Suckermouth catfish live in freshwater with
fast-flowing water. Usually, fishes that live in this type of habitat face two
major challenges which are the insufficient of suction feeding to extract food
and another one is the requirement to have a strong and continuous swimming
capacity. Suckermouth catfish has evolved the most intense adaptations. It has
a ventral sucker-like mouth and ventrally directed jaws [1].
A sucker mouth catfish body part carries many potential impacts on the local
fauna. Many researchers have carried out research on it’s taxonomy until now. There
are three main parts of the body which will be discussed in this post; mouth,
skin (scale) and eyes.
Mouth
The suckermouth of the suckermouth catfish functions
for inspirations, feeding and attachment to substrates. A proper functioning
suction device needs sucker without leakage and continuous subambient pressure
in the sucker cavity. High-speed external and X-ray recordings show that
suckermouth attachment influences respiratory parameters such as decreasing
excursion amplitudes of mouth floor elements, and the way water enters the
mouth via furrows in the lip disc. Respiration, however, continues during attachment
and is not blocked. Data show that the muscular oral
valve actively separates the post-valvular buccal cavity from the pre-valvular
sucker cavity. Volume changes of this pre-valvular cavity are opposite to those
of the post-valvular cavity and assure sucker function even during expiration
which occurs via gill slits [2].
This
type of fish is well known as to be able to respire during suction attachment
in which many species of fish do during a substantial proportion of their daily
activities. Regan et al. first assumed that flow would be bidirectional via the gill
slits. On the other hand, Hora et al. stated that the lips could not form a true
sucker. Another researcher found that there are muscles acting on the oral
valve [2].
The lip openings during inspiration and the suction attachment are observed in
Figure 1.
 |
| Figure 1. Lip openings and suction attachment of a suckermouth catfish |
(A)
and (B) shows the change in pre-vulvular cavity volume. (A) shows maximal hyoid
depression where as (B) shows maximal hyoid elevation. The pre-valvular cavity
in (A) is small. In (B) it is enlarged. (C) and (D) show the changing of the
suction cup. (E) shows the infolding lower lip during strong sucker attachment.
(F) illustrates the lateral lip furrow mediated by the movement of the barbell [2].
Skin (scale)
Suckermouth catfish is so unique that the body is made up of rough
skin surface which increases the friction simultaneously reduces drag with its
streamlined body profile [3].It has a smooth skin texture under its head and
belly surfaces and appears dark brown with various pale gray to whitish spots.
The dorsal is pale brown with dark to blackish bars crossing is body with
minimum three dots. A special characteristic of the sucker mouth catfish is the
armor, covering a huge part of the body, formed by dermal bone plate’s .The adult’s
maximum length is 13-15cm [2].The catfish has the ability to reduce drag force
which is similar as a shark’s skin. Upon investigation, structure called micro-riblets
was discovered, when aligned in the local flow direction, aid in the drag
reduction of the shark hence enabling the shark to be one of the fastest fish
in the sea .The micro-riblets functions in a way where it will reduce wall
shear stress by altering the distribution of the flow field. Based on this
discovery by scientist, it has since been widely applied at aircrafts and space
shuttle as it will reduce drag forces experienced by the aircrafts and ships
while moving through medium such as air or water. Hence, less power will be
needed by both transportation methods and energy could be saved.
Eyes
Most land vertebrates have an active pupil that it will change sizes in response to changes of retina illumination. This is in contrast to the situation in fish whereby the pupil, it take minutes to open and close. For a suckermouth catfish, the shape and size of its pupil is dynamic and based on the amount of available light. It possesses a special kind of iris that at times looks a lot like the Omega symbol Ω. During night time, or in dark areas the iris contracts and more light enters the pupil. In the daytime or underneath the bright lights of an aquarium the iris may expand until the iris looks more like the omega symbol.
The retina composes of single cones and large rods. Cones, the other type of vision cells, discriminate colors in daylight. Although behavioral experiments to determine a catfish’s ability to see color haven’t been done, the characteristics of their cones indicate that they discern colors. Besides, it also have a tapetum lucidum which may help enhance photon capture and increase low-light sensitivity. This is surprising, as catfish often inhabit low-light-level environments and might therefore be expected to have retinae ‘designed for sensitivity’ [4]. Figure 2 shows the omega iris of the suckermouth catfish.
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| Figure 2. The omega iris that adjust the amount of light that enters the eyes |
References:
[1] Geerinckx, T.
& Kegel, B. De, 2014. faunas. , (April), pp.197–208.
[2] T. Geerinckx, A.
Herrel and D. Adriaens, "Suckermouth armored catfish resolve the paradox
of simultaneous respiration and suction attachment: a kinematic study of
Pterygoplichthys disjunctivus", Journal of Experimental Zoology Part A:
Ecological Genetics and Physiology, vol. 315, no. 3, pp. 121-131, 2010.
[3] The Online Guide to the Animals of Trinidad
and Tobago. (2015). Loricariidae (Suckermouth Armoured Catfish). [online]
Available at: https://sta.uwi.edu/fst/lifesciences/documents/Ancistrus_maracasae.pdf
[Accessed 11 May 2016].
[4] R. H. Douglas, “The eyes of suckermouth
armoured catfish (Loricariidae, subfamily Hypostomus): pupil response,
lenticular longitudinal spherical aberration and retinal topography,” The
Journal of Experimental Biology , pp. 3425–3433, Aug. 2002.
