SURVIVAL AND HEMATOCRIT OF NET-CONFINED SUMMER FLOUNDER Paralichthys lethostigma: EFFECT OF SALINITY

Southern flounder (Paralichthys lethostigma) fingerlings are currently being produced and stocked in Texas bays for stock enhancement. Hatchery operations and stocking typically involved handling and transporting fish. This study assessed the ability of southern flounder fingerlings to tolerate net confinement in different salinities.

Twenty fish (9.8 + 0.58 g, mean + SD) were stocked into each of five 370-L recirculating systems. Salinities were adjusted to nominal 2 g/L (two systems), 12 g/L (one system), and 35 g/L (two systems). Temperatures averaged  25 + 0.4 C, pH ranged from 8.3 to 8.5. dissolved oxygen was > 5.7 mg/L, nitrite-N was < 0.1 mg/L, and total ammonia-N was <0.1 mg/L.

For one hour, fish were confined in a dip net, fully submerged, and over a stream of bubbles from an air stone. After the confinement period, fish were released into their original environments. Five fish were bled for hematocrit determination and removed from the study one day before the confinement, and daily for three days after the confinement.

All fish survived the confinement and three-day post-confinement period. Hematocrit averaged 25 over all sampling periods and was not affected by salinity (p=0.908). However, across all salinities, hematocrit decreased significantly (p=0.0049) over time with a pre-confinement average of 30 and an average of 24 three days after confinement. The basis for the reduction is not evident.

The results indicate that southern flounder can survive net confinement across a wide range of salinities. However, further work is needed to determine the extent, duration, and impact of the decreased hematocrits.

This project was supported by the State Wildlife Grant Program (TX T-115-1), a joint program between the US Fish & Wildlife Service and the Texas Parks & Wildlife Department.