Week 10 Fish Husbandry Flashcards
Fish are ectothermic - what does that mean ?
Cold blooded so body temperature is dependant on their surroundings
What protection from diseases and water chemistry do fish have ?
(3)
- Mucus layer
- Skin
- Immune system
What are disease causing pathogens in fish?
(4)
- Bacteria e.g. Fin-rot
- Fungi
- Parasites e.g. white spot
- Viruses e.g. Koi herpes virus (KHV), Spring viraemia of carp (SVC)
Name the diseases in fish
- Fin rot
- Fungus
- White spots
- Koi Herpes Virus
- Spring Viraemia of Carp
What is the cause of most health issues in fish?
Poor husbandry → poor environmental conditions for fish →
increased stress and lowered immune system → prone to diseases
What fish require from their environment?
(4)
- Good water quality
- Oxygen
- Stable conditions
- Complete and balanced diet
What are the 4 tank and water system types
- Marine (eg estuaries, ocean) or freshwater (lakes and rivers) – vary in salinity
- Tropical or temperate – vary in temperature
What factors must be monitored in water quality?
7
- Dissolved gases
- Nitrogenous compounds
- Temperature
- pH
- Hardness
- Alkalinity
- Salinity
Why must fish be very efficient at extracting oxygen from
water?
Water only holds 3% of the oxygen cf with air of the same volume
What is Hypoxia?
low oxygen levels
What causes hypoxia?
- High stocking density
- Overfeeding
- Many rotting organic matter being broken down by bacteria
- Excessive plants
How much dissolved oxygen is needed?
**Most fish require at least 6mg/l DO
**
- Vary with species, age, size and health of the fish
- Stress & feeding increase oxygen requirements in fish
How dissolved oxygen (DO) is measured?
- Photometer
- Electronic meter
- Chemical test kit
What happens if DO levels become too low ?
- Fish gasp and die
- Larger fish succumb first
- Orfe species are the first to die
- Fish look spotless/perfect = characteristic of death due to low DO
Cuases for low DO?
- High temperatures in summer
- higher demand for oxygen but warm water holds less oxygen
- During the night
- Pond plants use up oxygen
- Nights are muggy and warm making DO even lower
Describe extensive fish keeping
E.g. rivers
* Large area, low stocking density
* Low risk, low return
* Low risk of stress to fish
Describe intensive fish keeping
e.g. tanks, ponds, aquaria
* High stocking density
* High risk, high return - Need to input a lot of energy, food and
investment for it to work
* High risk of stress to fish
* High stocking density will decrease DO
What are other dissolved gases?
- Carbon dioxide - Produced by fish, bacteria and plants at night
- Nitrogen - Issue when nitrogen forced into water at high pressure and faster rate that it can diffuse out
- can cause air emboli in fish
Nitrogenous compounds
- Fish excrete ammonia (NH3) from gills & kidneys as a waste product
- Bacteria (e.g. Nitrosomonas) found in water & the filter convert NH3 to nitrite (NO2) by oxidation
- Other bacteria (e.g. Nitrobacter) then oxidise nitrite to nitrate (NO3)
Ammonia (NH3) → Nitrite (NO2) → Nitrate (NO3)
What can fish tolerate more nitrate, nitrite or ammonia?
Nitrate more than ammonia and nitrite
Ammonia & nitrite are both v. toxic to fish
Maximum nitrate: 50 mg/l
Maximum ammonia level: 0 mg/l
Maximum nitrite level: 0 mg/l
Describe the nitrogen cycle
- Fish faeces, uneaten food
and dead plants produce
ammonia - Nitrification: Ammonia
converted/oxidised to
nitrites and then nitrates
by bacteria - Nitrates are then
absorbed by plants, are
denitrified to nitrogen gas
or removed from the
water system with water
changes
How do bio filters work?
- Use naturally occurring bacteria to breakdown ammonia into nitrites and then nitrates (less toxic)
- Takes several weeks for these bacteria to grow in filters and function efficiently
What are the most common causes of ammonia/nitrite problem?
3
- Too many fish added to pond/tank too quickly or too many fish in a mature pond
- Immature filter – can take 3 months to fully mature (New Pond Syndrome (NPS))
- Overfeeding
How to measure nitrogenous compounds?
- Chemical test kit
- Ion-specific photometer
Why is temperature control important for fish?
- Fish are ectothermic
- Metabolic, feeding and growth ratesof fish depend on it
- Sudden changes in temp = stress so more prone to disease
- Higher temp = less DO + more ammonia
Describe fish in winter
In winter fish are inactive (<10°C) and resume activity and growth
in summer
Describe fish in Autumn
Fish ‘slow down’, their immune system so become suppressed therefore opportunistic pathogens (fin-rot, fungus) may cause infection
Describe the issue with transition from winter to spring
- As water starts to warm after winter, opportunistic pathogens increase quicker than the fish’s immune system (Spring Mortality Syndrome)
- Spring is a classic period for attack by viruses (Spring Viraemia of
Carp (SVC), Koi Herpes Virus (KHV)) with v. high mortality (95%)
Describe relation betwen temp and water density
- Water density changes with temperature
→ Highest density at 4oC
At ↑ temp: warm water floats above cold water
At ↓ temp < 4oC: cold water at the top and turns to ice → ponds outdoors need to be at least 1m deep so fish can survive in warm water underneath the ice
Why is water pH important for fish?
- Change of <1 unit in pH can be fatal for fish
- If will acclimatise fish then change pH a max of 0.3 units per day
- Most species kept by hobbyists are at pH range 6–8
Examples of underlying causes for low pH
- Use of tap water which has chlorine
- . Runoff from peaty soil into pond in heavy rain
Examples of underlying causes for high pH
- Runoff from limed soil/concrete into pond in heavy rain
- Build-up of ammonia
How to measure pH
Indicator test strips
Chemical test kit
Electronic meter
What is water hardness?
Amount of dissolved calcium and magnesium in water
→ important as affects the ability of fish to osmoregulate & control fluid balance
How is pH linked to water hardness?
Soft water usually acidic and hard water is more alkaline
How is water harness measured?
Chemical test kit
Colorimetric photometer
