Fish gill in the context of "Operculum (fish)"

Angling (from Old English angol, meaning "hook") is a fishing technique that uses a fish hook attached to a fishing line to tether individual fish in the mouth. The fishing line is usually manipulated with a fishing rod, although rodless techniques such as handlining also exist. Modern angling rods are usually fitted with a fishing reel that functions as a cranking device for storing, retrieving and releasing out the line, although Tenkara fishing and traditional cane pole fishing are two rod-angling methods that do not use any reel. The fish hook itself can be additionally weighted with a denser tackle called a sinker, and is typically dressed with an appetizing bait (i.e. hookbait) to attract and entice the fish into swallowing the hook, but sometimes an inedible fake/imitation bait with multiple attached hooks (known as a lure) is used instead of a single hook with edible bait. Some type of bite indicator, such as a float, a bell or a quiver tip, is often used to relay underwater status of the hook to the surface and alert the angler of a fish's presence.

When angling, the fisherman (known as the angler) will first throw the hook (i.e. "cast") to a chosen area of water (i.e. fishing ground), and then patiently wait for fish to approach and devour the hookbait. It is also not uncommon for the angler to scatter some loose bait (groundbait) around the target area before even casting the hook, to better attract distant fish with scents. If a fish has succumbed to its own feeding instinct and swallowed the baited hook (i.e. "bite" or "strike"), the hook point will likely pierce into and anchor itself inside the fish jaw, gullet or gill, and the fish in turn becomes firmly tethered by the fishing line. Once the fish is hooked (often colloquially called "fish-on"), any struggles and attempts to escape will pull along the line, causing the bite indicator to signal the angler, who jerks the fishing rod back to further deepen the hook anchorage (i.e. "setting the hook") and then tries to retrieve the line back, pulling the fish closer in the process. During the line retrieval, the angler will carefully monitor the line and rod tension to avoid equipment breaking. With stronger and feistier fish, the angler might need to temporarily halt or even reverse the line retrieval to prolong the struggle time and tire out the fish (i.e. "walking" the fish), before dragging it near enough to eventually lift it out of the water (known as "landing") for a successful catch. Sometimes a hand net (or "landing net") or a long-handled hook is used to make fetching the fish easier.

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 pharyngeal arches, also known as visceral arches, are transient structures seen in the embryonic development of humans and other vertebrates, that are recognisable precursors for many structures. In fish, the arches support the gills and are known as the branchial arches, or gill arches.

In the human embryo, the arches are first seen during the fourth week of development. They appear as a series of outpouchings of mesoderm on both sides of the developing pharynx. The vasculature of the pharyngeal arches are the aortic arches that arise from the aortic sac.