Fish Adaptations

Fish Adaptations

Otolith age calculation

  • The otolith is the ear part of the fish, which reveals how old the fish is

  • At the 9th ring, we measure the length from the ring to the nucleus as 6cm. The image is magnified. The otolith is not really 6cm, but the relative proportions are what matters. The relationship between the growth in one year on the otolith is proportional to the growth of the actual fish in one year.

What is the adaptive advantage?

  • How does it aid survival and/or reproduction so the genes for that trait are passed onto future generations?

Scales

  • Cycloid

    • salmon

  • Ctenoid

    • bass

  • Ganoid

    • gar

    • armor-like, hard to be eaten with teeth

  • Placoid

    • shark

    • reduces drag, helps it travel faster through water

How does each kind protect the fish?

  • protection from predators, being eaten

Adipose eyelid (in shad and herring, Clupeid)

  • Eyelid anatomy

    • found in layers

    • may cover more than the eye

  • There are 4 theories on the eyelid’s purpose:

    1. Increasing focus

    2. Increasing perception of polarized light

    3. Decreasing effect of ultraviolet light

    4. Physical barrier against objects

Adipose fin

  • Fleshy fin between dorsal and caudal fins of catfish, trout and salmon

  • Early hypothesis:

    • thought fin stored fat (adipose tissue), but studies have now shown that while fleshy, it doesn’t actually contain nutritional fat

    • Have evolved independently more than once, which suggests an adaptive advantage, but what is it?

Shoaling and schooling

  • Shoaling: when fish group together (feeding or mating)

  • Schooling: when fish swim together in a coordinated fashion

  • Adaptive advantage:

    • Predators cannot get all of them if they are in a group

    • Foraging: all benefit from what a group member finds to eat

    • Mating: mates are close to each other

Pharyngeal teeth

  • Pharyngeal teeth are opposing patches of teeth that occur in the upper and lower elements of the gill arches

  • Some species of fish that have pharyngeal teeth are:

    • Cyprinids, suckers, goldfish, loaches

  • Adaptive advantage

    • crushing things with hard shells like crustaceans

Barbels

  • Slender, whisker-like projections

  • Location on Fish

    • can be found on a variety of spots on the head, usually surrounding the mouth

    • Can be found on carp, catfish, goatfish, hagfish, sturgeon, and some sharks (saw-shark)

  • Usually on bottom-feeders

  • Adaptive advantage: Sensory, taste buds

External fertilization (Broadcast spawning)

  • When sperm fertilize eggs outside of an organism

  • examples: almost all fish

  • Adaptive advantage: no need to track down a mate in the wide ocean, more chances for fish to survive, promotes genetic diversity, low energy expenditure

Protandry and Protogyny

  • Sequential hermaphroditism

  • Protandry: fish change from male to female

  • Protogyny: fish that change from female to male during life

  • Adaptive advantage: fish can still reproduce if there are two of the same gender around, if females can reproduce asexually then the male can change to female and still reproduce

Nest Building

  • Common Nest Types:

    • pit diggers (sunfish)

    • cave spawners (cichlids)

    • mound-builders (chumbs)

    • borrowers (catfish)

  • Adaptive advantage: camouflage into the surrounding habitat, disguise from predators, courting to show fitness, declare territory to others, place for eggs to attach when no parental care

Countercurrent exchange

  • When a fish swims, water flows past its gills in the opposite direction of the blood flow

Shark Claspers

  • Specialized extension of the pelvic fin (only in males)

  • designed to deliver sperm inside of a female, inserted into the female’s cloaca to help channel the sperm delivery

  • Present in sharks, skates, and rays

  • Allows for internal fertilization

  • Higher chance of viability, higher chance that that individual is the parent.

Swim Bladder Respiration

  • Some fish can utilize atmospheric O2 when aquatic O2 levels unsuitable (gar, bowfin)

  • Allows for survival is areas unsuitable for other fish

Vivipary

  • Some sharks

  • Seahorses

  • Some perch and guppies

  • Greater protection for developing young