Dietary 22:6n-3 alters gut and liver structure and behaviour in larval striped trumpeter (Latris lineata)

The effect of dietary 22:6n-3 on larval striped trumpeter growth, morphology, feed intake and behaviour was investigated. A dose-response technique was used. Seven experimental emulsions were formulated with increasing concentrations of 20:5n-3 and 22:6n-3 and used to enrich rotifers (Brachionus plicatilis). Enriched rotifer 22:6n-3 concentrations ranged from approximately 2 to 16 mg/g dry matter (DM). Enriched rotifers were fed to striped trumpeter larvae from 5 to 18 days post-hatch (dph). No relationship was identified between larval growth or survival and dietary 22:6n-3, nor was there any significant relationship between larval response to salinity and temperature challenges to dietary 22:6n-3. Larvae fed low dietary 22:6n-3 displayed erratic swimming behaviour, suggesting inferior quality larvae compared with those fed higher dietary 22:6n-3. A significant inverse relationship between the syndrome, 'grey gut', and dietary 22:6n-3 was found. Histologically, grey gut was associated with extensive vacuolation of enterocytes, probably lipid droplets, indicating a dietary imbalance of fatty acid resulting in abnormal lipid assimilation, transport and subsequent deposition. Similarly, hepatocytes of larvae fed low 22:6n-3 were also highly vacuolated in comparison with the compact liver tissue of larvae fed high dietary 22:6n-3. Data suggests that striped trumpeter larvae benefit from the inclusion of dietary 22:6n-3, and failure to provide it above a minimum threshold can result in behavioural differences and problems in lipid assimilation and transport. Our study demonstrates that larval nutrient requirement studies can benefit from the use of dose-response techniques commonly used in larger fish.