Photophores in Stomiiform Fishes: Morphology, Distribution, and Putative Behavioral Roles

Bioluminescence is a common feature of the fishes inhabiting the dimly lit waters of the deep sea and is thought to play roles in prey attraction, predator avoidance, communication, and counterillumination. Stomiiformes, the most abundant and speciose order of deep-sea fishes, have a stunning variety of bioluminescent organs and tissues. While some of these structures have been well described, others are poorly characterized and rarely discussed in literature. Here we synthesize data in the literature on the four types of photophores found among stomiiforms (complex serial, complex minute, simple pigmented, and simple unpigmented photophores) and assess the size, density, and distribution of the little-known complex minute photophores, in particular, in 31 species in 25 stomiiform genera. The predicted orientation of light emitted from complex serial and minute photophores in 14 species in the stomiid subfamily Stomiinae was inferred from the placement of the lens (through which light is transmitted). Complex minute photophores were found, in addition to complex serial photophores, in all stomiines examined (and in one gonostomatid) and were notably smaller and occurred in higher densities than the complex serial photophores. The predicted ventral orientation of the light emitted by the complex serial photophores in all species presumably functions in counterillumination. However, the predicted direction of transmission of light produced by complex minute photophores appears to vary within and among species, suggesting multiple functions (e.g., camouflage and/or communication), warranting further studies of photophores in these intriguing and ecologically critical fishes.