Effects of pH and salinity on juvenile hatchery-reared red drum

Climate change with concomitant ocean acidification presents a problem to coastal ecosystems, including estuaries. It is well-documented that fish growth, development, and survival are dependent on environmental factors such as temperature and salinity. Considering the economic and recreational importance of red drum (Sciaenops ocellatus), it is important to understand both acute and long-term effects of environmental change on juveniles released into native waters as part of stock enhancement programs. Experiments were designed to compare survival, growth and body composition of juvenile red drum grown under different salinity and pH treatments.

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). Each trial was conducted for 14 days.

Results show 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); however, increased salinity significantly decreased growth (p< 0.05), and there was a significant interaction between pH and salinity. There was no significant impact from pH or salinity on protein retention (p≥0.05). At 40 the whole body ash increased as pH increased (p=0.003). Ash was also significantly different between pH values at salinity 30 (p=0.02). 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), and there was no significant interaction between pH and salinity affecting energy retention.

These results indicate that salinity is a more critical factor to consider than pH when engaging in stock enhancement efforts, especially at high salinity. The results of this study will help fisheries managers increase the rate of survival of hatchery-reared red drum when released into the wild. The results indicate that research should be conducted to investigate the effects of hypersalinity (>40) and pH on juvenile red drum as related to growth rates, and growth hormone production. Future research should also focus on the long term effects of low and high pH exposure of juveniles to adult life stages, and should examine otolith development, behavior and the effects on reproduction of red drum.

Norris B. J., 2016. Effects of pH and salinity on juvenile hatchery-reared red drum. MSc thesis, Texas A&M University, 58 p. Thesis (restricted access).

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