Total mercury contents in shark species commercialized in São Paulo-SP, Brazil. Total mercury contents in shark species - anjo, cação-azul, cambeva, caçoa, ...
www.scielo.br/scielo.php?pid=S0101-20611999000300024&script
=sci_arttext

This work, known as Projeto Cação (Cação is a Portuguese name for shark, ... One of the most common shark species caught by artisanal fisheries during the ...
www.flmnh.ufl.edu/fish/Organizations/SSG/sharknews/sn14/sha...

http://zipcodezoo.com/Animals/C/Carcharhinus_leucas/

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Note added at 34 mins (2008-08-28 19:33:07 GMT)
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More generally, a type o Requiem Shark:

The requiem sharks refer to all members of the Carcharhinidae family that includes a family of migratory, live-bearing sharks of warm seas, sometimes also found in brackish or fresh water, such as the tiger shark, blue shark, bull shark, and milk shark. The name comes from the French word for shark, requin.
http://en.wikipedia.org/wiki/Requiem_shark

A common type in Brazil:
The Brazilian sharpnose shark, Rhizoprionodon lalandii, is a requiem shark of the family Carcharhinidae, found in the tropical waters of the western Atlantic Ocean between latitudes 13° N and 33° S, at depths of between 3 and 70 m. Its length is up to about 77 cm.
The Brazilian sharpnose shark inhabits shallow coastal waters, on sandy and muddy bottoms, and is not normally found in lagoons and estuaries. It feeds on small bony fishes, including sardines and anchovies, also shrimp and squid. It is viviparous, having 1 to 4 young in a litter with size at birth 33 to 34 cm. Its flesh is highly appreciated and is marketed dried salted.
http://en.wikipedia.org/wiki/Brazilian_sharpnose_shark

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Note added at 38 mins (2008-08-28 19:37:11 GMT)
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In fact, many different types are called "cação" in Brazil; I'd probabbly go with the "sharpnose"...

There are many names for cação, please see http://www.flmnh.ufl.edu/fish/gallery/descript/smoothdogfish...
http://www.flmnh.ufl.edu/fish/Gallery/Descript/SpinyDogfish/...
http://www.answers.com/topic/bowfin
http://www.efsa.co.uk/record/spurdog.htm

according to Alan Davidson fish book and the site below:

Species: Mustelus canis (Mitchill, 1815)
synonym for Mustelus mustelus (Atlantic Smooth Dogfish)
Smoothhound, Smooth Hound, Smooth Dogfish, Smooth Dog, Nurse Shark, Grayfish, Dusky Smooth-hound, Dusky Smoothhound, Dusky Smooth Hound, Dogfish, Atlantic Smooth Dogfish

Sebastião, João-dias, Canejo, Cação-torrador, Cação-sebastião, Cação-fiúzo, Cação-fiúso, Cação-de-bico-doce, Cação-bico-doce, Cação-angolista, Cação Cachorro, Cação, Bodinho, Bico Doce, Tolo, Tubarão Angolista

http://us.mirror.gbif.org/species/13546466

see page 3:
http://faolex.fao.org/docs/pdf/por66243.pdf

though here it says it can also be applied to Mustelus asterias, known as the Stellate smooth hound below and in my above-mentioned fish book
http://us.mirror.gbif.org/species/13541820/

From SBS Visual Dictionary, page 158.

The definition of "cação" is quite varied, depending on which dictionary you use:

TAYLOR, J.L. - Portuguese - English Dictionary (page 120): A shark.

DICIONÁRIO MICHAELIS TRILÍNGÜE (page 41): Shark.

AURÉLIO (page 244): "Designação comum a todos os peixes elasmobrânquios com fendas branquiais laterais e corpo piciforme, de tamanho médio ou pequeno e cuja carne, embora de má qualidade, é consumida pelo povo."

(I personally can not imagine why Aurélio considers it to be "de má qualidade" - it is one of my favourite fish, especially when my darling wife cooks it for me, either fried or in sauce, with that extra touch of love that not even the best restaurant can provide).