Occurrence of inflated swimbladders in five species of lanternfishes (family Myctophidae) from waters off southern California

The swimbladders of three species of myctophid fishes (Symbolophorus californiensis, Tarletonbeania crenularis and Diaphus theta, collected in the Southern California Bight between 1963 and 1978), previously observed to have both inflated and noninflated swimbladders as adults, were examined to determine if the swimbladders either vary in their inflation on a diel basis or cease to be inflated and possibly become nonfunctional in some individuals. The swimbladders of two lanternfishes reported to lack inflated swimbladders as adults (Lampanyctus regalis and L. ritteri) were included in the study for comparison. Only the swimbladder of L. regalis did not increase in size with increasing fish size. In the remaining four species, both the lengths and volumes of noninflated swimbladders were positively correlated with fish standard length (SL). Although the swimbladder continued to increase in size, inflated swimbladders were not found in L. ritteri>2 mm SL. Inflated and noninflated swimbladders occurred in overlapping size ranges of S. californiensis, T. crenularis, and D. theta. Only 11% of the D. theta swimbladders were inflated, and the occurrence of inflated swimbladders dit not differ significantly with day vs night capture or fish size. Although the frequency of occurrence of inflated swimbladders decreased significantly in larger S. californiensis, both S. californiensis and T. crenularis caught at the surface at night with a neuston net had significantly higher proportions of inflated swimbladders than did those collected below the surface with either daytime or night-time trawls. The swimbladder does not appear to become nonfunctional in either species. Rather than maintaining either constant volumes or constant masses of gas in their swimbladders during their vertical migrations, both species may inflate their swimbladders only while in the surface waters at night, and have noninflated swimbladders while at other depths of their vertical ranges.