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 viable 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 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 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. This has lead to
a reduction of silvers in the wild and they are on the Potentially Threatened
List.
In the early 60s NSW Fisheries started breeding research at
Narrandera and ever since then NSW Fisheries have considered Silver Perch as a
ideal species for aquaculture in NSW.
NSW 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 farmers in NSW utilising
their own capital it is a very satisfactory effort.
I produce fingerlings and growout fish as well as
all sizes in between for all types of purposes from aquarium pets to fish and
snake food. We breed all our fish here
in our hatchery with our own stock accumulated over the last 20 years. We have genetically identified some of our
stock but as a rule its a very diverse mix we use.
We capture fish from at least 2 separate ponds for
breeding. One lot is old mature fish 4
6 years old and the other is new fish only 2 3 years old. We breed hundreds of thousands of small
silvers each year and when we harvest a fingerling pond we have a very marked
difference in size between individuals.
For years long forgotten we have been taking the best 1% of the
harvest. These are the shooters who
have grown the fastest and are general 10 times the size of the average
ones. Each year we have selected them
for future breeding stock attempting to grow a faster silver perch. These days we no longer select them but
those just a bit smaller but still at least 6 7 times bigger than the
average. We grow these fish up, select
the healthiest for breeding and sell the rest for food. Once we breed fish we dump them in a pond to
use again not next year but the year after.
Breeding Silvers is easy, these where the first fish species
we attempted in this hatchery. That
first time we used good size fish around 1Kg which we caught on fishing lines
that day. A mate of mine Steve Vidler
showed us initially how to do them, mind you after a day on the side of the dam
catching fish and drinking beer it was a miracle we even found the hatchery let
alone breed fish. Steve has fish blood
in his veins, he shot those fish up and they breed perfectly, I think even he
was surprised how well they went. It took
me 2 years to match that first success but it did not matter as silvers always
give you some result.
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 here and runs through to
April. 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 dont need any drugs to help them along. We 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 we would 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
We transfer silvers from the hatchery tanks to the
fingerling ponds by bucket as the larvae are small and fragile. Acclimatization is not a problem with
silvers as it only takes a couple of hours to let then adjust to the new pond.
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. We just drain the pond into a
pond below with a net erected in the pond.
As water flows out of the pond into the net the fish are captured and
can be scooped out for a salt bath and then into holding tanks in the shed for
sale or restocking for growout.
GROWOUT
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.
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.
In my opinion Silver Perch are not suitable for commercial
growth in recirculation systems. Do not
misunderstand me, Silvers grow extremely well in recirc systems, I just think
that at the end of the day you will not make any money when you sell them.
Silver Perch has a current (2004) market price of $6 to $10/Kg.