Silver Perch are one of the most common freshwater aquaculture species in NSW. The silver perch (Bidyanus bidyanus) is an Australia native freshwater fish. Its natural distribution extends through the western drainage of New South Wales, including most of the Murray-Darling Basin, but it is found now in many eastern drainages.

Silver Perch are a fast growing species that are known to grow up to 6 kg but in NSW the aquaculture industry basically grows 3 sizes for human consumption. We have smalls at 350-450 gram, mediums at 600-800 gram and large animals 800-1200 gram. They are fast growing and most people work on 2 years to sale size. They are a school fish that likes high densities so are suitable for both earthen ponds and tank recirculation systems. Most of the major production in NSW is from earthen ponds that are specifically designed for perch culture. You can grow silver perch in farm dams for your own consumption but commercially you are only allowed to culture them in specially designed pond or tanks, etc.

The commercial industry in NSW is generally divided into two industries. The hatchery industry and the grow out industry, some of the larger farms do both but the hatchery side is a specialised business and for most it is easier just to purchase fingerlings from an approved hatchery and then grow those fingerlings out.

NSW Fisheries began researching Silver Perch back in 1965 and over the years with the help of the Departments researchers and scientists the knowledge base on silvers has grown tremendously. In the 1970’s the Narrandera Fisheries Research Station began research on the hormone induced spawning of perch, and this technology was made available to industry in the early 1980’s. Since that time, a thriving hatchery industry has existed based on the hatchery production of silver perch and other native species. Silver Perch spawn in tanks in hatcheries by being induced with an injection of HCG a human gonadotrophin.

Tank Breeding Facts:

Water temp 24 – 25 Deg.  28 Max. Must aerate tanks, No dead spots. SPAWNING: 200 IU / Kg HCG. 32 –38 hours after inject spawn. 24 – 28 hours hatch. No Noise. No light. 125,000 eggs / Kg. Out day 4 to 7. Feeding starts day 6. Divide by 75 for both. Males can have 0. Reduce dosage towards end of season. Season = 1st September to mid February.

Perch are bred in hatchery tanks producing large numbers of eggs that will hatch 24-28 hours after being laid. These small larvae start to feed around day 6 and they are usually transferred to outside earthen ponds that have been prepared with an algae and zooplankton bloom and grown in these ponds to a fingerling size. They are weaned onto a commercial pellet in the ponds and then harvested and sold. Silver perch fingerlings are purchased by a mass of people for all sorts of reasons. Growing them in farm dams for personal consumption is common, growing them in home aquariums or aquaponic tanks is becoming more popular and of course there is the commercial aquaculture industry in NSW that grows some 200,000 kgs each year.

Silver perch can grow at high densities in commercial ponds and research indicates that 20,000 kgs per hectare of pond is possible but most farmers grow at much lower densities of 5-7,000kgs/ha. The silver perch industry in NSW is worth about $2.75 million (2017-2018) and promises to grow in the future.

Silver Perch Fingerlings are available from:

Murray Cod Available

Additional Information

Silver Perch

Bidyanus bidyanus

By
Robert B McCormack (AustSilvers)

The Silver Perch is a native Australian freshwater fish that is a native of the Murray-Darling River system. Just known as Silvers they are a widespread species that are a great sporting fish. They have small mouths and a large tail that will give you a great fight on light line. Unfortunately, silver perch in the wild are not as common as they used to be. There are many reasons for this but some of the main problems are alien fish species (carp, redfin, etc.), new alien diseases, habitat degradation, the construction of dams and weirs on the major rivers. This compounded by drought and then black water events has led to a serious decline of wild fish numbers in many areas. Australian federal government in 2013 listed wild silver perch as critically endangered on the EPBC Act list of threatened species. To read the Conservation Advice; http://www.environment.gov.au/biodiversity/threatened/species/pubs/76155-conservation-advice.pdf

Silver Perch are summer breeders that have very specific requirements. They need warm water, flood conditions and a migratory run. Silver perch in the wild have long migratory spawning runs up river to breed. This occurs over the summer breeding season and starts around mid October and lasts till mid march. Unfortunately, they need flood conditions over this summer period to have their migratory run and to spawn. Silver perch are prolific breeders with around 125,000 eggs per kilo of fish. The problem is that these eggs are negatively buoyant and will settle to the bottom. That is fine if there is a strong current with water moving past them, they will still develop and hatch. It is even better if the eggs themselves are rolling along the bottom, typically over the flood plain. It the eggs fall into a no current, no water movement area they will die and not hatch. This is the dilemma of the Silver Perch and the reason it is in such rapid decline in the wild. River floods that create ideal conditions for breeding and the survival of the eggs don’t occur very often these days and when they do the rivers are full of dams and weirs that stop the flow and create still water areas where any silver perch eggs will just drop to the bottom in dead water areas and die.
Many people stock their farm dams with silver perch and they survive well and grow tremendously in even relatively small farm dams. Unfortunately, the conditions in a farm dam are not suitable for breeding so they will not multiply in your dams. They will roe up and may even breed but the eggs will just settle to the bottom of the dam and die. In a farm dam you will only get back out what you put in.

Male Silver Perch from a farm dam with sperm ready to breed
Male Silver Perch from a farm dam with sperm ready to breed

Breeding Information

I’ve been breeding silver perch commercially for over 25 years. They are relatively easy to breed due to the robust nature of the species. We use a variety of broodstock to give us the best quality offspring possible. We have a selection of genetic bloodlines that we actual cross to give us the best fingerlings that are robust and fast growing. We use basically 5 strains of silvers, Murray Stock, Cataract Stock and our own Aquaculture improved bloodlines which includes stock from other fish farms like Narrabri and Queensland. Broodstock fish are held in farm dams through the year and we just catch fish out of our dams and take them to our hatchery for breeding. The adult silvers live on a diet of natural food that we supplement with a feed of specially formulated silver perch pellets. It is essential that we keep our broodstock fit, healthy and happy; if they are, they will breed easily and give us good progeny.

Seine netting silver perch broodstock in a large AustSivers dam
Seine netting silver perch broodstock in a large AustSivers dam
Seine netting silver perch broodstock in a small AustSilver's dam
Seine netting silver perch broodstock in a small AustSilver’s dam

Silver perch are “summer” breeders and dependent on where you are located will depend on when they breed. Here in the Port Stephens area (NSW) we have a very long breeding season due to the mild conditions. Our breeding season starts late September and runs through till the end of March. Each year we are noticing a bit of a change in the breeding season, it is starting earlier and ending earlier (early March 2019), whether or not you believe in climate change our fish,whether silvers or goldens with the milder winters and hotter summers are responding to changes in the climate. We capture fish from our dams as required and we use a variety of methods to do so. If we just want a few we may just use fishing lines and a piece of peeled prawn as bait. If we want a lot then we would seine net the whole dam with a knot less net or even sometimes we catch them in gill nets. If you use gill nets you need to be right on top of them and get them out immediately so they aren’t injured.

Cotton, slung gill nets easily catch fish from your farm dams
Cotton, slung gill nets easily catch fish from your farm dams

Once captured they are taken back to the hatchery for breeding in 500 to 1400 litre tanks. Silver Perch are a schooling fish so large numbers can be bred together. If they are 500 gram fish we may have 5 female and 5 male fish in the one 1400 lt tank. By having a good number of both males and females breeding together in the same tank we have a better genetic pool/mix in that tanks batch.

If we have large females 1-2 kgs each each we may use just her with 2 males in a 500 litre breeding tank. We always prefer to have at least 2 males, they will compete with each other to breed with her, so the fertility rate is normally near 100%. When we use just 1 male he gets lazy and doesn’t put in the effort to outdo the competition. Interestingly, in 2019 we had a dramatic reduction in males ripe for breeding. This is a first for us, for reasons unknown, the ripeness and fertility of all males was greatly reduced this year. Chatting with other hatcheries seems to indicate it was a widespread problem this year, lets hope its just a one off.

Typically we catch our fish in the afternoon and then breeding then around 5 to 6 pm later that afternoon/evening. Fish are stressed when captured and handled so we do try to be as gentle as possible and get it over as fast as possible, this ensures we always have good breeding successes.

We anaesthetise our fish, weigh them and hormone inject them to induce breeding. The fish are injected with HCG a hormone at a rate of 200 iu/kg of fish; this will induce them to breed approximately 36 hours after injection. This is why we inject them at 5-6pm so we know they will breed around 5-6 am 36 hours later. It is only the females that need to be injected to induce spawning but we would also inject half the males and the other half would not be injected. It’s just a cover all bases policy we use and seems to work exceptionally well for us. Once injected they are placed in 1400 litre conical bottom spawning tanks that are heated to 24ºC and heavily aerated to keep the eggs in suspension. If everything has gone to plan all the fish will have bred on time and we will check egg numbers in the tanks and then remove the adult broodstock. They will be returned to the dam and not be bothered again till next years breeding season or more likely they will be rested the next year and then used again the following year.

As a rule Silver Perch are not a fish that can be hand stripped. If they do not breed naturally themselves you can not strip them. As a species they are generally easy to breed so this is not a concern.

The eggs are either left in the breeding tanks to hatch or transferred to larval incubation tanks for hatching which will start to occur 24 to 28 hours after they are laid. Not all eggs hatch at the same time and hatching will continue for some time after up to 2 to 4 hours. Once the eggs hatch we reduce the aeration and keep the lava in these tanks until they are ready to feed some 6 days later. These larvae are them transferred to the fingerling ponds for grow out into fingerlings ready for sale. The fingerling ponds are prepared for the larvae by growing algae and zooplankton ready for the silver perch larvae to eat. As the larvae grow into fry and then fingerlings we will supplement their food with artificial food. Starting with a dust and then on to a No. 1 crumble. Some 7 to 9 weeks after they are released into the pond they are around 40 mm plus in length and ready for sale. The growth in the pond is dependent on the weather and the amount of fingerlings in the pond.

The fingerlings are drain harvested from the ponds and returned to tanks in the fish shed. There they will be graded, health checked and treated for any parasites etc. It is essential that the fish we supply to the public are disease free and very healthy. We will feed them up a bit and after 6 to 7 days in the tanks they will be ready for sale to other commercial aquaculture farms or the general public for stocking into farm dams, ponds, aquaponic tanks and aquariums, etc.

Stocking Information

Silver perch are fantastic farm dam fish as they thrive in those type conditions. They are a relatively tough hardy species that does not need a big dam to thrive. Other species like Aust Bass and Yellowbelly really need a dam over 1 mega litre in size. Silver perch can live in much smaller dams as they utilize the full range of foods available. They will eat the worms, shrimps and insect larvae that grow in dams just like the other fish but they also eat the weeds and algae utilising this material. This gives even a small dam a great deal of natural food available for your fish.

With silvers you have the added benefit that you can supplemental feed them in your dam. By far the best option is to purchase a bag of specially formulated silver perch pellets and just feed them that. The pellets float and the silvers will dart to the surface, grab a pellet and scoot back down creating a big swoosh making it very exciting to feed your fish. It also allows you to see your fish and see just how they are growing and how many you have in the dam. Some people feed their silvers bread and that is always a good stand by. You also have the added benefit that when you feed with bread, it is easy to put a bit of bread onto your fishing line and drop it into the swarm of feeding silvers and catch one out for dinner very easily. Bread is good as an occasional treat but nutritionally it does not have much benefit. If you feed your silvers lots of bread they will eat that and just not grow much at all. I recommend specially formulated silver perch pellets.

When stocking silver perch you usually stock a farm dam at a minimum rate of
200 fingerlings per Mega litre of water.
A mega litre is 1,000,000 litres
1 cubic mtr of water = 1000 litres.
200 fingerlings per meg of water is a good stocking that will allow the fish to grow fast and the dam will be able to naturally produce enough food for all the fish. Unfortunately, not all the fish will survive and you will as an average rule in an average farm dam lose between 30 to 50% of the fish you stock. We recommend that you stock heavily the first year and then add additional stock to the dam every second year. Large adult silvers do not eat the smaller fingerlings so that is an added bonus with silvers. You can have a number of different sized fish in the dam, if you catch a small one, just throw it back – catch and release – it will be big enough to eat next year.

Mixed Stocking

Silver perch are a great fish in that they can be stocked with a variety of other species. Most people would stock a large dam over 1 mega litre with at least 2 species. The bigger the dam the more species you can have together. There are no major problems with mixed stockings. Silvers are good with everything and go well with Australian Bass, Golden Perch (Yellowbelly) and Catfish. Silvers can utilise the other food resources that these fish are not eating such as the weeds and algae so it has little impact on the other species.

When doing a mixed stocking you would usually do it 50/50. So for example a 1 mega litre dam could be stocked with 100 silvers and 100 yellowbelly. In smaller dams you generally have Yellowbelly and silvers but larger dams you can have bass and silvers. Just be warned that predatory fish such as bass and Yellowbelly will eat their own and silver perch fingerlings when you restock. Restocking a dam with large predatory fish such as Bass or Yellowbelly just means that you should stock with 50% more to make up for any losses that may occur.

Silver Perch Aquaculture

Silver Perch are a fantastic aquaculture species and is one of the main freshwater species grown in Australia. A large aquaculture industry has grown around the silver perch and hundreds of tones of silvers are grown out each year for the restaurants and shops in Australia with also high demand for the export market. There is a large live trade into Sydney’s Asian restaurants with other smaller markets into both Melbourne and Brisbane. There are increasingly good prices being paid for “live fish” and demand is growing. Many farmers are also now targeting the regional markets and specialized niche markets with many farmers also looking at the fillet market where many think the future lies.

Anyone is allowed to grow silver perch for their own consumption without any permits or approvals. If however you want to sell silver perch then you will need a permit that is issued by your DPI or Fisheries Department. To obtain a permit you must meet certain criteria that ensures your commercial activities have no effect on the environment or the consumers of your product. In NSW you are not allowed to aquaculture silver perch for sale in farm dams. You are only allowed to grow them for your own consumption in farm dams.

Silver Perch are generally commercially aquacultured in earthen ponds, not farm dams. These are specialized ponds designed specifically for aquaculture of large numbers of silver perch. They are bottom draining ponds, with a bank all the way around to prohibit entry of surface runoff and they are aerated and monitored to ensure good water quality is maintained at all times. Silver perch are generally grown at up to 20,000 kgs per hectare of water surface area. Higher densities can be achieved but greater risk to the whole crop will occur. Typically, many farmers aquaculture smaller quantities 7-12,000 kgs/hectare with less management and risk. Silvers are generally grown for 2-2.5 years and harvested at 600 to 800 gram for the live trade although some farmers have markets for fish from 350-400 gram up.

Silver perch can also be grown in cages and are very suitable for cage culture and cage culture to me looks like the way of the future. Silvers can also be grown in tanks utilizing a recirculation system that filters and cleans the same water returning it to the system. Many people have home aquaculture systems that produce a surprising amount of fish for their own personal consumption. However these type systems would not be recommended by us for commercial operators but many home aquaponic farmers use silvers in their tank systems and for aquaponic tanks you can not get a better eating and easy keeping species.

Aquaponic grown Silver Perch
Aquaponic grown Silver Perch

Releasing Silver Perch
When you pick up your fingerlings or have them delivered to your door. You will have a foam box that is sealed. This will keep the temperature inside the box cool and staple. Inside the box is a sealed plastic bag with water and fish inside. The water in the bag may be an odd colour this is a mixture of chemicals we have added to keep the fish calm and healthy. The bag is filled with pure oxygen and this will sustain the fish for up to 48 hours in the bag. Dependant on how long you are going to have them in the bag will depend on how many will fit in the bag. See AustSilvers for packing/transport rates.

When you receive the fish take them to the side of the dam in the foam box. Open the foam box and sit the plastic bag upright so you can add water from the dam into the bag. This will acclimatize the fish to the dam and give them the very best start.

Open the plastic bag, add 2 litres of dam water and just wait 5 minutes. Then add 6 litres of water and wait another 5 minutes. Just spend those 10 minutes with the fish to ensure that it is not a big shock to them when you transfer them from the bag to the dam as the waters will be very different.

Releasing the fish is easy, just empty the bag into the dam and check when finished that no stupid ones have stayed in the bag. It is best to release these fish into 1 metre of water. You can just release them into the shallows but this can be stressful and dangerous for your fingerlings. The trouble is that these fish are most vulnerable to predation in that first 30 minutes. When they enter a new pond they are disorientated and frightened. Many may just dive to the bottom and try to hide, too scared to do anything or go anywhere. If this is shallow water then they are very vulnerable to birds and mosquito fish. Be warned, most farm dams on the eastern side of the great divide have mosquito fish (Gambusia holbrookie). Mosquito fish do not get large but they are a pest. They will not eat your fingerlings but they will bit their tails and can eat the tails right off the silver. They are a shallow water surface species that swarm in the shallows (200 mm). If you release the fingerlings at a depth of 1 metre then these mosquito fish will not cause any problems.

Catching Silver Perch

Once you stock Silver Perch fingerlings into your dam you will not see them again. Generally there will be no outward indication of the fish. They are native fish and are very fast and smart. They will not cruise the shallows or swim along the surface like a goldfish will do. No sign of silvers is a good thing so do not be worried. After 2 years most people would be keen to know how their fish are going and there are a few things you can do to check your fish.

• Feed them a floating food. It is recommended that you feed them proper silver perch pellets. These are a floating pellet that will bring the fish to the surface so you can see them. Otherwise you can feed them bread. Just a few slices of bread broken up into 25 mm square pieces is fine. Silver perch are creatures of habit; you must try and feed them the same time every day to get them into the routine. Generally in the afternoon after work is the best. It will take about 2 weeks for your silvers to recognize the food you are throwing in as food but once they do they will not forget. Just throw the food into the same spot every day at the same time. Initially you will see nothing but after a week you should start seeing the odd splash and after 2 weeks you should see them all as they are relatively fast learners. Just do it for another week and then you can start doing it intermittently as once they learn they will be in that spot everyday at that time looking for food.

Note the long shank hook
Note the long shank hook

• Go fishing. Just take you esky and a deck chair down to the side of the dam and throw in some fishing lines. Silvers will take flies and lures but it is very hard work for very limited results so bait fishing is generally the recommended method. Light lines and small hooks are the best. Garden worms or pealed frozen bait prawns the preferred baits. Only a third of a peeled prawn or one garden worm is best. Remember they have small mouths so small hooks and small baits. (NOTE: Use a long shank hook so they dont swallow it. You can use a float to suspend the bait near the surface or fish directly on the bottom. If you have been feeding your fish then that will make life easier as you can berly them up to you fishing area.

• Nets. The best and easiest method is just use a gill net. This is just a length of net 25 mtrs long on a rope which you suspend in the dam. Fish swim into it and get tangled and you just lift them out. It’s very effective and gives very surprising results. Gill nets capture all species, silvers, goldens and bass, etc. Gill nets are available from RBM Aquaculture.

Eating
Silver perch are excellent eating with a clean white flesh that can be cooked anyway you like. Unfortunately, they can have a muddy taste to them and this is known as an “Off Flavour”. This is usually from the weeds and algae they have been eating and commercial farmers would catch their fish out alive and purge them in clean clear water for 7 to 10 days before sale. This ensures they never have an off flavour. Off flavours come and go and you may not have it this month but get it next month. Unless you purge your fish not much you can do about it as you will not know until you cook them and go to eat them.

Generally it is from the algae in the dam and not from the mud. Contrary to popular belief, the muddier the dam the less chance of an off flavour as the turbid muddy water stops the algae growing which means the fish can not eat it so they don’t get any off flavours.

Cheers
Rob McCormack