Buoyancy control and diel changes in swim-bladder volume in cultured striped trumpeter (Latris lineata) larvae

Body density, swim-bladder volume, buoyant force and feeding in relation to growth, photoperiod and light intensity were investigated in cultured striped trumpeter larvae. Prior to initial swim-bladder inflation, body density was negative during both the light and dark phases, regulated on a diel cycle from 1.0275 to 1.0290 g cm-3 (seawater: 1.0265 g cm-3). After initial swim-bladder inflation, body density decreased markedly during the dark phase as swim-bladder volume increased on a diel cycle. Downward buoyant force from dry matter increased with age and was compensated for by increasing relative swim-bladder volume. Greatest difference in body density between light (1.0260 g cm-3) and dark phase (1.0245 g cm-3) was when larvae were from 6.5 to 7.5 mm (standard length) (seawater: 1.0260 g cm -3). Density of larvae without a functional swim bladder was always greater than larvae with a functional swim bladder, and the former had reduced growth. Diel buoyancy control exhibited by striped trumpeter larvae with low amplitude changes in swim-bladder volume is similar to other transient physostomes. Mortality events previously observed in striped trumpeter culture are possibly related to negative buoyancy before first feeding and positive buoyancy during the dark phase following initial swim-bladder inflation. © CSIRO 2005.