What is a fishery? A fishery is a population of a species of fish. Fishermen need to go to the river with an approach that is suited for the fish that they are trying to catch. Normally there is considerable diversity in the different species of fish. Some fish however are commonly targeted and they are called game fish. These fish are normally edible, widespread, and are exciting to catch. In the Eastern United states common game fish include Musky, Northern Pike, Walleye, Sauger, Smallmouth Bass, Brown Trout, Flathead and Channel Catfish.
Ecological Niche 
While a good angler can correctly identify and knows the general preferences of the kind of fish he is pursuing; an good angler uses an approach best suited for this type of fish. This approach is not based on species (kind) so much on the ecological niche that the fish occupies.
Sometimes one kind of fish might occupy more than one ecological niche. For example, small to medium trout are normally drift eaters that eat insects. However, Large trout overtime switch to a diet of minnows and small fish and utilize different water features to maximize caloric intake. An angler whom is targeting large trophy trout fish different waters, use different bait(lures), and approach a waterway completely different.
It is also normal for an angler to catch different species whom occupy the same ecological niche. For example, Northern Pike and Muskies are both top level predators in many rivers through the Northeast. It is very possible while fishing for them to catch a northern pike and one cast and a musky on another.
Generally you could summarize most game fish as belonging to the following ecological niches:
- Top level predator. Large predatory fish that attack large minnows and other game fish. They are generally not particularly wary but sometimes are picky; only striking at the most vulnerable target. Northern Pike, Musky and flathead catfish.
- Mid level predator. Predatory fish that get get most of there food in the form of minnows and other living creatures. However, Its smaller size makes it more wary. Smaller Pike, Large trout, bass and walleye.
- Small Food eaters. The last group of predatory fish eats primarily invertebrates (insects) or heavily feed upon fry, small minnows and/or crustaceans. Many immature game fish are in this category but generally only the trout focuses on insects through much of its life. Some kinds of panfish such as crappies are heavily targeted by anglers and are in this category.
- Diverse Eaters. This category is a catch all for those fish that don't easily fall into one of the other category. Fishing for these fish requires a specific focus on the fish and its feeding habits. Feeding habits can be very diverse; examples include channel catfish (that scavenge for dead organisms), fish that might have strong vegetarian tendencies (common carp) or fish that are in a waterway mainly to spawn that might strike a lure out of reflex (steelhead or river-run salmon).
Important common characteristics 
When we target a fish, we first seek a broad understanding of its ecological niche. Many approaches target an entire ecological niche and we may need no more specific understanding to be effective. Its important to keep in mind common characteristics of the fish in a given ecological niche. Generally, its feeding behavior is the most important common characteristic to keep in mind; as it helps us understand the location, and gives us insight into effective approaches. Anglers might want to even more specifically target a species. Each species in a given ecological niche will have minor differences. Being aware of these differences and tailoring out approach to them, can allow one to be a little more successful.
Specialization or Generalization 
thus one might think this advice is at odds. Should an angler carefully target a given species, even perhaps with a given technique, or should he be more general? Of course part of this depends on whether you are seeking a trophy, an experience or a meal... but I think the answer is that an angler should have a broad knowledge, experience with many techniques, and constantly experiment as he fishes. A fishermen will learn in time, what works and what doesn't. Common characteristics merely provide the beginning of his education. Once he starts catching fish we can vary his approach noticing what he is catching; given slightly different approaches, locations, and time. As he slowly builds his skills he can alter his approach for conditions and minimize fishless hours. This perspective, it seems is the best for those (such as myself) that value the experience, more than just fish in the freezer or just trophies on the wall.