jawed fishes day 2

Overview of Fish Scales

  • Fish scales provide several functional benefits, including strength and flexibility.

  • Two primary types of fish scales discussed: cycloid scales and tenoid scales.

Cosmoid Scales

  • thick, hard scales

  • little flexibility

  • lobe finned fish have these

Paloid Scales

  • projects from the surface with a spine extending posteriorly

  • tooth like

    • shark teeth are modified placoid scales

  • sand paper like texture

  • sharks and rays

Ganoid Scales

  • Rhomboidal shape

  • bony texture

  • brick-like arrangement

  • primitive bony fish

Cycloid Scales

  • Definition: Scale types characterized by a circular or elliptical shape, although not perfectly circular.

  • Structure: Only the outer edge of the scale is exposed, while the rest overlaps with the scales in front (anterior).

  • Orientation: Exposed portion always faces towards the tail; this orientation reduces friction when swimming through water.

Tenoid Scales

  • Definition: Similar to cycloid scales, but with a somewhat squared-off shape.

  • Unique Features: The exposed edges have small projections known as "teni," which resemble serrations.

  • Research Insight: The evolutionary purpose of tinnae is still uncertain; however, they are helpful for identifying fish types.

Scale Types in Relation to Fish Evolution

  • Fish scale types can indicate evolutionary history and relationships among species.

  • Cycloid and tenoid scales are predominant in modern fish families, whereas older types like cosmoid and ganoid scales are found in ancient fish species.

  • Example: Strong swimming fish like tuna and marlin typically have embedded scales to minimize friction and maximize speed.

Identification Through Scales

  • Fish scales can aid in identification of specific fish species and their families.

  • Examples of fish with specific scale types:

    • Tenoid Scales: Found in perch and sunfish.

    • Cycloid Scales: Common in carp and minnows.

Fish Anatomy and Physiology

Functions of Fish Scales

  • Protection: Scales protect fish from predators and pathogens in the water.

  • Trade-off: Scales can hinder flexibility and speed, leading to evolutionary adaptations depending on fish habitat and behavior.

    • Example: Scalless fish like catfish benefit from increased maneuverability in bottom-dwelling environments.

Aging Fish Through Scales

  • Fish scales contain concentric rings which can provide information about the age of the fish.

  • Variation by Species: Not all rings correspond to a single year; the number of rings that equate to a year varies by species.

    • Example: Bass may have 3-4 rings per year while carp may have a different number.

Lack of Scales in Fish

  • Some fish species, like catfish, do not possess scales and instead have thicker skin and more mucus for protection.

  • Other species, such as swordfish and marlin, exhibit embedded scales that are not easily visible.

Chromatophores and Coloration in Fish

Types of Chromatophores

  • Melanophores: Produce dark tones (blacks, browns, grays) that are prevalent in many fish.

  • Lipophores: Contain yellow and warm colors (yellows, oranges, reds) due to fatty pigments.

  • Cyanophores: Produce cooler spectrum colors, predominantly blues and greens.

  • Iridophores: Responsible for iridescence by reflecting surrounding light rather than containing pigments.

Color Change Mechanisms in Fish

Effects of Breeding Seasons

  • Fish can change colors rapidly during breeding for attraction or to signal fertility.

  • Two primary mechanisms:

    1. Change in shape of pigment cells.

    2. Redistribution of pigment molecules within cells.

Photophores and Bioluminescence

  • Photophores: Specialized cells that produce organic light, found in certain fish and used for communication, predation, and camouflage.

    • Involves the enzyme luciferase, responsible for the visible light emitted by organisms like fireflies.

Fish Fins

Types of Fins

  • Median (Unpaired) Fins:

    • Dorsal fins (anterior and posterior).

    • Anal fins.

    • Adipose fins (small, fleshy fin found in some species).

  • Paired Fins:

    • Pectoral fins (located behind the gills).

    • Pelvic fins (paired, lower on the body).

Functions of Fins

  • Fins serve multiple purposes including stabilization, steering, and propulsion.

  • Variations in fin shape, size, and position assist in fish identification.

Evolutionary Considerations in Fin Structure

  • Different fish species have varying adaptations and modifications of fins that serve specific ecological needs.

  • Importance of identifying traits: Certain fins may indicate relation to extinct or less common fish families.

Additional Notes

  • The presence or type of scales has no direct correlation with fish body shape; ancient scale types (e.g., cosmoid, ganoid) often indicate evolutionary branching rather than functional adaptations.

  • Notable example: Sharks possess unique cladoid scales that diverged from common scale development.

  • Special notes on specific fish populations (e.g., local species in Illinois) as discussed will help enhance identification skills during field studies.