FEEDING FISH: How Often and How Much?

[Kyle Sy]

Hi,

Newbie here. We just started our Aquaponics Raft System a few months ago, however we are still not sure when and how much to feed our fish. We feed them with pellets.

How often should we feed our fish? in addition, how much per feeding?

We have 40kg of Tilapia as of now.

Please help :) Your responses will be appreciated. Thanks!

Kyle Sy

Tagaytay, Philippines

[Carey Ma]

How much feed depends on what size your fish are more than how much one has. We feed every four to five hours during prime growth season. Temp/ season has effect on growth/ feeding rate as well. Quality/ makeup of feed makes a big difference too.

The following feed schedule is for recirculating systems:

Size of fish (grams) Amount of daily feed (% of fish weight)
0–1gr                    30–10%
1–5gr                    10–6%
5–20gr                    6–4%
20–100gr                4–3%
larger than 100gr    3–1.5%

In greenwater / pond culture, we feed once a day just to make sure but is actually unnecessary. Instead we fertilize the water for algae and bacteria production.

To find out your interval period, you should feed them according to my chart then determine how long it takes for your fish to digest and empty their stomachs.

[Kyle Sy]

Hi Carey!

Thanks for your helpful reply! :) We will try that out. Just to be sure, will this ratios work if you stop the circulation of water?

Our fish is placed in a 2000 Litre container, will once a day be applicable?

Thanks again!

[Carey Ma]

I would keep feeding them the way you normally do or as per my suggestion above unless they are overwintering and you are not growing crops, otherwise you will want them to eat as much as possible as often as possible.

[Kyle Sy]

Okay, Thanks very much! we'll update you regarding our progress :) 

Hopefully we'll get our consistency

[Joel G]

 

Hi, Kyle!

The feed ratio is recommended for optimum growth and mass conversion. It assumes that you have optimum water quality and sufficient dissolved oxygen (aeration).

 

I am assuming you are using a 2000liter IBC tank (or something similar). This is important because the level of dissolved oxygen (without air pumps) depend on the exposed/surface area of the water container and the degree of surface agitation (usually goes with the water circulation). So if you stop water circulation, you might end up suffocating the fishes.

 

Also, water circulation removes the fish wastes (poop, carbon dioxide, nitrite, nitrate, ammonia) from the fish tank (thus maintaining water quality).

Hope this helps. :)

Regards,

- Joel

( FYI I am based in Pasig. ) 

Kyle Sy said:

Hi Carey!

Thanks for your helpful reply! We will try that out. Just to be sure, will this ratios work if you stop the circulation of water?

Our fish is placed in a 2000 Litre container, will once a day be applicable?

Thanks again!

[Kyle Sy]

Hi Joel,

Thanks for your concern and help. Nice to know that we are living on the same soil!

The 2k Litre container as of now contains 40kg of Tilapia. We have stopped the circulation (since we tried to use coconust husks as biofilter but the water becomes red that is deadly for the fish). Ever since we stopped the circulation, we have oxygen pumps and replace the 40% of the water every day. What are your comments with the present situation?

Thanks!

PS. the water is being stored and used to water other plants in the soil, so we're not wasting the water that much :)

Joel G said:

 

Hi, Kyle!

The feed ratio is recommended for optimum growth and mass conversion. It assumes that you have optimum water quality and sufficient dissolved oxygen (aeration).

 

I am assuming you are using a 2000liter IBC tank (or something similar). This is important because the level of dissolved oxygen (without air pumps) depend on the exposed/surface area of the water container and the degree of surface agitation (usually goes with the water circulation). So if you stop water circulation, you might end up suffocating the fishes.

 

Also, water circulation removes the fish wastes (poop, carbon dioxide, nitrite, nitrate, ammonia) from the fish tank (thus maintaining water quality).

Hope this helps.

Regards,

- Joel

( FYI I am based in Pasig. ) 

Kyle Sy said:

Hi Carey!

Thanks for your helpful reply! We will try that out. Just to be sure, will this ratios work if you stop the circulation of water?

Our fish is placed in a 2000 Litre container, will once a day be applicable?

Thanks again!

[Joel G]

 

Hi, Kyle!

 

If I may ask,

a) how did you know that the red coloring is "deadly for the fish" ?

b) What means of increasing DO did you have before you stopped the water circulation?

 

Coco coir (husk) is an accepted grow bed media. Red water usually means tannins, which is actually very much desired by black water aquarium breeders. If you wait a few cycles, the tannins will eventually dissipate (or you can use activated carbon and/or boil the coir to make the process go faster.)

 

A 40% daily water change will prevent your system from becoming cycled, and possibly even push it back into "new tank syndrome". (which definitely kills fishes).

 

Regards,

- Joel

 

 

 

 

Kyle Sy said:

Hi Joel,

Thanks for your concern and help. Nice to know that we are living on the same soil!

The 2k Litre container as of now contains 40kg of Tilapia. We have stopped the circulation (since we tried to use coconust husks as biofilter but the water becomes red that is deadly for the fish). Ever since we stopped the circulation, we have oxygen pumps and replace the 40% of the water every day. What are your comments with the present situation?

Thanks!

PS. the water is being stored and used to water other plants in the soil, so we're not wasting the water that much

[RupertofOZ]

Joel G said:

 

Coco coir (husk) is an accepted grow bed media.

 

Not usually used as a grow bed media at all... unless in really hot environments...and/or with intermittant watering regimes

It simply retains too much moisture to be used in F&D... leading to root rot...

And in flood & drain.. breaks down rapidly...

Generally it is also very acidic... sometimes as low as pH 5.5....

And often very salty...

 

Kyle... I would suggest that there are much better mediums to use for bio-filtration...

[Kyle Sy]

Hi Joiel

We used Coconut Husks to act as biofilters for the system. About half of the grow bed is filled with it. Our plants are placed on plastic cups that are floated by holed styro boards.

After installing the husks in the system. we have experienced fish casualties for the next two days, especially when the color of the water becomes reddish as the husks stays longer in the water.

We dont want to take risks and harm the living animals, so we decided to stop the circulation. This will stop the reddish water from the grow bed from flowing down to our fish tank.

As of now, we are going to use ordinary aquarium filters, so that we will have less organic inputs in the system (easier to manage)

Thanks for the knowledge about the "new tank syndrome". If the system is not circulating, how many % of water do you suggest must be changed?

Thanks very much!

Joel G said:

 

Hi, Kyle!

 

If I may ask,

a) how did you know that the red coloring is "deadly for the fish" ?

b) What means of increasing DO did you have before you stopped the water circulation?

 

Coco coir (husk) is an accepted grow bed media. Red water usually means tannins, which is actually very much desired by black water aquarium breeders. If you wait a few cycles, the tannins will eventually dissipate (or you can use activated carbon and/or boil the coir to make the process go faster.)

 

A 40% daily water change will prevent your system from becoming cycled, and possibly even push it back into "new tank syndrome". (which definitely kills fishes).

 

Regards,

- Joel

 

 

 

 

Kyle Sy said:

Hi Joel,

Thanks for your concern and help. Nice to know that we are living on the same soil!

The 2k Litre container as of now contains 40kg of Tilapia. We have stopped the circulation (since we tried to use coconust husks as biofilter but the water becomes red that is deadly for the fish). Ever since we stopped the circulation, we have oxygen pumps and replace the 40% of the water every day. What are your comments with the present situation?

Thanks!

PS. the water is being stored and used to water other plants in the soil, so we're not wasting the water that much

[Vlad Jovanovic]

Hi Kyle, just out of curiosity, what's your system water pH like with that coco coir in the media bed?

[Joel G]

Hi, Kyle!

 

 "... If the system is not circulating, how many % of water do you suggest must be changed?" 

BFAR and SEAFDEC recommend (for a properly cycled and loaded tilapia system) a 10% to 20% weekly water change (as opposed to a daily 40% equivalent to 280% weekly volume). Please note that is a "general guide" or "baseline". More efficient filters (mechanical, biological and chemical) and sufficient aeration can allow you to increase your biomass (more tilapia per volume of water).

Vlad points out that you really should measure your PH (and probably hardness, ammonia, nitrite and nitrate) particularly when starting your cycle and/or adding a new component (like coir or even "fresh" water). In Cartemar, an API master test kit costs about P1000 and is good for up to 800 tests. 

I have to admit that we do not test either, but then we are developing/researching systems intended for low cost backyard aquaculture (in the PH setting).

 

 "... We used Coconut Husks to act as biofilters for the system. About half of the grow bed is filled with it. Our plants are placed on plastic cups that are floated by holed styro boards ...". 

Rereading your original post, I have to agree with RupertofOz that coir is usually not used, particularly for raft systems. They are probably best for wicking beds. He also pointed out that coir has a lot of downsides that you should be aware of (even though it is very convenient and virtually free for us in the PH). This was my point when I asked if you have scientifically determined the cause of your fish deaths, and only measurements can pinpoint for sure the said root cause (and thereby help you decide what to add/change).

By breaking the circulation between the plant and fish systems, you effectively have a separate raft-based plant system system and an aquaculture system, and lose the benefits of aquaponics. Raising 40kilos of fish while consuming 800 liters of water a day (40% of 2K liters) does not seem economical to me, so I assume you are now looking at other ways to reintegrate the plant and fish systems?

 

Regards,

- Joel

 

 

 

[Kyle Sy]

Hi Vlad,

We have been recording our PH everyday, and it averaged at 7.2

Vlad Jovanovic said:

Hi Kyle, just out of curiosity, what's your system water pH like with that coco coir in the media bed?