Literature Review

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.

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.