DOCSLIB.ORG

Table of Contents

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Table of Contents TABLE OF CONTENTS INTRODUCTION ........................................................................................................... 2 WHAT IS A FISH? ............................................................................................................... 2 FISH SHAPES ...................................................................................................................... 2 ORIGINS AND DIVERSITY OF FISHES ................................................................................... 3 CLASSIFICATION OF FISHES ............................................................................................... 4 1. BONY FISH ..................................................................................................................... 4 INTERNAL STRUCTURE OF A BONY FISH .......................................................................... 5 SCALES AND SLIME ......................................................................................................... 6 SWIMMING WITH FINS AND TAILS .................................................................................. 6 THE SENSE ORGANS ....................................................................................................... 7 FEEDING ........................................................................................................................ 8 HOW FISH BREATHE ....................................................................................................... 9 BUOYANCY IN WATER ..................................................................................................... 9 LIVING IN FRESH OR SALT WATER .................................................................................. 9 REPRODUCTION .......................................................................................................... 10 SEX CHANGES IN FISH .................................................................................................. 10 2. CARTILAGINOUS FISHES ............................................................................................... 11 EXTERNAL STRUCTURE OF A CARTILAGINOUS FISH........................................................ 12 CARTILAGINOUS FISH SKIN TYPES ................................................................................ 12 TAIL SHAPES ................................................................................................................ 12 INTERNAL STRUCTURE OF A CARTILAGINOUS FISH ........................................................ 13 FEEDING ...................................................................................................................... 13 FEEDING ...................................................................................................................... 14 REPRODUCTION OF BEARERS ........................................................................................ 14 3. JAWLESS FISH .............................................................................................................. 16 EXAMPLES OF FISHES FOUND IN THE OCEANS AROUND SOUTH AFRICA ............................. 17 1. COELACANTH ............................................................................................................... 17 2. SHARKS, RAYS, SKATES AND CHIMAERAS ...................................................................... 17 3. REEF FISH .................................................................................................................... 19 4. PELAGIC FISH ............................................................................................................... 22 5. EELS ............................................................................................................................ 22 5.1 MORAYS ................................................................................................................. 23 6. SEAHORSES .................................................................................................................. 23 7. SUNFISH ...................................................................................................................... 23 CONSERVATION THROUGH RESEARCH AND OBSERVATION ......................................... 24 CONSERVATION VERSUS ECONOMIC FISHING INDUSTRIES ................................................ 26 1. OVERVIEW ............................................................................................................... 26 2. STATUS OF CERTAIN FISH STOCKS IN 2001 ............................................................... 28 Two Oceans Aquarium Volunteer Manual – MODULE 5 -- FISH Page 1 INTRODUCTION WHAT IS A FISH? A fish is a cold-blooded vertebrate that lives in water, breathes by means of gills and has fins for stability and movement. Most, but not all fishes, have scales and a lateral line. FISH SHAPES Fishes can have many forms (see the illustration below). They can range in size from less than 1 cm (a goby) to over 12 m (a whale shark). A. Lamprey B. Hagfish C. Shark D. Ray E. Chimaera F. Lungfish G. Teleost They do not include seals, whales and dolphins (mammals), turtles and sea snakes (reptiles) or shrimps, lobsters, and crabs (crustaceans) or mussels (molluscs) Some marine and freshwater invertebrates (animals with no backbone) and some animals with shells (such as molluscs) are called ‘shellfish’. Therefore true fish may be called ‘finfishes’. ICHTHYOLOGY is the study of the classification and the biology of fishes. FISHERIES SCIENCE is the study of the management and utilisation of fish populations. Two Oceans Aquarium Volunteer Manual – MODULE 5 -- FISH Page 2 ORIGINS AND DIVERSITY OF FISHES The fish came first! Ancient fishes first appeared in the fossil records over 500 million years ago, more than 100 million years before any other vertebrate group. Fishes are therefore the most ancient, and all other vertebrate groups (amphibians, reptiles, birds and mammals) evolved from them. Fish first laid down the basic ground plan and functions of vertebrates. These include the 10 organ systems: skeleton, muscles, gills (respiratory), digestive, blood circulation, kidneys (urinary), reproductive organs, hormone (endocrine) systems and the nervous system (including the sensory organs), as well as the basic locomotion systems. But fishes are not primitive because they are ancient. Some of them are very advanced and have well developed senses of sight, taste, electro reception, vibration reception, in addition to internal fertilisation, parental care, placental nourishment of the young, live birth, learning and memory. Many of the ‘inventions’ of man were first evolved by fishes, for example – echolocation, sonar, camouflage, electro reception, electrical discharge and so on. Fish species constitute almost 50% of all living vertebrate species and the extinct fish species outnumber all other vertebrates. Pie chart of living vertebrate species. Two Oceans Aquarium Volunteer Manual – MODULE 5 -- FISH Page 3 CLASSIFICATION OF FISHES Fishes like other animals may be classified based on the ancestral relationships and on their feeding and breeding behaviour. This is known as Taxonomic classification. The evolutionary sequence of fish is thought to begin with the jawless fish, then the cartilaginous fish followed by the bony fish. The elephant fish shows characteristics of both cartilaginous and bony fish. However, for practical purposes, as there are a greater variety of bony fish than cartilaginous fish in the Two Oceans Aquarium, the bony fish are here dealt with first. The main groups of fishes that are described in the following pages are: 1. Bony fishes (Class: Osteichthyes) with a skeleton of bone such as lungfishes, coelacanth, and all ray-finned fishes. Their bodies are usually covered with thin scales. They have a single gill opening. 2. Cartilaginous fishes (Class: Chondrichthyes) with a skeleton of gristle or cartilage such as sharks, chimaera, skates and rays. Their scales are buried in their skin. There are several gill openings. 3. Jawless fishes (Super Class: Agnatha) such as hagfish, and lampreys that have no jaws or scales. The skeleton is made of cartilage. There are several gill openings. 1. BONY FISH As fishes live in water, a medium 800 times denser than air, and as water is buoyant they do not have to support themselves, but density causes friction against their bodies so they have to be streamlined. EXTERNAL STRUCTURE OF A BONY FISH Operculum (gill cover) Scales Water taken through Dorsal fin These are Eye the mouth is forced This single fin extremely thin, out over the gills Sight is well developed in most acts as the overlapping bony beneath this cover. fish and the eyes are most main ‘keel’ plates that protect In the process, Lateral line sensitive to yellow-green the preventing and streamline the oxygen is absorbed The lines of dots wavelengths that penetrate the fish body. They contain and waste products along the flanks are furthest into water. rolling during pigment cells, released. tiny holes leading to swimming. although apparent a canal that runs colour in many the whole length of fishes is produced the fish. Nerve Nostril by reflected light. endings respond to changes of water Many fish have a highly pressure enabling developed sense of smell. the fish to detect The nostrils do not connect vibrations in the to the mouth. water. Mouth Caudal fin (tail) The shape and position varies Most fish swim by between surface, midwater & sweeping the back bottom feeders. part of the body from side
Load more

Recommended publications
  • An Introduction to the Classification of Elasmobranchs
    An introduction to the classification of elasmobranchs 17 Rekha J. Nair and P.U Zacharia Central Marine Fisheries Research Institute, Kochi-682 018 Introduction eyed, stomachless, deep-sea creatures that possess an upper jaw which is fused to its cranium (unlike in sharks). The term Elasmobranchs or chondrichthyans refers to the The great majority of the commercially important species of group of marine organisms with a skeleton made of cartilage. chondrichthyans are elasmobranchs. The latter are named They include sharks, skates, rays and chimaeras. These for their plated gills which communicate to the exterior by organisms are characterised by and differ from their sister 5–7 openings. In total, there are about 869+ extant species group of bony fishes in the characteristics like cartilaginous of elasmobranchs, with about 400+ of those being sharks skeleton, absence of swim bladders and presence of five and the rest skates and rays. Taxonomy is also perhaps to seven pairs of naked gill slits that are not covered by an infamously known for its constant, yet essential, revisions operculum. The chondrichthyans which are placed in Class of the relationships and identity of different organisms. Elasmobranchii are grouped into two main subdivisions Classification of elasmobranchs certainly does not evade this Holocephalii (Chimaeras or ratfishes and elephant fishes) process, and species are sometimes lumped in with other with three families and approximately 37 species inhabiting species, or renamed, or assigned to different families and deep cool waters; and the Elasmobranchii, which is a large, other taxonomic groupings. It is certain, however, that such diverse group (sharks, skates and rays) with representatives revisions will clarify our view of the taxonomy and phylogeny in all types of environments, from fresh waters to the bottom (evolutionary relationships) of elasmobranchs, leading to a of marine trenches and from polar regions to warm tropical better understanding of how these creatures evolved.
    [Show full text]
  • Function of the Respiratory System - General
    Lesson 27 Lesson Outline: Evolution of Respiratory Mechanisms – Cutaneous Exchange • Evolution of Respiratory Mechanisms - Water Breathers o Origin of pharyngeal slits from corner of mouth o Origin of skeletal support/ origin of jaws o Presence of strainers o Origin of gills o Gill coverings • Form - Water Breathers o Structure of Gills Chondrichthyes Osteichthyes • Function – Water Breathers o Pumping action and path of water flow Chondrichthyes Osteichthyes Objectives: At the end of this lesson you should be able to: • Describe the evolutionary trends seen in respiratory mechanisms in water breathers • Describe the structure of the different types of gills found in water breathers • Describe the pumping mechanisms used to move water over the gills in water breathers References: Chapter 13: pgs 292-313 Reading for Next Lesson: Chapter 13: pgs 292-313 Function of the Respiratory System - General Respiratory Organs Cutaneous Exchange Gas exchange across the skin takes place in many vertebrates in both air and water. All that is required is a good capillary supply, a thin exchange barrier and a moist outer surface. As you will remember from lectures on the integumentary system, this is often in conflict with the other functions of the integument. Cutaneous respiration is utilized most extensively in amphibians but is not uncommon in fish and reptiles. It is not used extensively in birds or mammals, although there are instances where it can play an important role (bats loose 12% of their CO2 this way). For the most part, it: - plays a larger role in smaller animals (some small salamanders are lungless). - requires a moist skin which is thin, has a high capillary density and no thick keratinised outer layer.
    [Show full text]
  • Vertebrate Respiratory System Gills
    Dr. Medhavi Sudarshan Assist Prof nd B.SC 2 Year, Paper IV Deapt of Zoology JNL College , Khagaul Comparative Anatomy – Vertebrate Respiratory System Respiratory system is a system consisting of specific organs and structures used for the process of respiration in an organism. Respiration is the process of obtaining oxygen from the external environment & eliminating CO2. External respiration - oxygen and carbon dioxide exchanged between the external environment & the body cells Internal respiration - cells use oxygen for ATP production (& produce carbon dioxide in the process) In vertebrates the skin may be respiratory (e.g., anurans), while in some fishes and aquatic turtles, the vascular rectum or cloaca is respiratory. But there are two main types of respiratory organs- gills for aquatic respiration and lungs for aerial respiration. Both gills and lungs may occur in the same animal. Accessory respiratory organs are also present in some vertebrates. In both kinds of respiration two conditions are essential; 1. The respiratory organs must have a rich blood supply with very thin moist epithelium covering the blood vessels so that these blood vessels are through into close contact with the environment (water or air). 2. The organs of respiration the blood vessels should be reduced to thin capillaries which expose a large surface area to the environment, so that blood is brought into close contact with the water or air in the respiratory organs. Gills Cartilaginous fishes: Septal gills. Cartilaginous fishes (Sharks) use gills to breathe rather than lungs. There is 5 to 7 gill arches, each bearing one gill slit and covered by the operculum, which acts as a lid over the gill.
    [Show full text]
  • Cutaneous Exchange • Evolution of Respiratory Mechanisms
    Lesson 25 Lesson Outline: Evolution of Respiratory Mechanisms – Cutaneous Exchange • Evolution of Respiratory Mechanisms - Water Breathers o Origin of pharyngeal slits from corner of mouth o Origin of skeletal support/ origin of jaws o Presence of strainers o Origin of gills o Gill coverings • Form - Water Breathers o Structure of Gills Chondrichthyes Osteichthyes • Function – Water Breathers o Pumping action and path of water flow Chondrichthyes Osteichthyes Objectives: At the end of this lesson you should be able to: • Describe the evolutionary trends seen in respiratory mechanisms in water breathers • Describe the structure of the different types of gills found in water breathers • Describe the pumping mechanisms used to move water over the gills in water breathers References: Chapter 13: pgs 292-313 Reading for Next Lesson: Chapter 13: pgs 292-313 Function of the Respiratory System - General Respiratory Organs Cutaneous Exchange Gas exchange across the skin takes place in many vertebrates in both air and water. All that is required is a good capillary supply, a thin exchange barrier and a moist outer surface. As you will remember from lectures on the integumentary system, this is often in conflict with the other functions of the integument. Cutaneous respiration is utilized most extensively in amphibians but is not uncommon in fish and reptiles. It is not used extensively in birds or mammals, although there are instances where it can play an important role (bats loose 12% of their CO2 this way). For the most part, it: - plays a larger role in smaller animals (some small salamanders are lungless). - requires a moist skin which is thin, has a high capillary density and no thick keratinised outer layer.
    [Show full text]
  • A Comparative Study of the Spiracle in Cyclostomata, Elasmobranchii and Pisces
    University of Tennessee, Knoxville TRACE: Tennessee Research and Creative Exchange Masters Theses Graduate School 6-1939 A Comparative Study of the Spiracle in Cyclostomata, Elasmobranchii and Pisces Miser Russell Richmond University of Tennessee, Knoxville Follow this and additional works at: https://trace.tennessee.edu/utk_gradthes Part of the Animal Sciences Commons Recommended Citation Richmond, Miser Russell, "A Comparative Study of the Spiracle in Cyclostomata, Elasmobranchii and Pisces. " Master's Thesis, University of Tennessee, 1939. https://trace.tennessee.edu/utk_gradthes/4396 This Thesis is brought to you for free and open access by the Graduate School at TRACE: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Masters Theses by an authorized administrator of TRACE: Tennessee Research and Creative Exchange. For more information, please contact [email protected]. To the Graduate Council: I am submitting herewith a thesis written by Miser Russell Richmond entitled "A Comparative Study of the Spiracle in Cyclostomata, Elasmobranchii and Pisces." I have examined the final electronic copy of this thesis for form and content and recommend that it be accepted in partial fulfillment of the equirr ements for the degree of Master of Science, with a major in Animal Science. Barton C. V. Ressler, Major Professor We have read this thesis and recommend its acceptance: Henry Meyer, A. C. Cole Accepted for the Council: Carolyn R. Hodges Vice Provost and Dean of the Graduate School (Original signatures are on file with official studentecor r ds.) Kay 22, 1939 To the Committee on Graduate Study:. I am submitting to you a thesis written by Miser Russell Richmond entitled "A Comparative Study of the Spiracle in Cycloatomata, Elasmobranchii and Pisces." I reconmend that it be accepted for nine quarter hours credit in partial fulfillment of the requirements tor the degree of Master of Science with a major in Zoology.
    [Show full text]
  • Your Inner Fish
    CHAPTER FIVE GETTING AHEAD It was two nights before my anatomy final and I was in the lab at around two in the morning, memorizing the cranial nerves. There are twelve cranial nerves, each branching to take bizarre twists and turns through the inside of the skull. To study them, we bisected the skull from forehead to chin and sawed open some of the bones of the cheek. So there I was, holding half of the head in each hand, tracing the twisted paths that the nerves take from our brains to the different muscles and sense organs inside. I was enraptured by two of the cranial nerves, the trigeminal and the facial. Their complicated pattern boiled down to something so simple, so outrageously easy that I saw the human head in a new way. That insight came from understanding the far simpler state of affairs in sharks. The elegance of my realization—though not its novelty; comparative anatomists had had it a century or more ago— and the pressure of the upcoming exam led me to forget where I was. At some point, I looked around. It was the middle of the night and I was alone in the lab. I also 108 happened to be surrounded by the bodies of twenty-five human beings under sheets. For the first and last time, I got the willies. I worked myself into such a lather that the hairs on the back of my neck rose, my feet did their job, and within a nanosecond I found myself at the bus stop, out of breath.
    [Show full text]
  • On the Homology of the Posteriormost Gill Arch in Polypterids (Cladistia, Actinopterygii)
    Blackwell Science, LtdOxford, UKZOJZoological Journal of the Linnean Society0024-4082The Lin- nean Society of London, 2003 1384 495503 Original Article POLYPTERUS GILL ARCH HOMOLOGYR. BRITZ and G. D. JOHNSON Zoological Journal of the Linnean Society, 2003, 138, 495–503. With 3 figures On the homology of the posteriormost gill arch in polypterids (Cladistia, Actinopterygii) RALF BRITZ1,2* AND G. DAVID JOHNSON2 1Lehrstuhl für Spezielle Zoologie, Universität Tübingen, Auf der Morgenstelle 28, D-72076 Tübingen, Germany 2Division of Fishes, National Museum of Natural History, Washington D.C. 20560, USA Received October 2002; accepted for publication December 2002 Polypterids are unusual among ray-finned fishes in possessing only four rather than five gill arches. We review the two current hypotheses regarding the homology of the last gill arch in polypterids: that it represents (1) the fifth or (2) the fourth arch of other actinopterygians. Arguments for the alternative hypotheses drawn from different ana- tomical systems are compiled and evaluated. We conclude that in polypterids the last arch represents the fourth arch of other Actinopterygii and the fifth arch is absent. © 2003 The Linnean Society of London, Zoological Journal of the Linnean Society, 2003, 138, 495–503. ADDITIONAL KEYWORDS: branchial circulation – branchial muscles – branchial nerves – Erpetoichthys – Polypterus. INTRODUCTION cialized anatomy of the pectoral fins, a particular type of sexually dimorphic anal fin associated with a unique The African freshwater fish family Polypteridae com- mating behaviour, and a reduced number of gill arches prises two genera, Polypterus (bichirs), with ten spe- (Müller, 1846; Greenwood, 1984; Gardiner & Schaeffer, cies, and the monotypic Erpetoichthys (reedfish) (Poll 1989; Britz & Bartsch, 1998).
    [Show full text]
  • Sphyrnidae 497
    click for previous page Carcharhiniformes: Sphyrnidae 497 SPHYRNIDAE Hammerhead and bonnethead sharks iagnostic characters: Small- to large-sized sharks.Body elongate and moderately slender, cylindrical or Dsomewhat compressed. Anterior portion of head much flattened dorsoventrally and widely ex- panded laterally in hammer or shovel form, with the eyes at its outer edges; eyes with well-developed in- ternal nictitating lower eyelids; anterolateral teeth blade-like, with a single cusp; posterior teeth similar to anterolateral teeth or modified into keeled, molariform crushing teeth without cusps. Two dorsal fins, the first dorsal fin high and pointed, its base much shorter than caudal fin and wholly anterior to origins of pel- vic fins; second dorsal and anal fins much smaller than the first dorsal fin and either equal-sized or with the anal fin somewhat larger than the second dorsal fin; caudal fin much less than half of total length and strongly asymmetrical, with a well-marked subterminal notch and a small, but well-defined ventral lobe. Cau- dal peduncle slightly compressed, not strongly flattened dorsoventrally or widely expanded laterally, without lateral keels but with upper and lower precaudal pits present. Intestine with a scroll valve. Colour: back pre- dominantly grey or brassy, sometimes yellow or very dark grey, no prominent markings except dark fin tips in young of some species; underside white or light grey. anterior portion of head dorsoventrally flattened and expanded ventral view of head Habitat, biology, and fisheries: Hammerhead sharks inhabit all tropical and warm-temperate seas, from the surface, surf-line, and intertidal down to at least 275 m in waters near continents, continental islands, and oce- anic islands.Small species are confined to coastal continental waters;juveniles of large species are coastal off continents and islands, while adults are primarily semi-oceanic although they often approach coasts in search of food.
    [Show full text]
  • C: Chapter 3: Fish, Amphibians, and Reptiles
    33 Fish, Amphibians, and Reptiles o you know why frogs and salamanders live near ponds Dor streams? How do fish “breathe” underwater? What is the difference between alligators and crocodiles? In this chapter, you will find the answers to these questions. You also will read about the charac- teristics of animals known as chor- dates and vertebrates, and how fish, amphibians, and reptiles are classi- fied, reproduce, and develop. What do you think? Science Journal Look at the picture below with a classmate. Discuss what you think this might be. Here’s a hint: It can be found in a pond during the spring season. Write your answer or best guess in your Science Journal. 70 ◆ C ow much do you know about reptiles? For exam- EXPLORE Hple, do snakes have eyelids? Why do snakes flick their tongues in and out? How can some snakes swal- ACTIVITY low animals that are larger than their own heads? Snakes don’t have ears, so how do they hear? In this activity, you will discover the answer to one of these questions. Model how a snake hears 1. Hold a tuning fork by the stem and tap it on a hard piece of rubber, such as the sole of a shoe. 2. Hold it next to your ear. What, if anything, do you hear? 3. Tap the tuning fork again. Press the base of the stem firmly against your chin. In your Science Journal, describe what happens. Observe Using the results from step 3, infer how a snake detects vibrations. In your Science Journal, predict how different animals can use vibrations to hear.
    [Show full text]
  • Structure of Gills in Fishes
    Structure of Gills in Fishes Gill Slits: There are six or seven pairs of gills in cartilaginous fishes while four pairs in bony fishes due to the loss of spiracle (Fig. 5.1 a & b). Gill slits of bony fishes are covered by operculum while operculum is absent in cartilaginous fishes. In sharks gill slits are laterally situated while in rays they are ventrally placed. A pair of spiracle is present in Elasmobranchii anterior to first gill which corresponds to a vestigeal primitive first gill slit. Although spiracle is absent in bony fishes, in Actinopterygii it is replaced by a pseudo- branch which is free in some fishes but skin covered in others. Pseudo Branch: In carp and rainbow trout the pseudo branch is embedded in submucosal connective tissue of pharyngeal wall and shows a glandular appearance due to complete conglutination of branchial filaments. (Fig. 5.1a & Fig. 5.2). In some species, a pseudo branch with hemibranchs structure is located inside the operculum. However, in eel the pseudo branch is not present, it is also absent in cat fishes (Siluroidae) and feather back (Notopteridae). In glandular pseudo-branch, abundant distribution of blood capillaries is found in the parenchyma enclosed by connective tissue. It contains acidophilic cells in mitochondria and endoplasmic reticulum and is rich in enzyme carbonic anhydrase. According to Whittenberg and Haedrich (1974), the pseudo-branch regulates the flow of the arterial blood to the opthalmic artery to increase the amount of blood carbon dioxide. Parry and Holliday (1960) found that in rainbow trout extirpation of pseudo-branch induced melanophore expansion and body colour change, suggesting the secretion of a melanophore-aggregating hormone from tissue.
    [Show full text]
  • Basic Finfish Features
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by CMFRI Digital Repository Basic Finfish Features Vivekanand Bharti Fishery Resources Assessment Division 1 Taxonomy is the practice of identifying different organisms, classifying them into categories and naming them. The whole life (living or extinct) of the world are classified into distinct groups with other similar organisms and given a scientific name. The classification of organisms has various hierarchical categories. Categories gradually shift from being very broad and includes many different organisms to very specific and identifying single species. The most common system of classification in use today is the Five Kingdom Classification, proposed by R.H Whittaker in 1969. Five kingdom classification of living organisms is as follows: 1. Kingdom: Monera It consists of primitive organisms. The organisms are very small and single celled. It includes species like the Bacteria, Archae bacteria, Cyanobacteria and Mycoplasma. 2. Kingdom: Protista It is single-celled eukaryotes and mainly belongs to aquatic. It includes diatoms, euglena and protozoans like Amoeba, Paramecium, Plasmodium, etc. Training Manual on Species Identification 3. Kingdom: Fungi Kingdom Fungi is also called Kingdom Mycota and consists of network of thread- like structures called as mycelium. The bodies consist of long, thread-like structures which is called hyphae. These organisms are mostly saprophytes or parasites and also symbionts. This kingdom of fungi also includes Lichens, Mycorrhiza, etc. Example: Aspergillus. 4. Kingdom Plantae Kingdom Plantae is also known as Kingdom Metaphyta. It is eukaryotic, mutlicellular plants. This kingdom includes all types of plants like herbs, shrubs, trees, flowering and non-flowering plants.
    [Show full text]
  • In the Dogfish (Scyliorhinus Canicula)
    J. Exp. Biol. (1965), 43, 363-383 363 With 12 text-figures Printed in Great Britain THE MUSCULAR BASIS OF THE RESPIRATORY PUMPS IN THE DOGFISH (SCYLIORHINUS CANICULA) BY G. M. HUGHES* AND C. M. BALLINTIJNf Marine Biological Laboratory, Plymouth, and Department of Zoology, Cambridge {Received 17 March 1965) The mechanism of gill ventilation in the dogfish has been shown to be fundamentally the same as that found in teleost fishes (Hughes, 19606; Hughes & Shelton, 1962). Water enters the respiratory system through both the mouth and the spiracle during expansion of the oro-branchial cavity (Woskoboinikoff, 1932) and after passing across the gills it enters the parabranchial cavities before being ejected to the outside through the five pairs of gill slits. The flow across the gills is maintained partly as a result of the increased pressure in front of the gill resistances but also because of the suction pump action of the parabranchial cavities. The muscular activities producing the changes in volume of these two cavities and hence the required pressure gradient across the gills have not been established and descriptions of the relationships of muscles and skeleton are not always clear in detail. Woskoboinikoff (1932) and others were of the opinion that the coraco-mandibularis muscle was of importance during the phase of the cycle when the mouth opens and the oro-branchial cavity expands, but this was categorically denied by Balabai (1938) in a footnote to his paper. From observations on dogfish, anaesthetized so that they no longer pumped water across their gills, it was suggested (Hughes, 1960 a) that the main muscular action during the cycle was due to the constrictor muscles.
    [Show full text]