Rob
McCormack
Off Flavours can be quite common in freshwater fish and can
easily be removed if proper procedures are followed. When we talk about off flavours we are generally talking a muddy
or earthy type taste to fish. The
causes of this can be varied but generally they are caused by geosmin and 2
methylisoborneol. These are compounds
produced by blue-green algae and some bacterias. Silver Perch are very susceptible to off flavours as they eat
weeds and algaes in the pond and also consume large amounts of mud and
sediments as they feed off the bottom of the pond. Bass and yellowbelly are less susceptible as they eat more live
food but can still become tainted when they eat small Atyidae shrimp which they
suck from weeds etc and consume weed or mud as a bicatch.
Yabbies generally do not retain off flavours like fish do
however if they are fed aquatic weeds as a primary food source they can retain
an off flavour. Native primrose is
readily consumed by yabbies but does result in an off flavour and we no longer
use this weed as a food source.
It is essential that commercially grown fish be purged prior
to sale to ensure a premium flavour every time. In the past server damage has been caused in the market place by
unpurged fish being sold. These fish
referred to as road kill by commercial farmers can destroy the good name of a
excellent eating fish like Silver Perch.
A good Silver Perch is Excellent eating and equivalent or better than
most of its salt water competitors and a week in a purging system is all that’s
required to ensure your fish is excellent.(See Purging)
This refers to taking fish or crayfish from the pond and
holding then in a artificial tank to ensure a quality tasting product.
Silver Perch can have an off flavour (See Off Flavours) that
requires purging to remove. Generally
this is achieved by removing the fish from the ponds and transferring the to a
recirculation or flow through system under controlled conditions for
purging. Clean clear water is used with
3 – 4 grams of salt per litre of water added.
Excellent water quality is required to ensure the health of the
fish. Salt is added as a antiseptic for
any injuries incurred in harvest, as a anti fungal and parasite control and as
a stress reducer. Fish generally should
not be purged in cold water. The off
flavours they have are retained in the fatty tissue of the fish and the larger
the fish or fattier the fish the longer it will take to purge. Temperature in purging is critical as the
higher the temperature the faster the fishes metabolism will go and the faster
the process. Generally most farmers
purge for at least a week though in some cases 2-3 weeks may be required, taste
testing fish prior to sale should be standard industry practice. Generally water is fully exchanged in the
tanks within 2 hours of fish being deposited in them and then daily for the
first few days to ensure good water quality as if the water quality is poor the
fish will sicken and become valueless.
Yabbies are purged for approximately 3 – 4 days in clean
clear freshwater with a dash of salt added.
The aim of this exercise is to ensure the yabbies do not feed in the
purging or holding tanks. Pool salt is
usually used at a rate of 4 grams per litre of water and this helps to increase
the taste of yabbies as salt is a flavour enhancer and increases the crustacean
flavour in yabbies. Salt also helps
clean the yabbies of ectocommensals and other parasites etc. This is only a bi product of purging as the
aim of the exercise is to ensure the waste line through the meat in the tail
from the stomach to the anus is clean and clear. If it is clean and clear the chefs at the restaurant do not need
to devein the yabby and it is easier to prepare and the customers are
happier. It also gives the advantage to
the aquaculturalist over the wild catch which is not purged and gives you a
marketing advantage.