Purging

[syazwan]

Hey Aquaponic Community, I have a question regarding purging. I have a commercial aquaculture system (recirculating aquaculture system) and an aquaponic system for my family.

Recently I have taken out few of my Tilapia from my aquaponic system for us to eat (without purging), what I notice is that the Tilapia don't have the muddy odd taste to them, while my aquaculture system we have to purge the Tilapia to get rid of the muddy odd taste (at least a week or so for the taste to disappear), does anybody know why aquaponic system don't need to purge the fish? Is it because of the less stocking of fish in the aquaponics system compare to the aquaculture system? What I have read is that, the taste of Tilapia is from algae in the water, if my memory serves me right I think it was the green and blue algae. So does that mean that these algae is not presence in the aquaponic system or of lower quantity?

I apologize for my English mistakes, grammar spelling etc.. I hope some of you guys can shed some light into this. I would like to hear what you guys might know, think about this. Thanks =D

[Pices]

@TC - What method do you use to kill them quickly?

[Neal Westwood]

I've found that if I overstock my aquaponic system, then I have to purge.  But if I keep lower /proper densities of fish then I don't.

[syazwan]

Interesting, I never experience this one before. How many grow beds do you have? Have you try increasing the number of grow bed when you overstock your aquaponics system? 

Neal Westwood said:

I've found that if I overstock my aquaponic system, then I have to purge.  But if I keep lower /proper densities of fish then I don't.

[RupertofOZ]

"off flavours" commonly occur in pond based aquaculture... principally because it employs blue-green algael management... Or, in some countries some sort of "fertilisation"...

 

Generally. neither "causes" are found in RAS aquaculture.. or aquaponics systems...

Catfish are highly susceptible to "off flavours"

Two chemical compounds, Geosmin and 2-Methylisoborneol (MIB), have been identified as the cause of a majority of off-flavor incidents. Geosmin and MIB are secondary metabolic products of some species of bluegreen algae and actinomycete bacteria. MIB causes a flavor to be imparted to the flesh described as "musty" or "lagoon" and geosmin results in "earthy" or "woody" flavors. These two compounds are extremely potent. Geosmin and MIB can be tasted in the water by humans at concentrations of 0.01 and 0.03 parts per billion (ppb), respectively. In other words, if you added 1 ounce of geosmin or 3 ounces of MIB to a catfish pond that covers 600 surface acres, you would taste it.

A number of other less frequent off-flavors have been recognized such as moldy, astringent, rotten and sewage for which no chemical compounds have been identified. It should be noted that common farming chemicals can and do impart off-flavor in channel catfish. A good example is diesel fuel which has been recognized in a number of off-flavor cases.

http://www.uaex.edu/aquaculture/fsa/fsa9051.htm

[syazwan]

I have a RAS aquaculture, with 6 tanks. The off-flavours does occur in RAS. and we are not even using any chemicals or etc in the water. We have to purge this fish before selling them to the market. so in my opinion, where there are nutrients in the water, will lead to algae growth hence creating the off-flavour. That's what I think

RupertofOZ said:

"off flavours" commonly occur in pond based aquaculture... principally because it employs blue-green algael management... Or, in some countries some sort of "fertilisation"...

 

Generally. neither "causes" are found in RAS aquaculture.. or aquaponics systems...

Catfish are highly susceptible to "off flavours"

Two chemical compounds, Geosmin and 2-Methylisoborneol (MIB), have been identified as the cause of a majority of off-flavor incidents. Geosmin and MIB are secondary metabolic products of some species of bluegreen algae and actinomycete bacteria. MIB causes a flavor to be imparted to the flesh described as "musty" or "lagoon" and geosmin results in "earthy" or "woody" flavors. These two compounds are extremely potent. Geosmin and MIB can be tasted in the water by humans at concentrations of 0.01 and 0.03 parts per billion (ppb), respectively. In other words, if you added 1 ounce of geosmin or 3 ounces of MIB to a catfish pond that covers 600 surface acres, you would taste it.

A number of other less frequent off-flavors have been recognized such as moldy, astringent, rotten and sewage for which no chemical compounds have been identified. It should be noted that common farming chemicals can and do impart off-flavor in channel catfish. A good example is diesel fuel which has been recognized in a number of off-flavor cases.

http://www.uaex.edu/aquaculture/fsa/fsa9051.htm

[RupertofOZ]

Certainly can occur in RAS Syazwan.... often related to feed.... and/or feed levels...

 

And anyone selling fish commercially should probably purge before sale.. indeed it's often mandated...

 

But you shouldn't have any degree of algael growth in a RAS system...

And yep, we discourage any algael growth in aquaponics...

[Stephanie Grim]

I was told that fish taste like the water they come from.  I purge when it is convenient, but not all the time.  I don't notice a lot of difference with purged fish or non-purged ones.

[Neal Westwood]

At one point I had 300 fish in a 300 gallon tank, with 2 4x4 growbeds and a 4x8 floating raft.  Rule #1, don't overstock a system - everything is on the edge and they had the algae flavor,  Once the density got back down below 100 fish, it seemed to go away.