Respiration, Circulation and Metabolism
• Circulatory system
• Gills and Oxygen uptake
• Thermal regulation
Scombridae
Bigeye tuna
Thunnus obesus
Deep Scattering Layer:
Diel Vertical Migrators
Circulatory System
Properties of Water Related
to Exchange of Gases
•Water contains 1% O2 by volume, whereas air contains
21% O2 by volume
•Concentration of O2 dissolved in water varies inversely
with temperature and salinity
•Salting out effect
•High water temperature = Low O2 concentration
•CO2 is very soluble in water because it undergoes partial
disassociation and forms a weak chemical bond with water
(H2O + CO2 = H+ + HCO3- = H2CO3)
Ventilation and Respiration
• Aerobic Respiration
O2 + CH2O  CO2 + H2O + ENERGY
• Ventilation: process of directing oxygenated water
through blood capillary beds
• Diffusion:
Passive transport of O2 from water
across epithelial cells and into the capillaries
containing blood
CH2O  Lactate + energy
ANAEROBIC RESPIRATION
Lamprey
Shark
Teleost
Ventilation: unidirectional flow of water.
Gill Lamella
Counter current flow between blood and water maximizes
exchange between fluids.
Counter current systems
•If fluids flowed in same direction exchange would be
about 50%, regardless the length of the flow systems.
•With counter current flow exchange is more complete
and varies directly with length of the flow systems.
Thermal regulation: control of
body temperature
Body temperature of animals relative to
that of the environment
– Poikilotherms
– Homeotherms
Source of animal’s body heat
– Ectotherms
– Endotherms
Mechanisms of thermal
regulation in fishes
• behavioral
• physiological (endothermy)
Behavioral thermoregulation
Physiological thermoregulation (endothermy)
Lamnidae
Mako
Isurus oxyrinchus
Physiological thermoregulation (endothermy)
Alopiidae
Thresher shark
Alopias superciliosus
Physiological thermoregulation (endothermy)
Scombridae
Bigeye tuna
Thunnus obesus
Forms of Endothermy
• Systemic or whole body endothermy
– Lamnidae, Alopiidae, Scombridae
• Regional endothermy refers to
maintaining elevated temperatures
only in certain parts of the body:
– cranial endothermy (“brain heaters”)
– Istiophoridae, Xiphiidae
Cranial endothermy
(“brain heaters”):
•Billfishes (Istiophoridae)
Cranial endothermy (“brain heaters”):
Xiphiidae
Swordfish
Xiphias gladius
Systemic (whole body) endothermy
Shared presence of:
streamlined body
narrow caudal peduncle
crescent-shaped caudal fin
Atlantic Bluefin tuna (Thunnus thynnus)
Block et al. 2002
Muscle Temp = 28 – 30 oC / Water temperature = - 20 oC
Scombridae
Bigeye tuna
Thunnus obesus
Deep Scattering Layer:
Diel Vertical Migrators
Structures and functions involved
in systemic endothermy
• Distribution of blood vessels
• Distribution of red muscle (used for
sustained swimming, heat generating)
• Rete mirabile (heat exchanger)
Distribution of blood vessels
Ectotherm
Endotherm
Distribution of red muscle and blood
vessels in cross-section
Ectotherm
Skipjack tuna
Red
muscle
Bluefin tuna
Mako shark
Distribution of red muscle and blood
vessels in cross-section
Ectotherm
Skipjack tuna
Red
muscle
Bluefin tuna
Mako shark
Heat exchanging retia mirabile of tuna.