By Roger Grant

Various aquatic species may be held in tanks during the cycle of hatching, growing to market size, holding for distribution, transporting to market and displaying for sale.

In aquaculture, the cycle begins with hatching in specialized hatching jars. Then, fish are moved to ponds or raceways and grown to fingerling size. Bait fish go to market directly and food fish are further grown to market size.

Learning various aspects of this niche—tank requirements and corresponding treatment options—can provide another avenue for water treatment dealers to exploit their experience and knowledge.

Keeping options open
All tanks for aquatic applications are open-top tanks, ranging from 1-to-6 feet deep, and may be round or rectangular. They can be either in ground or aboveground and located indoors or outdoors. Round tanks are favored since some species can be injured by bumping into tank walls and round tanks are less expensive. The round shape uses material more effectively and can be built with thinner walls. Rectangular tanks are configured as long, narrow, shallow raceways, connected in parallel for better disease control. In general, disease among fish is spread by microbes in the water, which makes that very important. You don’t want water from one tank going untreated into another.

System water is supplied from wells or diverted flowing streams to open flow through systems. Flow-through systems are more economical due to lower energy requirements, if suitable water temperature and quality is available and environmental requirements for effluent water can be met.

Closed recirculating systems are a growing trend in aquaculture. Increased pumping and filtration capital and operating costs are offset by improved water temperature and quality control and reduced losses from disease. Site selection is much less critical and water usage and effluent is minimal. Intensive systems with as much as one pound of fish per gallon of water are successful, due to high re-circulation rates and adequate particulate, biological and chemical filtration, as well as ozone or ultraviolet disinfection for microorganisms control.

On-site construction
Tanks constructed on site can be built in-ground or aboveground, using three methods. Membrane tanks or raceways can be economically and quickly built using walls constructed of wood, concrete or cement blocks. Flexible PVC or Hypalon (nylon) material is draped inside and over the walls to contain the water. Bottom drain and water fittings can be glued into the liner. Shapes can be rectangular, round or free form with varying bottom contours. Bottoms are layered with sand before placing the liner. Many backyard ponds also use this method.

Masonry tanks can be constructed with a concrete slab bottom and walls of concrete block or poured concrete, with waterproof plaster interiors. Gunite (sprayed concrete and sand) can also be used and is good for in-ground installations with an irregular shape and bottom contour. Plumbing is installed first.

Manufactured tanks
Metal tanks aren’t used since metal ions in the water can be fatal to fish. Fiberglass reinforced plastics (FRP) are good material choices for larger tanks.

The need for a mold does limit size and shape choices without additional tooling cost. An interior resin gel coat provides color and an excellent finish, with “radiused,” or rounded, corners and no seams. The walls must be tapered out to create a “draft” for mold removal. Fittings are molded in place during tank construction, since the radius and draft make sealing bulkhead fittings difficult later.

Rectangular FRP tanks come in standard and custom sizes up to large volumes. The tanks are heavy. Therefore, shipping costs usually dictate locating a nearby supplier. Large supports and seismic tie downs may be necessary. Floor loading limits can be easily exceeded.

Small tanks
A wide variety of sizes are available in injection-molded and blow-molded tanks in nylon polypropylene or polyethylene materials. These are thin-walled tanks but are available with fiberglass casings for support. The tanks are translucent or black with UV stabilization which make them suitable for outdoor use. The shape can be round or rectangular. In addition, cone-bottom round tanks are available for complete drainage.

Transparent tanks
Glass is commonly used for aquariums for the home hobbyist and commercial user. They are fabricated from plate glass in frames and sealed with silicone. Acrylic is also used for aquariums. Tanks are available with colored sides and back for enhanced display. Acrylic tanks need to be cleaned carefully to prevent scratches. Glass tanks are heavy to ship and fragile but scratch resistant.

Rectangular tanks fabricated from PVC sheet material are a good economical choice. They provide straight walls with finished surfaces inside and out in any size without need for a mold. Flanges can be facing in or out. Hot gas-welded seams give excellent mechanical strength. Sizes are only limited by 4×8-foot PVC sheet size. Options include dividers, windows, lighting, and lids.

Holding tanks
Holding tanks for quarantine are the first stop for tropical fish headed to home or public aquariums. Stressed from being air-shipped halfway around the world, fish are monitored and treated to minimize introducing diseased fish into display tanks.

Quarantine systems can be a series of individual small tank systems or multiple small tanks on a closed central recirculating system (either freshwater or saltwater). Tanks are glass, acrylic or insulated construction in a variety of sizes mounted on multilevel stands, with a common circulation filtration and sterilization system. All tanks are connected in parallel, so water never flows into more than one tank without first passing through the central sump tank and filter system.

Similar systems are used by universities and research facilities for holding species like water frogs (Xenopus lavis) and zebra fish (Zebra danio) used in biomedical research. A variation on frog holding is to use drain and fill systems where water isn’t circulated but changed every few days since frogs seem to prefer a dark and quiet environment.

Display systems
Many restaurants and markets sell seafood live from insulated display tanks with designer exteriors, integral filtration and refrigeration, double-pane windows (to control condensation), lighting, dividers and lids. Some markets feature stacked tank systems with one level for freshwater fish, the other for saltwater species. Live freshwater bait-fish are sold from similar systems in convenience stores and bait shops.

Pet and fish stores display tropical fish, invertebrates, live coral and plants in multilevel, multi-tank recirculating systems. Paneled, lighted wall and island rack systems of glass or acrylic tanks segregate freshwater and saltwater species and include dedicated circulating systems.

All of these varied options for aquatic tanks offer opportunities for the dealer to expand their expertise and serve local businesses that use them. This is true whether it’s an office or business with fish on display, a restaurant with lobster presented for customer choice, a supermarket for similar reasons, pet and aquatic stores, hatcheries or public aquariums.

About the author
Roger L. Grant is vice president of Aquanetics Systems Inc., of San Diego, a supplier of life support equipment for aquatic applications worldwide. He has been with the company for 20 years and holds a bachelor’s degree in mechanical engineering from Purdue University. He can be reached at (619) 291-8444, (619) 291-8335 (fax) or email: [email protected]


Comments are closed.