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Tales From The Net-Cage


The most un-oxygenated cages farm in the Mediterranean

Imagine a farm located inside an active port – the biggest port in the country.

Now – imagine that the highest temperature reaches 31 degrees in high-summer.

Saying all that - now this is the only place you can safely build a fish-farm to grow your sea-bream.

There are many issues outcomming that fact, and in the future I will address them, but the main issue resulting from the fact we are growing sea-bream inside a port is the oxygen problem.

Since the location is basically a huge pond of sea-water surrounded by water-brake from the sea-side, it actually creates a pond in which, during summer time, although the water-brake is “breathing” and currents can go through, when temperature rises above 24 centigrade, the fish start to suffer from a lack of oxygen.

Everyone who grows fish can imagine the effect of the lack of oxygen on the behavior of the fish. The levels might be so low, one can see the fish literally asking for oxygen, swimming near water surface, weak and miserable.

During the years we had to develop the protocols of behavior in such hard conditions, starting with the fact that the feeders must be professional, they learn to understand the “language” of the fish and they know they need to translate it directly to the farm-manager or the farm-biologist, to avoid coming problems; they can’t start a feeding day without having a functioning oxygen-meter which is used in every single feeding in every cage, so that feeding will not happen under a certain level of oxygen, or else fish will die, and there are days that the farm is not-approachable due to oxygen level.

This situation is not familiar usually to the cage-farm growers.

In propose to avoid as many non-feeding days, and trying to avoid all the other side effects of low-oxygen levels on the fish (high FCR levels, low performances, diseases accrued more often, high mortality) we were travelling between traditional and non-traditional solutions to try and aerate and oxygenate the area.

The beginning was traditional – force-7 aerators, RIO mixer which pushes huge amounts of water, combinations with both of them, but it was too demanding; both maintenance and electricity power.

So – we had to look for more effective solution.

First step was to build a unique air-diffusing system which took the air deep down to the middle of the cage and help with the mixing and aeration of the cage. But sure enough – we understood this is not what we need, so we went to the next step: we develop a state of the art monitoring and operating oxygenation system, a system which made a safe oxygen supply to every single cage on a need-basis, so that oxygen will not run freely, but will be supplied only when the oxygen drops down below a certain level, so we practically turned the cage-farm into something closer to an intensive fishery application.

The results came immediately after we learned the fine tuning of the system: mortality dropped right away, and fish performances raised up. We could see better performances right away, so at the end of the day we could say that the combination between the aeration system and the oxygenation system made the best solution to the very unique system of making aquaculture inside an active port.

As for the other aspects of growing healthy fish inside a port – this will be left for future articles.

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