Anatomy, Physiology, and Ecology of Fishes IBiology of Fishes

10.18.12

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

Overview

Buoyancy and Locomotion Swimming Feeding Mechanisms

Anatomy, Physiology, and Ecology

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)

Buoyancy and Locomotion

Hydrodynamic Lift

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

Buoyancy and Locomotion

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

Hydrostatic Lift

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

Gas Bladder

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

Hydrostatic Lift

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.

Buoyancy and Locomotion

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

Swimming

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

Median or Paired fins locomotion

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…

Swimming