Soft Anatomy Chapter 4 Fish Muscle Muscle types • Fish have the same three basic types of muscles as other vertebrates: skeletal, smooth, and cardiac. • Skeletal: Voluntary, used for locomotion, comprises the majority of the fish’s muscle mass. • Smooth: Involuntary such as intestine, many organs, and the circulatory system. • Cardiac: Heart Skeletal Fish Muscle: •Essentially three types of fish muscle: red, white, pink. •Red muscle (oxidative): Highly vascularized, myoglobin containing tissue used during sustained swimming. Small diameter and high blood volume = rich O2 supply! Presence leads to strong flavor in some fishes (tuna). •White muscle (glycolytic): Little vascularization. Used during “burst” swimming. Large diameter fibers. •Pink muscle: This one is sort of in between red and white. Serves in sustained swimming, but not to the extent that red muscle is used. Red vs. White Muscle Fibers Red White Capilary beds Extensive Sparse Muscle fiber density Low High Myoglobin content High Low Glycogen content Low High Muscle mass Low High Alimentary Canal • Essentially the gastrointestinal tract (GI). • Two parts: (Antierior) mouth, buccal cavity, pharynx (Posterior) esophagus, stomach, intestine, rectum. • Mouth to esophagus & rectum is comprised of voluntary muscle while the stomach to posterior is involuntary. • GI tract varying considerably from spp. to spp. group. • Nutrient absorption increased by folding and increase of surface area (typhlosole, sprial valve). Alimentary Canal Oddities... • Esophagus (Peristalsis) -one-way trip for food! • Stomach (Killer pH!) -Some tilipia <2! Can actually break down plant cell walls in absence of appropriate gastric enzymes. • No stomach (lungfish, carp)! If no stomach, then no HCl = no shell or bone digestion. Alimentary Canal Oddities... • Intestine -Pyloric caeca are fingerlike pouches that may aid in nutrient uptake. GI (cont.) • Liver-fat storage, detox., oil source. Sharks—huge liver ~50% of gut space, but they don’t get cancer?? • Gallbladder—source of bile (fat emulsification). • Pancreas—source of digestive enzymes part of liver in some fish and crustaceans (hepatopancreas) Buoyancy • Fish regulate buoyancy several ways: (1) (2) (3) (4) Low density tissue (liver in sharks)—increase fat “Lift” from fin movement or hydrodynamics Reduced heavy tissue (bones and muscle) Gas (swim) bladder Gas Bladder • Used for buoyancy control. Physostomas-gas bladder is connected to the stomach. Buoyancy achieved by gulping air. Physoclistous-not connected to stomach. Fish has developed rete mirable and gas gland which serve to promote gas exhange. Smooth & Cardiac Muscles: Circulation and the Heart Circulatory System Mammals double circuit 1- heart to lungs 2- heart to body Fish single circuit heart gills body heart Special conditions for fish circulation – Environment is oxygen poor (1-8ppm on average) – Heart is simplest of vertebrates – Fish have less blood volume than other vertebrates • Adaptations by fish – Composition of blood (many different hemoglobins) – Morphology of circulatory apparatus – Behavioral responses to oxygen availability (move!) Functions of the Circulatory System • Delivers oxygen • Delivers nutrients • Removes metabolic waste • Fights pathogens Components of the Circulatory System to Study • Blood – Erythrocytes-red cells – Leukocytes –white cells – Structure of Hemoglobin • Vascular system – Heart – Vessels Formation of Fish Blood Cells • Formed from hemocytoblast • Blood forming site differs between fishes. – Agnatha • Mesodermal envelope around gut in hagfish • Fatty tissue dorsal to nerve cord in lampreys - “fat column” – Elasmobranchs • Leydig organ (near esophagus) • Epigonal organ (around gonads) • Spleen Formation of Fish Blood Cells continued • Teleosts – Kidney, Spleen, Cranium • Fish bone has no marrow! Leukemia an issue??? Erythrocytes-red cells • Most abundant fish blood cells • Nucleated • Size range exists (elasmobranchs usually larger, but fewer) • More active species have more red blood cellsWhy? Hemoglobin of Fish Erythrocytes • Primary means for transporting oxygen – In some fish up to 15% may be in plasma • A few fish have no hemoglobin (rare situation) When does this happen? – Environmental oxygen high – Low metabolic requirements Fish Hemoglobin Characteristics • Structure is different in different fish – Monomeric – Single-heme peptide molecules – Found in Agnatha • Tetrameric – Four peptide chains Fish Hemoglobin Characteristics • May differ in many features – Composition of amino acids – Affinity for oxygen (more on this later!) – Some salmonids have ~18 different kinds! Why?? Having Different Hemoglobin Types • Different hemoglobins have different responses to: - temperature - oxygen absorption • Allows fish to deal with changing conditions – Important for migratory species (salmon) • Some fish gain or lose types as they age Blood Oxygen Affinity • pH – Decreasing pH decreases affinity – Often associated with carbon dioxide • Carbon dioxide – Increase in CO2 drives off O2 (Bohr effect) – Decrease in blood pH magnifies Bohr effect Blood Oxygen Affinity • Temperature – Increase in temperature depresses oxygen affinity and capacity (total amount bound) – Results in fish having narrow temperature tolerances Fish Circulatory System • Primary circulation – Closed system • Heart • Arteries • Capillaries • Veins • Secondary circulation – Collects blood that is outside the primary – Originally thought to be lymphatic • No lymph or lymph nodes. Divisions of Primary Circulation • Branchial circulation – Blood from heart through gills • Systemic circulation – Blood from gills to body to heart • Blood flow is continuous from heart, to lungs, to body, back to heart Proximity of Heart & Gills Exceptions to Normal Circulation • Hagfish have accessory inline hearts • Lungfish have pulmonary circulation • There are also many small adaptations in some species. Structure of the Fish Heart • Four chambered heart • All four chambers are in line • The heart pumps only venous blood • Except for a few air breathing fish, all blood is pumped to the gills (Vascular circulation in lungfish.) Chambers of the Fish Heart (1) Sinus venous – Collects blood from venous ducts (2) Atrium – Accelerates blood flow (3) Ventricle – Large muscled chamber – Provides propulsive flow for circulation (4) Bulbus arteriosus (bony) Conus arteriosus – Changes blood from a pulse to continuous flow Conus vs. Bulbus Arteriosus • Conus Arteriosus – Contractile – Cardiac muscle – More than one valve • Bulbus Arteriosus – Elastic – Mostly connective tissue – One valve dividing it from ventricle Regulation of the Fish Heart • Self-regulating • Timing can be modified by brain (influence on the autonomic nervous system) • Pace is set by pacemaker cells • Many areas show pacemaker activity The Hagfish Heart • Most primitive • Sinus venous well developed – Divided into two parts to receive different veins • Bulbus arteriosus • Have 3 additional hearts – Cardinal heart in head – Caudal heart near end of tail – Portal heart – pumps blood through liver Lamprey Heart • Largest of fish hearts • Atrium overlies ventricle • Bulbus arteriosus Elasmobranch Heart • Conus arteriosus • Sinus venosus with almost no cardiac muscle • Ventricle has two muscle layers – Compacta = compact outer layer – Spongiosa = inner layer Teleost Heart • Variation exists across the group • Sinus venosus is thick-walled • Most have bulbus arteriosus • Some have conus arteriosus (usually more primitive) Lungfish Heart • Atrium is divided into two parts by an incomplete septum – Functional 3 chamber heart – Like amphibians – Right atrium larger than left – Right = deoxygenated from sinus venosus – Left = oxygenated from pulmonary vein Blood and Freezing Temp. • Osmolality • fp = delta freezing point – -0.06 FW – -0.75 SW • Ice fishes – Nototheniidae – glycoproteins • Winter Flounder -- Pleuronectes Circulatory Systems of Fishes: Functions • Delivery of needed substances for metalolism to tissues where needed: – – – – oxygen nutrients (sugars, lipids, proteins) minerals hormones Functions of Circulatory System • Delivery of waste products away from tissues: – – – – carbon dioxide nitrogenous wastes (NH3, NH4+, urea) excess minerals invading organisms (pathogens) Functions of Circulatory System • Maintenance of stable pH via buffer system: – H20 + CO2 = H2CO3 = HCO3- + H+ = 2H+ + CO3= – Last step only at pH > 10, so not in fish blood Components of Fish Circulatory Systems • Blood: – aqueous solution – solutes (proteins, sugars, minerals) – blood cells • erythrocytes (red blood cells) • leucocytes (white blood cells) – – – – lymphocytes thrombocytes monocytes granulocytes Components of Fish Circulatory Systems • Plumbing: – heart • • • • sinus venosus atrium ventricle bulbus (conus) arteriosus • Blood vessels – arteries – veins – capillaries Nervous Systems of Fishes Sensory, Motor and Integrative Functions Organization of the brain (anterior to posterior) • Telencephalon (forebrain): – olfactory sensation – coordination of smelldriven activities – receives visual and mechanical information, too • Diencephalon: – homeostasis – pineal organ (gland) – light sensitive – endocrine functions (hypothalamus) Brain Organization (anterior to posterior) • Mesencephalon (mid-brain): – Optic tectum (dorsal portion of mesencephalon): • receives visual input (optic nerve) • central processing center • coordinates visual input with other sensory inputs • sends out motor signals to musculature, e.g. escape response from sight of predator Brain (cont.) • Metencephalon (cerebellum): – coordinates swimming activity – coordinates: • balance input with motor response • electrical sense input with motor response Organization of the brain (anterior to posterior) • Myelencephalon (medulla obongata): – relay system for the senses – receives sensory input from cranial nerves 3 - 12: • acoustic • tactile • taste • lateral line • electrical (some)