Fish Anatomical Features

Overview of Fish and Reptile Anatomy in Forensics

  • Discussion on focusing primarily on anatomical features relevant to forensic investigations.

Bony Fish vs. Cartilaginous Fish

Key Differences

  • Skeletons   - Bony fish have a stiffer skeleton reinforced by calcium salts.   - Cartilaginous fish have skeletons made of cartilage.

  • Senses   - Bony fish possess an excellent sense of smell, along with acute eyesight.

  • Buoyancy   - Bony fish utilize a swim bladder, a gas-filled organ that aids in buoyancy control.

Bony Fish Anatomy

Swim Bladder

  • A gas-filled chamber located under the bony skeleton.

  • Can have a connection with the digestive tract for oxygen extraction in some species.

Operculum

  • A flap on each side of the fish that covers the gill chambers, allowing breathing without swimming.

Other Notable Features

  • Fins   - Bony fish have paired fins and many teeth.   - The dermal scales cover the skin.   - Usually feature numerous vertebrae.   - Types of bony fish:
        - Ray-finned fish: Characterized by thin, flexible skeletal rays.     - Lobe-finned fish: Have muscular fins supported by bones; e.g., coelacanth.

Size Variation in Bony Fish

Smallest Species

  • The dwarf pygmy goby, with adult males reaching 15 mm and females 9 mm in length.

Largest Species

  • Oarfish: Reaches 11 meters (36 feet).

  • Ocean Sunfish (Mola Mola): Can reach 3.3 meters (10.8 feet) and weigh about 5,000 pounds.

  • Beluga Sturgeon: Can grow to 5 meters and weigh about 2,000 kg (4,000 pounds).

  • Black Marlin: Can grow to about 4.7 meters and weigh around 1,600 pounds.

  • European Catfish: Can reach 5 meters and weigh around 600 pounds.

Body Shape of Bony Fish

  • The typical body shape of bony fish is cylindrical, tapering at both ends, known as fusiform shape, which is energy-efficient for swimming.

  • Variations in body shape include:   - Compressively shaped   - Depressively shaped   - Elongated   - Laterally compressed   - Flattened

Fins in Bony Fish

Types of Fins

  • Paired Fins: Pectoral and pelvic fins.

  • Median Fins: Dorsal, caudal (tail), and anal fins.

Functions of Fins

  • Pectoral Fins   - Help in turning and, in some fish, they function to maintain perch on surfaces or assist in gliding.   - Mudskippers use them for support on land.   - Flying fish can glide using elongated pectoral fins, achieving distances of up to 150 meters and remaining airborne for 20 seconds.

  • Pelvic Fins   - Provide stability and can assist in swimming speed adjustment. Some species adapt these as sucking appendages.

  • Dorsal Fins   - Used for direction and stability, sometimes acting as lures or helping in movement.

  • Caudal Fins   - Main organ for propulsion, with variations in shape (e.g., forked, lunate) depending on swimming ability.

  • Anal Fins   - Add stability or aid in reproduction by distributing sperm over eggs.

Gills and Nostrils

Gills

  • Protected by the operculum; most bony fish have one pair of gill openings.

  • Eels possess gill pores or holes not covered by operculum.

Nostrils

  • Typically not connected to the mouth; configuration of nostrils can vary widely among species based on habitat and diet.

Mouth Size and Shape

  • Key indicators of feeding habits.

  • Varieties include:   - Mouths facing forward for general feeding.   - Bottom-feeders have mouths angled downwards.   - Surface feeders angle mouths upwards to capture prey.   - Species like butterfly fish have thin snouts for accessing food in crevices.

Internal Anatomy of Bony Fish

Skeletal System

  • Composed of bones and cartilage, including vertebral column, cranium, jaw, ribs, and intramuscular bones.

Muscles

  • Muscle arrangement called myotomes aids in movement, appearing zigzagged (similar to a sideways 'W').

Nervous System

  • Composed of three sections: forebrain (smell), midbrain (vision, learning), and hindbrain (coordination, balance).

Cardiovascular System

  • Contains a two-chamber heart (atrium and ventricle) and features like the sinus venosus and bulbous arteriosus.

Thermoregulation in Fish

  • Predominantly ectothermic, relying on environmental temperatures.

  • Some fish, notable tunas, can maintain elevated body temperatures using specialized circulatory systems that retain heat.

Digestive and Respiratory Systems

Digestive System

  • Esophagus is short but expandable, with gastric glands aiding digestion.

Respiratory System

  • Gills facilitate underwater breathing; not all fish rely solely on gills—some can absorb oxygen through their skin.

The Swim Bladder

  • E.g., Totoaba species; essential for buoyancy control, sound production, and has economic implications due to its medicinal use in traditional remedies.

Conservation Issues

  • The illegal fishing practices surrounding the Totoaba threaten both its population and other species, such as the vaquita, which is critically endangered.

  • Declining populations are linked to illegal practices despite protective measures in place.

Identification Features

Fins and Tail Shapes

  • Fins can have various configurations (spines vs. rays) and roles in swimming.

  • Tail shapes like heterocircle, proto circle, homocircle, and difa circle are essential for identification but can complicate forensic inquiries in processed fish (e.g. fillets).

Quiz Section

  • Assessment of fin and tail identification with answers provided in the continuation of the lecture.