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Permaculture Animal: Silver Perch (Bidyanus Bidyanus)

Silver-perch-tank
Silver perch in tank. Photo by Arthit Chamsat

Silver perch are useful, hardy native fish suitable for farm dams, aquaponics and other aquaculture systems. They are easy to feed and as they’re native to a wide swath of the Murray-Darling river system, they’re adaptable to a range of conditions.

Description

As the name suggests, silver perch have a silvery grey appearance. They are darker on top and lighter on the belly with spiky dorsal fins along the back. They can grow up to 50 cm and 6 kg, but are unlikely to reach these sizes in farm dams.

Functions In A Permaculture System

Silver perch are good eating fish. They have a very high level of omega-3s, making them a particularly useful addition to a permaculture diet. They are generally eaten when under a kilogram.

They may be useful in keeping some problem species, such as mosquitos and filamentous algae, at bay.

They can be stocked with other species such as yellow perch to create a more diverse polyculture. Australian aquaculture authority Nick Romanowski suggests that silver perch, catfish and yabbies are an ideal combination for farm dams.

Stocking, Breeding And Growth

Young silver perch fingerlings (young fish around 5 cm long) are available from native fish farms for stocking farm dams or other systems. About 200 fingerlings per megalitre of water in a dam is recommended.

In aquaculture systems where the water is aerated, additional feed given and wastes removed, stocking rates can be very high. The actual numbers will depend on how well your system functions, rather than the volume of water. If you’re just learning to use a system, it’s best to start with a low stocking rate.

In warmer parts of the country and optimally controlled aquaculture systems, silver perch may reach eating size in 18 months, but in open farm dams in the cooler regions of Australia it’s likely to take two or three years.

It is possible but not common for silver perch to breed in farm dams. In more controlled aquaculture systems, breeding can be facilitated by varying the water temperature and movement in tanks, but in dams you will probably have to restock with fingerlings every few years.

Feeding

Silver perch eat both plant and animal matter, making them easy to feed. In a farm dam with a good ecology they shouldn’t need supplementary feeding, as they’ll forage on aquatic insects, shrimp, algae and other plants. Feeding them an occasional treat of bread encourages them to come to the surface for food, making them easier to observe (and to catch later on).

In a more intensive aquaculture system, it’s common to feed silver perch formulated pellets, however these are unlikely to come from a sustainable source. Alternative feeds such as algae, duckweed, and invertebrates (e.g. black soldier fly, worms) are relatively easy to produce. Some green waste scraps can also be incorporated into their diet.

Silver-perch-dam
Silver perch caught from a dam. Photo by Beck Lowe

Habitat

The larger the dam the better, but at a minimum the dam should be around 15 metres in diameter. In areas smaller than this, aeration will be required to maintain adequate oxygen levels.

If your dam has recently been completed, it’s worth waiting a year or so for small invertebrates to colonise before you add fingerlings. In the meantime you can establish plants at the edges and shallows to provide habitat for a range of small species.

Large branching tree limbs submerged in your dam will provide habitat for the fingerlings and help hide them from predatory birds. Add ‘furniture’ to your tanks, such as small branches or old ceramic sewer pipes.

Silver perch do best in water temperatures around 20–30 °C but they can cope with a much wider temperature range, although they will stop growing in cooler months. At higher temperatures they become vulnerable to the low oxygen levels of warmer water.

Catching And Eating

In smaller systems nets will generally be used. They can be fished with a rod from farm dams using a small hook and bait.

If the fish have been grown in a typical farm dam they may need purging before they’re killed and consumed, otherwise they may taste muddy. This can be done by keeping them in a large container of clear, fresh water for a couple of days, and changing some of the water daily. Older fish are often skinned before cooking.

Silver perch can be prepared in any of the standard ways to cook fish.

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