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

Overview

 Exam I – Return & Review next week

 Presentations & Other Assignments

 Introduction to Anatomy, Physiology, and Ecology of Fishes

Anatomy, Physiology, and Ecology

 Buoyancy and Locomotion

 Swimming

 Feeding Mechanisms

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

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

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)

Hydrodynamic Lift 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

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

Gas Bladder

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

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

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

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.

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).

Swimming

 Types of swimming (6 primary forms)

 Anguilliform locomotion

 Subcarangiform locomotion

 Carangiform locomotion

 Thunniform locomotion

 Ostraciiform locomotion

 Median or paired fins

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

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

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

Swimming 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

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

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

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

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

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

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

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…