Bioluminescent Bacteria and the Deep Sea Anglerfish

The anglerfish is referred to as one of the most bizarre looking marine species on earth, but I guess your appearance is not all that important in the dark. The deep sea anglers generally live below depths of which sunlight is incapable of penetrating, in the Atlantic and Antarctic oceans. There are over 200 species of anglerfish which belong to the order Lophiiformes, the majority of deep sea anglers share a symbiotic relationship with bioluminescent bacteria. Bioluminescence, meaning ‘living light’ is generated by specialised bacteria as a result of chemical reactions.

Figure 1.0 Deep Sea Anglerfish (Bufoceratias wedli). Photographer: N.J. Marshall (2010)

The female deep sea angler is equipped with an esca or ‘lure’ which is a modified dorsal fin filled with bioluminescent bacteria. The bacteria emit light from a chemical reaction known as the luciferin luciferase reaction; it utilizes oxygen to react with the lucerifin while luciferase acts as the catalyst. The reaction is so efficient there is almost no heat lost and results in a cold glow also know as cold light. The esca is not only an attractive device for prey but also for attracting a permanent male mate. The bacteria share a mutualistic relationship with the deep sea angler benefiting from the nutrient rich environment the angler provides in the esca, whilst the angler benefits by having an attractive, maneuverable appendage. The evolution of this relationship is not fully understood but is thought to have originated in early cretaceous period; in some species of angler, the bacteria are incapable of luminescence independent of the fish, whilst being species specific (Haygood and Distel, 1993).

Figure 2.0 The luciferin luciferase reaction. T.Wilson (2014)

The distending jaw and largely expandable stomach are characteristic of the Lophiiformes order, these increase their ability to feed on a large range of prey items, as meals can be far and in between. By visual analysis it can be depicted that these predators are not built for speed rather an ambush approach. When an unsuspecting meal is lured near the mouth of the angler, the female fish inhales pulling water and the prey into its large mouth trapping it with its large translucent teeth, the water is able to exit the fish via the gills leaving the prey to be swallowed. The anglers rely heavily on movement detection rather than on vision at such depths, extremely sensitive organs known as lateral lines detect movement and vibrations (Pietsch, 1972).   

These creatures exhibit sexual dimorphism which is a phenotypic difference in males and females of the same species. Male deep sea anglers are several magnitudes smaller in comparison to the female and seem to serve one purpose and that is to find a female and mate with her. He does this by permanently attaching himself to her becoming a parasite using her blood supply and nutrients. After he has attached himself enzymes are released by the males which dissolve his organs except the testes, which supply the female with sperm. The female can carry multiple parasitic males on herself at one time as a method of ensuring adequate sperm supply (Pietsch, 2005).

The evolutionary history of the deep sea angler is farm from understood as are many creatures that inhabit the depths of the oceans. Survival is by any means possible and the angler have certainly demonstrated that life is possible in very extreme environments.

Video with thanks to BBC Earth https://www.youtube.com/watch?v=UXl8F-eIoiM

References:

HAYGOOD, M. G. & DISTEL, D. L. 1993. Bioluminescent symbionts of flashlight fishes and deep-sea anglerfishes form unique lineages related to the genus Vibrio. Nature, 363, 154-156.

PIETSCH, T. W. 1972. A Review of the Monotypic Deep-Sea Anglerfish Family Centrophrynidae: Taxonomy, Distribution and Osteology. Copeia, 1972, 17-47.

PIETSCH, T. W. 2005. Dimorphism, parasitism, and sex revisited: modes of reproduction among deep-sea ceratioid anglerfishes (Teleostei: Lophiiformes). Ichthyological Research, 52, 207-236.

Figure 1.0 N.J. Marshall (2010) Deep Sea Anglerfish (Bufoceratias wedli). Accessed 13/04/2015 from http://australianmuseum.net.au/image/a-deepsea-anglerfish-bufoceratias-wedli

Figure 2.0  T. Wilson (2014). The luciferin luciferase reaction. Accessed 13/04/2015 from http://animals.howstuffworks.com/animal-facts/bioluminescence3.htm.