Mechanism for initial swim bladder inflation in larvae of greater amberjack Seriola dumerili inferred from larval rearing experiments and ontogenetic development of a swim bladder

¹Department of Marine Biosciences, Tokyo University of Marine Science and Technology, Minato, Tokyo 108-8477, ²Kamiura Laboratory, National Research Institute of Aquaculture, Fisheries Research Agency, Saiki, Oita 879-2602, ³Shibushi Laboratory, National Research Institute of Aquaculture, Fisheries Research Agency, Shibushi, Kagoshima 899-7101, ⁴Yaeyama Laboratory, Seikai National Fisheries Research Institute, Fisheries Research Agency, Ishigaki, Okinawa 907-0451, ⁵Komame Laboratory, National Research Institute of Aquaculture, Fisheries Research Agency, Ootsuki, Kochi 788-0315, ⁶Seikai National Fisheries Research Institute, Fisheries Research Agency, Tairamachi, Nagasaki 851-2213, Japan

To understand the mechanism of the initial swim bladder inflation of greater amberjack Seriola dumerili larvae, we reared larvae from two days after hatching (DAH) in tanks in which the water surface was sealed with liquid paraffin. This treatment prevented the larvae from access to air through the water surface. Furthermore, we examined the ontogenetic development of larval swim bladders. Percentages of larvae with inflated swim bladders were very low in tanks with the sealed water surface compared with those in the tanks in which the oil film was removed from the water surface. A swim bladder was formed as a protuberance from an upper portion of the intestine. A pneumatic duct which connected the swim bladder to the intestine was observed in larvae of 3 DAH. The pneumatic duct was obstructed and separated from the swim bladder in larvae of 5 DAH. Our experiments revealed that a mouth-opened larva of greater amberjack inflates its swim bladder by gaping air from the water surface and introducing it into the swim bladder through the pneumatic duct from 3 to 4 DAH.

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