nursed at three densities (125, 250, and 500 fish/m(3)) using underground water without water changes for 80 days. The 125 and 250 fish/m(3) groups showed similar culture performance, suggesting that the nursing density can be up to 250 fish/m(3) under these conditions. These results provide empirical data for establishing the best nursery practice of spotted scat, which will be particularly useful for small-scale farmers.