THE MOUTH AND GASTROINTESTINAL TRACT OF POMADASYS JUBELINI
A LOOK INTO THE MOUTH AND GASTRO-INTESTINAL TRACT OF THE SOMPAT GRUNT, POMADASYS JUBELINI
The Gastrointestinal tract (GIT) is also known as the digestive tract, as with all animals digestion in fish involves the breakdown of eaten food into its smaller component parts, which can then be used to build up new fish body.
All fish eat and defecate, like all animals the fish's body is basically a long tube that is twisted up on itself a bit in the middle and has a layer of muscles and ancillary organs around it. This tube has the mouth at one end and the cloaca at the other. Mostly we consider the mouth to be the entrance to the tube and the anus to be the exit, food items come in and faeces go out. Different things happen in different parts of the tube. The mouth takes in or brings food into the body with the help of jaws, tongue and modified teeth. The tongue of fish is generally very simple, being a thick, horny and immovably pad in the lower jaw which may often be decorated with small teeth.
Pomadasysspecies belong to the Order Perciformes, family Haemulidae. Pomadasys jubelini is commonly called the Sompat grunt.
Pomadasys jubelini is identified by its oblong compressed body with large ctenoid scales, which are rough to feel and denticulate. The head is slightly convex and covered by scales, except the snout and chin region. It has a small terminal mouth with thick protactile lips.The preopercule is moderately serrated.
Pomadasys jubelini is of high economic and nutritive value and in high demand in the coastal cities of Nigeria. Pomadasys jubelini has promising aqua-cultural potential, its domestication can be made possible by the proper understanding of its biology moreso,making the management and maximum utilization of this economically important fish species viable.
Pomadasys jubelini has a terminal mouth which is wide and protractile, with scales around it. The snout is pointed and elongated
The mouth of Pomadasys jubelini
The mouth opens as wide as 20% of its total length. This allows the fish to seize its prey easily. It also has a tongue which arises as a fold from the floor of the buccal cavity. There are no teeth on the tongue.
The presence of the multi-serial bands of setiform teeth enables the fish to grip its prey firmly in the mouth for suffocation before swallowing
The gape mouth of Pomadasys jubelini
The teeth of the upper jaw are premaxillary (teeth present in the front margin of the upper jaw)
The upper jaw of P. jubelini exhibiting premaxillary teeth (arrow).
while the lower jaw has teeth arranged in a mandibular position (teeth present on the margin of the lower jaw).
The lower jaw of P. jubelini exhibiting mandibular teeth.
Teeth are also present on the pharyngeal bones at the back of the mouth (in the throat) on the ventral and dorsal surfaces.
The ventral surface is made up of a pair of pharyngeal teeth. These teeth are in the form of smooth pebbles adapted for crushing bone, shells and crustaceans before swallowing.
The pharyngeal teeth (arrow) of P. jubelini as situated in the pharynx.
The lower pharyngeal band of teeth is triangular in shape
The upper pharyngeal teeth of P. jubelini
The gills are made up of four arches on each of the left and right sides (a total of 8). The gill arch is thick and cartilaginous and has thick, long, sparsely arranged spiky gill rakers (18).This confirms that P. jubelini is carnivorous. The gills are also a tool used for identification of fish species. The shape, size, length and no of gill rackers and filaments are key items used.
One gill arch of Pomadasys jubelini
The gut of P. jubelini is made up of a large, long and distensible oesophagus which leads directly into the stomach. The length of the gut of a fish species is related and modified to accommodate its feeding habit.
The long and distensible oesophagus is characteristic of carnivorous and predatory fish species. The stomach is large, thick–walled, flask-like and elongated with the anterior part (intestinal bulb) larger than the posterior. The intestinal bulb is meant for storage and reduced at the posterior part. Generally, the thick-wall of the flask-shaped stomach aids in masticating food. The duodenum is slim and leads to the pyloric caeca. The pyloric caeca is the anterior part of the intestine which gives rise to a number of finger-like, tubular outgrowths (6-7). The number and shape of caeca might be peculiar to this species and it is used as one of the structures for its identification, it also serves as accessory food reservoirs and may also play an important role of secreting enzymes for food digestion and absorption. The number of pyloric caeca varies from species to species. For example, only a single caecum is found in Polypterus while up to a hundred are found in mackerel.
The intestine is not distinguished into small and large, it is short, about 50% of the total length of the fish and it is not coiled, which is known to be common to carnivores.
The rectum is much slimmer than the intestine and ends in the cloaca of the fish.
The gastrointestinal tract of Pomadasys jubelini.
O, Oesophagus; S, Stomach; D, Duodenum; PC, Pyloric Caeca; I, Intestine; R, Rectum; C, Cloaca
Agbugui, M. O., Oniye, S. J., Auta, J., and Bolorunduro, P.I. (2016). Gastro-Intestinal tract of Pomadasys jubelini (Cuvier, 1830) in the New Calabar-Bonny River, Rivers State, Nigeria. International Journal of Scientific and Engineering Research, 7(10): 1086 - 1105
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Ugwumba, A.A. and Ugwumba, O.A. (2007). Food and Feeding Ecology of Fishes in Nigeria. JodetanVentures. Ibadan. (70pp).