| Summary: | This text has as its objective a synthesis of the ecology and biogeography of small lake fish systems, as illustrated by the North American fauna and, specifically, the cool temperate one of the northeast of the continent. Freshwater systems are ancient. They go beyond the Paleozoic. North America is a water rich and diversified continent, with latitudinal range from the Arctic to near the Tropics. A fossil record of fishes going back to the Ordovician testifies for a long period of fish evolution with an increasing diversity of body forms for freshwater fishes over time. Water has distinctive attributes. With high viscosity and density, it provides physical bodily support for its inhabitants and buoyancy against gravitational pull. Aquatic organisms live suspended in their environment. Light penetrates water poorly, meaning that most productivity is near the surface. Oxygen is optimal near the surface. The best habitat is along the shoreline and near the surface. Cold temperature is a great limitation to fish occurrence and activity. In the north, fish are relatively inactive in winter. Patchiness is a big factor in the distribution of aquatic organisms, as on land. Benthic invertebrates, all important as fish food, relate to cover, substrate (mud, sand, rock), particle size and diversity, grain spacing, organic content, and vegetation height and type. Fish species may be habitat specialists (for example, confined to cover), or generalists utilizing multiple habitats. Age classes within species often use different habitats. This is a very important factor of habitat use by fishes. The characteristic body shape of fishes, fusiform, is demonstrably the most efficient shape for passing through the aquatic medium. Absence of legs limits overland movement between water-bodies. Body morphology and all other systems, physiologies, annual cycles, reproductive methods, and ecologies, are specially adapted to the aquatic environment. Different body shapes, fin positions, mouth sizes, angles of mouth opening shapes and ...
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