Fish

Year 2 Exotics

What are the 3 main categories of fish species?

jawless (Agnatha)

cartilagenous (Chondrichthyes)

ray-finned (actinopterygii)

How do fish survive in sub-zero waters?

they have antifreeze in their blood

What is required in a fish environment?

adequate water salinity depending on species

specific temperature

correct oxygen concentration depending on requirements

high water quality

territorial fish housed alone, shoal fish housed together

surface/substrate feed or live food

correct pH water

correct water hardness

enough space

What are the features of the Rainbow Trout?

purely freshwater forms and anadromous forms

can tolerate 0-25 degrees

need fast-flowing water

aggressive predator

What are the features of the Common Carp?

fresh water required

can tolerate 4-35 degrees

social

minimal aggression

over a metre long

Why are Rainbow Trout kept?

for laboratory research

Why are Common Carp kept?

for food, farming for angling and ornamental

What are the features of the Sea bass?

saltwater but can tolerate brackish

can tolerate 4-28 degrees

social

grow fast

Why are sea bass kept?

for food or racing

What are the features of the Mudskipper?

up to 25cm long

brackish water

spends most of time out of water

requires a humid environment to prevent desiccation

males are very aggressive

Why are Mudskippers kept?

in aquariums and occasionally as pets

Why does fish tank water need filtration?

fish release metabolic waste ammonia from their gills and urine which is very toxic, and their faeces will decay in the water

What are the 3 stages of water filtration?

1. mechanical

2. biological

3. chemical

What are the 4 main methods of mechanical filtration?

filter matts

swirl filters

sand filters

brushes

What is the purpose of biological filtration of fish tanks?

to encourage the growth of beneficial autotrophic bacteria which will break down toxic nitrogenous waste into a harmless form via nitrification

What is the purpose of mechanical filtration of fish tanks?

to physically trap and remove large debris

What is the process of nitrification of nitrogenous waste?

1. toxic ammonia is converted to nitrite by ammonia oxidising bacteria

2. nitrite is then converted to less toxic nitrate by nitrite oxidising bacteria

What does this diagram show?

the cycling of a fish tank:

ammonia levels increase and then decrease as ammonia is converted to nitrites, and then to nitrates

the sudden drop in the line is when the water of the tank is changed

What is the purpose of chemical filtration of fish tanks?

to remove specific undesirable substances from the water

What are the 3 main methods of chemical fish tank filtration?

carbon granules - remove colour from water

zeolite - removes ammonia from freshwater

phosphate removing granules - prevent algae growth

What are the 3 main management systems of fish?

open

semi-closed

closed

What are the features of an open fish management system?

caged environment in rivers, lakes, seas etc

rely on the natural system to maintain water quality

vary in density of fish kept and active feeding

Which fish tend to be kept in open systems?

sea bass and salmon

What are the features of a semi-closed fish management system?

inland aquaculture system which flows through raceways

has an inlet and outlet with fast continuous water flow which maintains a high water quality

can be fresh or brackish water

can house high densities of fish

requires active feeding and a continuous water source

Which fish are often kept in semi-closed systems?

trout, catfish and tilapia in freshwater

sea bass and sea bream in brackish water

What are the features of a closed fish management system?

minimal water and land use

water is reconditioned and recirculated

can be marine or freshwater

houses high fish densities

needs very controlled growth conditions

produces less waste water

needs very efficient biofiltration

expensive to set up and maintain

requires highly trained staff

produces more greenhouse gas emissions

What are the features of a good fish tank?

cover to prevent water evaporation and escape

lamp to provide light-dark cycle for fish and to control plant growth

filter - can be undergravel or external

food

enrichment

What are the external features of cartilagenous fish?

unpaired median fins

2 sets of paired lateral fins

pectoral fins act as hydrofoils

pelvic fins with claspers in males - act as intromittent organ for internal fertilisation

5 gill slits with 4 internal gill arhces

spiracle (in some)

lateral line organ of mechanoreceptors which detect water pressure changes on the body surface

What remnants of ears do fish have?

semicircular canals

What features of ears do fish not have?

outer ear

inner ear

cochlea

What are the external features of ray-finned fish?

lateral line

first and second dorsal fin

caudal fin

anal fin

pelvic fin

What are the external features of lobe finned fish?

unique supportive elements in skeleton of girdle and limbs

secondary reduction in some lungfishes

some air breathers (facultative and obligatory)

variable fins

How does breathing in water compare to air?

requires more energy for ventilation

more difficult to retain body heat

water contains much less oxygen so higher ventilation rates are required to meet the oxygen demand

A

spiny (dorsal fin)

B

soft-rayed (dorsal fin)

C

dorsal fin

D

caudal fin

E

anal fin

F

pectoral fin

G

pelvic fin

Which 3 things were facilitated by fish moving onto land?

highly active lifestyles

higher metabolic rates

endothermy

What are the features of a fish gill?

pressure pump

4 gill arches on each site

each gill arch has 2 rows of filaments

filaments contain hundreds of lamellae

Which direction does water flow through a fish during gas exchange?

into mouth through gills (unidirectional)

What are the adaptations of fish gills?

large surface area

highly efficient counter-current flow of water and blood

thin lamellae with short diffusion distance for respiratory gases

How can you tell the freshness of a dead fish from its gills?

gill colour - brighter red shows the fish died more recently and brown shows the fish is older due to haemoglobin breaking down

What features of a fish reduce drag caused by water?

rounded body

maximum diameter making up a quarter of the fish’s length

maximum diameter at 30-40% along the length of the body

reduced scale size

mucus cover

What are the different locomotion strategies used by fish?

movement type is either undulation (smooth movement up and down) or oscillation (rapid hitting up and down)

species can use their trunk/caudal fin/ dorsal fin/ anal fin/ pectoral fin for generation of power

What is enabled by fish who move using their dorsal/anal/pectoral fin?

precise hovering, manoeuvering and backing

What is enabled by fish who move via undulation using their trunk?

extreme flexibility in complex habitats

What is enabled by fish who move via undulation/oscillation using their trunk and caudal fin?

efficient fast start

What is enabled by fish who move via oscillation using their trunk and caudal fin?

continuous cruising

1

food

2

fish waste (ammonia)

3

excess food and decomposing plant matter (ammonia)

4

ammonia oxidising bacteria

5

nitrites (NO₂^-)

6

nitrite oxidising bacteria

7

nitrate ions (NO₃^-)

What role do gills have in excretion?

nitrogenous waste is excreted through the gills as ammonia (urea or uric acid as well in some species)

How does a saltwater fish osmoregulate?

1. water and salt ions enter fish through food and drinking seawater

2. salt ions are excreted from gills

3. water is lost through the gills and other parts of the body surface via osmosis

4. salt ions and small amounts of water are excreted via very small amounts of urine in kidneys

How does a freshwater fish osmoregulate?

1. water and some ions from food are taken in by the fish

2. salt ions are also taken up by the gills

3. water is gained through the gills and other parts of the body surface via osmosis

4. large amount of water are excreted in dilute urine produced by the kidneys

How does water retention behaviour differ between saltwater and freshwater fish?

saltwater fish actively drink a lot more water and produce a lot less urine than freshwater fish

How do fish thermoregulate?

most species are ectotherms, meaning that their body temperature is determined by the environmental temperature

many tuna species and some sharks are partial endotherms

How does partial endothermy in fish work?

counter-current vascular heat exchangers allow warm venous blood leaving working muscles to heat incoming cold arterial blood from the gills (occurs in muscles, liver, eyes and brain)

What system of circulation do fish use?

single loop

low pressure in the whole system

no blood pooling in lower appendages