On the diet of two endemic and rare species of Trichomycterus ( Ostariophysi : Trichomycteridae ) in the Jordão River , Iguaçu River basin , southern Brazil

The diet and the eect of body size on the feeding habits of Trichomycterus crassicaudatus and Trichomycterus stawiarski, collected in the Jordão River, an import tributary of the Iguaçu River basin, were investigated. Samples were collected in august 2003 during the Jordão River Energetic Complex Aquatic Fauna Rescue and Monitoring program. Stomach contents were evaluated through the frequency of occurrence, permutational multivariate analysis of variance (PERMANOVA), similarity percentage analysis (SIMPER) and non-metric multidimensional scaling analysis (MDS) methods. A total of 86 stomach contents of T. stawiarski and 36 of T. crassicaudatus were assessed. The species presented an insectivorous feeding habit, with dierences in the diet composition of the “smallest” and the “largest” individuals. Ephemeroptera nymphs, larvae and pupae of Diptera, organic detritus and plant fragments were the most important food items. Both species feeding habits were based mainly in benthic aquatic immature insects. [P]


Materials and methods
ϐ (25° 38´ S -52° 00' W), an important tributary of the lower Iguaçu River basin with many rapids and waterfalls.All specimens were caught in August 2003 during the impoundment of Santa Clara hydroelectric power plant (downstream) as part of the Jordão River Energetic Complex Aquatic Fauna Rescue and Monitoring program, under the authorization of IBAMA (process number 02017.000523/03-18).Specimens were collected using manual sieves (5 mm mesh) and dip nets (5 mm mesh).Captured ϐ ϐ ͳͲΨlin solution and brought to the laboratory where were measured (mm) and dissected.Digestive tracts were removed and their contents analyzed ϐched using a stereomicroscope.Voucher specimens ϐ de História Natural Capão da Imbuia (MHNCI 12297 and MHNCI 12299).
A similarity matrix with the presence/absence data of food items was generated using the Jaccard similarity coefficient.Two-way crossed permutational multivariate analysis of variance (PERMANOVA) examined the effects of species and size classes (factors) on the diet composition.Significant factors were further analyzed using a PERMANOVA pair-wise comparison.Similarity of percent contribution (SIMPER) analysis was employed to investigate prey categories most responsible for the separation among factors.

Introduction
The Iguaçu River basin is considered a global biodiversity hotspot (Abell, Thieme, Revenga, Bryer, Kottelat, Bogutskaya, et al. 2008), because of the diǡ ǡ ϐ ȋ Ƭ ǡ ʹͲͲͶǢ Ƭ ǡ ʹͲͲͺȌǤ of endemism of its ichthyofauna has been mentio-ȋǤǤ Ƭ ǡ ͳͻͻͶǢ Garavello, Pavanelli & Suzuki, 1997), and is probably due to its geographic isolation imposed by the Iguaçu falls.In the Iguaçu River, ten species of Trichomycterus The Neotropical catfish family Trichomycteridae comprises more than 200 species of small--sized fishes (de Pinna & Wosiacki, 2003) which in general inhabit fast-flowing rocky streams ȋ ǡ ͳͻͺ͵Ǣ ǡ ͳͻͻͺȌǤmarkable range of habitats and feeding habit, which includes trophic specializations such as haematophagy and lepidophagy, there is little information on trichomycterids natural feeding ecology.For the genus Trichomycterus, a probably non-monophyletic group of catfish with pronounced intraspecific variation in color pattern (de Pinna & Wosiacki, 2003), the few available data are greatly disproportional to the large number of species.Available evidences for the genus Trichomycterus suggest that the group is represented by generalized predators of aquatic inver- In the present work we describe the feeding habits of individuals of T. crassicaudatus and Trichomycterus 13 items.Ephemeroptera nymphs, larvae and pupae of Diptera, organic detritus and plant fragments were the most representative food items for T. crassicaudatus and T. stawiarski.Table 1 shows all food items recorded.Ǧ ϐ differences between species and between size classes (Table 2a).Pair-wise comparisons (Table 2b) deϐ T. crassicaudatus size class 2 (76 -110 mm) had different diet from size class 5 (176 -210 mm), whereas T. stawiarski size class 1 (25 -45 mm) had different diet ε Ǣ T. stawiarski size class 2 (46 -65 mm) had different diet from individuals > ͺ Ǥ ϐ analysis of diet composition according to size classes' categories (Figure 1).SIMPER analysis found that the highest contributors to dissimilarity (43.5%) between diets of T. crassicaudatus and T. stawiarski were frag-ȋͳǤͳΨȌ ϐ pupae of Diptera (16.3%).The highest contributors to dissimilarity (> 43%) of diet composition between the "smallest" and the "largest" individuals of T. stawiarski ϐ (16%), Ephemeroptera nymphs (16%), fragments of plants (15%) and Plecoptera larvae (13%), whereas multidimensional scaling analysis (NMDS) to visually assess the dispersion of samples.All analyses were performed using Primer v6 software (Clarke & Gorley, 2006).Because of the lack of information on Trichomycterus ȋ ϐ ǡ growth, and reproduction), size classes (total length) and corresponding length intervals were obtained from Sturges' formulation (Vieira, 1980).
Aquatic insect larvae and pupae are common ϐ the highest contributors to dissimilarity (58%) of diet composition between the "smallest" and the "largest" individuals of T. crassicaudatus ϐ ȋʹͲΨȌ ϐ ȋͳͲΨȌǤ

Discussion
Considering the fact that this study represents a short-term survey on the feeding ecology of these ǡ ϐ that T. crassicaudatus and T. stawiarski feed mostly on autochthonous food, and its feeding habit can be characterized as insectivorous, due to the high importance of benthic aquatic immature insects in the stomach contents.The exploitation of aquatic immature insects was already recorded for several Trichomycterus ȋǡ Ƭ ǡ ʹͲͲʹǢ ǡ Ǥǡ ʹͲͲͷǢ ǡ Ǥǡ ʹͲͲǢ ǡ Ǥǡ allow the coexistence of both species in the studied area.

Table 1 -
Frequency of occurrence of items consumed by T. crassicaudatus and T. stawiarski LQ WKH -RUGmR 5LYHU ,JXDoX River basin, according to each size class considered