jawwed fishes day 5

Overview of the Digestive System in Fish

  • Introduction to The Digestive System

    • Discusses the importance of understanding the digestive tract in relation to various species.

  • Teeth and Dentition

    • Teeth are numerous and vary in location.

    • Often thought to be aligned along the jawline, but vary significantly in many vertebrates.

    • Locations of teeth can include:

      • Roof of the mouth

      • Tongue

    • Acrodont Dentition

    • Refers to teeth attached directly to the surface, not seated in bony sockets as human teeth are.

    • Indicates that teeth are lost regularly and replaced continuously.

      • Example: Sharks lose teeth when feeding but have them replaced constantly.

    • Polygonal Teeth

    • Many sets of teeth developed over a lifetime due to continual replacement.

    • Thecodont Dentition

    • Rare in fish; teeth are seated in bony sockets.

      • Example species involve sheep's head and Pacu fishes.

    • Shark tooth structure:

    • Diagram of a shark's jaw illustrates the conveyor belt system of tooth growth.

    • Functional teeth emerge from the gum line, peak, and fall out when feeding.

  • Digestive Pathways

    • Standard organs in sharks:

    • Food enters through the mouth to the pharynx.

    • Gills equipped with gill rakers guide food to the esophagus.

    • The stomach is enlarged relative to other organs, producing enzymes for digestion.

    • Spiral Intestine

      • Contains a spiral valve that maximizes nutrient absorption during digestion.

      • Efficient design leads to nutrient uptake without excessive length of the intestine.

    • Bony Fish Differentiation

    • Similarities to sharks but with key differences:

      • Presence of pyloric caeca, pouches producing specialized enzymes for breaking down fat.

      • Longer intestine enabling better nutrient absorption in contrast to sharks.

      • Waste exits through rectum to anus, separated in many species.

    • Dietary Implications

    • Bony fish demonstrate varied diets; many assimilate fat differently due to specialized structures.

    • Herbivorous fish tend to have longer digestive systems due to complexity of plant matter.

  • Swim Bladder

    • Functions primarily for buoyancy control, evolving eventually into lungs in terrestrial vertebrates:

    • Hydrostatic organ that allows fish to regulate air volume for depth control in water.

    • Essential for vertical positioning; especially important for those residing in still waters.

    • Types of Swim Bladders:

    1. Physostomous

      • Primitive swim bladder connected to the digestive tract (e.g., climbing perches).

      • Allows filling from air gulped at the water surface.

    2. Physoclistous

      • Highly evolved, lacks direct digestive connection.

      • Capillaries surrounding the swim bladder allow gas diffusion for buoyancy adjustment.

      • Common among species residing at greater depths.

    • Note that cartilaginous fishes lack swim bladders and rely on oil-filled livers for buoyancy.

  • Shark Physiology

    • Cartilaginous fishes utilize oil (from the liver) for buoyancy as they do not possess a swim bladder.

  • Brain Structure and Function

    • The shark brain exhibits structures of significance:

    • Olfactory Bulbs and Lobes:

      • Extensively developed for strong olfactory senses, crucial for survival.

    • Cerebrum:

      • Responsible for basic cognitive functions; less developed than in advanced vertebrates.

    • Cerebellum:

      • Vital for body orientation, especially underwater.

    • Medulla Oblongata:

      • Acts as a connection to the spinal cord, responsible for basic life functions.

  • Comparative Fish Brain Structures

    • Differences in olfactory and optic development between cartilaginous and bony fish.

    • Presence of the Pineal Organ:

    • Acts as a light detector, significant for migration and reproductive behaviors.

  • Vision in Fish

    • Differences in eyesight capabilities between marine and freshwater species.

    • Eye Structure:

    • Bony fish have round, spherical lenses, limiting depth of focus as opposed to humans.

    • Varied adaptations notable in different environments (e.g., clearer marine vs. murky freshwater).

  • Lateral Line System

    • Purpose: detects water movements and pressure changes via neural mast cells.

    • Enhances coordination, especially in shoaling fish; inter-fish communication through movements detected chemically.

  • Hearing in Fish

    • Internal ears with connection to the swim bladder; vibrations transmit to brain for processing.

  • Taste in Fish

    • Gustatory cells located throughout the mouth, fins, and whiskers enhance bottom feeder capabilities.

  • Excretory System

    • Contrasts in marine species (sharks vs. bony fish):

    • Sharks manage salt balance through specialized rectal glands, removing excess salt at the end of the digestive tract.

    • Nitrogenous waste primarily expelled as ammonia in various fish species, potentially polluting surrounding waters.