Fish Tanks, Fish Species, Grow-Bed Types
& More
& More
Hi folks – back again with another edition of my bi-monthly DigiLetter, “Aquaponics: The Definitive Reference”. Last issue, among other topics we looked into the importance of stands and the universal need for bio-filters in aquaponics. This issue we are going to start off with more about fish tanks and fish species, so let's get right to it.
Unless one chooses to implement used or second-hand items, there is little chance of finding a better, cheaper or more suitable product for use as a large-scale fish tank than HDPE rain-water tanks. The industry of rotational moulding behind these products is a mature one, with a long history and plenty of exposure to competition. This guarantees that there is no point looking elsewhere for suitable product alternatives. Large, food-safe vessels, designed to contain potable water and exist in outdoor conditions for decades, make up the core business of the roto-moulding industry. They come in sizes from under 300 litres to over 50,000 litres and are found in both rectangular and round configurations the world over. In some countries and jurisdictions (such as some places in the US) there are laws pertaining to rainwater collection and in these economies the roto-moulding industry is smaller. I was stunned to learn that this was actually true.
In the image above we can see a HDPE water tank altered and customised by the author. With a large access window cut high into the wall of the tank and lined with rubber hose, we can access and view our fish comfortably. All water tanks are rated to only 80% of their internal volume, so half the depth of a rainwater tank is more than half of its labelled rating. In the case of the 3000 litre tank pictured above, filling the tank with water to the bottom of the window is around 2,650 litres.
One of the truly great things about HDPE rain water tanks is just how big they can go. The property we purchased and moved into just over 12 months ago came with two enormous 50,000 litre tanks. Unfortunately, we use them for the purpose they were actually designed for and they are apparently off-limits for aquaponics (for now). The size of these vessels allows for agricultural-scale aquaponics systems. In the image below, filling the water tank to the level below the pipe access holes is around 12,000 litres. So far, this is my record for the largest fish tank.
One of the numerous advantages to using these tanks this way, is that they provide a semi-enclosed environment. This has many, many benefits such as: greater heat retention, reduction of evaporation, reduction of algae, protection from leaves and falling debris, hiding the fish from birds, providing nowhere for cats to perch and access the fish, reduction of 'escapees' (e.g. jumping trout or climbing crayfish species), ease of plumbing and last but certainly not least, it provides a structure from which to hang and support devices and objects. One such object should be a waterproof power distribution box (see edition #2).
Fish Species Selection
This is a very sensitive topic and one that I feel extremely passionate about. One of the single greatest environmental factors impacting on our waterways, is the human-assisted movement of aquatic species, to areas outside of their natural range. Almost all major water-catchments on the planet are under enormous strain from the impact of one or more introduced 'noxious' species. Since there are literally too many examples to mention, I will relate just my own experience.
As a child I was brought up in country Victoria, Australia. Although I didn't know it at the time, the early 1980's marked the very end of widespread native fish in Victoria. The impact of the preceding 150 years of decimation had not properly sunk in to the minds of the general public, let alone me. In my earliest memories of our regular family fishing sojourns, Golden Perch, Murray Cod, River Blackfish and Silver Perch were all part of a day’s fishing. I thought that was normal. It turns out we were just fishing some of the last remaining native populations. Already, Redfin (European Perch) had taken over most inland waterways. Trout had displaced many species and decimated others with disease. By the mid-80's introduced carp had reached plague proportions and by the mid-1990's there simply were no more native fish to be found.
In the past 20 years desperate efforts have been undertaken by government – in partnership with universities, private industry and N.G.O's – to reverse this damage. Expectations were low in the beginning and many people including myself suspected that these unique animals and their unique environment were likely lost forever – another tragic case of too little, too late. But surprisingly, we have discovered that much can be done. Just like our careless and thoughtless actions have had such a pronounced effect on the environment in the past, so too can our targeted and thoughtful actions have a pronounced effect on the environment in the future. There are now many examples where native fish populations have demonstrated strong recovery alongside the diligent efforts of concerned scientists and individuals. Given a chance, most of our native species can adapt to new environmental scenarios. But it is only with thoughtfulness and care that we can make progress. No ecosystem and no species are truly lost until they are declared extinct and every location and every species on the planet alive today, still has a chance at a better environment. This is why fish species selection in aquaponics is so important. People will release fish into the wild, rather than kill them. Floods and structural failures will sweep fish away and into the wild.
No harm is done, only when these fish are an endemic, local species.
Australia is blessed with a broad biodiversity of freshwater fish species, but this is not entirely unique. All freshwater catchments of the world have their own list of endemic native species. These could be native species of trout, char, perch, bass, catfish, eel, crayfish, shrimp, mussels or any other related native species. As mentioned in previous editions, aquaponics doesn't have to be about growing food – but it is certainly better when it is. Edible fish species give your aquaponics system the protein output it otherwise lacks. If this native, local, edible species also happens to breed in a recirculating aquaculture system, then you have your perfect species.
Indeed, there are certain foreign species that will do incredibly in aquaponics – species like carp and tilapia. Some of these specimens can live in water quality approaching sewerage and quite literally live on a diet of mammal droppings. Believe it or not, every few months I hear of another 'revolution' in aquaponics, where the next person has worked out that some species of fish will actually live off Guinea Pig faeces. Without going into expansive detail, this is not a good idea. Besides the associated health implications of actually eating this stuff, it is these exact robust survival characteristics, that make these species so dangerous to a foreign ecosystem.
Other Grow-Bed Types
A robust aquaponics system of sufficient maturity and bio-filtration, can be viewed in the same way that a nutrient tank is viewed by a hydroponicist. In this sense, once all other bases are covered, an aquaponicist can start adding growing techniques usually limited only to nutrient-rich hydroponic applications – growing methods such as 'nutrient film technique' (NFT), 'deep water culture' (DWC) and even another
invention of mine: a 'vertical trickle bed'. I will give a brief description of each of these shortly.
In the early stages of an aquaponics system, the population of AOM's (see edition #4) is still expanding. As a result, the water is not nutrient-rich enough. Focussing on anything beyond increasing that population in deep, media-filled beds and bio-filters is a distraction. However once the fertility of the system reaches a certain point, such additions can be made. The single greatest benefit that these methods offer is that they require very little extra water from the fish tank, unlike the flood-and-drain beds. This means we can increase our growing capacity without having to increase our water volume.
