Instinct is a biological concept, so why object to discussing it in those terms? You can philosophize about instinct, but that doesn't affect what it IS, it only affects what it means.
Your discussion of subject / object here is also a matter of your level of resolution. I can talk about the universe, which contains all animals and all environments within one concept. Or I can talk about the Amazon jungle, which contains all of its constituent animals and all of its constituent microenvironments as one concept.
But if we're talking about the nature of instinct in Amazonian coral snakes, then the only way to understand their behavior is to understand the specific features of the environment and regard there to be a sensory interface between the two.
reality is subject and object as one, separate them and you have nothing
Subject and object are always separated, otherwise you cannot specify action or predication, no concepts, and no language. It is developmentally innate for us to understand the difference between subject and object, or at least those would be the findings of people like Noam Chomsky.
Can one ernestly hold the concept of fish in the absence of water for long, without thinking dead.
This analogy has nothing at all to do with what I was talking about, and this should be pretty obvious from my posts. Again, this is pretty simple -- instincts are behaviors or impulses to behaviors; they are performed by animals in response to external sensations from the environment or internal sensations from their own body. If a jaguar is running after prey, its internal sensation of hunger and the vision of external prey trigger its instinct to pursue. In other words, you are not ignoring the external environment at all, and you're only separating it insofar as the animal itself needs to have an independent definition for its unique biology to be understood.