An Aquarium for Oysters

Aquarium Set-up and Maintenance

Preparing a tank does take some careful planning. Choose an appropriately sized tank according to the amount of space available. Make sure you have access to all sides of the tank when you choose a location. You will also need the following equipment:

• 20 lbs crushed oyster shells, crushed coral or dolomite for bottom substrate.
• an air pump, tubing and airstones and undergravel filter plate with lift tubes

* a powerhead may also be used in place of the air pump, tubing and airstones and provides superior water circulation through the substrate and undergravel filter plate.
• mechanical filter to remove particulates that hangs on the back of the tank or is a canister style that sits next to or below the tank.
• water supply with chlorine removed. This can be performed with chemicals supplements or by allowing the water to sit out overnight.
• synthetic sea salt (Instant Ocean is reliable) * or make your own
• bacterial culture for biological conditioning of water in the tank and the filter
• hydrometer for specific gravity measurement
• thermometer
• invertebrate diet, liquid (Kent Marine) or solid blocks (Reef Care) *or make your own.

Adding Substrate

Water Preparation Options

Use tap water that has had the chlorine removed, distilled or deionized (DI) water. Water that has evaporated from the tank should be replaced on a daily basis to keep the water level and salinity constant.


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Initial Fill of the Tank and Filtration

Place a plastic lid or plate on top of the substrate in the tank and fill the tank. The lid will prevent the water from disturbing the arrangement of the substrate.

Once the tank is filled, connect the air pump, tubing and airstones to the lift tubes or connect the powerhead to the lift tube. If you are using an air pump use two lift tubes, if you are using a powerhead one will be sufficient. However, two powerheads will develop a more even flow through the undergravel filter. Plug in the air pump or powerhead and ensure proper operation. The goal here is to establish water flow through the substrate and undergravel filter plate up the lift tube and back into the main body of water in the tank. By doing so the substrate becomes a valuable bacterial filter bed for the conversion of toxic ammonia wastes produced by the oysters. We'll talk more about wastes and the nitrogen cycle later.

Connect the mechanical filter to the back of the tank and fill it with tank water to prime the pump. Plug it in and ensure proper operation. The goal of a mechanical filter is to remove particulates and debris so that the undergravel filter bed does not become clogged. A clogged undergravel bed will result in reduced water flow and water quality problems. There are many options for mechanical filters. Aquaclear® make excellent mechanical filters that hang on the back of the tank. Fluval® make excellent canister filters that can stand next to or below the tank in a cabinet. If you can afford the canister filter it provides many benefits in terms of easy access for cleaning, power, reduced water evaporation and quiet operation. The price of a canister filter may only be a few dollars more than a hang on type. The canister filter also allows more space for filter media to improve biological activity and water quality.

Once the filters are running add the appropriate amount of synthetic sea salt (Instant Ocean® or Marinemix® are good brands) so that the salinity closely matches the environment where the oysters lived. A range of 14-21 parts per thousand(ppts) or 14-21 grams per liter is sufficient. Check the salinity the next day and either add more salt or remove some water and add some tap water. Leave the tank undisturbed for 48 hours after the final salinity adjustment before adding any organisms. The temperature of the water should, like the salinity, be as close to the natural temperature as possible. Room temperature is fine, no heat is required.


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Biological Filtration and the Nitrogen Cycle: The Basics

There are 2 common soil bacteria, Nitrosomonas and Nitrobacter, that can convert toxic waste products from animals into non-toxic forms. These 2 genera of bacteria perform the same function in both freshwater and marine ecosystems. The chemical process is known as nitrification. Since this process is aerobic, good water flow and high dissolved oxygen levels will allow the process to proceed at a higher rate. Nitrosomonas converts ammonia, the initial and most toxic waste product, into nitrite.

NH₄+ + O₂ (Nitrosomonas) --------------> NO₂ (nitrite) + H₂O (Nitrosomonas)

Nitrite is still toxic to aquatic organisms. The second step of the nitrification process is performed by Nitrobacter. Nitrobacter converts nitrite into nitrate.

NO₂ + O₂ (Nitrobacter) ---------------> NO₃ (nitrate) + (Nitrobacter)

Nitrate is basically non-toxic but can cause stress if it is allowed to build up to high levels. Removal of nitrate is accomplished by performing 25% water changes each month.


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Adding Oysters to the Tank

After 48 hours the tank will be ready to accommodate a few oysters. If you add too many oysters at the beginning you are likely to have a tank full of dead oysters since a bacterial population has not been established to convert their ammonia wastes into non-toxic forms. Oysters may be acclimated to the tank temperature by placing them in a plastic bag and hanging them in the tank for 30 minutes. Add the bacterial conditioner at the same time you add the oysters. Varieties of bacterial conditioners like BactaPur® and Fritzyme® are reliable. Remember to add only a few oysters the first week to allow the water to become biologically conditioned to the oyster waste products. Later, the tank will be ready to house a larger number. You may notice the water becoming cloudy in a few days. This is due to the "bacterial bloom" that occurs as the population grows by feeding on the oysters' ammonia based waste products. Some oysters may die initially. Remove dead oysters ASAP. An oyster that will not close when disturbed is dead or dying. If the water is cloudy and has the odor of ammonia this indicates that the bacterial population is not able to handle the amount of wastes produced by the oysters at the present time.  As long as you do not overstock the tank at the outset the water will clear and the odor will disappear.


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Feeding
Oysters are filter feeders so they will need a diet that sustains them in the tank. Under normal conditions in nature during growing seasons oysters have an abundance of food. You will be able to feed your oysters, but do not expect them to grow. Since they are filter feeders the mechanical filters should be turned off while feeding. The powerhead can remain on since this simply recirculates water. There are a wide variety of liquid and solid invertebrate diets available today. If the expense of these is too great you can make your own by placing an algae based fish food in a blender with some tank water and make an oyster "milkshake". This type of food is less concentrated than the commercial brands but will supply them with some of the nutrition they need to sustain themselves. The oysters can live for up to a year in a well established system. Algae that grows on the sides of the glass of the tank can be scraped and added to the "milkshake" so that it does not go to waste. Healthy oysters can rapidly filter the food from the water but feed only 3 times per week with the mechanical filter off for a 30 minute period.  If you use a commercial brand of food there will be a feeding guide on the container.  If you make your own food you will have to experiment with the amount at feeding time. Be sure to plug the mechanical filter back in so that excess food does not create a water quality problem.


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Monthly Water Changes

Water changes are important for health of the organisms in the tank. If you are using a 20 gallon tank prepare 5 gallons of saltwater with the same salinity as the tank water the night before and you will be ready the next day. Remove 5 gallons of water from the tank with a siphon tube. The first time you do this let the water run into a bucket so you know exactly how much water you are removing. When 5 gallons has been removed make a mark on the side of the tank with a pen at the water level. Next time you perform a water change just drain the tank down to the mark. It may be necessary to unplug the filters during a water change so that the motors do not run dry during the process.

By performing a water change you will remove:

• nitrates in the tank water which can cause stress that are not broken down or converted chemically by bacteria.
• proteins that do not get removed by normal filtration
• excess nutrients in the tank that can lead to algae blooms
• by performing a water change you will replenish fresh water valuable salts, minerals and trace elements

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Inquiry: You can  track the levels of ammonia, nitrite and nitrate in your tank by purchasing a water test kit from the pet store. At the start up of the tank it can be a great learning process  by graphing the levels of ammonia, nitrite and nitrate on a daily basis for the first 2 weeks and then periodically afterwards. There will be a definite increase and decrease of ammonia and nitrite over the first 3 weeks before they reach undetectable or trace levels. Nitrate will continue to increase after this period and can be monitored before and after monthly water changes. Students can utilize the data to understand the nitrification cycle in aquatic ecosystems.
 

Study Extension:

One can  research the other 3 components of the nitrogen cycle (ammonification, denitrification and nitrogen fixation) and develop hypothetical or practical models for testing each process. Also research the importance of N based building blocks in organisms.


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The above is based on  Maryland Sea Grant
Visit their website at: http://www.mdk12.org/instruction/curriculum/hsa/biology/oysters/oys5e.htm