My problem with this concept is that fish are cold blooded and require much less oxygen to maintain their metabolisim than mamals.

Typical lung capacity is ~1.2l and at-rest breathing rate is ~15 breaths/min rising to 60 - 75 for hard physical activity so for maintained diving we would need an air supply of up to 1.2*60l/min = 70l/min. If there is only 1.5% disolved air at 200m then it would require up to 4800l/min (4.8 tonne/min!) of completely de-airated water to provide that volume of air. That's a lot of water to process and expell, a lot more if the process is less than 100% efficient.

Cavitation on the equipment would also be a problem and I think the noise generated would be horrific.

There may be other factors to consider too (I don't know a lot about disolved gasses at depth but water will disolve a lot more CO2 than O2 this may further complicate the problem. Also working submerged for long periods has its own dangers from saturation and the lenght of time required for decompression.

The guy seems to be touting for funding despite the 'interest' of government and diving agencies - I don't think I would invest in his idea.

Edit: typo

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