Fishes from the Itapecuru River basin , State of Maranhão , northeast Brazil

The Itapecuru is a relatively large river in the northeastern Brazilian state of Maranhão. During several expeditions to this basin, we collected 69 fish species belonging to 65 genera, 29 families and 10 orders. Characiformes and Siluriformes were the orders with the largest number of species and Characidae, Loricariidae, Cichlidae, Auchenipteridae and Pimelodidae were the richest families. About 30% of the fish fauna of the Itapecuru basin is endemic or restricted to northeastern Brazil. Just over a fifth (22%) of the species is also known to occur in the Amazon basin and only a few are more widely distributed in South American.


Introduction
The Itapecuru River basin is a relatively large coastal drainage system in northeastern Brazil.It is situated in the mid-east of the state of Maranhão, between latitudes 2° 51 S and 6° 56 S, and longitudes 43° 02 W and 43° 58 W. It encompasses a total area of 52,972.1 km 2 , corresponding to approximately 16% of the state.The Itapecuru River is limited to the southeast mainly by the Parnaíba basin, the Itapecuru mountains and the Azeitão plateau, to the southwest by the Mearim basin and to the northeast by the Munim basin.The Itapecuru River has three physically distinct areas.The upper Itapecuru, from its source to the east of the town of Colinas, is dominated by plains, plateaus and cuestas and has a strongly undulating relief rising to 350 m a.s.l. in the Itapecuru, Alpercatas, Croeira, and Boa Vista ranges.The middle Itapecuru from Colinas to Caxias is in an area of low plateaus with gently to strongly undulating relief and many plateaus, with a difference of
Grande do Norte, the Jaguaribe and São Francisco rivers in Pernambuco, and Teresina in Piauí.Fowler's (1941) paper included his drawings and the vernacular names recorded by R. von Ihering.As noted by Rosa et al. (2003), Fowler's species names are often synonyms -e.g., Hassar woodi and Hassar iheringi, which are both synonymies of Hassar affinis Steindachner -while some descriptions are based exclusively on small juveniles (e.g., Ancistrus salgadae, with approximately 2 cm SL).A recent survey of the Mearim River in Maranhão recorded 60 species (Soares, 2005).
The aim of the present paper is to present and comment on an inventory of fish species from the Itapecuru basin in the Brazilian state of Maranhão.
The most comprehensive contribution to the scientific knowledge of the fish species of the Brazilian Northeast is the study of Fowler (1941), who analyzed material collected at several sites by Rodolpho von Ihering, one of the pioneers of pisciculture in Brazil.Von Ihering's collection contained 823 specimens representing approximately 104 species, 36 of which were described by Fowler (1941).Many specimens were from Ceará, Lago Papary in Rio

Results
A total of 1563 specimens were collected, representing 69 species, 65 genera, 29 families and 10 orders.Characiformes, with 24 species and Siluriformes with 25, were the richest species orders.Characidae, with 13 species, Loricariidae with seven, Cichlidae, Pimelodidae, and Auchenipteridae, all with five, were the richest species families (Table1).
The maximum possible diversity for the 69 species collected from the Itapecuru River would be 6.108 bit per individual, although our results returned a diversity of 5.025 bits per individual with an equitability of 0.822, which indicates a high diversity, but with a certain degree of homogeneity among the species collected in the basin.Both diversity (H') and equitability (E) were highest on the mid Itapecuru in November, 2007 (H' = 4.334, E = 0.885), which is the dry season.The lowest values were recorded in the upper part of the river in the wet season, in March 2008 (H' = 3.226, E = 0.678).The largest number of specimens (644) and species (55) was collected in the lower Itapecuru, followed by the mid section, with 540 specimens and 36 species, and the upper river, with 411 specimens belonging to 29 species.44° 14' 60'' W), one at Itapecuru-Mirim (03° 31' 39'' S and 44° 24' 19'' W) and the third near Aldeias Altas (04° 44' 09'' S and 43° 27' 54'' W).On the middle section of the river, two sites were sampled near Caxias (05° 02' 44 '' S and 43° 24' 45'' W and 05° 07' 33'' S and 43° 33' 60'' W), and one at 05° 26' 37'' S and 43° 52' 03'' W near the town of Governador Eugênio Barros.The upper stretch was sampled at 06° 22' 26'' S and 44° 22' 60'' W in the proximity of Mirador and near the town of Colinas town (06° 01' 60'' S and 44° 18' 60'' W).Additional sampling was conducted in tributaries, targeting mainly small-sized fishes.
Fish were captured using gillnets (15-35 mm meshes), cast nets (12-35 mm meshes), and hand nets (5 mm mesh).Specimens were transported on ice to the laboratory, where they were preserved in 10% formalin solution and finally conserved in 70% ethanol.The specimens were deposited under the numbers 104552-104603 in the fish collection of the Museu de Zoologia da Universidade de São Paulo, in São Paulo, and at the Universidade Estadual do Maranhão, CESC in Caxias.
The diversity of species was estimated using the Shannon-Wiener diversity index (H'), and the uniformity of the distribution of the species was assessed using the equitability index (Krebs, 1998a, b).

Discussion
The fish fauna in the Itapecuru River comprises 69 species, of which 20 or approximately 30%, are endemic to northeastern Brazil, known to occur from the Pindaré-Mearim Rivers in Maranhão to the Jaguaribe River in Ceará (see Table 1).One species, Oreochromis niloticus, is an introduced African cichlid.A few species are known to be widespread, occurring in several South American river basins: Astyanax bimaculatus, Hoplias malabaricus, Apteronotus albifrons, Sternopygus macrurus, Arius rugispinis, Hexanematichthys couma, Ageneiosus inermis, Parauchenipterus galeatus, Pseudauchenipterus nodosus, Callichthys callichthys, Hemisorubim platyrhynchus, Pimelodus blochii, Pimelodus ornatus, Sorubim lima, Centropomus parallelus, Plagioscion squamosissimus, and Synbranchus marmoratus.Some of these species (e.g., Astyanax bimaculatus or Synbranchus marmoratus) may represent species complexes, rather than distinct taxa, and are in need of taxonomic revision.A number of other species are known to occur in the Amazon basin (in some cases ranging as far as the Orinoco and coastal rivers in Surinam and the Guyanas), a distribution pattern predicted by Agassiz and Agassiz (1975).This is the case of Poptella compressa, Pygocentrus nattereri, Serrasalmus rhombeus, Cynodon gibbus, Hemiodus argenteus, Aspredo aspredo, Ageneiosus ucayalensis, Hemiodontichthys acipenserinus, Loricariichthys acutus, Pterygoplichthys punctatus, Pseudoplatystoma punctifer, Strongylura marina, Anchovia surinamensis, Pterengraulis atherinoides, Anableps anableps, and Pachypops fourcroi.The present register of the latter three species are new records for northeastern Brazil (Casatti, 2002;Ghedotti, 2003;Kullander and Ferraris, 2003).Fifteen taxa could not be identified to the species level due to the poor taxonomic resolution.A few of these are new records for northeastern Brazil and may even represent undescribed species.Pseudopimelodus sp. is the first Pseudopimelodidae known to occur in the region (Shibatta, 2003), while the specimens of Serrapinnus sp., Aphyocharax sp., and Hypoptopoma sp.represent new records for these genera.
Several species (Apionichthys dumerili, Anableps anableps, Centropomus parallelus, Strongyrula marina, Anchovia surinamensis, Pterengraulis atherinoides, and Pseudauchenipterus nodosus) were only collected on the lower Itapecuru, indicating a preference for estuarine environments.This is a first systematic inventory of the ichthyofauna of the Itapecuru River.Most of the coastal rivers of the Brazilian Northeast are still poorly known.Due to the predominance of Amazonian species in the Itapecuru basin, it might be predicted that the region's fish fauna becomes more species-rich towards the Amazon delta, i.e., present an east to west gradient of species richness.

Table 1 .
List of species of fishes collected in the Itapecuru River basin.