Potential for Aquaculture:
Golden perch are considered by many to be Australia ‘s prime freshwater table fish, and they have long been considered for aquaculture. Finding a suitable food for them in captivity has been problematic.
They take fresh foods well ( eg yabbies, meat, worms) but there have been problems maintaining them on pellet foods in pond grow out situations. Weaning juvenile golden perch onto artificial diets has been one barrier to development of golden perch aquaculture.
Golden perch growth rates in the wild indicate they could reach market size in under two years, as they reach up to 700g in two years.
The high demand for golden perch for recreational fishing ensures good supplies of cheap fingerlings , which are produced by commercial hatcheries. In short, golden perch meet the requirements of availability of seed stock, ready market and high price.
Market:
Market in a niche market at present. The primary buyers are of Chinese origin who like eating fresh water fish, and also prefer moist flesh. The yellow colour of the fish is very important in this market, as the standard was the wild caught fish from the rivers of New South Wales .
The preferred size about 600-800 g, as determined by interviews and market studies of golden perch buyers. However, they will buy anything between 400 -1400g.
Aquaculture product will in the foreseeable future compete against wild caught gilled and gutted fish. Aquaculture golden perch received slight premium on wild caught when gill & gut taken into account, but this varied slightly.
Market priced were also dependent on when fish were sold-if there were problems on the market floor or of aquaculture fish were put on sale late in the morning poor prices resulted.
Additionally, Sydney fish market prices are somewhat determined by availability of all fish, so if supplies are huge then prices drop. Since SARS , fish prices have been generally low. Market would prefer cleaned fish, we were unable to do this because we were not licensed to do so. Any operation would have to consider the cost of doing this.
Fish of the lighter colour preferred by the market were produced in turbid water. The market has historically reached up to 1000t/year (Sydney/Melbourne), although recently 400T is about the average.
This is based on assuming that an equal quantity of fish is sold outside of the Sydney fish market in Sydney , and that the Melbourne market is equal to the Sydney market.
As colour is important we tried ‘bleaching’ fish by keeping them in turbid water, using kaolin clay. This worked well, but when fish were held iced for three days (the length of time it takes to get from Tropical North Queensland to the Sydney markets) they darkened.
We did find that killing them in a pale coloured chill bin appeared to retain the lighter colour and fish processed in this way appeared similar to wild caught product on the market floor.
Purging:
Purging of golden perch in clean water resulted in significant weight loss (10%) over one week. We purged based on Queensland industry standards initially, then reduced the time. However, after extensive taste testing we tried pond purging.
In pond purging (no feeding for four days) prior to harvest works well. No muddy flavours were detected in fish-all ponds were always sampled before harvest.
The Queensland Aquaculture Association ran some tests and found that women are far more likely to detect off flavours . We found that wives and mothers-in-law were particularly good at tasting the fish-so much so that supply had to be limited.
Strains:
There are three distinct strains of golden perch in Australia . The most commonly grown and sold are Murray-Darling strain, because impoundments for recreational fishing are mainly in this catchment stocking guidelines permit stocking of this strain in areas outside their natural distribution in Queensland.
The Fitzroy subspecies ( Central Queensland ) is darker than the Murray-Darling strain. The Lake Eyre basin species is longer and thinner, and is generally more silver than the Murray-Darling strain.
The Fitzroy golden perch are produced to order by Queensland hatcheries. They appear to grow more evenly than Murray-Darling fish, but their darker colour is a serious issue that would need to be addressed.
Lake Eyre basin golden perch look like a silvery marine perch, some look almost like jewfish due to their larger head. The market does see them from time to time, as there is a capture fishery in South Australia after floods bring them in from Queensland .
However, the capture methods can be rough, consisting of chain mesh dragged through waterholes between two tractors. There have been some difficulties in breeding to date preventing experimental grow out.
Recently one fish hatchery in Queensland produced substantial quantities and found them easier to wean and with excellent growth in the very early stages. However, there were substantial losses with handling and grading which would need to be addressed.
Disease:
Golden perch suffer from the usual aquaculture fish diseases, particularly as fry and fingerlings. As larger fish they are very tough, handling poor water quality (pH > 10, ammonia > 3mg /L). We do not recommend these conditions, as they will restrict growth. However, the fish can handle them for short periods with apparent ill effect.
However, they can suffer from bacterial septicaemia , skin infections and are particularly vulnerable to Tetrahymena corlissi . Use of probiotics eliminated problems with bacteria, but did not stop Tetrahymena . Tetrahymena caused major losses of both Fitzroy and Murray-Darling fish.
We believe that this was because the fish were naïve to the Tetrahymena in our area, which may have been brought in by guppies in the channel water. All commonly used chemotherapeutants were used without any effect-even 1000 mg/L of potassium permanganate and 250 mg/L of formalin with 10‰ salt had no effect on the animals.
We have problems a second year when using probiotics and found that bacterial septicaemia associated with the previous year’s infection was absent. In the second year the infections were found to be primary, that is the parasites initiated lesions in the fish skin. Eventually we decided to try systemic treatment (works from within the tissues) and it was extremely effective. However, it is not registered for use in Australia and no fish treated were sold.
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