Adaptation
One of the most striking features of all anglerfish is their
peculiar method of predation. Ironically this boney fish is
aptly named for its technique of fishing using the jig like
structure called the esca. For Ceratias holboelli the esca is
bioluminescent, production electromagnetic radiation throughout
the visible spectrum, but averaging from 470 nanometers to 490
nanometers. Colors of light can range from pink to purple,
including white, yellow, orange, yellow-green, blue and a
blue-green. It is the blue green light that gains the most
transmittance through deep oceanic water. Therefore organisms
that dwell in the deep ocean have developed eyes that are most
sensitive to this wavelength or turquoise color of light.
An important distinction is that Ceratias holboelli itself is
not bioluminescent, but rather the esca houses luminescent gram
negative non-endospore producing bacteria that exist in
symbiosis with the Krøyer's anglerfish. Recent research suggests
that these bioluminescent bacteria differ from species of
ceratioid, done by sequencing the 16s ribosomal RNA. For
holboelli the most common type of bacteria is vibrio harveyi,
which produces a range of light from 475 nanometers to 510
nanometers. It is currently unknown when or how the anglerfish
receives these symbionts. Most certainly from the environment
but how or why has eluded researchers thus far.
The esca is a highly specialized structure. Not only must the
esca house these bacteria and keep them thriving but it must
also control the intensity of light fluoresced. Since often the
light given off is not constant but rather a pulsating event,
lasting from around 1 second to up to 10-12 seconds, with
variation from individual to individual. One of the most
interesting observations of these bacteria is when they exist
out in the environment no luminescence is observed. Therefore
there must be an unknown x-factor produced by the anglerfish
allowing or perhaps causing the emission of light. It is
hypothesized that the control of escal luminescence is by
control the bacterial nutrients through the glandular body. This
is thought to be done by controlling the blood supply to the
esca, which delivers oxygen to the bacteria and are therefore
able to respire. Although outside of the esca these bacteria are
able to respire, yet unable to produce light. There must be
something key to the anglerfish granting light emission
capability to vibrio harveyi. This x-factor is thought be in the
secretions from the glandular body.
On the inside of the esca there is a photo-pigment that can
absorb light emitted from the bacteria, controlling what
wavelength of light is emitted from the esca. Interestingly
there is an absence of nervous integration in the glandular body
and therefore independent of nervous control. Nonetheless there
is certainly more to discovered of these fascinating creatures,
which are inherently difficult to observe due to the
environment
disconnect between us and Ceratias holboelli.