Lecture 1 -- Fish Diversity, Husbandry, and Form & Function

Are fish ectothermic or endothermic?

Fish are ectothermic (cold-blooded)

• Do not regulate a constant body temperature and rely on environmental temperature

What temperature range can fish physiologically cope with?

From hot soda lakes (~43°C) to sub-zero Antarctic waters (-2°C).

What are the temperature ranges fish can tolerate?

• Polar: -2 to +2°C

• Temperate: 0 to 20°C

• Tropical: >20°C

Why does seawater in Antarctica not freeze at -2°C?

Dissolved salts depress the freezing point to about -2°C, so Antarctic seawater remains liquid

Why would fish normally freeze in sub-zero seawater?

Because their internal osmotic concentration is lower than the seawater, making them susceptible to freezing

What is the main adaptation that allows fish to survive in sub-zero waters?

Many fish have antifreeze proteins in their blood to prevent ice crystal formation.

What types of water salinity do fish live in?

• Freshwater淡水

• Brackish 鹹水

• Marine 海魚

How do freshwater and marine environments compare in fish species diversity?

Freshwater environments contain ~42%

Marine environments ~58% of fish species

How variable are oxygen requirements in fish?

Highly variable

• Some need cold, O₂-rich streams

• Some survive in high altitude warm springs

• Some survive months without oxygen in ice covered ponds and lakes

What adaptations in the fish respiratory system allow them to survive in oxygen-depleted environments, such as ice-covered ponds?

They perform anaerobic respiration, producing lactic acid → They convert lactic acid into ethanol that diffuses out through the gills

Describe the primary feeding behavior of fish.

Fish can be surface or substrate feeders, with roles ranging from predators, herbivores and planktivores 食浮游生物者

How does mouth morphology relate to feeding habits?

Surface-feeding fish usually have an enlarged lower lip and upward-facing mouth for easier access to surface food

What are the main considerations when keeping fish?

• Environment

  • Oxygen

  • Temperature tolerance

  • Salinity

  • pH requirements (Acidic vs basic water)

  • Space requirement

  • Water hardness

• Behaviour

  • Territorial species?

  • Agression?

  • Shoaling vs Solitary

• Health

  • Water quality

What is the main metabolic waste excreted by fish?

Ammonia

How do fish excrete ammonia?

Through the gills (75%) and urine (25%)

Do most fish produce urea or uric acid as birds do?

No

What happens to faeces and other solid waste in water?

Decay in water → Increase harmful chemicals and clouds the water

What are the methods for removing nitrogenous waste from water?

Filtration system

What are the three stages of filtration?

• Mechanical

• Biological

• Chemical

List all the examples of mechanical filtration systems and their functions.

1. Swirl 漩渦 filtre

   • Create a spiral flow of water → Solid waste particles can sin to the bottom for removal

2. Filter matts

   • Water is pumped through the mats → Solid particles get trapped and retained

3. Sand filters

   • Water passes through large beds of sand → Filter out the solid particles and produce clear water

4. Brush filters

   • Brushes are hung inside tanks → Filter chambers to catch and hold solid debris

What is the purpose of biological filtration?

To encourage the growth of beneficial autotrophic bacteria that break down toxic nitrogenous waste through nitrification

What is biological filtration?

Process of using beneficial bacteria to break down toxic nitrogenous waste (Ammonia and nitrite) in water into less harmful substances (Nitrate) through nitrification

Describe the two steps of nitrification, including the bacteria involved and the compounds converted at each stage

Step 1: Ammonia oxidising bacteria e.g. nitrosomononas species, convert ammonia into nitrite by using ammonia as energy source

Step 2: Nitrite oxidising bacteria e.g. nitrobacter species, convert nitrite to nitrate (less toxic than ammonia and nitrite)

What should be tested to determine if aquarium water does not need to be changed?

Measure the ammonia level by measure the pH level

• Low pH indicates more ammonium acid (NH4+)

• High pH indicates more ammonia (NH3), which is more toxic

Because of the nitrogen cycle in the tank, nitrate levels continue to increase until a water change is carried out. How much water change is usually enough to maintain stability in a tank?

~ a quarter of water change is enough to keep the temp and everything stable

What is the main purpose of chemical filtration?

To remove (adsorb) specific undesirable substances from the water by locking them up

What does “adsorb” mean in chemical filtration?

When dissolved substances stick to the surface of filter media

List all the examples of chemical filtration and explain how they work

1. Carbon granules

   • Remove “colour” from water

2. Zeolite

   • Removes ammonia from water

3. Phosphate removing granules

   • Prevent algae growth

What substance does activated carbon granules remove?

Phenols and other organic chemicals

P.S. Phenols give water a yellow colour

In what type of water is zeolite used?

Freshwater only

How does zeolite remove ammonia? What special feature does zeolite have?

By ion exchange.

It can be recharged.

What is the name of this aquaculture system?

Open system

What are open systems in aquaculture?

Caged environments located in natural waters such as rivers, lakes, estuaries 河口, and the open sea

How is water quality managed in open systems?

They lack intensive water quality management → Rely on natural systems to maintain water quality

Name two fish species commonly reared in open systems

Sea bass and salmon

What range of fish densities can open systems have?

From low densities with natural feeding to very high densities with active feeding

Why are open systems considered controversial?

• Potential pollution

• Health risks to both wild and captive fish

• Escaped captive fish may interbreed with wild fish → Reduce the genetic purity of endangered native stocks

What is the name of this system, and what is this aquaculture system also known as?

Semi-closed system

= Once through system/ Flow through system/ Raceways

Where are semi-closed systems usually located?

Inland aquaculture facilities 內陸水產養殖

How is a once-through system in a semi-closed aquaculture system maintained?

Water is diverted from the river through an inlet into a raceway, then flows out through an outlet back into the river

Which freshwater fish are commonly farmed in semi-closed systems?

Trout, catfish, and tilapia 吳郭魚

Which brackish water fish are farmed in semi-closed systems?

Sea bass and sea bream

What is required in a semi-closed aquaculture system?

• Fast continuous water flow through inlets and outlets

• Concrete canals or basins to hold the fish

• Active feeding to support higher densities of fish

What is a major disadvantage of semi-closed systems?

High water consumption

What is the name of this system, and what is this aquaculture system also known as?

Closed system

= Recirculating aquaculture system (RAS)

How does water move in a closed system?

Water is re-conditioned, treated, and recirculated.

What type of filtration is essential in closed systems?

Very efficient biological filtration

What types of fish are reared in closed aquaculture systems?

Marine and freshwater fish

What is the advantages of closed systems?

• Minimal water and land use

• Allow high fish densities

What is the disadvantages of closed systems?

• Expensive to set up

• Needs highly trained staff → Expensive to maintain

• Higher greenhouse gas emissions than open or semi-closed systems

What should be included in an ornamental aquarium setup?

• Tank

• Cover

  • Prevents water evaporation

• Filter

  • External filter - Separate unit connected to the tank and filled with filter material e.g. activated charcoal

    • Help removes chemicals and odors

    • Provide surface area for beneficial bacteria

  • Under-gravel filter

    • Create bubbles → As the bubbles rise, they pull water upward through the tube → Create a flow of water down through the gravel 碎石 → Gravels acts a mechanical and biological filter → Trap particle and host beneficial bacteria

• Food

• Enrichment

• Oxygenator

• Thermostat 恆溫器

• Timed lights

  • Control light duration to support algae growth

Why is the traditional goldfish bowl not acceptable for keeping fish?

• No proper filtration → High fluctuating water parameters e.g. ammonia and nitrite

• No environmental enrichment

• No hiding places for fishes

• Poor oxygen supply

Why can some goldfish survive in harsh, low-oxygen environments?

• They have the ability to prevent lactic acid build-up during anaerobic respiration

  • Fish convert lactic acid into ethanol → Ethanol then diffuse across the gill membranes into the surrounding water

• They store glycogen in the liver in summer

  • During summer, they feed actively and store glycogen in the

    liver. In winter, when oxygen is scarce, glycogen becomes

    the main fuel for anaerobic metabolism

What is the pathway of glycogen metabolism during anaerobic respiration?

Glycogen → Glucose → Pyruvate + ATP + Lactic acid (later converted to ethanol)

What type of fish is shown in the picture?

Chichlids

What type of fish is shown in the picture?

Parrotfishes

What type of fish is shown in the picture?

Gobies

What type of fish is shown in the picture?

Salmonidae

What type of fish is shown in the picture?

Groupers

What type of fish is shown in the picture?

Catfish

What type of fish is shown in the picture?

Foxface rabbitfish

What type of fish is shown in the picture?

Brown trout

What type of fish is shown in the picture?

Crownfish

What type of fish is shown in the picture?

Cardinal tarta

What type of fish is shown in the picture?

Angelfish

What type of fish is shown in the picture?

Betta fish = Siamese fighting fish

What type of fish is shown in the picture? What type of water does it live in? How is their behavior described?

• Rainbow trout

• Freshwater

Why are Rainbow Trout considered “messy” fish?

They produce lots of faeces that float around, making cleaning difficult.

How is their behavior described?

Aggressive predators, which has implications for captive maintenance

What type of fish is shown in the picture?

Common carp

What type of water does common carp live in?

Freshwater with pH 6.8–8.2

How is the behavior of common carp described?

Social with minimal aggression.

What type of fish is shown in the picture?

Sea bass

What type of water can sea bass live in?

Marine water with pH 7.6-8.4, but they can tolerate brackish water

How is sea bass farmed?

In sea cages or raceways

How is their behavior described?

Social

What type of fish is shown in the picture?

Mudskipper

What type of water does it live in ?

Brackish water; pH 7.2–8.4

Where is this fish commonly seen?

Public aquariums and occasionally as a pet

What is unique about its behavior?

It spends most of its time out of water on a ‘beach’.

How is male behavior described and what does it imply for keeping them?

Males are very aggressive; sex ratios must be considered, with no more than one male per group.