Luminous bacteria of a monocentrid fish (Monocentris japonicus) and two anomalopid fishes (Photoblepharon palpebratus and Kryptophanaron alfredi): population sizes and growth within the light organs, and rates of release into the seawater

Abstract

The light organs of monocentrid and anomalopid fishes consist of bacteria-filled tubular invaginations of the epidermis which are connected to the surrounding seawater by ducts. We used the release of bacteria from the light organs to estimate bacterial rates of growth in the light organs. For one monocentrid fish (4 specimens of Monocentris japonicus collected at Jogashima, Japan in 1980) and for two anomalopid fishes (2 specimens each of Photoblepharon palpebratus collected at Sebu, Phillipines in 1981 and Grand Comore Island in 1975 and Kryptophanaron alfredi collected at Parguera, Puerto Rico in 1982) we measured rates of release of bacteria into the surrounding seawater and the bacterial population sizes in the light organs; from this information we calculated doubling times of bacteria in the light organs. In addition, we determined the luminescence of bacteria after their release into the seawater. For M. japonicus, two specimens released 1.1 to 6×10⁶ and 2×10⁷ bacteria h⁻¹, respectively; the light organs contained about 1.5×10⁸ bacteria. For P. palpebratus, one specimen released 2.2×10⁸ bacteria h⁻¹; a second specimen had light organs containing 5.2×10⁹ bacteria. For K. alfredi, one specimen released 7×10⁷ bacteria h⁻¹ and had light organs containing 5.6×10⁸ bacteria; a second specimen released 3.6×10⁷ bacteria h⁻¹ and had light organs containing 7.3×10⁸ bacteria. Bacterial doubling times in the light organs of these three fishes were variable and ranged from 7.5 to 135 h in M. japonicus and 8 to 23 h in the anomalopids. Bacteria released from M. japonicus into the seawater remained viable, but bacteria from all of the fishes soon ceased to emit light.