Aquaponics 101 – The challenges of Winter

Tilapia grow optimally in a temperature range of 26-32 deg C.  While they can comfortably handle temperatures around 20 deg and still grow, the results are far from ideal.  Also, if you are breeding your Tilapia, they will cease spawning as the temperature drops below about 24 deg.  The number of daylight hours per day is however, also a factor in spawning.

After that, it’s all downhill for this sub-tropical species.  Between 15-20 deg they don’t grow at all, seem very lethargic and eat about 1/3 of their normal requirements.  Between 10-15 deg they stop eating all together and are very prone to a fungal infection that attacks their skin.  Below 10 deg they invariably die.

Heating is thus the only option if you want to raise Tilapia in your aquaponic system.   Your choices here are either solar or electrical heating.  Solar is great but, is only of use during daylight hours.  Electricity is expensive, especially considering that Tilapia is not considered a high value species. There is also the option of heating the water with a boiler, burning wood, diesel or gas, but this is probably only an option for larger commercial systems.

You must also bear in mind that your grow beds are like massive radiators and absorb heat during the day from the sun, but at night rapidly lose this heat to the environment, thus cooling the system.  If you have a heat pump connected to your system, you’d obviously like to set your timers to run more at night to heat the water, but this also means that the water will also run through the grow beds and lose more heat than normal.  Catch 22. Here is what a typical heat pump looks like.

heatpump1

It’s not really a “pump” at all as you need to pump water through it to work. It operates identically to an air-conditioner, but in reverse. What it does is extract heat from the air around it and transfer it, by heat exchange and compression, to the water flowing through it. The colder the ambient temperature, the less “heat” there is to extract so the harder it works and the less efficient it is. We normally try and achieve a heating capacity of 10 deg over ambient. So if the temperature plunges to 5 deg, you can’t really expect the heat pump to give you more that 15 deg out.

Fortunately, water heats and cools quite slowly, so an overnight drop to 5 deg doesn’t mean that your system temperatures will drop to 15 deg as it takes some time to drop.

Two survival tips here, are firstly to provide as much insulation as possible. Enclose your tanks in a greenhouse, insulate the floor and walls of the tank and cover them at night to retain the heat. The second tip is to, if possible, reduce the volume of water to be heated. This could be achieved by dropping the water levels in your ponds and sump for the duration of Winter, or maybe even reducing the number of ponds to be heated. I use a combination of both strategies in both my home and commercial systems.

If you intend breeding Tilapia through Winter additional heating (normally with an element) is required as well as supplementary lighting. If you provide Tilapia with 26 deg temperature and 18 hours of light per day, they will spawn year round.

Just prior to Winter I decided to do some size sorting at one of the commercial systems that I built for a client last year. One of the problems that we have with O.Mossambicus Tilapia is that they grow at vastly different rates and this is more than apparent in the images that follow.

Here’ s a shot of the “guys” in their first dip in one of the ponds.

firstdip]

Here is a shot of a batch of Tilapia from the same cohort. They are all about 90 days old and vary in size from 60g (at the back) to 170g (at the front).

varyingsizes

This is a real problem in commercial systems as regular sized fish make harvesting and processing far easier. Personally, I think that a lot of the problem is that Tilapia are vegetarian and unlike other species that are highly cannibalistic, the mild-mannered Tilapia only preys on their smaller brothers and sisters for the first 2 or 3 weeks.

Some feedback on my NFT efforts. All is going well, the plants are growing and they have suffered no signs of root rot, I think mainly due to the heavy aeration near the roots. Here is what the plants look like a few days ago.

nft220509

Enough for now.

Synaptoman

About these ads

One Response

  1. Hey Synapto,

    You do a lot with the irrigation pipes. Why not burry about 100 meters of them a way down in the earth have a screened air intake on the far end and the other end open right in front of your air intake of your heat pump? The Mother Earth News did a passive setup like this to provide stable temp air exchange for a house and the only problem they had was sags in the pipe collecting water and stagnating. This wouldn’t be a problem for you since the air just gets blown back outside anyway.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Follow

Get every new post delivered to your Inbox.

Join 164 other followers

%d bloggers like this: