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Fish Anatomy Guide

If you are new to the hobby.

Fish Anatomy Guide

Postby Mick » Sun Mar 14, 2010 4:55 pm

There are approximately 22,000 species of fish that inhabit this planet, they first evolved about about 480million years ago and many species have evolved certain physical features that have adapted to suit their surroundings. All fish have a spine, fins and most species are covered in scales but not all.

Body shape
Most fish have evolved a body shape to suit their surroundings and looking at a fishes bodyshape will always give you a good clue as to their natural habitat. Flat bodied fish with upturned mouths are normally surface dwelling fish whereas fish with tall bodies inhabit slow waters. Streamlined fish with long slender bodies usually inhabit fast moving waters, bottom dwelling fish have flattened bellies and often their mouths are below their bodies.

The Mouth
The shape and size of the mouth is a great indicator as to which diet a certain fish will eat in the wild. The size of the mouth indicates what size prey they are capable of eating.
Surface feeders will have upturned mouths as they predate on surface insects etc.
Predatory fish have large mouths whereas omnivorous fish will have smaller mouths.
Bottom feeding fish often have their mouthparts below the body and quite a few species also possess barbels which are used as sensory organs for locating food in dark and murky waters. Loricadae species will also possess rasping mouthparts for scraping away algae from rocks or wood.

Lateral Line
The lateral line is a series of fluid filled ducts that run across the body of the fish. These are used for detecting movement in the water and detecting prey or even the detection of predators that see the fish as food. The ducts are located just below the scales and even a fish without vision can detect its whereabouts using this organ.

The fins are used for propelling the fish, keeping the fish balanced and they are also often used in the spawning process. Fins can either be found single or paired but in the wild long and extended finnage is not often seen, this is normally the result of selective breeding.
The caudal fin (tail fin) is used for propelling the fish. Fish with forked caudal fins are fast swimmers, fish with rounded caudal fins are capable of sudden, swift movements such as predatory fish and fish with extended caudal fins use these to display to the females.
The anal fin is located in front of the caudal fin and is used to keep the fish stabilised. Some fish have extended anal fins and these are often used to help propel the fish
The ventral fins (pelvic fins) are also used for stability, fish such as Corydoras will also use these fisn to hold their eggs during the spawning process.
The pectoral fins are located near the gill plates and are used for steering the fish. Several species of bottom dwelling fish have adapted these to stand them upright and use them to perform a walking motion across the substrate.
The dorsal fin is located on the fishes back and is also used for stability.
The adipose fin is only found on certain species of fish.It is very small and located between the dorsal and caudal fins.

Apart from a few species of fish, most freshwater fish have scales covering their bodies. There are basically two types of scales (Ctenoid scales are rough edged and jagged, Cycloid scales have smooth , rounded edges.) Several species of catfish have bony plates which are used the same as scales.

These are the breathing organ of the fish. The filaments in the gills can absorb the oxygen and expel carbon dioxide. They constantly expel water and some species of fish have modified their gills to enable them to breathe gases from the atmosphere. The plates covering the gills are commonly known as the operculum.

Swim bladder
This is an air filled organ that provides buoyancy to the fish. Many bottom dwelling fish have adapted this organ so that the fish does not become buoyant allowing them to rest on the substrate and some species of fish have modified swim bladders that can extract oxygen from the air in the swim bladder sac.

Fishes eyes are capable of seeing colour and they take on a more rounded shape than many terrestrial creatures to compensate for the refractive nature of water.

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