Northern pike in the context of "Esox"

A food chain is a linear network of links in a food web, often beginning with an autotroph (such as grass or algae), also called a producer, and typically ending at an apex predator (such as grizzly bears or killer whales), detritivore (such as earthworms and woodlice), or decomposer (such as fungi or bacteria). A food web is distinct from a food chain. A food chain illustrates the associations between organisms according to the energy sources they consume in trophic levels, and the most common way to quantify them is in length: the number of links between a trophic consumer and the base of the chain.

Studies of food chains are essential to many biological studies.

Branchial arches or gill arches are a series of paired bony/cartilaginous "loops" behind the throat (pharyngeal cavity) of fish, which support the fish gills. As chordates, all vertebrate embryos develop pharyngeal arches, though the eventual fate of these arches varies between taxa. In all jawed fish (gnathostomes), the first arch pair (mandibular arches) develops into the jaw, the second gill arches (the hyoid arches) develop into the hyomandibular complex (which supports the back of the jaw and the front of the gill series), and the remaining posterior arches (simply called branchial arches) support the gills. In tetrapods, a mostly terrestrial clade evolved from lobe-finned fish, many pharyngeal arch elements are lost, including the gill arches. In amphibians and reptiles, only the oral jaws and a hyoid apparatus remains, and in mammals and birds the hyoid is simplified further to support the tongue and floor of the mouth. In mammals, the first and second pharyngeal arches also give rise to the auditory ossicles.

Most vertebrates are aquatic and breathe with gills, where water comes in contact for exchanging dissolved oxygen before flowing out through a series of openings (gill slits) to the outside. Each gill is supported by a cartilaginous or bony gill arch, which helps to maintain the gill's surface area. Bony fish (osteichthyans, mostly teleost ray-finned fish) have four pairs of arches, cartilaginous fish (chondrichthyans) have five to seven pairs, and the more basal jawless fish ("agnathans") have up to seven. The Cambrian ancestors of vertebrates no doubt had more gill arches, as some of their chordate relatives have more than 50 pairs of gills.

The bluegill (Lepomis macrochirus), sometimes referred to as "bream", "brim", "sunny", or, in Texas, "copper nose", is a species of North American freshwater fish, native to and commonly found in streams, rivers, lakes, ponds and wetlands east of the Rocky Mountains. It is the type species of the genus Lepomis (true sunfish), from the family Centrarchidae (sunfishes, crappies and black basses) in the order Centrarchiformes.

Bluegills can grow up to 16 in (41 cm) long and about 4+1⁄2 lb (2.0 kg). While their color can vary from population to population, they typically have a very distinctive coloring, with deep blue and purple on the face and gill cover, dark olive-colored bands down the side, and a fiery orange to yellow belly. They are omnivorous and will consume anything they can fit in their mouth, but mostly feed on small aquatic insects and baitfishes. The fish are important prey for bass, other larger sunfish, northern pike and muskellunge, walleye, trout, herons, kingfishers, snapping turtles and otters, and play a key role within the food chain of its freshwater ecosystem.

The Amur pike (Esox reichertii), also known as the blackspotted pike, is a pike native to the Amur River system in east Asia, as well as freshwater habitat on the island of Sakhalin. Closely related to the northern pike, it reaches a length of 115 cm (3 ft 9 in), a weight of 12.5 kg (28 lb), sporting a silvery body with small, black spots. Like other pike, this species is prized for sport fishing.

It is not commonly found outside its native range. However, it was introduced to Glendale Lake, Cambria County, Pennsylvania (United States), by the Pennsylvania Fish and Boat Commission (PFBC) in 1968. The lake is just south of the native range of the northern pike. Pure Amur pike were last spawned in 1971. All of the Pennsylvania Fish Commission's brood stock was lost in the summer of 1976. That same year the world record Amur pike was caught from the lake. The year after, the PFBC also stocked 168 northern pike x Amur pike hybrids into the lake. With a lack of success, the Amur pike program was cancelled. Glendale Lake was chosen because its outflow leads into heavily polluted waters in which fish cannot survive. Pure northern pike are found in the lake today, however it is likely no pure or hybrid Amur pike remain.

Carrigadrohid Lake (Irish: Loch Charraig an Droichid) is a lake on the River Lee in County Cork, in the province of Munster, in the south of Ireland. Situated upstream (westward) of Carrigadrohid village, the lake is actually a reservoir, created for the Carrigadrohid hydroelectric power station, which was erected in the 1950s.

The lake also serves as a fishery for bream, rudd, roach, northern pike and perch.

The Trent River is a river in Southeastern Ontario that flows from Rice Lake to empty into the Bay of Quinte on Lake Ontario. The river is part of the Trent-Severn Waterway, which leads to Georgian Bay, and is 90 kilometres (56 mi) long. The Trent drains a large portion of South-Central Ontario including most of the Kawartha Lakes and their supplying watersheds.

The river is host to numerous species of birds, amphibians and fish. Some species of fish in the river include Smallmouth bass, Largemouth bass, Pike, Walleye, Freshwater drums, Crappie, as well as other smaller fish such as Sunfish, Rock Bass and Bluegill.