Crenicichla ypo ( Teleostei : Cichlidae ) , a new species from the middle Paraná basin in Misiones , Argentina

A new species of Crenicichla, C. ypo, is described from the Arroyo Urugua-í, a left-hand tributary of the middle Paraná River, Misiones province, Argentina. The new species is recognized by 6 to 8 irregular blotches along the upper lateral line, absence of scattered dark spots on flanks, low number (47-55) of E1 scales, and a slightly prognathous lower jaw. Females have a distinctive coloration of the dorsal fin, with a wide black longitudinal stripe on the distal portion with an equally wide red stripe below it.


Introduction
The genus Crenicichla Heckel includes at present about 80 valid species and is the most speciose genus within the family Cichlidae (Kullander, 2003(Kullander, , 2009;;Casciotta et al., 2006).Most Crenicichla species are found in tropical and subtropical cis-Andean drainages (Kullander & Lucena, 2006), although few of them, such as Crenicichla lepidota Heckel, C. vittata Heckel, and C. scottii (Eigenmann) also inhabit temperate waters in the La Plata River basin in Buenos Aires province and northern Patagonia in Argentina (Casciotta, 1987).
The aim of this paper is to describe a new species of Crenicichla restricted to the arroyo Urugua-í, middle Paraná basin, Argentina.

Material and Methods
We use the following nomenclature in naming of drainages.River is used to designate large international drainages (e.g.Uruguay River), while arroyo ("stream" in Spanish) is used for smaller, exclusively Argentinean drainages (e.g.arroyo Urugua-í).This nomenclature bypasses the confusion between similar names of distinct drainages (e.g.Portuguese spelling of Uruguai for the Uruguay River vs. arroyo Urugua-í).
Division of the Paraná River into sections differs substantially between various authors (e.g.Carolsfield et al., 2004;Iriondo et al., 2007).In this text we refer to the middle Paraná River as to the section from its confluence with the Paraguay River upstream to the Saltos del Guairá.Today this natural upper barrier of the middle Paraná is replaced by the Itaipu hydroelectrical dam.
Specimens were cleared and counterstained (c&s) following the method of Taylor & van Dyke (1985).Measurements and counts were taken as described by Kullander (1986).Pharyngeal teeth description and counts of frashed zone concavities follow Casciotta & Arratia (1993).Holotype values are indicated by an asterisk.Body length is expressed as standard length (SL).E1 scale counts refer to the scales in the row immediately above that containing the lower lateral line (Lucena & Kullander, 1992).

Crenicichla ypo, new species
Figs Crenicichla ypo is easily distinguished from C. semifasciata in having the ascending arm of the premaxilla longer than the dentigerous one, the blotches on flanks including the upper lateral line and extending 3 to 4 scale rows above and below it, and having about half of the caudal fin scaled vs. ascending arm of the premaxilla shorter than the dentigerous one, the flanks bearing quadrangular blotches placed below the upper lateral line or lateral band, and caudal fin scaled in most of its surface.
The new species differs from C. yaha in having the lower jaw slightly prognathous and head depth 14.5-17.6% of SL vs. isognathous or upper jaw slightly prognathous and head depth 17.9-20.8% of SL.Females of C. ypo are distinguished from females of C. yaha by having dorsal fin with a wide black stripe above a red stripe vs. dorsal fin with a wide black irregular stripe.
Females with head, upper half of flank, and caudal fin deep grey.Yellow and orange pigment on flank at level and behind pectoral fin.Dorsal and anal fins of females lacking small dark dots, few of them present on caudal fin.Females with a distinctive coloration of the dorsal fin, with a wide black longitudinal stripe on the distal region of dorsal fin and an equally wide red stripe below it (Fig. 3).

Colour in alcohol.
Similar to that of live specimens with a tendency to become pale.Conserved specimens lack the carotenoid pigments, such as orange dots on flank of males, yellow or orange area on flank of females, and wide red stripe in dorsal fin of females.
Etymology.The specific epithet ypo, is a Mbya Guaraní word y po that means water dweller.
Habitat.Crenichla ypo was collected both before and after the Urugua-í hydroelectrical dam was built in 1989 (see material);  the species presently occurs also directly in the reservoir (pers.obs.).The arroyo Urugua-í is a moderately fast flowing river with tributaries of an average depth of 1 m outside of the dam influence.Macrophytes such as Echinodorus uruguayensis Arechavaleta and Potamogeton pseudopolygonus Hagström are present.The bottom consists of mud, sand with gravel and/or bedrock.After dam construction some parts of impoundment lake are up to 6 m deep and some previous localities like Isla Palacio are below the water surface.Crenicichla ypo is sympatric with C. yaha and one additional undetermined Crenicichla species (pers.obs.).

Discussion
The new species, Crenicichla ypo, is in its morphology more similar to other species of Crenicichla from the Paraná River basin, than to species from the Uruguay River (C. celidochilus, C. empheres, C. gaucho, C. hadrostigma, C. igara, C. jurubi, C. minuano, C. missioneira, C. prenda, C. scottii, C. tendybaguassu).These Uruguayan species are traditionally included in the C. missioneira and C. scottii species groups (Lucena & Kullander, 1992; extended by Kullander et al., 2010), and differ from the herein discussed taxa in a combination of color-pattern and meristic characters (Lucena & Kullander, 1992).The relationships of the new species with the Paraná River Crenicichla is also confirmed with analysis of molecular data (mitochondrial genes ND2 and cytochrome b) which included all at-present-known species from the Misiones province (Piálek et al., in prep.).Therefore a detailed morphological comparative analysis was directed towards the Crenicichla species from the Paraná River basin.
Crenicichla ypo inhabits the arroyo Urugua-í basin, a left-hand tributary of the middle Paraná River that drains roughly 3,000 km 2 of the northern part of Misiones.This river as well as most of the other tributaries of Paraná, Uruguay, and Iguazú basin in the central and northern portions of the province are divided from their main streams by a significant number of waterfalls, highest of which are invariably found closest to their mouths (pers.obs.).The isolation by high-level riverbed drops lasted apparently long enough so that many endemic taxa have evolved within these streams.
High level of endemism of the Misioneran ichthyological ecoregion (López et al., 2002;López et al., 2005)  Crenicichla ypo is yet another faunal element of the unique hydrography of Misiones, an hyperdiverse area lying at the intersection of three major drainages (Paraná, Uruguay, and Iguazú).

. 1-4
Crenicichla ypo has a distinct caudal spot, inconspicuous or absent in C. jaguarensis.Crenicichla ypo lacks the lateral stripe displayed in C. jaguarensis, C. mandelburgeri, and C. vittata.Crenicichla ypo differs from C. jupiaensis in having lower jaw slightly prognathous, having a well-developed suborbital stripe composed of spots, and the cheek bearing up to 8 scale rows vs. isognathous jaws, a suborbital stripe reduced to a few spots posterior to the orbit, and a naked cheek.Crenicichla ypo does not bear well developed vertical bars which are reduced to irregular blotches.This distinguishes this species from those with complete vertical bars: C. jupiaensis, juveniles of C. mandelburgeri, and C. niederleinii.Crenicichla ypo differs from C. niederleinii and C. vittata in having a low number of E1 scales (47-55 vs. 56-65 and 78-85, respectively).Parallel and thin longitudinal stripes are absent in C. ypo vs. present in C. scottii.

Table 1 .
Proportional measurements in percents of standard length of holotype and 16 paratypes of Crenicichla ypo.SD = Standard deviation.