What do fish need from their environment?
- Water
- Oxygen
- Stable conditions – water chemistry and temperature
- A complete and balanced diet
What is the result of poor husbandry in fish?
- Increased stress and faeces production
- Decreased immunity
What must be maintained to maintain water quality?
- Maintain correct stocking density
- Maintain filtration system
- Maintain aeration
- Monitor temperatures
- Regular cleaning and partial water changes
- Regular water quality testing
What are 3 things to keep in mind for fish husbandry?
- Keep compatible species together
- Quarantine new fish for 4 weeks before adding to existing stock
- Provide good quality food
What are the components of water quality?
Dissolved gases
Nitrogenous compounds
Temperature
pH
Hardness
Alkalinity
Salinity
Other solutes
List the gases dissolved in water of significance.
Oxygen, nitrogen, carbon dioxide
What is the oxygen content of water compared to air?
Water holds 5% of oxygen compared to the same volume of air
What is hypoxic water caused by?
- Overstocking
- Overfeeding
- Lots of rotting organic matter being actively degraded by bacteria
- Too many plants
What is the main source of oxygen in water in fish tanks?
Main source of dissolved oxygen in most bodies of water is from photosynthesis by submerged plants. But plants respire during the night and use up oxygen so greatly decrease levels at night if there are too many plants present.
Dissolved oxygen levels should be measured throughout the day but especially early morning.
Can you have too much oxygen in water?
Yes, in oxygen toxicity.
How does oxygen requirement vary?
- Varies with species, age, size and health of fish.
- Increases with feeding and stress
- Most fish require at least 6mg/L
How is carbon dioxide present in water?
- Produced via respiration by fish and bacteria and by plants at night.
- Dissolved levels highest just before dawn
- High levels develop if fish are left is sealed plastic bags for long periods.
What are the nitrogenous compounds in water?
- Fish excrete ammonia from the gills and kidneys as their main waste product of protein metabolism.
- Bacteria/Nitrosomonas in water and filter use ammonia as an energy source and convert this to nitrite.
- Other bacteria/Nitrobacter oxidise nitrite to nitrate
- Ammonia and nitrite are both very toxic to fish
Describe the nitrogen cycle present in fish tanks, for example.
Fish eating plants and aquatic weeds and fish food and producing ammonia. Dead plants and uneaten food also contribute to ammonia production. In the filter, ammonia oxidised and converted to nitrite by bacteria, and nitrite oxidised to nitrate by bacteria. Nitrate can be removed by being taken up by plants and aquatic weeds, denitrification to nitrogen gas or removed by changing the water.
What are the optimum levels of nitrogen compounds in water?
Optimum level of ammonia = 0mg/l
Optimum level of nitrite = 0mg/l
Optimum level of nitrate = <50mg/l
How is tank syndrome prevented?
It takes several weeks for bacteria to become established for filter to function efficiently in new tank/ponds. Need to allow this to occur before adding fish. Otherwise fish die off in new tank syndrome, initially ammonia levels increase and then fall and nitrite levels rise, which then fall and nitrate levels rise. Nitrate levels are then controlled via plants plus regular water changes. Excessive amounts can cause algal blooms and plant growth. Water is changed to bring down these levels again.
What are the 2 bacteria types needed to establish a filter?
Nitrosomonas
Nitrobacter
How can filter cycling be sped up?
- Seed the filter with part mature media from an established tank
- Use concentrated bacteria
- Use hardy seed fish – ethics?
Why must water parameters be monitored?
To determine when more stock can be added. The addition of each new animal will increase ammonia and require more bacteria to grow. Nitrate levels are then controlled via plants plus regular water changes. Excessive nitrate levels can cause excessive plant growth/algal blooms.
Describe fish temperature requirements.
Fish are ectothermic.
Temperature requirements depend on species bit all have an optimum range but some tolerate a wider range, such as goldfish that can tolerate from 2-40˚C.
Metabolic, feeding and growth rates all depend on temperature.
What do rapid changes and increases in temperature cause?
Rapid changes cause stress and reduce resistance to disease.
Increased temperature leads to decreased dissolved oxygen and increased toxicity of ammonia.
What is the pH level for most fish that are kept?
Within the range of pH6-8.
What happens if water pH changes?
Change of less than 1 unit may have fatal effects on some fish.
Changes of 0.3pH units or less per day are recommended during any acclimatisation period.
What are some underlying causes of low pH?
- Runoff from peaty soil into pond during heavy rain, due to poor drainage design.
- Tap water can be mildly acidic due to chlorine.
