LABORATORY FISH HUSBANDRY

Transcription

1 LABORATORY FISH HUSBANDRY Fish The use of fish in research has seen a dramatic rise (more than tripled in use) in the past 5 years. Fish are being studied in laboratory settings, in fish farms and in the wild. They are being used for teaching, research and regulatory testing such as biomedical research, food safety and toxicity testing. While the use of fish has increased there is still much unknown about fish physiology. Species Some of the more common species of fish used in research today include; zebrafish, trout, goldfish, fat head minnows, sturgeons and salmon. Currently at the University of Saskatchewan there are northern pike, pearl dace, lake chubb, brook stickleback, white sturgeon, lake sturgeon, rainbow trout, medaka, zebrafish, trout, fathead minnows and goldfish being used in studies. Zebrafish are one of the most commercially readily available fish. Because of their small size and rapid reproduction they are becoming more popular. There are strict regulations for importing fish which can make them difficult or sometimes impossible to obtain. Researchers often have to collect the fish themselves from lakes, rivers and oceans. Zebrafish Sturgeon Pike Page 1

2 Facilities Housing and husbandry Fish live and breathe in the same water that they eat, sleep, defecate, and mate in. Because of this water quality is of the utmost importance when it comes to housing fish. There are 4 main categories for water management in tank systems: Flow through: The water is constantly being replenished with fresh water. The effluent (the water leaving the tanks) is treated and discarded. Recirculating: After the system is filled, the same water will be treated and replaced into the tanks. This is a closed system with little to no new water being added. Zebrafish rack (recirculating system) Static Systems: Systems in which no new water is continuously added from outside or recirculation sources. Static systems are often challenging to maintain, have very low inherent biological carrying capacity and are prone to water quality changes. Mesocosms: Aquatic systems used to recreate the ecosytem of the fishes natural habitat. Examples of tanks: Zebrafish racks, living streams, holding tanks, MEPSs (Mass Embryo Production System) and glass aquariums. Page 2

3 Left-goldfish tank Right-living stream There are two possible water sources; well water or municipal water. Municipal water will be chlorinated which will need to be removed prior to use. You can do this by chemical means or with a carbon filter. With well water you need to be concerned about possible ground contamination. Extra filtration that most research facilities use can include carbon filters, UV light, reverse osmosis, micron filters and ozone. Aquatic environments should be designed to meet the established physical and behavioral requirements of the fish in terms of shelter, social grouping, overhead cover and lighting. Water Quality Testing A comprehensive analysis of water quality parameters should be conducted before a fish holding/testing facility is planned to ensure that the water supply is suitable. A protocol should be developed to check the water quality on a regular basis before and while fish are being held in a facility. An example of a water quality checklist could include; CO2 levels, Nitrate Levels, Nitrogen levels, Chlorine (levels as low as 0.04mg/L will kill fish), Dissolved O2, Turbidity, Ammonia and PH levels. Consult the appropriate guidelines for the particular species being housed. Page 3

4 Tank Density Tank density is extremely variable between species. The maximum and minimum number of fish in a tank will vary with the size of the tank, research parameters, size of the fish, water temperature, pathogen load, dissolved oxygen, metabolic rate of the fish, feeding rate and water exchange rate. In fish farms in the ocean you may have tens of thousands of fish in one tank. With large populations it becomes harder to control the spread of disease. Ensuring prompt removal of deads helps to slow the spread of disease. Having an inappropriate number of fish can lead to aggression, stress, fear and disease. Enrichment Enrichment needs to be added to help reduce stress and help maintain a more natural environment. When choosing enrichment you need to consider the species of fish. Prey fish like objects they can hide under or behind such as PCV tubes cut in half to make a tunnel or rocks and plants to hide behind. Fish that live in rivers often need an artificial current in their tank. Fish that live in still water ponds may enjoy lily pads. You can use real or artificial plants as long as you are aware of how it will affect the research and water quality. Page 4

5 Restraint and Handling of fish Danger potential: Fish can bite, sting and abrade the skin of the handler. Certain species can generate powerful electric charges. Many species of fish have venomous spines that inject secretions of varying degrees of toxicity. Physical restraint: The primary means to catch a fish is with a net. You can also use plastic to wood panels to herd fish into a smaller area of the tank to facilitate capture more easily. Fish are covered with a mucous secretions on the skin to protect them from pathogenic bacteria. As much as possible it is best to have minimal physical contact with the fish to avoid rubbing off this protective film and reduce stress to the fish. Some cons associated with the use of nets can include abrasions to the eyes of the fish which usually protrude from the body, fins and scales can become entangled in the webbing and fish can see the net coming which can cause them to self-traumatize while trying to elude the net. The use of polyurethane bags can be an alternate method of capturing fish. The bag is transparent, thus the fish experience less fear and may be easier to catch. Another benefit of the plastic bag is that they are disposable therefore less likely to spread disease. Methods of Identification There are several methods of identifying fish including; tagging (clothing tagger, fishing line with beads), numbered tag implanted beside the clear area of the eye, neon dye in the fin or transmitter surgically implanted. More invasive forms of identification including branding, tattooing or clipping important fins should only be used if there is evidence provided to the animal care committee that alternate methods are not sufficient to achieve the desired results. Unique physiological facts Trout can tolerate much higher doses of Morphine, up to 3 times higher than mammals Fish have less than 5% C-fibers, the pain nociceptor for chronic pain. Humans have 80% Gills have 10x the surface area of the fish Fish can tell kin and non-kin based on olfactory senses to avoid inbreeding There are no approved analgesics for use in fish Siamese fighting fish can withstand anoxic water Eels can be shipped moist Page 5

6 Breeding Reproductive maturity can be judged more accurately by size rather than age of the fish. Reproduction is effected by density, water temperature, nutrition, water quality and intensity of production. Fish have been shown to prefer shallow water over deep (this can be accomplished by propping the tank up on an angle), vegetative surroundings and a gravel bottom over silt. Some species can spawn daily. Pheromones trigger spawning. Ovulation typically occurs just prior to dawn, spawning usually starts 2 hours after daylight. When spawning, the male swims parallel to the female and wraps his body around hers, triggering oviposition and releasing sperm simultaneously. There are two types of breeding practices you can employ: Intank Places spawning sites (marbles or boxes with mesh tops) into the tanks of already established fish Pro: you minimize handling of fish and you can continue to have circulation of water. Con: facilities with thousands of tanks make it impractical to use the marble technique as it is time consuming to collect. The breeding boxes with mesh tops are not commercially available at this time and would have to be custom made. Static tank Removes the fish from their tank and places them in off-system breeding chambers Pro: Hierarchies formed in established colonies of fish are eliminated. You can alter the water chemistry to promote spawning Cons: Water quality deteriorates over time, there is added stress to the fish from being handled, it is labor and space intensive. **Reproduction will vary between species of fish. Page 6

7 Eggs Spawning tank Health and management Signs of ill health As with all animals fish experience stress. Examples of common stressors for fish include; capture, transport, overcrowding, handling, injections, sorting, malnutrition, change in temperatures, variations in salinity and oxygen, contaminants and pathogens. When a fish is stressed you will notice a marked behavioural change. They may be hyperactive or lethargic. You may notice an increase or decrease in feed consumption. Other signs that a fish may be stressed include color change or hyperventilation. It is important to keep stress to a minimum as fish become more susceptible to infection when they are stressed. When a fish is in pain or ill you will notice similar clinical signs as with stress. There will be changes in behaviour such as flashing (showing the white side of their belly while rubbing their backs on the bottom of the tank), attempting to jump from the water, rapid opercular movements, changes with feeding, growth and reproduction. Whether or not fish experience pain is still questionable. Research has been done with no conclusive evidence. Page 7

8 Fish in the center of the picture is a lighter color then the others due to stress Infectious diseases Wild caught, or fish from a non-reputable supplier need to be quarantined for a period of 3 weeks to be monitored for signs of disease. You can also use preventative antibiotics to increase the survival rate. Miscellaneous diseases v Saprolegnia- aquatic fungus. Lives on dead tissue. Spreads quickly. Early treatment is key. Usually from stress or contamination. v Flavobacteria- stress induced, causes interlamellar cell proliferation v Parasites: o Gyrodactyllus(ectoparasite-lives on the outside of the body) o Protozoa (Trichodina, Ichthyobodo), Irritating to the fish, symptoms include dyspnea, coughing and piping (fish gulping for air at the top of the tank) if gills are affected. v Excess mucus production- increases respiratory distance making breathing more difficult Diseases caused by improper management v Excess Ammonia- Ammonia levels should not exceed 1ppm. Ammonia is toxic to the gills and can affect the nervous system v Gas bubble disease- Caused by excessive Nitrogen in the water. Fish will swim erratically, float to the surface, show nervous signs, fin rot, dyspnea, tachypnea, popeye, bubbles in skin and eyes. v Chlorine toxicity-very small amounts of bleach will kill fish!! Page 8

9 Euthanasia Before using a physical or chemical method of euthanasia, fish must first by anesthetized. The fish should be anesthetized to the point of loss of equilibrium. Physical techniques include methods such as percussive stunning and gill cutting. You can also use a stunning blow to the head followed by pithing or cervical dislocation by experienced personnel. Chemical means of euthanasia include an overdose of TMS. Carbon dioxide or suffocation are not acceptable means of euthanasia. Page 9