Algumas considerações sobre a incorporação da régua de cálculo circular na formação inicial de professores de matemática

The fish diversity and distribution investigated in the Mahabad-Chai river of the Lake Urmia basin, over the years 1998-1999. Gillnet, beach seine, cast net and electro-shocker used to catch fishes seasonally in 16 stations within 5 regions of the river. We identified 18 species of fish belonging to four families of the bony fishes. The family Cyprinidae with 15 species was the most abundant comprising 98.2 % of the catch, present in all the stations. Families Balitoridae, Siluridae and Poeciliidae were represented only by one species and were the least aboundant, with the Balitoridae being present in all the stations. Of the identified fish species, Capoeta capoeta was the most aboundant, Chalcalburnus atropatenae was the second most abundant and Acanthalburnus urmianus was the third most abundant comprising 41.61%, 34.16% and 7.91% of the catch respectively. The least aboundant species were Abramis brama and Gambusia holbrooki with other 13 species coming in between in all regions while other species were present only in some of the regions. Of the identified fish species 11 were native and seven were alien species introduced by Caspian Sea Bony Fishes Research Center. Presence of Pseudorasbora parva and Rhodeus sericeus amarus reported for the first time in the region. Also, among the identified fish, Leuciscus ulanus, Ch. atropatenae and A. urmianus are endemic to Iran, living in the Lake Urmia basin. Having a small stock and narrow distribution in the wild, the Leuciscus ulanus is of especial importance to the fishery managers.