Anatomy, Physiology, and Ecology of Fishes I Biology of Fishes 10.18.12

1. Anatomy, Physiology, and Ecology of Fishes IBiology of Fishes10.18.12

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…