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Abstract
The present investigation deals with the study of the olfactory organ of two freshwater fish, Liza ramada and Bagrus bayad, inhabiting different habitats, in order to explain the reflection of feeding habits on the anatomy and ultra-structure of their olfactory organ.
Liza ramada is an active pelagic fish feeds on planktonic organisms (planktonic feeder) in mid and surface water. It is considered as pelagic dwellers.
Bagrus bayad lives in deep water, spends nearly the whole day in the crevices (bottom dweller). It feeds on small bottom fishes and crustaceans as well as plant and animal detritus. So, it is considered as bottom feeder.
Studying the olfactory organ of the two species by using light, scanning and transmission electron microscopes reveals the following:
● It has been observed that, in Liza ramada and Bagrus bayad the olfactory organs are represented by a pair of olfactory chambers, open externally by two nostrils inlet and outlet. Each olfactory chamber is occupied by an olfactory rosette, which is oval in L. ramada and elongated in B. bayad .
● The olfactory rosette is composed of olfactory lamellae, the number of these lamellae in L. ramada is moderate in comparison to that of B. bayad which has a great number of lamellae. This means that the olfactory faculty of B. bayad is more well developed.
e general structure of the olfactory surface or the olfactory epithelium of each lamella in the two species studied, has been distinguished into sensory and non-sensory epithelia. The fine structure of each lamella reveals the presence of receptor, supporting, basal and mucous cell.
● The non-sensory epithelium in the two fishes under investigation is differentiated into glandular (peripheral) area and medial (ciliary) area.
● The glandular area of L. ramada and B. bayad is characterized by the presence of indifferent epithelial cells which bear microridges on their free surface. In L. ramada these microridges arrange themselves in a finger print-like pattern. Nonetheless, in B. bayad the indifferent epithelium not reveals these finger print-like projections.
● The ciliary medial area of the non-sensory epithelium is characterized by the presence of ciliated non-sensory cells designated as Type 1 ciliated cells. They are very dense in B. bayad but in L. ramada these cells are rarely distributed in random appearance. The ciliated non-sensory cells (Type 1 ciliated cells) are of respiratory functions, acts for ventilation and respiration.
● The basal bodies of the cell’s cilia are provided with striated rootlets which by contraction, the ciliary beating for ventilation may functioned in co-ordination or directional control .
● The olfactory sensory epithelium in the two species studied revealed the presence of three different types of sensory receptor cells:
A- Flagellated receptor cells which considered as Type 2 ciliated cells. The cilia of this cell type arise from an olfactory knob.
B- Microvillous receptor cells having microvilli arising also from an olfactory knob. This type of cells are more observed in L. ramada than in B. bayad.