COMPARATIVE STUDY ON THE STRUCTURE OF THE EYE AND OLFACTORY ORGAN IN TWO BONY FISHES IN RELATION TO THEIR FEEDING HABITS | ||||
| Egyptian Journal of Zoology | ||||
| Article 12, Volume 60, Issue 60, December 2013, Page 189-222 | ||||
| Document Type: Original Research Papers | ||||
| DOI: 10.12816/0003291 | ||||
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| Author | ||||
M. A. Salem 
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| Zoology Department, Faculty of Science, Zagazig University, Zagazig, Egypt | ||||
| Abstract | ||||
| The anatomy and structure of the eye and olfactory organ were investigated by means of light and electron (scanning and transmission) microscopes in two marine teleost fishes living in different habitats, Carangoides bajad (Carangidae) and the Epinephelus chlorostigma (Serranidae).This study revealed that, the Carangoides bajad seemed to be a microsmatic fish where the olfactory organ is poorly developed, and it can classify to the eye-nose fish where it depends on the vision in its habitat and thus possesses a well-developed eye as demonstrated by various structural features of its retina and cornea: 1) various types of photoreceptors with square mosaic pattern to increase the visual sensitivity or give acute vision, 2) well-developed pigment epithelium with tapetal spheres (tapetum lucidum), which act to increase retinal sensitivity by reflecting light back through the photoreceptor layer, 3) presence of an iridescent layer of the cornea that allows the fish to focus objects at different distances, and thereby increasing the field of vision, 4) presence of the retinomotor movement phenomenon, which reflects high sensitivity in dark and light adaptation between the photopic and scotopic states and therefore enables the fish to find their prey under light and dark conditions. Accordingly, the eye in Carangoides bajad seems to play an important role in fish habitat. In contrast, the Epinephelus chlorostigma seemed to be a macrosmatic fish where the olfactory organ is well developed, and it can classify to the nose-eye fish where it depends mainly on olfaction in its habitation and thus possesses a well-developed olfactory organ as demonstrated by various ultrastructural features of its olfactory rosette: 1) the olfactory rosette has an elongated rosette containing numerous olfactory lamellae that show behavioral responses to olfactory stimulation and thus increase the olfaction area of the olfactory organ, 2) presence of three distinct receptor cell types, i.e. ciliated, microvillous and rod cells, probably gives a wide range for food selection and/or detection of the prey or enemy location, 3) presence of a huge number of ciliated non-sensory cells, which may help in increasing the flow of water through the olfactory chamber, and accordingly increase the efficiency of the olfactory organ to acclimatize at the deep distances in water. The present results probably are the first attempt to describe the ultrastructure of the eye and the olfactory organ of the Carangoides bajad and Epinephelus chlorostigma. | ||||
| Keywords | ||||
| Bony fish; Cones; Feeding habits; Olfactory organ; retina; Rods | ||||
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