Respiration Circulation and Metabolism Circulatory system Gills and

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% O 2 by volume, whereas air contains 21% O 2 by volume • Concentration of O 2 dissolved in water varies inversely with temperature and salinity • Salting out effect • High water temperature = Low O 2 concentration • CO 2 is very soluble in water because it undergoes partial disassociation and forms a weak chemical bond with water (H 2 O + CO 2 = H+ + HCO 3 - = H 2 CO 3)

Ventilation and Respiration • Aerobic Respiration O 2 + CH 2 O CO 2 + H 2 O + ENERGY • Ventilation: process of directing oxygenated water through blood capillary beds • Diffusion: Passive transport of O 2 from water across epithelial cells and into the capillaries containing blood CH 2 O 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 o. C / Water temperature = - 20 o. C

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.