Selecting best material for Hatchery Tanks


Selecting best material for Hatchery Tanks

Over the course of the past few articles we have dealt with many of the finer points of hatchery tanks management such as options for handling fish and flow measurement. We may have skipped over one basic thing, and that is where do you put your fish in the first place!

In aquaculture the options for what you can hold fish in are almost limitless. Some of the most basic ideas such as earthen and clay-lined ponds are actually holding more fish mass than all other types of tank construction combined. Given that many people who read this magazine are likely to be involved in the design and operation of recirculation systems and technically advanced hatcheries, I will focus this article on more common tank types used in aquaculture. I will also focus on
just the materials that these tanks can be made from as the discussion and debate on raceways versus circular tanks, and single vs. double drains and the like, is another story yet again.

In general most hatcheries and recirculation facilities tend to use tanks made from one of the following four choices: concrete, fibreglass, polyethylene or glass/epoxy coated steel.

hatchery tanks

1) Concrete:
Concrete tanks are used around the world in hatcheries because of their flexibility in design, their longevity, and their structural strength. Concrete tanks can be made in virtually any size and shape although the economics of concrete construction tend to favour larger tanks. Some research facilities use quite small concrete raceways less than one meter wide and deep and less than 5 meters long, and some commercial farms use circular tanks as large as 100 meters in diameter. Concrete also has a significant advantage over other materials in wall stiffness. This allows for system
designers to build tanks with straight wall sections. This can save on footprint size (floor area) inside buildings, as many recirc system designers who target the economics of constructing the whole facility are tempted to do. Materials with less inherent structural stiffness can be made into squares or octagon-shaped tanks, but these require more external bracing.

 

2)Polyethylene:
Polyethylene or “poly” tanks as they are called are very economical and practical for a wide variety of tank applications in hatcheries and recirc systems. Although they are generally Concrete tanks at a hatchery near only available in specific stock sizes the wide variety of available shapes and sizes generally means that there is a tank close to the configuration desired by the farm manager or hatchery designer;unless very large tanks are required. The largest molded poly tank I have ever seen in use at an aquaculture facility was about 7m (23 ft) in diameter. If you include field-welded or polyethylene-lined tanks and ponds, the maximum size would jump into the almost unlimited category, but I am focusing this article on the common rotomolded tanks that are typically seen in hatcheries.

3) Glass-lined Steel Tanks
Glass-lined steel tanks are commonly built from steel panels that have been coated at the factory with a thin layer of glass or epoxy. These tanks can only be built into circles but the circles they make can be of any diameter greater than about 6m (20 ft), and can be built to substantial heights. If you have doubts about their ability to support large volumes and high water columns you need only look at steel grain silos for reassurance. Many of the tank panels used in aquaculture today are salvaged from decommissioned silos. This can be both a blessing and a curse. On one hand the second-hand nature of these panels allows for the construction of large volume tanks relatively cheaply. On the other hand, the panels have already seen hard use, and often look badly worn. In general this is not a big problem but if the interior surface of the tank needs to be re-coated, the work could be as expensive as buying new panels, or selecting fibreglass tanks in the first place. In many cases however they are good enough and they can be shipped easily and economically as the panels stack well.

Aquarium Indoor fish farm tank

4)Fibreglass Tanks

Fibreglass tanks are perfect! Actually, I only say this because our sister company builds them; it is not really the whole truth. Fibreglass tanks are not perfect, nothing is, but in spite of my bias toward them they do have lots of good features. Fibreglass, or fibre reinforced polyester (FRP) tanks can be made in practically any shape or size, they have good mechanical properties for adding other equipment to them, they can be cleaned thoroughly and easily (provided they have a smooth gel coat or resin-rich finish), and have a long service life. They don’t have the mechanical stiffness of concrete tanks therefore you will not see large raceways made of FRP. They are generally more expensive than Poly or second hand glass-lined steel tanks.

frp fish tank

Most FRP tanks are either hand laid on a mould using mats or woven roving made of glass fibre, with resin painted on heavily to impregnate the fibres. Alternatively they are built with chopper guns which spray a mix of chopped glass fibres and resin onto the mould. Some combine the two techniques. Some companies that do large numbers of cylindrical shaped mouldings use a winding process in which the mold is held in a large clamp while mechanical arms that dispense resin soaked continuous fibre are retated around the mould. Either the machine or the mold will travel back and forth lengthwise while the arms are rotating, to ensure a uniform distribution of the fibres over the mold. In some cases specific patterns can be programmed into the winders’ travel to reinforce the moulding and impart specific strength attributes. If no gel coat is used, FRP tanks made from a light-coloured resin can be translucent; alternatively they can be totally opaque in any colour desired

On 30, 7, 2013, posted in: FRP Farming News by Tags:

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