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Biology of Cultured Fish
Developed by the Harbor Branch ACTED staff
Freshwater Fish
Less than 1% of the Earth is freshwater
• 40% of fish are freshwater
• less than 5000 m deep
• species are a result of evolutionary
isolation and ecological adaptation
• No global species
• Two species are circumpolar
Marine Fish
Earth is 71% saltwater
• 60% of fish are marine
• Less evolutionary variable and
ecologically isolated
• The oceans provide much bigger space
• Many have large ranges
• 7000 m deep
• 130 global species
Tuna
distribution
in southern
oceans
Where are most fish found?
And at what depth?
Ichthyology
“the study of fishes”
• 25,000 living species
• 53,000 scientific names
• 200 new species each year
Some definitions…
Fish – singular and plural for a species
Fishes – refers to more than one species
Fish
Fishes
Why classify organisms?
Taxonomy – scientific classification
Systematics – the study of the
relationship among taxa; studies the
history of life
How are plants and
animals classified?
Who? Carolus Linneaus, 1700’s, Europe
What? Developed binomial nomenclature
• Kingdom
•Phylum
•Class
•Order
Red Snapper
•Family
Lutjanus campechanus
•Genus
•Species
How would an aquaculturist
classify fish?
• Temperature
• Salinity
• Reproduction
Temperature
Cold (trout, salmon)
Temp: below 15 C
Cool (catfish, striped bass)
Temp: 15 – 25 C
Warm (tilapia)
Temp: above 25 C
Salinity
Freshwater (< 1ppt)
Brackish water (1-15 ppt)
Saltwater (15-36 ppt)
Euryhaline – adapts to
different salinities
Stenohaline – cannot adapt
to different salinities
Osmoregulation
• Aquatic species may be classified in terms of
their salinity tolerance as either:
•
•
•
saltwater species
brackish water species
freshwater species
• Salinity requirements may differ for a given
species at different stages in its life cycle.
• Species adapted to a narrow range of
salinities are described as stenohaline .
• Species which are able to tolerate a wide
range of salinities are described as euryhaline.
Osmoregulation
Osmosis
The net movement of a solvent across a
permeable membrane from the side with
the lower concentration to the side with the
higher concentration.
Less Concentrated
Membrane
More Concentrated
Solute particles
Solvent
Net Direction of Flow
Osmoregulation
• For fish we can think of the body fluids as
one solution, the surrounding water as the
other solution, and the parts of the body
separating the two solutions as the
membrane.
• In most organisms the gills are the primary
membranes where osmosis occurs.
Osmoregulation: Marine Fish
• The body fluids of saltwater species are
hypotonic (dilute) relative to the surrounding
water, so these species tend to lose water to
the environment.
• Osmoregulation in saltwater species
requires intake of water and excretion of
excess salts.
Osmoregulation:
Marine Fish
Osmoregulation: Freshwater Fish
• The ionic composition of the body fluids
of freshwater species is hypertonic
(more concentrated) to the surrounding
water, so these species tend to
accumulate water from the environment.
• Osmoregulation in freshwater species
involves excretion of water and active
uptake and retention of salts.
Osmoregulation:
Freshwater Fish
What is a fish?
Photograph by HBOI
Anatomy & Physiology
• Lives in water?
• Carnivore, Omnivore, Herbivore
• Vertebrate
• Poikilotherm “cold blooded”
• Fins
• Gills
• Senses
• Lateral line
• Scales
• Slime (mucus)
• Swim bladder “buoyancy compensator”
• External or Internal Reproduction
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