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 Fishy Ecuador

 

 

 
 

Pisces  



 

There are some 800 species of fish found in the freshwater habitats of the Amazon and other regions of Ecuador. Only half that number or some 450 species are found in the Pacific ocean surrounding the  mainland and the islands. This discrepancy in numbers is due to the much higher nutritional value found in the murky Amazon waters where fruits, seeds and other organic materials are present in much higher proportion compared to the much clearer waters of the Pacific ocean. 



 

Fish are very abundant in the Amazon waters and provide an important food source for the native people there. From the large catfish (see left photo) to smaller fish like the oscar (see below, also valued for fish tanks) the selection is great. A giant among Amazon fish is Arapaima gigas, commonly called paiche in Ecuador. It can reach 3m in length and provide thus plenty of proteins for the lucky fisherman and his family. It inhabits lagoons and one can observe it coming up to the surface to breathe air. Doing so it is harped and caught. Unfortunately in many regions it is quite rare now due to extensive hunting them. Other well-known fish although not for food are the electric eel which reach lengths of 1.8m and can discharge some 650 volts, enough to stun the biggest preys. Many species play an important role as seed dispersers as they depend on fruits and seeds for their diet. Some fish even feed on leaves and other fallen detritus from the forest. 



 

Most feared by many outsiders are the piranhas. Just looking at their sharp teeth it is not hard to imagine why. But natives are not that much afraid and swim happily among them being more concerned about stepping on stingrays. Piranhas do not attack and concentrate on dead or hurt animals fulfilling roles of aquatic vultures. 



 

Stingrays are mostly encountered lying on sandy bottom in often shallow waters. On some sandy ocean beaches in Ecuador at certain times of the year, you have to be very careful to wade into the water as stepping on them elicits a poisonous sting which is very painful and somehow sours the beach vacation. That also goes for rivers and lagoons in the Amazon where they lay hiding in the mud. They are the only member of the shark and ray family which successfully invaded freshwater habitats. Stingrays mostly feed on fish, crustaceans and mollusks. 



 

Sharks are most often found resting on the sea bottom as they miss a swim bladder to give them buoyancy. Other characteristics is that they lack true bones but that is more than made up by a strong cartilaginous structure which provide them also with ever growing teeth strong enough enough to crush turtle shells. The gills are not covered by a protective shield (operculum) and are so visible.



 

  For Fishes of Galapagos go to galapagos.biodiversity.fish

 
 Natural History
 

The first fish-like creatures appeared in the Cambrian seas some 530 million years ago. They were soft-bodied, jawless and limbless fish similar to today's hagfish and lampreys. From those fish the first vertebrates (animals with a true backbone) evolved. So a fish is the common ancestor of all vertebrate animals (amphibians, reptiles, birds and mammals) to come. Heavily armored jawless fish known as ostracoderms evolved along with jawed and limbed fish, the placoderms (both extinct now). Sharks make their first appearance in the Ordovician times. Later in the Silurian period the first bony ancestors of our ray-finned and lobe-finned fish appeared. In the Devonian period also called the "Age of Fish" all of them roamed the waters with the ostracoderms being the most dominant among them. From among the lobe-finned fish a specie evolved air-breathing lungs from the swim bladder and enabled it to live for periods on dry land. This one became the ancestor of all tetrapods as it ventured more and more out the waters and adapted better to life on dry land until it was completely independent of the liquid neighborhood. That happened some 415 million years ago but some other lungfish did not evolve thus and six species of lungfish are still presently alive.

 
 
 
 Fish Classification
 

Fish are not a true clade but a paraphyletic group.  There are some 28 000 known species which comprises half of all species of the vertebrates.

 

Petromyzontidae

40 species of lampreys

Myxinidae

some 65 species of hagfish

Chondrichthyes
(cartilaginous fish)

360 sharks
 500 rays, skates and stingrays

Osteichthyes
(bony fish)

26 000 ray-finned fish
1000 lobe-finned fish

 
 
 
 Biologically Speaking
 

Fish are cold-blooded aquatic animals being abundant in all waters. They are covered with scales and have two sets of paired fins and several unpaired ones. They have gills for taking up oxygen dissolved in the water (although lungfish evolved lungs). Another characteristic is their swim bladder which gives it buoyancy in the water. Rays and sharks lack however swim bladders and have to continuously swim as not to sink to the bottom. Almost all fish lay eggs into the water where they are fertilized by the male's sperm and then left to themselves. Some fish however are known to watch over eggs and fish like the skates give births inside the female body.

 
 
 
 
 

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