Fish

What are the main roles of fish in society?

• Pet fish (tropical, marine, coldwater and ponds)

• Aquaria (wide ranging plus other aquatic taxa)

• Laboratory (mostly zebrafish)

• Farmed (mostly salmon and trout in the UK)

What should you consider when mixing different species in community tanks?

• Water parameters and habitat

• Schooling or solo

• Swimming levels

• Compatibility

• Aggression or intimidation

• Predators

Label the basic external features of a typical fish species

Label the basic internal features of a typical fish species

Describe how gills are used in fish

• Primarily for gas exchange in water

• Water passes into mouth, and out through gills

• Rakers prevent damage from debris, arches hold the gill in position and filaments and lamellae create a large surface area for absorption

• Gills also assist in excretion of nitrogenous waste, and have a role in the immune system and the acid-base balance
  

Label the structure of gills and how water moves into the gills (side on and view from below)

Draw out how osmoregulation occurs in freshwater fish

Describe how osmoregulation occurs in seawater fish

Describe how ammonia and nitrate should be considered relevant to keeping fish

• There is constant pollution from fish, food and plants

• Both ammonia and nitrate are highly dangerous, causing stress and physical damage to sensitive tissues

• There are no detectable levels of ammonia and nitrate

• Biological filtration, surface area and sterilisation

• Keep a good level of ‘good’ bacteria to maintain biological filtration

Describe how oxygenation/CO2 should be considered relevant to keeping fish

• Most important to consider in ponds

• Water movement allows surface dissolution

• Air stones

Describe how chemically clean water should be considered relevant to keeping fish

• Free of pesticides, chlorine, heavy metals, organophosphates

• Chlorine/chloramine gill tissue necrosis

• Chemical filtration (charcoal/zeolite)

Describe how water hardness/salinity/pH/temperature should be considered relevant to keeping fish

• Different species have specific requirements

• There may be narrow limits

Describe how organic pollution should be considered relevant to keeping fish

• Fish faeces, uneaten food, algae and other detritus decompose

• Build-up of dissolved/particulates encourages disease, parasites and bacteria

• Mechanical filtration (sponges)

Describe how stability should be considered relevant to keeping fish

• Substantial fluctuations of pH, temperature and other parameters can occur over a 24-hour period (not typically in the wild)

• Constant changes within the preferred ranges are stressful, as fish must constantly adapt to changing conditions

What are the key pieces of equipment needed when keeping pet fish?

• Filter: chemical, biological and mechanical filtration aerates and circulates water

• Heater and thermostat: heats and maintains water at a set temperature

• Substrate and enrichment: anchors plants, hides fish faeces, provides forage

• Non-return valve: prevents water backing up into the air pump

• Air pump: provides aeration via air stone

• Thermometer: checks water temperature

• Hood and hight: to provide a day/night cycle and protect inhabitants

Describe the 3 different types of fish in terms of how they feed

1. Surface feeders: have an upturned mouth for skimming the water surface for food

2. Mid-range feeder: have a mouth that appears straight from the face, to gather food as it falls through water

3. Bottom feeders: have a downturned mouth for feeding from the bottom surface

Describe the considerations when feeding fish

• Fish are opportunistic feeders- overfeeding is common in home aquaria

• Fatty liver disease (hepatic lipidosis) is a direct effect of overfeeding, and is fatal

Describe how feeding fish incorrectly can impact their environment

• Blue-green and red algae blooms from inc. dissolved organic material, nitrates and phosphates in the water contribute to low oxygen

• Decaying organic matter contributes to fungus growth, and ‘harmless’ pest species rapidly reproduce

Describe the nutritional requirements of herbivorous and omnivorous fish

• Less nutrient-dense diet, have a long intestine to allow for digestion and absorption of vegetable material

• Herbivores may graze aquarium plants, algae/seaweed tablets and small pieces of fresh vegetables

• Omnivores thrive best when given a varied diet of formulated feeds (pellets, flakes and granules), fresh foods, live foods and frozen foods

Describe the nutritional requirements of carnivorous fish

• Need a nutrient-dense, high protein diet, often top predators (e.g salmon and tuna), have a short intestine with rapid digestion and absorption

• Some carnivore species prefer live prey that they can hunt before eating, whereas others will eat frozen cubes or freeze-dried invertebrates

What should you assess upon clinical examination of a fish?

• Behaviour

• Body

• Skin

• Opercular/gill movements

• Swimming patterns

• Population and interactions

Draw out the nitrogen cycle in relation to fish tanks

What are some behavioural concerns when assessing a fish in practice?

• Circling

• Bottom sitting (normal for sedentary species and sleeping fish)

• Drifting and hovering (normal for angel fish and hatchet fish)

• Head standing, tail-walking, flashing

• Piping or gasping

• Colour changes (confused for sexual maturity/seasonality)

List some physical signs of illness in fish

• Ulcers

• Fin haemorrhaging

• Fin rot

• Costia (grey sheen over body)

• Intestinal/anchor worms

• Leeches

• Mouth/skin fungus

• Cloudy, bulging eyes

• Gill/skin flukes

• White spots

• Dropsy (pineapple scales)

• Carp pox (viral infection, no known cure)

• Velvet (gold-grey spots)

How can you obtain a diagnosis from a fish using histology?

• Minimise handling, but perform a thorough examination

• Primary diagnostics on exam:

  • Skin scraps: use a slide or coverslip to drag cranial-caudal, add a drop of tank water and examine immediately

  • Gill clips: lift the operculum, cut only gill tissue with fine-tip scissors, examine with microscopy (some bleeding will occur)

  • Fin clips for histology

How can you obtain a diagnosis from a fish using radiography?

• Cases with abnormal body shape, swimming and buoyancy disorders and suspected foreign bodies

• Give anaesthetic, remove from water for radiography

How can you obtain a diagnosis from a fish using an ultrasound?

• For soft tissue and internal structures (tumours, sexing)

• Gel is not needed in water, be careful with equipment

How can you obtain a diagnosis from a fish using biochemistry?

Blood sampling:

• Use the tail vein (ventral to spine 90 degree angle)

• Ensure lab can ‘do fish’- some labs have ‘koi health profile’

• Assesses oxygen transport capacity, immune potential, level of stress, disease, intoxication, nutritional status and more

• A smear can be analysed for cellular abnormality

How should you use anaesthetics on fish in clinical practice?

• Sedation is recommended before handling, or a brief out-of-water examination

• Preparation for GA should involve a 12-24hr starvation period to limit regurgitation     into gill tissue and excretion of nitrogenous waste

• GA is usually induced via immersion in a dissolved anaesthetic agent