Fish Biology

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Fish Biology
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Fish shapes

• Cold-blooded aquatic animals with backbones,
  gills, and fins
• Most are torpedo-shaped (fusiform) for efficient
  travel through water, but they may be flattened
  and rounded (flounder), and vertical and angular
  (sea horses)

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Fish Size

• Fish range in size
• the pygmy goby, which reaches only 12mm long and
  1.5g in weight sexually mature at 6mm
• The whale shark grows to 18m and weighs over 20
  tons

• The tiny coral reef-dwelling fish called the
  pygmy goby has taken the record as the
  shortest-lived vertebrate. The pygmy goby lives
  an average of 59 days, pipping the previous
  record holder, an African fish which lives for
  just over two-and-a-half months. (BBC News)

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Fish Distribution

• Found throughout the world
• Altitudes of more than 5000m to depths of about
  10km
• Some inhabit hot springs, such as Cyprinodon,
  where water may reach 45C
• Others are found in the Antarctic seas, such as
  Chaenocephalus, where it may be less than 0C
• 107 species are distributed worldwide in tropical
  and subtropical waters, but many species have
  limited ranges

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Fish Distribution

• There are 20 000 or more fish species
• 60 live in marine waters
• 40 are found in fresh water
• Most of the worlds fish are continental - either
  in freshwater on land, or in the sea close to the
  coast
• Coasts are good for fish as they are rich in
  nutrients such as nitrates and phosphates from
  rivers, upwelling, aeration from the surf and
  tide, and the sunlight

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Fish Anatomy

• Three classes
• Agnatha (jawless fishes) that consists of hagfish
  and lampreys
• Chondrichthyes (cartilaginous skeleton) that
  consists of sharks and rays
• Osteichthyes (bony-skeleton) all other fish

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Skeletons

• Skeletons of the three groups are very different
• Hagfish and lampreys have a notochord, a rod-like
  structure composed of unique tissue

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Skeletons

• Sharks and rays have a notochord that is
  surrounded and constricted by the vertebrae, to
  form a backbone. The remainder of their skeleton
  is composed of cartilage, not bone (but it can be
  hardened by calcareous salts)
• Primitive bony fishes have vertebrae that are
  mostly cartilaginous, but advanced fish have bony
  vertebrae united to form a backbone, with no
  notochord

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Fins

• Fins are either median or paired
• Median fins are along the centerline of the body,
  at the top, bottom, and the end
• Dorsal fin (top) may be one or several fins (one
  behind the other), and may include a fleshy fin
  (adipose) near the tail
• Bottom (anal) fin is located on the belly behind
  the anus
• End fin is called the tail, or caudal fin

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Fins

• Pectoral fins are at the front of the body,
  behind the gill openings and usually provide
  maneuverability
• Pelvic fins (ventral fins) are along the bottom
  of the body but can vary in their placement (can
  be in the middle of the belly, below the
  pectorals, or in front of the pectorals.) Can
  provide maneuverability

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Scales

• Scales are colorless
• Coloring of the fish comes from the structures
  beneath or associated with the scales
• Not all species of fish have scales, or they can
  be so tiny it would appear that they do not have
  any
• Scales may only be present on small areas of the
  body
• Arranged in imbricate (overlap like shingles) or
  mosaic (fitting closely together or barely
  separated)

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Four Basic Scale Types

• 1. Placoid scales (dermal denticles)
• are on sharks and rays, and are tooth-like in
  structure (enlarged ones are actual teeth in
  sharks)
• Scales do not increase in size, so new scales
  must be added as the shark grows

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• 2. Cosmoid scales
• Coelacanth have them
• Also in lungfishes (only single-layered)
• Four-layered bony scale

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• 3. Ganoid scales
• Found on gars
• Typically squarish
• Single bony layer

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• 4. Leptoid scales
• Derived from ganoid scales by the loss of the
  ganoin layer
• Single layer of bone
• Found on the higher bony fishes and occur in two
  forms cycloid (circular) and ctenoid (toothed)

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Fish Circulation

• Blood transports oxygen, nutrients, and wastes
• Single circuit heart-gills-body-heart
• Fish heart is two-chambered, with an upper atrium
  and lower ventricle
• Other organisms may have three or four-chambered
  hearts

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Fish Respiration

• Fish must extract oxygen from the water and
  transfer it to their bloodstream
• This is done by gills, lungs, specialized
  chambers, or skin
• More difficult than extracting oxygen from air
• Some fish can extract as much as 80 of the
  oxygen in the water passing over the gills
  whereas humans can only extract about 25 of the
  oxygen from the air taken into lungs

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Gills are efficient because

• Large surface area gills have 10 to 60 times
  more than body surface area
• Short distance for oxygen to diffuse blood in
  the gills is close to the water
• Countercurrent circulation blood flows forwards
  while the water flows the other so that there is
  always less oxygen in the blood than in the water
• Water flows one direction only over the gills

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Fish Body Temperature

• Cold-blooded body temperature varies with
  external temperature
• Blood passing through the gills loses heat to the
  water so that a fishs body temperature is
  usually within a degree of the water temperature
• There are some warm-blooded fish (tuna, mackeral
  sharks) they have a countercurrent circulatory
  network that keeps their bodies 5 to 12 degrees
  warmer than the water

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Fish Water Balance

• Blood of freshwater fish is more salty than the
  water in which they live
• Osmotic pressure causes water to diffuse into the
  fishs body through the gills, mouth membranes
  and intestines
• Must eliminate excess water so they produce very
  dilute urine (ex. Lampreys may create an amount
  of urine up to 36 of their body weight per day)
• A gain in water means a loss in salt, so they
  absorb salt from the water with their gills

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• Marine bony fishes have blood that is less salty
  than sea water, so they lose water and absorb
  salt
• So they drink seawater and produce little urine
• Excrete excess through gills or anus

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• Hagfish have a salt concentration equal to that
  of seawater
• Sharks retain the excess salt to keep the sharks
  blood at a higher salt concentration than seawater

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Fish Gas Bladder

• Reducing body weight is important to fish so they
  expend less energy to keep at a given depth
• Total body density equal to that of water would
  be weightless, not floating or sinking
• Fat is less dense than water, so some fish have
  up to 1/3rd of their weight in fat (such as deep
  sea sharks that have large livers that contain
  squalene)

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• Many fishes have a gas-filled bladder
• The amount of body volume that it takes up will
  depend on whether the fish is freshwater or
  marine
• Freshwater is less dense and is less buoyant, so
  they need a larger gas bladder to keep from
  sinking
• -Gas bladders can be 7-11 of body volume in
  freshwater fish, and 4-6 in marine fish

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• Gas levels within the bladder must be adjustable,
  or the fish would always remain at the same depth
• In some fish, air is gained through gulping fresh
  air, and expelling it through the mouth and
  gills in others the gas is exchanged through the
  blood system

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Fish Lateral Line System

• This is sensitive to differences in water
  pressure
• Can be due to changes in depth or waves
• Consists of a neuromast, which is a bundle of
  sensory and supporting cells that have hairs that
  are enclosed in a gelatin
• Neuromasts send out nerve impulses and when
  pressure causes the hairs to move, the nerve
  impulses will increase or decrease

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• Neuromasts may be single, in small groups (pit
  organs), or in rows (lateral line system)
• Lateral line system runs along the sides of the
  body onto the head, where it divides into three
  branches two to the snout and one to the lower
  jaw
• Another fish swimming will cause a pressure wave
  in the water that can be detected by the lateral
  lines of other fish
• When a fish is swimming towards something, the
  pressure waves will change around its body, which
  will tell the fish to swerve to avoid the object

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Fish Reproduction

• Most are egg-layers
• Some bear live young
• Live-bearing fish are either ovoviviparous (eggs
  hatch within the female) or viviparous (unborn
  are supplied with nutrients from the mothers
  tissues)
• Live bearing and some egg-layers have internal
  fertilization and they have modified structures
  that will introduce sperm into the females body

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• Three modes of reproduction
• Heterosexual (most popular)
• Hermaphroditic
• Parthenogenetic

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Heterosexual

• In some live-bearing fishes the female may be
  able to store the sperm for up to 10 months and
  is used to fertilize new batches of eggs as they
  develop
• Some females may carry sperm from multiple males

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Hermaphroditic

• Single fish could be both male and female,
  produce eggs and sperm (either at the same time
  or at different times) and will mate with another
  hermaphrodite
• External self-fertilization can occur, or
  internal self-fertilization
• Some fish will switch their sex as they age

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Parthenogenetic

• Unfertilized eggs develop into embryos known to
  one fish species, Poecilia formosa, of the Amazon
  River
• Development will continue without fertilization,
  but mating with a male is still required to
  stimulate egg development

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Parental Care

• Some fish form huge schools of males and females,
  release their eggs and sperm, and then leave
• Other fish build nests and care for eggs and
  newly hatched young
• Others will carry the eggs with them in such
  places as their mouths, gill cavities or other
  cavities

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The most fascinating thing about the Arrowana is
that it is a mouthbrooder,capable of carrying
hundreds of eggs in its mouth and even after they
hatch, the little fish live in their mother's
mouth till the time they learn the ways of the
world
http//hubpages.com/hub/The-Mouthbrooder-Dragon-Fi
sh-Arowana