Biology of Cultured FishBiology of Cultured Fish

Developed by the Harbor Branch ACTED staff

Freshwater FishFreshwater FishLess 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 FishMarine FishEarth 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?Where are most fish found?

And at what depth?And at what depth?

IchthyologyIchthyology“the study of fishes”

• 25,000 living species• 53,000 scientific names• 200 new species each year

Some definitions…Some definitions…Fish – singular and plural for a species

Fishes – refers to more than one species

Fish Fishes

Taxonomy – scientific classification

Systematics – the study of the relationship among taxa; studies the history of life

Why classify organisms?Why classify organisms?

How are plants and How are plants and animals classified?animals classified?

Who? Carolus Linneaus, 1700’s, Europe

What? Developed binomial nomenclature

• Kingdom•Phylum

•Class•Order

•Family•Genus

•Species

Red Snapper

Lutjanus campechanus

How would an aquaculturist How would an aquaculturist classify fish?classify fish?

• Temperature• Salinity• Reproduction

TemperatureTemperatureCold (trout, salmon)Temp: below 15 C

Cool (catfish, striped bass)Temp: 15 – 25 C

Warm (tilapia)Temp: above 25 C

SalinitySalinityFreshwater (< 1ppt)

Brackish water (1-15 ppt)

Saltwater (15-36 ppt)

Euryhaline – adapts to different salinities

Stenohaline – cannot adapt to different salinities

OsmoregulationOsmoregulation• Aquatic species may be classified in terms of Aquatic species may be classified in terms of

their salinity tolerance as either:their salinity tolerance as either:• saltwater species• brackish water species• freshwater species

• Salinity requirements may differ for a given Salinity requirements may differ for a given species at different stages in its life cycle.species at different stages in its life cycle.

• Species adapted to a narrow range of Species adapted to a narrow range of salinities are described assalinities are described as stenohaline .

• Species which are able to tolerate a wide Species which are able to tolerate a wide range of salinities are described asrange of salinities are described as euryhaline.

OsmoregulationOsmoregulationOsmosis The net movement of a solvent across a permeable The net movement of a solvent across a permeable

membranemembrane from the side with the lower concentration from the side with the lower concentration to the side with the higher concentration.to the side with the higher concentration.

Net Direction of Flow

More ConcentratedLess Concentrated

Solvent Solute particles

Membrane

OsmoregulationOsmoregulation• 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 FishOsmoregulation: 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: Osmoregulation: Marine FishMarine Fish

Osmoregulation: Freshwater FishOsmoregulation: Freshwater Fish• The ionic composition of the body fluids of The ionic composition of the body fluids of

freshwater species isfreshwater species is hypertonic (more (more concentrated) to the surrounding water, so these concentrated) to the surrounding water, so these species tend to accumulate water from the species tend to accumulate water from the environment.environment.

• Osmoregulation in freshwater species involves Osmoregulation in freshwater species involves excretion of water and active uptake and excretion of water and active uptake and retention of salts.retention of salts.

Osmoregulation: Osmoregulation: Freshwater FishFreshwater Fish

What is a fish?What is a fish?

Photograph by HBOI

Anatomy & PhysiologyAnatomy & 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