Oxygen, Metabolism, and Bioenergetics

Oxygen:

• Require oxygen to produce sufficient energy to support metabolic needs

• Acquiring Oxygen from water is challenging

  • Water is more viscoius than air

    • More energy is required to move water across respiratory surfaces

  • Saltwater holds less O2 due to diminished solubility of gases in water = more solute concentration, the less gas dissolution occurs

  • Warmer waters: gas solubility in liquids decreases with increasing temperatures

  • Also affected by:

    • High rates of decomposition that use O2 to break down organic matter

    • Deeper areas of still water; No oxygen mixing

  • Oxygen levels in water are 1% in volume

Aquatic Breathing

• Efficient respiratory organs: Gills

  • Large surface area

  • Secondary Lamellae: thin membranes that uptake O2

    

  • Countercurrent Gas Exchange: blood in the secondary lamaellle flows in the opposite direction than the oxygen water flowing in

    • Oxygen rich blood meets oxygen-rich water: results in more oxygen being exchanged towards the end of the current because it is not all used up

• Function only when water is kept moving over gills: from anterior to posterior

• Methods of Water Movement

  • Actively pumping water across gills (energetically expensive)

  • RAM ventilation: Swimming with mouth open for water to pass over gills

    • Ex: tunas

  • Larger fish can rely on both mechanisms: ram ventilation for swimming, but rely on pumping while still or moving slowly

    • Ex: Sharks

• Non-gill-driven respiration techniques:

  • Cutaneous respiration: gas exchange across skin

    • Improaint in smaller fishes with a larger SA/V ratio

    • This occurs in young fish whose gills have not fully developed

  • Aquatic Air breathers:

    • Facultative air-breathing: supplement gill respiration when necessary

      • Seen in areas with low oxygen conditions, such as tropical freshwaters

    • Obligate air breathing: must have access to air or will drown

  • Amphibious air breathers: ability to breathe oxygen and survive without water

    • Cope with drought: lungfishes

    • Forage marine intertidal area: mudskippers

  • Air Breathing Organs:

    • Derived from Gut: Lungs, Gas Bladder, Stomach, Intestine

    • Structures of the head: modifications of gills, mouth, pharynx, opercles

      • Walking Catfish: modified treelike branches above gill arches

    • Skin: Cutaneous respiration

      • Ex: mudskipper

Metabolic Rate

• Metabolism: sum total of all biochemical processes taking place within an organism

• Rate of oxygen consumption: indicator of metabolism

• Higher metabolic rates in higher temps

  • Temperature increases a fish's need for O2-> while warm wter holds less oxygen

  • Evolution of air-breathing in many tropical fishes

• Metabolic Costs:

  • Swimming: favors traits that reduce metabolic costs of movement

    • Fusiform streamlined bodies

    • Fin shape and placement such as dorsal fin distance

    • Stream fishes

      • Body shape or use of fins to hold position

    • Buoyancy regulation

    • Tucking away fins in grooven when swimming

      • Ex: sailfish

  • Buouyancy regulation:

    • Also energetically expensive

    • Need to regulate the volume of the gas bladder-> effect of changing pressure as fish changes depth

    • Physostomous condition: connection of gas bladder to the gut

    • Physoclistous condition: gas bladder is sealed off

    • Gas bladder may disappear all together in evolution of benthic organisms

  • Bioenergetics Models:

    • Obtain energy to meet metabolic demands: feeding

    • Energy budgets:

      • How energy that is consumed is allocated

    • Energetic costs of activities:

      • Estimated by measuring the heat produced by an organism or the oxygen consumption (ask for clarification)

      • The energy remaining after basic needs-> used for growth and reproduction

    • C = E + R + P

      • C= energy consumed

      • E= energy excreted

      • R: energy used in respiration

      • P: energy used in production

    • Predicts individual growth, reproduction, or feeding rates

      • Energy budget: based on energy resvirors and transfers

      • Unit of energy flow: grams/C or cal/day

      • Balanced bodel: energy input is balanced by energy used or lost

    • Depend on:

      • Body size

      • Developmental stage

      • Water temperature

      • Food quality

      • Quantity of food

    • Includes component predictions based on body size, temperature and food parameters

    • Uses:

      • Predict fish population dynamics

      • Model-based on consumption or growth of an individual from ahtcling to death: multiple to create individual based models

• Energetic Costs:

  • Some food is never digested

  • Mechanism of lose:

    • Excretion of nitrogenous waste

    • Providing energy for digestion

    • Routine metabolism

    • Swimming

    • Maintaining homeostasis

    • Immune system function

    • Physiological maintances

  • Affected by environmental factors-> affect the amount of energy needed to sustain metabolism

Homeostasis

• Regulated by the neuroendocrine system

• Endocrine System:

  • Releases hormones in blood

  • EDC: Endocrine disruption compounds from industrial chemicals and pharmaceuticals

    • Effect all areas of the nervous system

    • Effects levels of sex homormes, creating intersex individuals

    • Affect hatching success

• Regulation of internal osmotic environment cocnentration of ions (NaCl)

• Most fish are Osmoregulators:

  • Regulation of internal osmotic enviroment

  • Within a narrow range

• Osmoconformers: internal osmotic concentration is the same of that as sea water (isomotic)

  • Hagfishes(Class Mixini)

  • Occurs in environments where salinity is stable

• Elasmobranchs:

  • Osmoregulators

  • Method:

    • Conversion of nitrogen water into urea and retain high concetrations of it in their blood

  • Hyperosmotic: saltier than the environment

    • Causes water to move into the fish and salt concentrations to move out

  • FW elamobranch(FW stingray) do not produce uera

• Sacropterygians:

  • Osmoregulators

  • Hyperosomtic

  • Convergent evolution with sharks

    • Colecacanths: maintain elevated elvels of urea in their blood

    • Lungfishes(Dipnoi):

      • FW, so do not retain urea EXCEPT during estivation

      • Store nitrogen waste in a less toxic form than ammonia and as a way to retain water

• FW Teleosts:

  • Hyperosmotic:

  • osmoregulators

  • Tend to gain water and loss solutes by diffusion across secondary lamaelle and oharnyx

  • Needs to prevent osmotic lysis:

    • Excrete a large volume of dilute urine and actively transport solutes back into their blood

  • Uptake of Ions:

    • NA and Cl are taken up through ionoregualtory cells in gills

    • Kidneys recover ions from urine before release

• Marine Teleosts:

  • Osmoregulators

  • Hypoosmtoic (less salty than envriometn)

    • High salt concentrations draws FW out, and ions diffus in across the permeable membranes

  • Regulation techniques:

    • Prevent dehydration-> drinking seawater

    • Actively extreme excess salt in highly concentrated urine

  • Ionoregulatory cells: uptake ions from body fluids-> which then diffuse out of gills

  • Permeable bladder:

    • Diffusion within the fish-> excretion of urine that is isosmotic to their blood

• Diarmous Teleosts:

  • Osmoregulatros

  • Adjustments must be made in the ionoregulatory cells at the gills

  • Regualted by hormones,

    • Growth hormoze

  • The number and size of chloride-transporting ionoregulatory cells is increased and the activity of enzymes associated with sodium-potassium exchange is enhanced

  • Occurs in euryhaline fishes

  • Various other hormones-> Increase water permeability, enhance gene expression of proteins that transport ions across cell membranes

Temperature

• Ectotherms

• Lack of mechanism for heat production and retention

• Make internal adjustments:

  • Genes switch on and off to cope with flucating temps

• Heterothermic: evolutionary adaption in large, active, pelagic marine fishes

  • Use internally generated heat to maintain warm temps in swimming muscles, guts, brain, eyes(what ways do they do this that is different than other fish species)?

  • Heterothermy: evolved independently among fishes

  • Different mechanisms and diversity of heterothemic fishes

    • Manta and Sicklefin devil ray under debate

Sensory Systems

• Accessories to nervous system that act as transducers

• Mechanorecpetion (Pressure sensing)

  • Lateral line: detects disturbances in the water, helping fish detect currents, capture prey and maintain position in school

  • Inner part: fish equilibrium and balance, healing

• Electroreception:

  • Evolved over 500 mya

  • Lost and secondarily evolved in several different groups of fishes

  • Organs:

    • Ampullary receptors: sensitive to low frequency electric fields; many groups of primitive fishes

      • Ampullae of Lorenzini

      • Ex: Lungishes, reedfishes, coelacanths, sturgeons paddlfish, chondrichtyes, lampresy

    • Tuberous receptors: detect higher frequency electric field

      • Produce their own electric field (active electrolocation)

      • Limitedto FW Fish

      • Used in prey detection

      • Also canbe used to attach and defend (electric eels)

• Vision:

  • Eyes: corena, lens, pupil, and sensory cells: rods and cones

  • Rods: sensitive to low light

    • HIGH ROD:CONE RATIO: nocturnal and deep-sea fishes

  • Cones: require brighter light; provide greater resolution:

    • HIGH CONE:ROD Ratios: highest in diurnal fishes

• Chemoreception:

  • Used for finding and identifying food, habitat, communication, avoiding predators

  • Olfaction(smell)

    • Detect a broad range of chemical stimuli

    • In anadromous species: identify suitable spawning streams(detect chemical released by juveniles, and male pheromones)

  • Gustation: focused on food recognition

Magnetic Receptions

• Detection of magnetic fields, direction information with respect to compass headings

• May be connected to spawning site location in mightly migrational species

• Unknown

Feeding and Locomotion:

• Adaptions in these two areas are the reasons teleosts diversified so quickly

• Caudal Fin locomotry complex: homocercal tails:

  • Change of the caudal fin to heterocercal-> abbreviated heterocercal-> homocercal

    • Abbreviated heterocercal: moderately asymmetrical; bowfin, gar

  • Heterocercal tail:

    • Provides lift-> useful for heavily armored primitive actionpterygian species to get off the bottom

    • Axis of rotation: oblique-> push down as well as back

      • Upward and forward rotation of read end of the fish (somersault effect)

      • Sommersualt effet must be counteracted by large planning pectoral fins

        • Does not allow for frequent locomotion

      • Homocercal tail:

        • Vertical axis of rotation

Pushes directly backward

Fish is pushed forward

• Increased efficiency in horizontal swimming=> thrust provided by the locomotory organ is purley horizontal

Locomotory organ (caudal peduncle and tail)

• Associated with:

Loss of heavy bone armor and heavy scaltion

Modification of lungs to act as hydrostatic organ-> evolution of swim bladder makes body plan that accounts for lift obsolete

• Increased veraility of pared fins:

Pectoral fins no longer serve as planning devices

Serve other locomotory functions

Shift from horizontal insertion low on the body to vertical insertion high on the body

Greater maneuverability

• Feeding Mechanisms (upper-jaw mobility)

  • Greater upper-jaw mobility: protrusible upper jaw

    • Promoted highly successful food exploitation

  • Opened new trophic possibilities for teleosts

    • Increases in ecological niches and evolutionary potential of mouth parts

    • Variety of specialized predaceous and non-predaceous feeding types

• Swimming in Sharks: alternative approach

  • Enhance efficiency of swimming despite not convegrning with fusiform shape (in most cases)

  • Trends towards homocercal tails in osteichthyan: capitalize off of stress than is placed on rigid, bony skeleton and the forces achievable by muscle masses attached directly to the skeleton

  • Sharks have a softer skeleton-> different path

  • Swim bia undulations of body or pectoral fins

    • Anguilliform locomotion

  • Increased thrust available from the large heterocercal tail

    • Homocercal tail: pelagic Lamniformes converged with tunas and dolphins

    • Large amplitude of wave in the casual fin region

  • Interaction between skin and body musculature: (read this chapter in the book)

    • Skin:

      • Inner sheath, stratum compactum(made up of collagen fibers)

      • Fibers from layers of alternately oriented sheets that run in helical paths around shark’s body-> readily bendable

    • Inside the skin: hydrostatic pressure varies from activity level

      • Faster swimming-> higher internal hydrostatic pressure

      • Hydrostatic pressure: fluid in the bloodstream is pulled down by gravity, causing higherpressure near the barrier, causing fluid to be forced out

      • Unkown source of hydrostatic pressure-> due to changes in surface area of contracting muscles relative to skin area and to changes in blood pressure in blood sinuses that are surrounded by muscle

    • Elastin covering

    • Pressure cylinder with an elastic covering

    • Higher internal pressure + stiff skin = increases the energy stored in the stretched skin

      • Body muscles attach via collagenous septa and the inside of the skin

      • Muscles on right side contract/ muscles and skin on left side area contracted->when right side releases, skin on left side releases energy, aiding muscles at a point when they provide little tension

      • Skin initiates the pull of the tail across the midline and increases the power output at the beginning of each propulsion stroke

    • Elastic recoil from stretched skin:

      • Muscles attached to skin form a large cylindrical external denon

      • Fibers of th dermis extend onto the peduncle and caudal fin

        • Adds rigidity to both

        • Stores elastic energy during each swimming stroke

      • Muscles pull on skin: propuslive energy that exceeds the thrust derived from muscles attached to verbal column

  • Swimming with a heterocercal tail”

    • Tail pushes back a down (F reactive)

    • Chases rotation around the center mass

    • Counteracted by head and pectoral fins

    • Shape and body angel: generate lift forces that are added to the lift of the tail

      • Equal and opposite to the weight of the shark in the water

• Placement of dorsal fin:

  • First is larger than the second, separated by a gap

  • Dorsal lobe of heterocercal tail-> “third median fin” in line with dorsal fins, separated from second dorsal fin by a considerable gap

  • Fin tapers posteriorly, leaving behind a wake

    • Displaced laterally by sinusoidal waves passing down the fish, so the wake is sinusoidal path that moves posteriorly as the fish moves through the water

  • Ideal distance between fins: maximize the thrust of the second dorsal fin and tail

    • Trailing fins can push against water coming towards them laterally from the leading fin

    • Enhances thrust from trailing fin

    • Median fins as thrusters