EFFECTS OF pH AND SALINITY ON JUVENILE HATCHERY-REARED RED DRUM Sciaenops ocellatus  

Red Drum (Sciaenops ocellatus) is a recreationally and economically important fish that is the subject of stock enhancement. Consideration must be given to differences in pH and salinity between the rearing facility and the location for release of juvenile red drum into the wild.  Research was conducted in a closed recirculating system with juvenile red drum (42±9.9 mm) randomly stocked at a density of 13 fish/tank and fed daily to satiation (~6% body weight). Fish were subjected to salinity treatments of 40 or 30 and a pH of either7.5, 8.1, 8.5, or 9.0 (n = 8 replicates per treatment), for a trial duration of 14 days. Results showed that at a salinity of 40, there was a significant difference between survival of the juvenile red drum at pH 7.5 and 9.0 (p=0.03).  Survival was not significant between pH levels at salinity of 30.  Results indicated pH had no significant effect on specific growth rate (SGR, p ≥ 0.05) of experimental fish; however, increased salinity significantly decreased growth (p< 0.05), and there was a significant interaction between pH and salinity.  There was no significant effect from pH or salinity on protein retention (p≥0.05). At a salinity of 40, whole body ash content increased as pH increased (p=0.003). Whole body energy was not significantly affected by pH (p ≥ 0.05); but increased salinity caused a significant decrease in energy retention (p < 0.05), with no significant interaction between pH and salinity. These results indicate that salinity is a more critical factor to consider than pH when stocking fish into diverse bodies of water, especially under  high salinity conditions.  The results of this study will help fisheries managers increase the rate of survival of hatchery-reared red drum when released into the wild.  These results also suggest that research should be conducted to investigate the effects of hypersalinity (>40) and pH on growth of juvenile red drum.