 Silver Perch is a fish of Australian origin and lives comfortably in a pH range that suits a wide variety of plants. They also survive well in a range of temperatures and are a very common option of aquaponics enthusiasts. Though I have never eaten them, reports are favourable for their flavour.
Physically they are a fairly typical looking fish and as the name suggests are silver / grey colour which varies to a grey/brown or grey/green dependent on the water quality and other environmental conditions. Their belly tends to be lighter and in comparison to other perch (such as the Golden Perch) they have smaller scales. They are considered a medium to large freshwater fish and have a streamlined, oval shaped body with a small head, small eyes and small mouth which is quite pointed. They typically grow to around 45cm and 7 to 8kg, though are considered ready for market at 500g. Females grow to a larger size than males. Their dorsal fin begins as a rigid, spined fan coming out from the peak of the back downwards to a second dorsal fin that is softer and rounder. These dorsal fins along with the caudal fin (tail) are darker in colour compared to the pelvic fins. The anal fins lie somewhere in between in colour. The small size of the scales creates a visually appealing pattern of a compact dark grey fishnet stocking over a paler silver background. Apart from the small head and facial features of the fish in comparison to its body, along with the spined dorsal fin, it is probably this fine fishnet pattern of scales that make it more easily distinguishable.
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I've just done an initial test of my bore water here in the Largs Bay area and I found the pH was quite alkaline at around 8 with some ammonia and about 5ppm nitrates. What does that mean? Well, the high pH might come from the parent rock beneath the surface leaching into the water. Thanks http://soilquality.org.au/factsheets/soil-ph-south-austral for this diagram.  Some ammonia in the water is natural, as there may be decaying matter beneath the surface. The nitrates can be an issue apparently, but according to some up to 10ppm is considered safe for drinking water (but that doesn't mean go ahead and drink it folks). You may have heard that some add nitrates to bacon as a preservative and bacon hasn't had the greatest health wrap of late. Tastes bloody good though.   A concrete pond is possibly the best and longest lasting type of water storage facility but can be permanently ruined through poor construction and is also potentially the most expensive to build. A concrete pond should be poured in one continuous process to ensure all seams and joins bond before setting. They are much like a swimming pool. First ensure drainage pipes and framework are in place then after the pour use a concrete vibrator to settle the mix and remove air pockets. Cure, clean with acetic acid and fill and drain the pond to remove lime over a period of weeks. Concrete livestock troughs could be a good small alternative and at around 5000 litres are relatively portable and multipurpose. These are precast so simply purchase and have delivered. Lined ponds can be created starting with earthmoving and followed by laying a liner, of which there are many options. The earth should be free of sharp objects, flattened out with a layer of sand and a trench need to be dug around the outside of the dam as an anchor point. Seams are "welded" using an adhesive. Anchor by laying the liner over the outer trench and fill with sandbags.. Any pond or dam being made may need approval and and safety should be at the forefront of the owners mind - consider fences and also a slow decline at the ponds edges. Ensure animals can't tread on the edges leading to potential damage. According to Nick Romanowski, zooligist and author, 1 in 3 lined ponds leak. This will lead to regular maintenance. Lined ponds are also somewhat difficult to drain. An earth lined pond is an option by which clay soils are used to resist the water. Bentonite is now often used as a layer to seal the pond which is a clay product. Clays can dirty the water so a layer of loamy soil can be used over the top of the clay. Bentonite can be applied in a few different ways, it can be rotary hoed into the top layer of the soil, it can also be applied as a blanket over the soil after it has been flattened and rolled, or finally, while the dam contains water it can be sprinkled over the water surface though this method is somewhat less reliable. Fibreglass tanks are another option where if a prefab design is used it can be cost effective. Smaller tanks are easier to manufacture and are more economical. They are created using a resin which is mixed with a hardener and glass fibres that are sprayed into a mould. Fibreglass can become brittle over time when exposed to the elements but such a tank is relatively light weight compared to concrete and thus has the bonus of being mobile.   When you are selecting a site for a freshwater enterprise initially there are two main considerations. Flat ground is a high priority, largely due to earthmoving costs if dams are being constructed. If this is the case then heavy clay soils are necessary. Also, understanding what the land was used for prior to the venture is important. What fertilisers / chemicals were used previously? There are other considerations. What infrastructure does the site already offer? Are there sheds and other useful buildings? Is there a bore and what is the quality of the water? Are there any sites available that already have dams, ponds or tanks that can be converted easily for use? The climate is important. How balanced is the weather system? How much artificial input would be required to support the production system? Does the climate match both animals and suitable plants? How does water runoff occur and what is the potential for harmful chemicals to pollute this water? What lies upstream and what possibility is there that excess agricultural chemicals and nutrients will cause an issue? Location also impacts access to consumables, materials and manufacturing. Is the site close to concrete / fibreglass manufacturers or to feed suppliers as excessive transport could incur extra costs. Likewise, you have to consider the transport costs for exporting the produce. It's also necessary to think of what access you will have to laboratories or experts in the field and what other agricultural enterprises are in the area that your business could link with to value add to your product. Finally consider what government policies are in place. Are there state bans on certain species? Are there grants/support in that state.  Aquaculture interests me far more than working with cattle, sheep or horses. Having had aquariums as a kid sparked my interest and gave me a basic understanding of aeration and filtration and the importance of water quality.
The initial readings I undertook proved extremely positive. Per metre square, aquaculture can sustainably produce more protein than other land based farming. You've got me sold! The way that you can tie in fertilization of a crop from the waste water is another appealing benefit, creating a more sustainable system and aquaculture ties in very closely with the principles of permaculture. In that respect I think that ideally all aquaculture farming should include a degree of land based farming, even producing a crop that can be used as fish feed. Because the large scale intensive production methods are still relatively new and research into the habits of the animals is not as comprehensive as the research carried out on land based animals it may not be as attractive as a new enterprise, however this could also be seen as a positive in that there are still many avenues left unexplored, allowing a farmer to set themselves apart and develop a niche market. There is greater potential for failure and loss of stock, however with time and practice, aquaculture should be able to be extremely profitable and on top of this any advancements made could help starving populations of the world and the environment by allowing overfished oceans to restock. |
