Biology of Cultured Fish Developed by the Harbor Branch ACTED staff

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

Less than 1% of the Earth is freshwater 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 Family Genus Species Red Snapper Lutjanus campechanus

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 • saltwater species 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. Net Direction of Flow More Concentrated Less Concentrated Solvent Solute particles Membrane

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