SILVER PERCH INFORMATION
The Silver Perch is a native Australian species. Basically a native of the Murray Darling drainage system, this species over the years has been widely distributed across NSW and many eastern flowing streams now have small populations. Silver perch are omnivores with a very varied diet consisting of small food items such as insects, insect larvae, shrimps, yabbies, molluscs, worms, weeds and algae. They do not grow to extreme size and specimens over 3Kgs are rare. Rumour has it they grow to 8Kgs but I have seen them up to 4Kg only. Generally in farm dam situations they will grow to approximately 2Kgs.
Silver Perch are one of the main Aquaculture species in NSW, the reasons for this are numerous, but some of them are given by Stuart Rowland from NSW Fisheries as:
1. Established hatchery techniques
2. A hardy fish that can be held in captivity at high densities.
3. Rapid and uniform growth.
4. Omnivorous.
5. Amenable to artificial feeding.
6. Non – cannibalistic.
7. Diseases under hatchery conditions known.
8. High meat recovery of 40%.
9. Marketing attributes, including an Australian native fish.
10. Attractive appearance and colour.
11. Excellent cooking and eating qualities.
12. White flesh, few bones.
Silver Perch also have a few disadvantages, these include:
1. The readily take up off flavour compounds from growout ponds.
2. This requires post harvest purging to remove off flavours.(Earthy taste)
3. Purging takes 1 – 3 weeks and increases production costs.
4. This requires gentle capture and handling to ensure survival in purging tanks.
5. Silver Perch are not as robust as some species and are very sensitive to mishandling.
6. Silver Perch have been sold in the past unpurged, referred to as road kill these fish have damaged the market potential of good quality purged fish.
7. Fish build up large fat contents in gut cavity.
8. Feed costs are high and growing.
Silver Perch are not only grown commercially but are widely stocked into farm dams as a recreational species. There are two main reasons for this, firstly Silvers are very fast growing and most people can start catching and eating silvers 12 - 18 months after initial stocking. They are also excellent sporting fish on light line and accept worms or peeled prawns readily. They do not however actively attack lure like bass, we occasionally catch silvers on lures but they are generally chasers not biters. They also eat bread and many people feed their fish bread in the pond. This burlies the fish up to the surface and creates considerable satisfaction for the farmer who can now see how well the fish are growing and show them of to his family and friends, after bringing them to the surface with bread, a quick catch can always be made by adding a bit of bread to a hook.
Silvers do not breed in a pond, they are basically a river fish and need flowing water. This means you only get out as many fish as you put in so most people would add extra stock each year. As silvers are not cannibalistic and have a small mouth adding little fellers in with the big guys is not a problem as it is with other species.
Silver perch are a river species that generally spawn in summer during flood condition. In the wild these fish school together and have a migratory run upriver to spawn. They travel considerable distances even hundreds of kilometres upstream and like to spawn when the river is in flood with water over the flood plain. The eggs once released roll in the current across the bottom down river and hatch 24 hours later. By spawning in flood the predators for the eggs are few and far between and survival is high. Unfortunately the construction of weirs and dams has severely restricted the movement of spawning Silvers upstream and reduced flood events. Silver perch eggs also don’t like salty water so the increase in salinity levels in many inland streams is detrimental. All this has led to a reduction of silvers in the wild and they are on the Potentially Threatened List.
In the early 60”s NSW DPI Fisheries started breeding research at Narrandera and ever since then NSW DPI Fisheries have considered Silver Perch as a ideal species for aquaculture in NSW. NSW DPI Fisheries has devoted considerable resources to Silver Perch culture over the years and thanks to those efforts we now have a 300 tonne per year aquaculture industry in NSW. This may be small by international standards but for the small family farmers in NSW utilising their own capital it is a very satisfactory effort.
Breeding Silver Perch – Unfortunately silver perch do not breed naturally in farm dams. This means you only get out what you put in. Silver perch breeding is a specialised business that is conducted by commercial fish hatcheries. These hatcheries artificially breed silvers and then supply the fingerlings (small fish) to other commercial farmers for ongrowing or direct to the public to stock their dams. Breeding silvers requires capture of adult sexually mature fish from ponds. Though the fish do not naturally breed they do roe up ready to go. Breeding season starts mid September and runs through to April depending on where in NSW you are located. Fish captured are anaesthetised with clove oil weighed and injected with HCG (human chorionic gonadotropin) at a rate of 200IU/Kg. The hormone is just that little push the fish need to get them to breed. Females are always injected but males are usually ready to go most times and don’t need any drugs to help them along. Most breeders use a ratio of 2 males to 1 female, generally one of those males is injected and one is not. Silvers are a school fish so in a 1500 litre tank you could use 3 females on 6 males. This gives us a good genetic mix in any given batch of fish.
36 hours after injection the fish spawn naturally in the tank. This is the beauty of hormones it makes all the fish breed at the same time. We try to inject fish at 6pm in the afternoon so they will breed 36 hours later at 6 am. We usually leave the fish an hour for the eggs to water harden then use a scoop net to remove the fish. The eggs are kept in the dark at 24 Deg C and with high aeration to keep the eggs in suspension. Fertility rates of the eggs vary between batches but anything over 80% is good. Silver perch have approximately 125,000 eggs per Kg of fish so quite a few in the tank. The eggs hatch 24 hours after spawning and we start putting them out into the ponds 4 – 7 days after they hatch. We prepare the outside fingerling ponds by adding lime and fertilizer then flooding with water. It is critical that ponds are dry and cracked between batches of fish to ensure that no contamination occurs. Depending on the weather and the long range forecast we may fill the ponds with water up to a week before we inject the fish. Other times we fill the pond on the same day we inject the fish. It’s a real balancing act, we are trying to grow zooplankton in the ponds to feed the larvae when released. If we fill the pond too late the food does not have enough time to grow and the fish starve. If we fill it too soon the zooplankton is too big and eats the fish larvae and we end up with nothing. Air and water temperatures are the key as everything grows faster in warm water then cold.
Once in the pond is when the real fun begins as Silvers when small are vulnerable to all types of problems from water quality to disease or parasites. We regularly check the water and the fish to attempt to solve minor problems before they become major ones.
For the first two weeks after fish are released into the pond no feeding is required as they live of the zooplankton in the pond. After 2 weeks we start adding artificial food. This is fingerling dust, a fine powder which is thrown by hand into the pond twice daily. The small silvers eat both the dust and zooplankton initially but as they grow and their hunger increases the zooplankton can not reproduce fast enough and numbers drop. Silvers grow fast and 6 – 8 weeks after release they are ready for harvest. Fingerlings are captured from the ponds and then held in holding tanks where they have a salt bath and are checked for any disease, parasites of deformities. If everything is OK they are ready for sale to other commercial silver perch farms or direct to the public for aquarium pets, aquaponic stock, fish ponds or farm dams. etc.
If you would like to buy Silver Perch fingerlings then try one of these fish hatcheries:
Silver Perch Commercial Aquaculture Farming - The Silver Perch is the centre of a large freshwater pond aquaculture industry in NSW. Fingerlings are generally purchased from specialised fish hatcheries and then on grown in outside earthen ponds. Growing silvers in small numbers is easy but if you want commercial quantities then it is not so easy. We take fingerlings at 1 gram each and place them in a pond and feed them up till they are 100gram, we then harvest them all and sort them into 3 different sizes as silvers all grow at a different rate. Basically we grade into small, medium and large. Each size is then restocked into a new pond and fed a commercial pellet till over 450 gram and ready for sale.
It takes 18months for silvers to reach a marketable size. Prior to sale fish need to be harvested and transferred to purging tanks and kept for 1 to 2 weeks in pristine water to ensure they have a pristine flavour and no off flavours.(See Off Flavours) Silvers can have a muddy/ earthy flavour straight from the pond so purging is essential to ensure a high price in the market place.
The growout of Silver Perch is a extensive subject which needs serious study by potential farmers before they jump into aquaculture. Many TAFE courses are available on aquaculture and the culture of Silver Perch and I would recommend you do one of those before you start commercial farming. NSW DPI Fisheries also has some excellent publications (books) available and every Commercial Silver Perch farmer has a copy of these - they are a must.
Silver perch farming is a life style choice and can be very rewarding from that point of view, however it is not necessarily a recipe for making money, most people are in it for love not money and any serious farmer will warn you that “If you kill enough fish eventually you will learn how to keep them alive.”
It is possible to culture up to 20,000Kgs of Silvers per hectare however, not many people do that amount as it is running the razors edge. One small mistake and you have 20,000Kgs of dead fish. Most serious farmers run at a production level of 7,000 to 10,000 Kgs per hectare of water. This gives you more control of the situation and smaller chance of losing the whole crop with one small mistake.
Growing Silvers requires the following
1. Well designed ponds.
2. Well prepared ponds.
3. Good quality/healthy stock.
4. Good feeding practices.
5. Regular water quality sampling.
6. Regular fish sampling. (For health and Size)
7. Good predator control.
8. Good estimating of biomass.
9. Good weather.
10. Good harvesting techniques.
11. Good purging facilities.
12. Good luck.
Silver Perch grow well in water temperatures over 24 Deg C but water over 30 Deg C slows growth. I know people can grow Silver Perch anywhere in NSW but if you want to do it commercially viably then you must take off the rose coloured glasses and seriously consider your region. Will your water temperatures be in the 24 – 30 degree mark for long or short periods. If short then Silvers may not be a viable species for you.
Silver perch are commercially grown as a food fish for human consumption. They have a clean white flesh with a great flavour. They are sold both live and chill killed and marketing can be a problem. The best prices will be received selling direct to the restaurants or general public and this is fine for small quantities but most fish farmers will produce large amounts of fish so they need large markets. There are wholesalers that will buy your fish or you can send them to the Sydney Fish Markets (SFM). If only a few hundred kilos of silvers available on the market floor then you will receive a very good price but if there are a few thousand kilos that day on the auction floor then the price will drop considerably.
It’s important for farmers and talk to the other farmers, if we all work together then we can all benefit. It’s so much easier if everyone talks to each other, its good to know what other farmers are doing, you can all learn from each other. It’s all about information in any industry, you need to be kept informed of whats happening to your industry, whats the latest developments and problems. The NSW Aquaculture Association creates a forum for this to occur, it creates an opportunity to meet and get to know other farmers and keeps you informed of latest developments about your industry.