1. Anatomy, Physiology, and Ecology of Fishes I Biology of Fishes 10. 18

2. Overview Exam I – Return & Review next week
Presentations & Other Assignments
Introduction to Anatomy, Physiology, and Ecology of Fishes

3. Anatomy, Physiology, and Ecology
Buoyancy and Locomotion
Swimming
Feeding Mechanisms

4. Buoyancy and Locomotion
Movement in water
Water ~800x denser than air
High density provides upward force – force buoyancy
Buoyancy – major force supporting a fish
Typical mean density of a fish carcass = 1075 kg/m3
Density of freshwater = 1000 kg/m3
Density of saltwater = 1025 kg/m3

5. Buoyancy and Locomotion
Weight of fish slightly greater than buoyancy force – fish must produce an upward force or life force that overcomes the downward pull of gravity not compensated for by buoyancy of water
Mechanisms for generating lift
Hydrodynamic lift
Hydrostatic lift

6. Buoyancy and Locomotion
Hydrodynamic lift
Achieved using pectoral fins like airplane wings – generate lift as fish swims; thrust applied via caudal fin
Most common method for supporting weight of fish in water
Also used by fishes that regulate buoyancy in other ways
Costs increase as speed decreases – primarily due to increases in drag
Examples
Sharks, tunas, mackerels (fast-swimming teleosts)

7. Hydrodynamic Lift

8. Buoyancy and Locomotion
Hydrostatic lift
Achieved by storing light or low-density materials in the body – same mechanism as in submarines, hot air balloons, blimps
These materials include gas, lipids, and low-density fluids
Gas
Contained within the swim bladder – gas-filled sack just under spinal column
Recall characteristic of bony fishes is presence of lungs
Lung in primitive actinopterygians
evolved into swim bladder

9. Hydrostatic Lift Gas – contained in the swim bladder
Physostomous – bladder-gut connection – can gulp or burp air (primitive condition)
Physoclistous – bladder is sealed – must secrete into or diffuse gas out (Paracanthopterygii and Acanthopterygii)
Gas provides greatest amount of hydrostatic life per unit volume, but presents a few problems
Unstable in roll – fish can easily tip side to side
Gas changes volume with pressure; pressure increases with depth (1 atm pressure for every 10 m depth). Fish must continuously add or remove gas to remain neutrally buoyant if fish changes depths.
Doesn’t respond quickly to changes in position

10. Gas Bladder
Most fishes have gas/swim bladders, but some have lost them in favor of other strategies – benthic life, lipids, low-density fluids.

11. Hydrostatic Lift Lipid (fats, oils, related molecules)
Found in livers of sharks and in the swim bladder wall, skeleton, dermis, and muscle of other fishes
Most common in deep water fishes that live near the bottom; also mid water fishes that make large vertical migrations

12. Hydrostatic Lift Low-density fluids
Water content of the fish is increased, bones are reduced, decreases the density of body fluids and tissues
Only possible for marine fishes
Found in deep water fishes

13. Buoyancy and Locomotion
Trade-offs of various buoyancy mechanisms
Swimming speed
Hydrodynamic lift is more economical at higher swimming speeds – cost of drag increases at low speeds, also harder to steer (maintain position) at slow speeds
Hydrostatic lift is more economical at slow swimming speeds
Gas is cheaper than lipids
Depth
Gas becomes expensive at large depths – high pressure makes it costly to fill, difficult to prevent diffusion into blood
Exceptions to trends – adaptations to specific habitats
Sculpins, darters, etc.

14. Swimming
Recall density of fish is close to density of water – therefore fish do not have to use their skeletons and muscles to support themselves (in contrast to terrestrial organisms).
As a result, all fins and the body can be used for locomotion.
To swim, fish must generate thrust and overcome sources of resistance (drag, inertia).

15. Swimming Types of swimming (6 primary forms) Anguilliform locomotion
Subcarangiform locomotion
Carangiform locomotion
Thunniform locomotion
Ostraciiform locomotion
Median or paired fins

16. Swimming Anguilliform Locomotion – “eel like”
Successive waves of muscle contraction passed backward on alternate sides of body – throws body into series of S-shaped curves
Amplitude increases toward tail
Body wave pushes mass of water backward – inertia of water
Nearly all of body participates in undulatory, side-to-side motion
Inefficient mode of swimming – body is long, most of body (especially anterior) participates. Tail wags the head, therefore high drag

17. Swimming Anguilliform Locomotion – “eel like”
Considered primitive mode of swimming – seen in hagfish, lamprey, many sharks
Also seen in some more advanced groups such as eels
Mode also used by many larval fishes – flexible skeleton is poorly developed, other muscles and fins aren’t yet available for use

18. Swimming
Most fishes do not swim using anguilliform locomotion – most are “tail waggers”
Instead of using most of the body to push against water for forward propulsion, most fishes rely on a much smaller portion
If smaller portion of body undulates, side-to-side movement of head is reduced
Reduction of side-to-side movement also accomplished by tapering of the body towards tail; large forward body mass increases inertia, making side- to-side movement difficult
Evolutionary trend away from anguilliform, instead towards more caudal type propulsion found in most bony fishes

19. Swimming

20. Swimming Subcarangiform Locomotion
Two-thirds to one-half of the body is involved in producing the propulsive wave responsible for forward motion
Side-to-side movement of head greatly reduced compared to anguilliform
Fish using this method typically have large flexible caudal fins
Most of swimming is accomplished by the waves passing down the body
Caudal fin probably evolved for use in fast turning, hovering, and fast starts
Examples: trout, salmon, minnows, cods

21. Swimming Carangiform Locomotion
Side-to-side undulations are confined to the last third of the body
Fish using this method typically have stiff caudal fins that are deeply forked with elongated upper and lower lobes
Fin design is easier to move through the water (less drag) but still generates great force
Two major evolutionary developments to counteract side-to-side movement of the head:
1 – trend towards deeper body with more weight concentrated towards head
2 – caudal peduncle is greatly reduced
Examples: clupeids, mackerels, jacks

22. Swimming Thunniform Locomotion
Carangiform locomotion developed to the extreme
Represents the end-point in evolutionary trend toward greater speed in underwater locomotion among fishes – burst swimming speeds over 40 mph and cruising speeds ~10 mph
Very little of the body is involved in producing forward movement
Thrust generated almost entirely by tall, stiff, and deeply forked caudal fin – easy to move, very powerful
Drag is greatly reduced by extremely narrow caudal peduncle

23. Swimming Ostraciiform Locomotion
Only seen in those fishes that are unable to move body side to side
All propulsion comes from “wagging the tail”
Slow-moving fishes, not streamlined
Typically bodies of these fishes are encased in armor
Example: boxfishes

24. Swimming Median or Paired fins Locomotion
Wide variety of fishes that typically swim without using their body or caudal fin
These fishes use either their median (anal and/or dorsal) or paired fins (pectoral) to move
Generally tend to be slow-moving fishes
Continuum of those that use undulation to those that use oscillation
Median fin undulation
Paired fin undulation
Intermediate
Oscillation

25. Median or Paired fins locomotion
Median fin undulation (bowfin, electric fishes)
Paired fin undulation (rays, skates)
Intermediate (triggerfishes, porcupine fishes)
Oscillation (puffers)
Highly maneuverable; exploit complex habitats (e.g. coral reefs, dense vegetation)
Most can also use caudal fin for propulsion

26. Swimming Important considerations in fish locomotion
Many fishes have a specialized form of swimming
Specialization for 1 function usually involves a tradeoff in another function
Tunas are specialized for high-speed cruising – great distances at high speed, but not very maneuverable and poor swimmers at low speeds
Cichlids and reef fishes are specialized for high maneuverability, but lower speed – deep bodies, high dorsal/anal fins, large paired fins allow for precise movements in complex environments
Pikes are specialized for accelerating – large caudal fin with dorsal/anal fins set back on body

27. Swimming Important considerations in fish locomotion
We can identify some fishes that are specialized for one trait, however, most fishes use a variety of modes of swimming and are locomotor generalists as opposed to locomotor specialists
Most fishes must cruise to get from place to place, accelerate to eat and avoid being eaten.
Largemouth bass can raise dorsal/anal fins to gain thrust in a “fast start” attack, and can depress fins to reduce drag while chasing prey. Can also raise dorsal/anal fins to aid in maneuvering.
Not all fishes fit neatly into these categories. These specializations are likely related to how fish feed…