1. Bony vs Cartilaginous Fish
Bony and cartilaginous fish differ not only in their gill and endoskeletal structure, but also in their response to meeting the challenges of an aquatic existence
kmle.co.kr

2. Why water aerobics are a great workout
Water is ~800 times denser than air, and 100 times more viscous
Impedes moving effectively at low speeds
Nekton have evolved special adaptations to efficiently move through the water column

3. The dynamics of swimming
To avoid sinking out of surface waters, fishes must increase their buoyancy or swim continually
Cartilaginous fish store various lipids in their liver and tissues, which are less dense than the surrounding seawater
Their cartilaginous skeletons are ~one half as dense as the skeletons of bony fishes

4. The dynamics of swimming
Most pelagic bony fish have air bladders to compensate for the relative heavy bony skeleton
Air bladders, or swim bladders are gas-filled floats which provide more buoyancy than the storage of body lipids
Found in pelagic, not benthic, fish
Why?

5. Air bladder
One major disadvantage: gas responds to changes in pressure by expanding and contracting
Modern fishes have a series of blood vessels and capillaries connected to the swim bladder which fill (and remove) air to control their buoyancy

6. Can someone give me a lift?
Another way to avoid sinking out of the pelagic zone is to employ dynamic lift
Sharks generate lift by their large, stiffened pectoral fins
Bernoulli’s principle: An increase in speed causes a decrease in pressure; water travels faster over the top of the fin creating a region of low pressure (lift)

7. How airplanes (and sharks) fly
Thrust is generated by engine
Lift provided by wing of the airplane
Air traveling over the wing is deflected upwards over the top surface and downwards beneath the lower surface; but because of the shape of the wing, air is deflected differently such that pressure is lower above the wing (air travels faster), generating lift

8. Sharks are really, really fly
The shape of a shark’s pectoral fins and their position relative to their body generates upward lift in the same way that planes do!
Requires constant forward motion (need thrust to generate lift)!

9. Just keep swimming, just keep swimming
Pelagic fishes usually have stream-lined shapes that make their propulsive efforts more effective
Reduces drag
torpedo shape most effective
Mahi mahi (dolphinfish)

10. Body shape
The body shape of a fish is directly related to its lifestyle
Fast swimmers like sharks and tuna have a streamlined body that help them slice through the water
Body shape can be especially useful for camouflage
An irregular shape can be an excellent means of concealment

11. Can you find the pygmy sea horse?

12. Finding Nemo…

13. Just keep swimming, just keep swimming
Fishes must swim to obtain food, find mates, and escape from predators
Most fish swim with a rhythmic side to side motion of the body or tail, produced by bands of muscles called myomeres
Make up to 75% of weight in active fishes

14. Just keep swimming, just keep swimming
Paired fins combined with a tail and a relatively inflexible body propel fish through the water

15. Swim class
Bony fish use their pectoral fins, not for lift, but rather maneuverability
They can brake, hover, and change position
The dorsal and anal fins act as rudders, and provide stability

16. Respiratory system of fishes
Fish obtain oxygen using paired gills
Gills are specialized extensions of tissue that ‘project’ into the water
Large surface area
High blood flow
Works by way of a counter current exchange system

17. Gills maximize gas diffusion
Gas exchange involves diffusion across membranes
The external environment must always be aqueous
Diffusion is passive; driven by the difference in O2 and CO2 on the two sides of the membrane
The rate of diffusion is governed by Fick’s law of diffusion

18. Fick’s Law of Diffusion
D = diffusion constant (molecule specific)
A = area over which diffusion occurs
Dp = pressure difference between two sides
d = distance over which diffusion occurs
Rate of diffusion =
D A Dp d
Maximized by increasing surface area, increasing the concentration difference, and decreasing the distance over which diffusion occurs

19. Gills maximize gas diffusion
Gills maximize gas exchange by consisting of many rows of thin plates or lamellae which increase surface area ( A) and contain capillaries ( d), along which counter-current gas exchange occurs
H20
( p)
Rate of diffusion =
D A Dp d

20. Countercurrent gas exchange

23. Gas exchange in fishes
Bony fish have four gill arches on each side of their heads
Each gill arch is composed of two rows of gill filaments, which consist of lamellae

24. Gas exchange in fishes
In contrast, cartilaginous fish have 5-7 pairs of gills
The first pair of gill slits is modified into a pair of spiracles

25. Gas exchange in fishes
Mobile fish (cartilaginous fishes and tunas, etc.) swim with their mouth open to continuously move water passed the gills; this is known as ram ventilation

26. Gas exchange in fishes
Most bony fish use pumping action (not ram) to ventilate; but many alternate between ram and pumping to move water across their gills

27. Gas exchange in fishes
Benthic sharks, skates, and rays pump water through their spiracles
Moves water over the gills while resting on the mouth
Important for rays and skates when buried

28. White meat or dark?
Hemoglobin in the blood carries oxygen through the fishes body; Muscles also contain myoglobin which can also store oxygen
Strong swimmers have a higher proportion of myoglobin and thus a higher proportion of red muscle, as opposed to white, which is used for short bursts of speed

29. The return of endothermy!!!
Some fish are “warm-blooded” in that they can increase the internal temperature of their body to one higher than the external environment
Counter-current heat exchange system
Body surface remains at water temperature; body core is elevated

30. Something smells fishy
Most fishes have a highly developed sense of smell which is used to detect food, mates, predators and sometimes to find their way home
Salmon memorize the sequence of smells on their way out to sea, so they may return to spawn
Sense of smell is particularly well-developed in the sharks
Can detect a drop of blood in concentrations less than one part per million

31. Sensory organs of fishes
Fishes have a unique sense organ called the lateral line that enables them to detect vibrations in the water
The lateral line consists of a system of small canals that run along the head and body
Lined with sensory cells, or neuromasts that are sensitive to vibration via clusters of hair
Allows fishes to avoid collisions and predators, detect prey, orient to currents, and maintain position in a school

32. Lateral Line of Fishes

33. Sensory organs of fishes
In addition to a lateral line, cartilaginous fish have sensory organs in the head known as ampullae of Lorenzini that can detect weak electrical fields
Helps locate prey, may also aid in navigation
caribbeansharks.com

34. You’re about to get schooled
Many fish form well-defined groups, or schools
Some, including herring, sardines, and some mackerels school throughout their lives
Schools function as well-organized units, with no known leader
The individual fish tend to keep a constant distance between themselves; turning, stopping and starting in near perfect unison

35. You just got schooled
Fish use vision, lateral line, scent and sound to keep track of one another and maintain unity
Protection against predators (safety in numbers)
Also aids in feeding, swimming, and finding mates

36. Reproduction and Life History
The sexes are usually separate in fishes, although a few marine fishes are hermaphroditic (both male and female)
Some hermaphrodites are simulataneous, simultaneously being both male and female, while others are sequential, beginning life as a male (or female) and changing into a female (or male)

37. Reproduction and Life History
Sex reversal occurs in several groups of marine fishes, but it is prevalent among sea basses and groupers, parrotfish, and wrasses
Makes the most sense to begin as male and become female; why?

38. Finding (the truth about) Nemo
Some species of anemone fish begin life as males; each anemone is inhabited by a single, large female that mates only with a large, dominant male
All the other fishes on the anemone are small, non-breeding males; when the female dies, her mate changes into a female and the largest of the non-breeding males becomes the new dominant male

39. Reproduction and Life History
Most fish reproduce via external fertilization where eggs and sperm are released, or broadcast into the water
Internal fertilization occurs mainly in cartilaginous fishes via male copulatory organs called claspers

40. There’s always a bigger fish…