Professional Anglers Association|
BRITISH FRESHWATER FISH
There are around 50 species of freshwater fish found in Britain, and they can be divided into four main groups: - 1. fish of the salmon family, including salmon, brown trout, rainbow trout and their relatives (such as grayling) They may be migratory or non-migratory; they prefer cooler, well-oxygenated water; they are adapted to fast-flowing rivers; and they are characterised by the presence of an adipose fin. 2. cyprinid fish - members of the carp family - which are essentially non-predatory. They inhabit a wide variety of habitats, from fast-flowing rivers (e.g. chub & barbel) to rivers of moderate flow (chub and dace) to stillwaters (bream, tench & carp). Some species, such as roach, can adapt to all these habitats. Cyprinids are characterised by the presence of pharyngeal teeth (pairs of bony throat teeth). 3. predators, such as pike, perch and zander, which feed largely or exclusively on other fish. Their common feature is that their jaws carry numerous, backward-pointing teeth. 4. minor species which hold little angling interest (but which are often important to the ecology of a fishery) - stone loach, bullhead, and stickleback are examples. A Typical Fish The shape and external characteristics of all fish follow a basic form, although separate species have evolved modifications to it.
Fins Typical fish carry three single fins and two sets of paired fins. The single fins are the dorsal fin (on the fish’s back), the anal fin, underneath, near the vent; and the tail (or caudal fin). They are use to keep the fish upright, with the tail aiding propulsion, and in some species these fins are also used in displays. The paired fins lie (a) just behind the gill covers (the pectoral fins) and (b) further back along the underside of the fish (the pelvic fins). These fins may be used for slow paddling, but mostly they are use to as brakes to enable the fish to steer or to come to a halt. Members of the salmon family also carry a small, fleshy adipose fin behind the dorsal fin, although it appears to serve no real purpose.
Shape Many fish are round or oval in cross-section, this streamlined shape allowing them to swim against fast currents. Others are more flattened (e.g. rudd, bream); and those with flattened under-bellies are adapted to hugging the bottom of rivers – such as bullhead and barbel. Interestingly, the shape of the mouth can indicate how a fish feeds. A pollack's lower jaw is longer than its upper jaw. This fish swims upwards chasing its food whereas, a cod's or carp's upper jaw is slightly longer than its lower jaw. Both of these fish grub about on the bottom in search of food. So, careful observation of your chosen quarry can indicate where or how you should be searching for them,. Internal Features The internal processes of fish are organised into what are usually termed systems, each designed to fulfil certain vital functions. Digestive System Food is taken in by the mouth, passes into the stomach - if present - and thence into the intestine. Waste food and excess water is passed out through the vent. The mouth may carry teeth, although cyprinid fish are characterised by their pharyngeal teeth (or ‘throat teeth’). Food usually swallowed whole. Predatory fish have a stomach and relatively short intestine; omnivorous and herbivorous fish lack a stomach but have a long intestine. Food is digested by enzymes in the stomach and intestine, aided by digestive juices released by other organs - the liver and pancreas, for example. Associated with the intestine is the swim bladder, the internal buoyancy organ. Gas can be absorbed or released by a tube connected to the back of the mouth or via special glands. Respiration System Fish are able to breath through their gills by extracting oxygen dissolved in water. With the gill-slits closed, the fish draws water into its mouth by lowering the mouth floor. It then closes its mouth, raises the floor and opens its gill-slits, forcing water out. A valve across the gullet stops water going the wrong way! As water passes over the fine blood vessels in the gills, oxygen enters the blood system and waste gasses pass the other way. Note that fish would ‘drown’ if water passed in through the gills and out through the mouth. Urinary System Urine is produced by the kidneys and consists of water and waste materials.
Reproduction Fish are either male or female, although very rarely a fish may change sex during its life. Externally, it is difficult to tell the sexes apart, but:
Among British fish, tench can be distinguished by the size and shape of their pelvic fins - in males they are broad and paddle-shaped, whereas in females they are narrow and spear-shaped. Internally, males develop creamy-white testes and females develop ovaries, but neither is easy to see outside the breeding period. Fish eggs develop slowly and increase rapidly in size prior to spawning as they mature and absorb water. All British fish lay eggs or milt; none are live-bearers. Depending on the fish species, eggs are laid on plants or on the bottom substrate (most coarse fish), or they are shed into depressions cut by the fish in the bottom substrate - such ‘redds’ are typical of trout and salmon. Milt from the male is then shed over them. Trout and salmon lay fewer, larger eggs which are often covered with sand or gravel for protection. Coarse fish, lay more, smaller, unprotected eggs.
There is a similar variation in the speed with which eggs hatch:-
In both cases the young fish must consume planktonic food once the yolk sacs have been exhausted... by spring or early summer in Britain. |
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