WEEK 5, VERTEBRATE ZOOLOGY 03051: THE BONY FISHES 2/15/00
Text (7th ed.): Ch. 27, pp. 591-605. Dr. W. Crone (303 FTZ, 629-7439, cronewil@hvcc.edu, http://www.hvcc.edu/academ/faculty/crone/index.html)
possible web site: http://www.fishbase.org/ (a wide-ranging resource)
http://www.odysseyexpeditions.org/indexfish.htm
(many pictures, with coverage of a variety of fish topics)
possible HVCC audio/visual resources: VT 3373,"Eyewitness: Fish" (to be seen in recitation)
VT 1182,"Life on Earth: Bony Fishes" (footage and discussion of many different fish and their lifestyles)
LIFE IN THE WATER:
Movement: Fish are streamlined, and bony fish in particular are lubricated (mucus secretions), pushing through water with fins and their body. One can see a contrast between the entire wiggling body of an eel or other elongated fishes vs. the caudal fin/posterior body propulsion of most fish.2 Muscle bundles (myomeres) are in a zig-zag pattern, and so contractions can affect a large portion of the body wall. The myomeres bend the spine, and hence the body, when they contract, allowing the body to push against the water. There are dorsal epaxial and ventral hypaxial muscles: the tall spinous processes of fish vertebrae are associated with the epaxial muscles.
Nutrition: Most fish are predators, actively hunting. Others are filter feeders that can use the the gill rakers off of the gill arches to direct food inward.1 Fish have a stomach for storage of large, infrequent meals. In the case of a typical fish such as a perch, this is broken up into cardiac (anterior) and pyloric (posterior) aspects of the stomach, with a pyloric valve (sphincter) limiting the amount of stomach contents that enter the intestine. The intestine has outpocketings or pyloric ceca in some bony fish. Pancreas, liver, and gallbladder are additional digestive organs.
Gas exchange and tissue oxygenation: We live in air, 20% O2, but fish live in water, 2.5% O2, so fish must pass a lot of water over their gills. Most fish pump water over the gills with pharyngeal and opercular muscles. There are separate oral and opercular cavities. Gill arches support gill filaments which are covered by gill lamellae. Blood in the capillaries and water rushing over the gills flow in the opposite direction, or countercurrent mechanism. This allows the maximal extraction of oxygen possible out of the water. A heart with atrium (blood-collecting) and ventricle (blood-pumping) chambers pumps the blood in a one-pass circulation through the gills and then to the rest of the body.
Buoyancy: Fish use four ways of regulating buoyancy:3
The cartilaginous fishes use strategies #1-3 (as a supportive tissue, cartilage is lighter than bone), but the bony fishes, in particular, use strategy #4.
Swim bladder: originally, and as still seen in primitive bony fish (chondrosteans and holosteans) and many fresh-water fish, the gas chamber or pneumatic sac is connected to the digestive tract, so that by swallowing air, one could get air into it (or if sufficiently vascularized, it could function as a lung). Lungs are endodermal derivations from the posterior pharynx, and so are homologous to the swim bladder. Most of the advanced bony fish (teleosts) have lost this digestive tract connection, and instead rely on gas release from the blood via a vascular capillary network called the rete mirabile that feeds a gas gland. This allows a bony fish to regulate the amount of gas in the swim bladder, depending on the depth the fish is swimming in.
Nervous and sensory functions: The central nervous system of a vertebrate consists of a brain and spinal cord. Some bony fish, e.g. salmon, rely heavily on the sense of smell to find their way back for spawning. Fish eyes are lidless and lenses are round and firm. Inner ear function in fish is similar to other vertebrates, but more emphasis on semicircular canals for balance and equilibrium than in hearing (fish lack outer ears, but can hear, given water's density).3 A lateral-line system is seen in fish, where a collection of pits along the side of the fish allow sensation of pressure changes in the water.
Excretion and osmoregulation: Regulation of a proper balance of water and ions is osmoregulation. Fish do this by gills and by kidneys. Fish kidneys are dorsal and retroperitoneal (under the peritoneal lining) just like ours, and contain the functional units of nephrons. In general, there are two major osmoregulatory concerns:
|
freshwater fish: |
need to control excess buildup of water, so rarely drink, and excrete large amounts of dilute urine. |
|
saltwater fish: |
need to control water loss, so drink water, and can excrete toxic ammonia across the gill surfaces. |
Imagine the challenge of the lifestyles of eels and salmon, as they spend parts of their life cycles in both salt and freshwater.
Reproduction: Cartilaginous fish lay only a few eggs at a time, but bony fish reproduce by producing many, many eggs, with only a few surviving. Most fish are oviparous (egg-laying) and externally fertilize. In a perch, there is a single ovary in the female, but paired testes in the male. Even this reproductive capacity is hard-pressed to keep up with levels of human fishing.
THE BONY FISHES:
Major characteristics of the bony fish (Class Osteichthyes) that distinguish them from the cartilaginous fish are: some bone in skeleton and/or scales; operculum covering gill slits; dermal scales; swim bladder (and/or lungs); terminal mouth; homocercal tail.2
Structural elements: Skeleton of bone, with axial and appendicular components. We see ribs in the bony fish. In contrast to the tooth-like placoid scales of sharks, the bony fish have three possibilities: ganoid scales ("bright") (seen in the gar and coelacanth) that have an enamel (ganion) on top and bone on the bottom; cycloid scales ("circular") (seen in teleosts) with anterior grooves and concentric growth lines; and ctenoid scales ("comblike") (advanced teleosts) with small posterior teeth.1 These dermal scales show growth rings, and are covered by a mucousy epidermis that accounts for a fish's slipperiness.
Ray-finned fish, Subclass Actinopterygii ("ray fin/wing"), with three main groups:
a) The chondrosteans ("cartilage bone") are an ancient group from the early days of the dinosaurs (beginning of Mesozoic Era), with only a few species alive today. They have fossil representatives with bony skeletons, but today's species have a lot of cartilage in their skeletons (and a heterocercal tail, and a spiral valve in their intestine--does this sound familiar from another group?): sturgeons (famous for caviar), paddlefish (the paddle or rostrum is evidently sensory), and bichirs, with lung-like swim bladders, which must gulp air to live.
b) The holosteans ("whole bone"), or nonteleosts, which also flourished in the Mesozoic, have two American representatives left: the gar and the bowfin. Holosteans have more bone in their skeletons than chondrosteans (check out gar and bowfin skulls in lab), but have other primitive features, e.g., an intestinal spiral valve. Gars are characterized by ganoid scales, and long snouts good for hunting; bowfins are so named because of their fin shape.
c) The teleosts ("complete bone") include most of our modern bony fish.
Fleshy-finned fish, Subclass Sarcopterygii ("fleshy fin/wing") with two main groups:
a) the lungfishes. Modifications seen in circulation with lungfishes: blood vessels off of aortic arch VI form the pulmonary artery to the lung. In lungfish, blood returns to the heart through pulmonary veins to enter the left side of the heart. Partial divisions in the atrium and ventricle help to keep the oxygenated/deoxygenated blood flow separate, and a spiral valve in the conus arteriosus helps to direct blood to either the pulmonary artery off of aortic arch VI vs. to the other aortic arches (thus establishing a distinction between pulmonary and systemic circulation).2,3
b) the lobe-finned fish. 1938: a modern coelacanth was discovered in deep waters off of Madagascar. Ancient lobe-finned fishes evidently had a functional lung along with sturdy, fleshy-based fins. A skeleton like that of Ichthyostega indicates a close relationship between the ancient lobe-finned fish and the first amphibians. Features to notice: limbs (with hypaxial muscles); development of neck to free forelimb girdle from the skull.
1 L Harris, Concepts in Zoology, 2nd ed. (HarperCollins, New York, 1996), pp. 765, 766.
2 CP Hickman Jr, et al., Biology of Animals, 7th ed., (WCB McGraw-Hill, Boston, 1998), pp. 592, 596, 607.
3 SA Miller, JP Harley, Zoology, 2nd ed. (WC Brown, Dubuque, IA, 1994), pp,. 425, 427, 428.
|main page| |background| |03028: Physiology| |03048: Anatomy|
|03050: Invertebrate Zoology| |03051: Vertebrate Zoology| |03074: Economic Botany|
Please send comments and questions to: cronewil@hvcc.edu
Copyright 1999, 2000 by Wilson Crone
External and unofficial links are not endorsed by Hudson Valley Community College
This web page last updated on February 15, 2000