THE ZOOGEOGRAPHY AND DIETARY INDUCTION OF BIOLUMINESCENCE IN THE MIDSHIPMAN FISH,PORICHTHYS NOTATUS

Abstract

Non-luminous northern midshipman fish, members of the species Porichthys notatus, are shown to exist as two disjunct populations, one previously known from the Puget Sound area, and the other in waters near San Francisco, where nearly half of the fish collected are non-luminescent or exhibit diminished luminescent capacity. The San Francisco population represents the northernmost occurrence of the southern Porichthys notatus population, in which non-luminescent fish are rare or absent. Between the San Francisco and Puget Sound populations a zone between Capes Flattery and Mendicino appears to completely lack midshipman fish in near-shore waters. The distribution of the luminescent ostracod, Vargula tsujii, corresponds to that of the luminescent southern fish in that its northermost extension is in the Monterey-San Francisco region. Northern, non-luminescent midshipman fish are rendered luminescent by feeding with Vargula tsujii. Feeding with seven other luminescent organisms that might contribute to the Porichthys diet did not induce luminescence in northern Porichthys. The presence of ultraviolet-excited, 524-nm photophore fluorescence was strongly correlated with luminescence capability in both natural populations and experimentally fed fish. Northern midshipman fish in which luminescence capability was induced by feeding Vargula were shown to still posses a behavioral luminescence control system indistinguishable from normally luminescent fish. The bearing of these observations on the origin of bioluminescence and its significance in the life of the midshipman fish are discussed.