You've invited me to wade into some deep waters and talk about systems that I don't have direct expertise in modelling myself. But it turns out that actually in one of my courses just last week we were talking about this very subject, so I've had a chance to think about it a little bit. I was a bit prescient.
I wouldn't say they're analogous, because one of the major differences is that cattle on pasture are essentially foraging for themselves. It's basically a solar-powered food collection system. In contrast, in a net pen we've already moved them away from that. We've already substituted a bunch of technologies for their foraging behaviour. We're talking about tractors, fishing boats, processing plants, transport trucks, and barges that bring food to them.
The closer analogy might be between cattle in a full confinement feedlot sort of setting with fish in a net pen. But again, we're also talking about very different animals with different metabolic needs. Cattle are warm-blooded and need to burn a lot more fuel in terms of food to keep themselves alive than fish do. There are also very substantial differences in the basic biology, the fecundity of these two production systems. It's difficult to just isolate and talk about a cow standing alone in a field and a salmon alone in a net pen and try to make direct comparisons, because you really need to think of the whole system.
But to get back to your direct question, I would say these things—a cow in a pasture and a salmon in a net pen—are not very good analogies for each other from a technology perspective, because we're substituting technologies for foraging behaviour in the net pen.