Sense organs and their functions in Fish

The sensory systems of fish are crucial for their survival, enabling them to perceive and respond to their environment effectively. Fish rely on their senses of sight, smell, taste, hearing, and the mechanosensation provided by the lateral line system to navigate, locate prey, avoid predators, and communicate. Their eyes, with complex structures and visual pigments, allow them to perceive light, shapes, colors, and movements underwater, adapting to varying lighting conditions. The olfactory and gustatory systems detect chemical cues, helping fish find food, identify mates, and navigate. Specialized receptors and taste buds enhance their sensitivity to chemical stimuli. The lateral line system detects water movements, vibrations, and pressure changes, aiding in spatial orientation, predator avoidance, and prey detection. These integrated sensory systems enable fish to thrive in diverse aquatic habitats. Understanding fish sensory perception is vital for conservation, fisheries management, and aquaculture practices.

1. College of Fisheries Science Kamdhenu University Sub: Functional Physiology of Fishes (FRM 603) Submitted By Rajesh V. Chudasama, Reg. No. 231303002, Ph.D. (AQC), 1 st Sem. COF-VRL, KU. Submitted To Dr. H. L. Parmar, Assistant Professor, FRM Dept., COF-VRL, KU. 1

2. Sense Organs and Their Functions in Fish Hearing Mechanisms Optical System Lateral Line System Olfaction Taste Buds

3. 3 The highly specialized organs that receive physical and chemical stimuli from the environment and various body parts, and transform them into stimuli are called sense organs or sensory receptors. Closely associated with the nervous system. Physical Stimuli Change of heat Light intensity and quality Acoustical stimuli

4. 4 Functions of Sensory Organs Acquiring food (prey) Defending against predators Schooling with others of their own species

5. 5 HUMAN FISH Lungs Gills Stomach Stomach Liver Liver Kidneys Kidneys Ears Lateral Line, Otoliths Skin Scales & Slime Layer Nose Nares Arms Pectoral Fins Legs Pelvic Fins

6. 6 Hearing Mechanisms in Fish (Mechanosensation)

7. 7 Hearing in Fish: Fish rely heavily on their well-developed hearing system, crucial for detecting predators, prey, and mates in their aquatic environment. Underwater conditions affect their hearing, as sound travels faster and with reduced clarity compared to air.

8. 8 Hearing Mechanisms: Fish detect sound through specialized sensory organs like lateral lines, which sense pressure changes in the water, and otoliths (ear stones), which respond to sound vibrations. Some fish species, such as carp and herring, enhance their hearing by using their swim bladders to amplify sound waves.

9. 9 Carp Hearing: Carp possess a unique adaptation called the Weberian organ, which consists of specialized vertebral processes that transmit vibrations from the swim bladder to the inner ear. This adaptation significantly enhances their ability to detect subtle underwater vibrations and sounds.

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11. 11 Shark Hearing: While difficult to test directly, sharks are believed to have a keen sense of hearing. They have small openings on each side of their heads leading directly to their inner ears, allowing them to potentially detect prey from considerable distances by picking up low-frequency sounds.

12. 12 Anatomy of Fish Inner Ear: The inner ear in fish is critical for both hearing and maintaining balance. It consists of membranous sacs housed within chambers on either side of the fish's skull. These sacs include the pars superior with semicircular canals for balance and the utriculus, and the pars inferior containing the sacculus and lagena primarily responsible for hearing.

13. 13 Pars Superior: The pars superior of the inner ear includes three semicircular canals oriented in different planes (one vertical and two horizontal), along with their ampullae, which detect rotational movements and changes in head position. The utriculus detects linear accelerations and maintains equilibrium. Pars Inferior: The pars inferior includes the sacculus, which detects vertical movements, and the lagena, a small extension of the sacculus involved in hearing. Together, these structures play a crucial role in detecting sound vibrations and maintaining balance in fish.

14. 14 Inner Ear Functionality: The inner ear not only detects sound vibrations but also plays a vital role in maintaining the fish's balance and orientation in water. Otoliths, small calcareous structures within the inner ear, help fish perceive gravitational forces and movements, aiding in their navigation and spatial awareness.

15. 15 Comparative Anatomy and Physiology: The Weberian ossicles in some fish, like Ostariophysi, connect the swim bladder to the inner ear, enhancing their hearing sensitivity. Otoliths in bony fish are composed of calcium carbonate secreted by sensory cells and play a crucial role in detecting sound and maintaining balance. Neural impulses from hair cells in the inner ear transmit sensory information to the brain, triggering motor responses that help fish maintain stability and navigate their environment effectively. Water's higher density compared to air makes it a more efficient conductor of sound pressure waves, facilitating underwater communication and sensory perception in fish.

16. 16 The Optical System of Fishes

17. 17 Fish possess a complex optical system that is essential for their survival, aiding in navigation, foraging, and predator avoidance. This system consists of various structures and adaptations tailored to their underwater environment.

18. 18 Structure of Fish Eye

19. 19 A. Cornea: The cornea, situated at the front of the eye, is typically of constant thickness in teleosts . It consists of three layers: corneal epithelium, stroma, and endothelium. In most species, the cornea is transparent, allowing light to enter the eye. B. Sclerotic Layer: Surrounding the eyeball, the sclerotic layer provides structural support and toughness. In elasmobranches , this layer is supported by fibrous tissue, while in some species like Latimaria , it has a thick cartilage layer.

20. 20 C. Choroid or Reflecting Layer: Situated beneath the sclerotic layer, the choroid is highly vascularized. It contains a choroid gland that secretes oxygen to meet the metabolic demands of the retinal tissue. D. Iris: The iris, positioned between the cornea and lens, regulates the amount of light entering the eye. While some species have a fixed pupil, others, like elasmobranches , possess muscles to adjust pupil size.

21. 21 E. Lens: Located behind the iris, the lens focuses incoming light onto the retina. It is filled with aqueous humor and is transparent, composed primarily of non-collagenous protein. F. Adjustments in Lens Shape: Fish can adjust the shape of their lens to focus on objects at different distances without changing its shape.

22. 22 Retina and Visual Pigments The retina, lining the inner surface of the eye, is responsible for detecting light and converting it into neural signals. It consists of two main layers: A. Outer Granular Layer: Heavily pigmented layer containing rod and cone visual nerve cells. Rods are responsible for low-light vision, while cones contribute to color vision and daylight vision.

23. 23 B. Inner Less Pigmented Layer: Contains various types of nerve cells, including horizontal cells, bipolar cells, and amacrine cells. These cells facilitate the transmission of visual information to the optic nerve. Visual pigments, located in the outer segments of rods and cones, are crucial for light detection. These pigments consist of opsin proteins linked to vitamin A1 or A2 aldehyde and vary in their sensitivity to light.

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25. 25 Functioning of the Eye The fish eye operates through a series of complex processes: A. Vision Process: When light enters the eye, it stimulates the visual pigments in rods and cones. These pigments undergo chemical changes, which are converted into electrical impulses. Nerve cells transmit these impulses to the brain via the optic nerve, where they are interpreted as visual stimuli.

26. 26 Adaptations for Lighting Conditions: Fish eyes exhibit various adaptations to optimize vision in different lighting conditions. Retinomotor movements and melanin pigment redistribution regulate light exposure. Reflecting tapetum enhances low-light vision by reflecting light back through the retina.

27. 27 C. Refractive Index and Lens Function: Refraction primarily occurs in the lens, which varies in refractive index across its diameter. Lens movement allows for adjustments in focus, enabling fish to see objects at different distances without changing the lens shape. The optical system of fish is finely tuned to their aquatic habitat, providing them with essential visual capabilities for survival and navigation in diverse underwater environments.

28. 28 Lateral Line System

29. 29 The lateral line system is a unique sensory system found in fishes, integral to the acoustico lateralis system. It involves sensory lines distributed on the head and body, comprising the lateral line canal and neuromast organs. Structure of the Lateral Line Canal The lateral line canal exists as a continuous groove on the head and body, extending to the base of the caudal fin. It contains sensory receptors arranged in rows and follows the path of nerves. In some species, such as lung fishes, the canal may be partially roofed over by denticles, with pores opening on the skin surface.

30. 30 Development and Distribution of Lateral Line Canals During embryonic development, the lateral line canal differentiates as grooves along the longitudinal axis. The dorsal and ventral canals disappear later, leaving only the lateral canals in adults. Canals may terminate into branches in the head region or lose connection with trunk canals.

31. 31 Functionality of the Lateral Line System The lateral line system helps fishes sense sounds, vibrations, gravity, and water displacements. It responds to linear and angular accelerations of the fish's body, providing a sense of direction in three-dimensional space. Fish can detect objects through echolocation using reflected waves. Components include sensory lines, pit organs, and ampullae of Lorenzini .

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33. 33 Neuromast Organs and Sensory Cells Neuromasts develop as thickenings on the head, extending into definite lines along the body. Sensory areas develop from two types of cells: sensory and supporting cells. Neuromasts are receptors containing hair cells and cupulae , sensitive to movements of the watery endolymph fluid through canals.

34. 34 Hair cells in neuromasts continually send neural impulses to the brain, responding to cupulae flexion. Afferent nerve fibers carry information to the brain, while inhibitory efferent fibers switch off cells. Sensory fibers of the facial and vagus nerves innervate different parts of the lateral line system, joining with the auditory nerve in the medulla oblongata. Neural Impulses and Innervation

35. 35 The lateral line system detects both particle displacement and sound pressure. Near-field effects involve particle displacement close to the source, while far-field effects relate to sound pressure at a distance. Canal-based receptors offer protection from continuous water stimulation during rapid swimming, allowing detection of weak water displacements. Detection of Sound

36. 36 Olfaction (Smell)

37. 37 Anatomy of Olfactory Organs in Fish Fish possess a pair of oval-shaped olfactory rosettes located in a chamber on either side of the head. The olfactory rosettes are connected to the olfactory lobe of the brain via olfactory nerves. Lampreys and hagfish have a single chamber and single nostril, with variations in the structure of their olfactory organs.

38. 38 Structure of Olfactory Receptors Olfactory receptors are typically located in ciliated olfactory pits, which have incurrent and excurrent nostrils or channels divided by a flap of skin. Movement of cilia, muscular movement of the branchial pump, or swimming creates water flow into the olfactory pit, creating a pressure difference between incurrent and excurrent nostrils.

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40. 40 The olfactory sensory epithelium consists of four types of receptor cells: olfactory (receptor), supporting ( subtentacular ), basal, and mucous (secretory) cells. Sensory cells are uniformly distributed on both sides, with primary and secondary neurons distinguished. Basal cells give rise to other cell types and replace degenerating cells. Types of Olfactory Cells

41. 41 Olfactory receptor cell dendrites show intense alkaline phosphatase activity and less acid protease activity. Lipids are widely found in the olfactory epithelium. Mucous secreted by mucous cells contains mucin protein and acid mucopolysaccharides, forming a protective layer around sensory hair. Biochemical Composition and Functionality

42. 42 Olfactory stimuli are communicated to the olfactory lobe of the brain through the first cranial nerve. Carnivorous and predatory fishes generally possess a better olfactory sense than herbivorous fishes. Olfactory cues are crucial for migratory fish like salmon to locate their native streams. Olfactory Stimuli and Sensory Perception

43. 43 Taste Buds in Fish

44. 44 Gustatory sensory cells, or taste receptor cells, occur in clusters called taste buds in epidermal locations, including the oral cavity and lips. Taste buds are also found on the head, barbels, fins, and flanks in some species. Taste buds contain different cell types, such as tubular or light cells, based on morphology and staining affinity.

45. 45 Neuroanatomy and Neurotransmission in Taste Cells Taste buds are innervated by nerve endings, with neurotransmission likely involving ATP in teleost, elasmobranch, and lamprey taste cells. Serotonin, glutamate, and GABA are localized in some teleost taste cells, serving synaptic, paracrine, and autocrine functions. Cranial nerves innervating taste buds are multimodal, with sensory afferent and motor efferent fibers playing different roles in food search, ingestion, and palatability determination.

46. 46 Conclusion The sensory systems of fish are crucial for their survival, enabling them to perceive and respond to their environment effectively. Fish rely on their senses of sight, smell, taste, hearing, and the mechanosensation provided by the lateral line system to navigate, locate prey, avoid predators, and communicate. Their eyes, with complex structures and visual pigments, allow them to perceive light, shapes, colors , and movements underwater, adapting to varying lighting conditions. The olfactory and gustatory systems detect chemical cues, helping fish find food, identify mates, and navigate. Specialized receptors and taste buds enhance their sensitivity to chemical stimuli. The lateral line system detects water movements, vibrations, and pressure changes, aiding in spatial orientation, predator avoidance, and prey detection. These integrated sensory systems enable fish to thrive in diverse aquatic habitats. Understanding fish sensory perception is vital for conservation, fisheries management, and aquaculture practices.

47. 47 References Bone, Q., & Moore, R. (2008).  Biology of fishes . Taylor & Francis. Diana, J. S., & Höök, T. O. (2023).  Biology and ecology of fishes . John Wiley & Sons. Dijkgraaf , S. (1960). Hearing in bony fishes.  Proceedings of the Royal Society of London. Series B. Biological Sciences ,  152 (946), 51-54. Douglas, R., & Djamgoz , M. (2012).  The visual system of fish . Springer Science & Business Media. Hara, T. J. (Ed.). (2012).  Fish chemoreception  (Vol. 6). Springer Science & Business Media. Kasturi Samantaray , K. S. (2015).  Physiology of finfish and shellfish  (pp. 250-pp). Kasumyan , A. O. (2003). The lateral line in fish: structure, function, and role in behavior .  Journal of Ichthyology ,  43 (2), S175. Sloman , K. A., Balshine , S., & Wilson, R. W. (Eds.). (2005). Fish physiology: Behaviour and physiology of fish. Smith, L. S. (1982).  Introduction to fish physiology  (p. 352pp).

48. 48 Thank You !! rajesh.chudasamaa @gmail.com