Spain – The Spanish Experiments Part 6

Aquaponics and Hydroponics

I found out about the tilapia when I was investigating hydroponics and aquaponics. As you are probably aware, these are systems for growing plants for food, using very little water. In fact, they use the same water via a flood and drain system, where the water goes through the plants or pots, and is recycled rather than disappearing down into the soil. With hydroponics, nutrients are added to the feeder tank, and with aquaponics, the nutrients are obtained from the waste produced by the fish in the water.

By the way – do you know the plural of fish?

It’s fish

It’s fishes…

No, it’s fish…..

Actually both of these are correct. ‘Fish’ relates to a shoal of one type of fish. Fishes relates to an aquarium, tank or lake of different species of fish. So now you know….

We decided on Nile Tilapia, and have two species – red and silver. Here they are:


We couldn’t quite decide which was the best system – hydroponics or aquaponics –  although we knew that it was a good idea to grow plants in water that you could use time and time again. Many systems are being set up around the world to feed more people in drought areas, and the Dutch are masters at growing things like lettuces in a rotating floating system. With aquaponics, we know that this system has been used for farming as far back as the Aztecs, who floated rafts of plants on rivers and lakes that were rich with nutrients from fish(es). You can even buy your own home aquaponics system, consisting of an aquarium with a floating bed of plants on top of the water.

Check out this video which shows you how commercial ventures are growing lettuces. You will be absolutely amazed!


We have a trial 48 pot system for hydroponics. Last year was our first year, and due to the fact that we set it up rather late in the season, we simply threw a load of pepper plants into the pots and a few late tomato plants just to grow something. Within a short while we had them coming out of our ears from plants that grew taller than me! We were eating them raw, cooking them, giving them away, composting them….


The hydroponics system

The aquaponics did very well too, although I think the result was a little less impressive than the peppers. However, we now had around 100 tilapia fry, imported from the UK, growing nicely – so the aquaponics can provide both meat and plant produce. By the way – you can just use goldfish if you want to. In fact, I would recommend it, because you have to keep the water heated for tilapia, whereas goldfish can survive in warm or cold water. Tilapia will not survive in water less than 20 degrees. 28 degrees is the preferred range. And that takes a lot of electricity, which is why solar power is so necessary.


The aquaponics system

My advice regarding which of these systems to choose is really simple. Unless you want to learn all about ph, nitrites, ammonia, balancing the tank water, breeding etc., stick to hydroponics! We have been through a massive learning curve. Initially we started to wonder why the small fish were dying off. Then we discovered it was due to too much ammonia and nitrites in the water. After many sleepless nights, studying of youtube videos and reading online reports, learning all about bacteria, etc., we finally started to learn how to balance the water. It is an art form, and the nitrites etc. can ‘spike’ at any time, causing the whole fish population to be wiped out overnight, let alone if a heater packs up without you knowing, a filter gets blocked or you remove some plants from the aquaponics beds, causing another change in a delicate eco system…..

We were down to about 75 fish before we finally started to get the balance right, and things settled down. The fish started to grow and put on weight. Then we realised that they were attacking each other, fighting for territory. We would often go into the greenhouse to find a dead fish floating on the water, which is quite heartbreaking after spending so much time and effort in keeping them alive.

Eventually, we found out about breeding the tilapia. This was our idea – to have a regular supply of fish for our table, whilst selling the surplus fish.  The Spanish love their fish. They love fresh fish even more. So we knew there was a huge market, especially now that it has been revealed that the producers in the far east raise their tilapia and all other forms of fish and seafood on pig faeces! Yes, it is true. If you ever go to buy prawns, salmon –any kind of frozen fish, check the packaging for the origin. If it is from the far east, put it back….

So we bought two second hand aquariums for our breeding fish. These tanks are big, about 1m long by 80cms wide and deep, again requiring heated water, pumps and filters. Thank goodness for solar……

So we put a dozen of the larger fish in each tank, as we didn’t know which ones were male or female. We hoped they would soon identify themselves if we watched them closely. How wrong could we be! After a few days, we found a dead fish floating in the tank, then another, then another…..soon we were left with one fish in each one, in solitary confinement, with no mate.


It was back to studying how to sex the fish. This involves trying to catch them  holding them and inspecting them. They have distinct genitals which are only really noticeable under a magnifying glass, and these fish fight for their lives when being handled! Alex, our Spanish assistant, helped me with this operation but soon we were drenched and none the wiser, even after inspecting 20 fish. I did see a video where the person used food colouring to make the genitals more visible. I didn’t have any, but I did have beetroot powder, which I mixed in a cup with some water. Not a good idea – due to the fish thrashing about, the mixture was spattered up the walls, along the floor and all over us, so we ended up looking like Burke and Hare after dismembering a body!

I then realised the awful truth. We had been sold all male tilapia, even though I had asked for a mixture….and to get female tilapia in the breeding season is like trying to get hold of rocking horse poop. So for now, we have to try to keep the remaining fish alive, by providing them with hiding places in the big tank. For the last couple of weeks this seems to have worked fine with no more losses, we simply put some breeze blocks in the tank, stacking them so there were gaps and hiding places amongst the blocks.

You may wonder if because tilapia are so common, why not buy them in Spain? As far as we can make out, you can raise them in Spain, but you cannot sell live tilapia for some reason. So for the time being, we are stuck on that project. That is a shame, because we built the huge ponds in the garden to grow the tilapia on in the summer months. Still, we have a beautiful water garden now, if nothing else, and the aquaponics system is producing food for us. And we move on, older and wiser….

Look out for Part 7!