Mottled Pattern Research Articles

Jaw malformation in striped trumpeter Latris lineata larvae linked to walling behaviour and tank colour

Jaw malformations are a recurrent obstacle in the hatchery production of high quality juveniles of many marine finfish species. Whilst nutrition and temperature are often cited as the most likely causes, this study investigated manipulation of the physical culture environment and larval behaviour to reduce jaw malformations. The onset of jaw malformation after metamorphosis in striped trumpeter, Latris lineata, follows changes in larval behaviour from an even distribution throughout the water column to close association with the tank walls, often with vigorous swimming into the walls known as ‘walling’ behaviour. Larvae were reared through metamorphosis, 16 to 44 days post-hatching (dph), in twenty four 300-l hemispherical tanks with six different wall colours, black, blue, green, marble (a black, grey and white mottled pattern), red and white. Walling behaviour and jaw malformation were assessed. The highest proportion of severely malformed jaws at 44 dph occurred in red tanks, followed by green, white, blue, black and marble. More fish walled in coloured tanks (25–44%) than in black and marble tanks (9.6 and 3.4%, respectively). The proportion of fish with jaw malformations at 44 dph was positively correlated with fish walling behaviour. Both black and marble tanks had more than 50% of fish with normal jaws at 44 dph, and close to 80% with no or very minor malformations. Growth and survival to 44 dph were highest in the black (15.7 ± 1.3 mm fork length, 7.9 ± 0.9 mg dry weight, 71 ± 6%) and marble (15.6 ± 1.2 mm, 7.6 ± 0.5 mg, 58 ± 17%) tanks, compared with the lowest values in red tanks (14.2 ± 1.1 mm, 6.4 ± 0.4 mg, 11 ± 6%). Potential mechanisms for the influence of walling behaviour on jaw malformation are mechanical damage and poor nutrition, via reduced feed intake and increased energy expenditure. The study highlights the often overlooked importance of hard-surface interactions in the growth and survival of some cultured marine fish and demonstrates a cheap and effective technique for assessing tank background colour as a means of reducing malformations in cultured fish.

Cephalopod dynamic camouflage: bridging the continuum between background matching and disruptive coloration

Individual cuttlefish, octopus and squid have the versatile capability to use body patterns for background matching and disruptive coloration. We define--qualitatively and quantitatively--the chief characteristics of the three major body pattern types used for camouflage by cephalopods: uniform and mottle patterns for background matching, and disruptive patterns that primarily enhance disruptiveness but aid background matching as well. There is great variation within each of the three body pattern types, but by defining their chief characteristics we lay the groundwork to test camouflage concepts by correlating background statistics with those of the body pattern. We describe at least three ways in which background matching can be achieved in cephalopods. Disruptive patterns in cuttlefish possess all four of the basic components of 'disruptiveness', supporting Cott's hypotheses, and we provide field examples of disruptive coloration in which the body pattern contrast exceeds that of the immediate surrounds. Based upon laboratory testing as well as thousands of images of camouflaged cephalopods in the field (a sample is provided on a web archive), we note that size, contrast and edges of background objects are key visual cues that guide cephalopod camouflage patterning. Mottle and disruptive patterns are frequently mixed, suggesting that background matching and disruptive mechanisms are often used in the same pattern.

Mesophyll freezing and effects of freeze dehydration visualized by simultaneous measurement of IDTA and differential imaging chlorophyll fluorescence

Infrared differential thermal analysis (IDTA) and differential imaging chlorophyll fluorescence (DIF) were employed simultaneously to study the two-dimensional pattern of ice propagation in leaves and mesophyll freeze dehydration as detected by a significant increase of basic chlorophyll fluorescence (F(0)). IDTA and DIF technique gave different insights into the freezing process of leaves that was highly species-specific. IDTA clearly visualized the freezing process consisting of an initial fast spread of ice throughout the vascular system followed by mesophyll freezing. While mesophyll freezing was homogeneously in Poa alpina, Rhododendron ferrugineum and Senecio incanus as determined by IDTA, DIF showed a distinct pattern only in S. incanus, with the leaf tips being affected earlier. In Cinnamomum camphora, a mottled freezing pattern of small mesophyll compartments was observed by both methods. In IDTA images, a random pattern predominated, while in DIF images, compartments closer to lower order veins were affected earlier. The increase of F(0) following mesophyll freezing started after a species-specific time lag of up to 26 min. The start of the F(0) increase and its slope were significantly enhanced at lower temperatures, which suggest a higher strain on mesophyll protoplasts when freezing occurs at lower temperatures.

Silcrete and alunite genesis in alluvial palaeosols (late Cretaceous to early Palaeocene, Duero basin, Spain)

An extensive formation of silcretes occurs in the upper half of a late Cretaceous-to-Palaeocene Siderolithic Unit consisting of conglomerates, sandstones and sandy mudstones along the western margin of the Tertiary Duero basin (Spain). The unit is arranged in fining-upward sequences that were deposited in a fluvial braided system with floodplains subject to periodic events of exposure and drying out. The original mineralogy of the Siderolithic Unit is seen in the less altered levels, where it consists of quartz, illite–white mica, kaolinite and, at the top of the unit, K-feldspar, all coming from the palaeoalteration mantles developed on the metasediments of the Variscan Basement. The unit is characterized by a marked development of alluvial palaeosols at the uppermost part of each sequence. At field scale, the pedogenic structures and features are evident from the mottled pattern, burrowing, cracking planes and root traces; at micromorphological scale, an intense development of birefringent fabrics is seen in clays. Micas and feldspars show evidence of alteration due to hydrolysis, while the more resistant quartz grains show common corrosion gulfs and have become the only surviving elements in the most silicified beds. The neoformed minerals are related to the pedodiagenetic processes developed on the floodplains. The main neoformed phase is opal (probably amorphous silica in origin that aged to opal-CT), which ranges from local cementations in pores to an almost complete replacement of the rock, specially the finest components (matrix). Kaolinite is the most abundant neoformed clay. Locally, veinlets of alunite accompany the opalized levels. All the processes described occurred in a seasonal tropical climate. During dry episodes, strong evaporation resulted in an increase in pH, favouring the hydrolysis of the original silicates. The paucity of Mg 2+ and Ca 2+ in the groundwater would have favoured the increase in pH. In ensuing wetter periods, pHs fell rapidly, resulting in the precipitation of kaolinite and also favouring the precipitation of opal and alunite. The alunite could have formed either by oxidation of the iron sulphides developed in reducing areas of the flood plains or by evaporitic concentration of sulphate in Ca 2+- and Mg 2+-free groundwaters.

Study of clinical and morphological features, immunophenotype and Epstein-Bar virus infection in situ of infectious mononucleosis

To study the clinical and morphological features, immunophenotype and in situ detection of Epstein-Barr virus (EBV) infection in infectious mononucleosis (IM) to enhance the knowledge and diagnosis of the disease. Using routine haematoxylin and eosin staining, immunohistochemistry and EBER in situ hyhridization together with clinical data analysis, 15 cases of IM were evaluated for their clinical features, morphology, immunophenotype and EBV infection status. IM was common in children and young adults with a median age of 18 years. It was an acute disease with lymphadenopathy and frequently fever. Most of the patients had a rapid recovery. Every case showed a markedly T zone expansion with a mottling pattern, composing of small to large lymphocytes, plasma cells and histiocytes. The cells also showed a B-cell differentiation profile ranging from activated lymphoblastoid cells, immunoblasts, plasmablasts, plasma-like cells and plasma cells. Many small lymphocytes in the expanded T zone expressed CD3. Some of the activated lymphoblastoid cells and immonoblasts were CD20 and CD30 positive with variable intensity signals. EBER positive (nuclear staining) cells were seen in every case. The number of EBER positive cells ranged from 10 to more than 100 per high power field. These cells included small to large lymphocytes locating mostly in the expanded T zone and a few were in the follicular germinal centers. IM is an EBV related acute sell-recovering lymphoproliferative disease, having distinct clinical, morphological and immunophenotypic characteristics as well as EBV infection. Taking these features into consideration will facilitate the correct diagnosis of IM.

Inheritance of Resistance to Alfalfa Mosaic Virus in Soybean PI 153282

Alfalfa mosaic virus (AMV) infects soybean [Glycine max (L.) Merr.] causing mosaic or mottle patterns on leaves. Resistance to AMV has been identified in soybean, but no AMV resistance genes have been mapped or assigned gene symbols. The objective of this research was to study the genetic basis of resistance to AMV from plant introduction (PI) 153282. This resistance was studied in a population of F4:7 lines developed from a cross between this PI and the susceptible cultivar Syngenta (NK) S19‐90. Results from the F4:7 population were confirmed in F2 and F2:3 populations developed by crossing the same parents. A major AMV resistance gene was mapped as a quantitative trait locus (QTL) near the simple sequence repeat marker Sat_226 in the F4:7 population. For this QTL, the resistance allele was from PI 153282, the LOD score was 45.5, and the QTL explained 79% of the genotypic variation for resistance in the population. The identification of an AMV resistance gene near Sat_228 was confirmed in the F2 and F2:3 populations and the resistance gene showed complete dominance in the F2 population. This AMV resistance gene identified from PI 153282 is named Rav1 and it should be useful in breeding for resistance to this virus.

Cuttlefish camouflage: The effects of substrate contrast and size in evoking uniform, mottle or disruptive body patterns

Cuttlefish are cephalopod molluscs that achieve dynamic camouflage by rapidly extracting visual information from the background and neurally implementing an appropriate skin (or body) pattern. We investigated how cuttlefish body patterning responses are influenced by contrast and spatial scale by varying the contrast and the size of checkerboard backgrounds. We found that: (1) at high contrast levels, cuttlefish body patterning depended on check size; (2) for low contrast levels, body patterning was independent of “check” size; and (3) on the same check size, cuttlefish fine-tuned the contrast and fine structure of their body patterns, in response to small contrast changes in the background. Furthermore, we developed an objective, automated method of assessing cuttlefish camouflage patterns that quantitatively differentiated the three body patterns of uniform/stipple, mottle and disruptive. This study draws attention to the key roles played by background contrast and particle size in determining an effective camouflage pattern.

Distribution of pigments in the shell of the gastropod Littorina obtusata (Linnaeus, 1758)

The patterns of pigment distribution in the shell of the gastropod Littorina obtusata were studied. It was determined that the background coloration of the periwinkle shell resulted from the coloration interaction of the external and internal parts of the ostracum. The coloration of the latter can be monochromatic or twolayer. The external and/or internal zones of the ostracum can be colored purple, white, orange, yellow and greenish. Only 11 of 25 possible color combinations were recorded. Four additional versions of shell background coloration resulted from partial depigmentation of external or internal parts of ostracum. The mottling pattern corresponded to white or depigmented lenticular sites in the external part of the ostracum. The bands on the shell may be subdivided into two groups according to their means of formation. The bands that appeared due to redistribution of pigments forming background coloration belonged to the first group, the bands arising as a layer of additional (white, yellow, orange) pigment belonged to the second group. Various band versions could occur simultaneously in the same individual.

Different Fundus Autofluorescence Patterns of Retinoschisis and Macular Hole Retinal Detachment in High Myopia

To report difference in fundus autofluorescence (FAF) results between macular hole retinal detachment (MHRD) and myopic foveoschisis (MF) in highly myopic eyes. Observational case reports. Total of 20 highly myopic eyes were included in this study (MHRD, six eyes; MF with macular hole [MH], three eyes; MF without MH, 11 eyes). The authors observed both standard and near-infrared FAF images using the Heidelberg Retina Angiograph 2 (HRA2; Heidelberg Engineering, Heidelberg, Germany). MHRD typically showed extensive hypo-FAF and foveal hyper-FAF. Hypo-FAF and hyper-FAF seemed to account for RD area and MH, respectively. Some cases of MF had almost normal results, except for a subtle mottled pattern of hyper-FAF. MHRD and MF showed different patterns of FAF, and this fact could be helpful in diagnosing MHRD from MF. Hyperviscous subretinal fluid might have blocked FAF signal in MHRD, but not in MF.

Perception of visual texture and the expression of disruptive camouflage by the cuttlefish,Sepia officinalis

Juvenile cuttlefish (Sepia officinalis) camouflage themselves by changing their body pattern according to the background. This behaviour can be used to investigate visual perception in these molluscs and may also give insight into camouflage design. Edge detection is an important aspect of vision, and here we compare the body patterns that cuttlefish produced in response to checkerboard backgrounds with responses to backgrounds that have the same spatial frequency power spectrum as the checkerboards, but randomized spatial phase. For humans, phase randomization removes visual edges. To describe the cuttlefish body patterns, we scored the level of expression of 20 separate pattern 'components', and then derived principal components (PCs) from these scores. After varimax rotation, the first component (PC1) corresponded closely to the so-called disruptive body pattern, and the second (PC2) to the mottle pattern. PC1 was predominantly expressed on checkerboards, and PC2 on phase-randomized backgrounds. Thus, cuttlefish probably have edge detectors that control the expression of disruptive pattern. Although the experiments used unnatural backgrounds, it seems probable that cuttlefish display disruptive camouflage when there are edges in the visual background caused by discrete objects such as pebbles. We discuss the implications of these findings for our understanding of disruptive camouflage.

Morphological and Acoustic Comparisons of M. okinavensis (Anura: Microhylidae)

Morphological and acoustic comparisons were made for three morphologically poorly defined Microhyla species, M. ornata, M. fissipes, and M. okinavensis on the basis of samples from south India, Taiwan, and three islands (Iriomotejima, Okinawajima, and Amamioshima) of the Ryukyu Archipelago, Japan. These three species differed from each other in various external characters, and could be separated by multivariate discriminant analyses. Mean SVL of males was significantly smaller in M. fissipes than in M. ornata and M. okinavensis. The length of the hindlimb relative to SVL increased from west (India) to east (Amamioshima). Microhyla ornata showed a remarkable diurnal-nocturnal color change and had more extensive mottling on the throat and venter than the other two species. The Iriomotejima population of M. okinavensis had a unique ventral mottling pattern that differed from the patterns in the other two conspecific populations examined, as well as from those in M. ornata and M. fissipes. Excepting the Iriomotejima population, M. okinavensis had more extensive toe webbing than M. ornata and M. fissipes. Temporal acoustic features, especially pulse repetition rate, clearly discriminated the three species. The taxonomic status of the Iriomotejima population deserves future investigation.

Picturing System

Technology has never been the exclusive domain of science, any more than expressivity has been the vaunted preserve of art. Clearly, ample room for integration and crossover exists-for example, with hybridization of traditional artists' tools through software programs and standardization of artists' methods. There is much confusion these days about the relation of art to technology. Picturing is a matter of seeing into streaked and mottled patterns, of recognizing in physical terms their links to space and time. The computer provides a higher quality, higher density image than a hand-generated dot matrix. Patterns interpenetrate and provide different answers, depending on which theorems drive the questions asked. Picturing system has turned out to be a work of imagination; there are no formulas, mathematical or otherwise. These spirited tropes, however, are essential to pictures; indeed, to how images are formed and re-formed through the mathematical processes of the brain. The value of picturing system has proven to be its applicability and remarkable adaptability as a working method in different media.

Fundus Autofluorescence Before and After Photodynamic Therapy for Choroidal Neovascularization Secondary to Age-Related Macular Degeneration

To describe fundus autofluorescence patterns in choroidal neovascularization secondary to age-related macular degeneration before and after photodynamic therapy (PDT). Sixty-eight consecutive eyes were indicated for PDT after standard fluorescein angiography, which showed completely classic choroidal neovascularization (CNV) (n=52), occult with no classic CNV (n=7), and predominantly classic CNV (n=9). Standardized PDT was performed and patients were examined 2 to 3 months later. Angiography and autofluorescence measurements were performed again and compared with preoperative values. At baseline, autofluorescence was mainly decreased in areas of completely classic CNV (79%), but showed a regular or mottled pattern in occult CNV. A slightly increased (50%) or normal (50%) autofluorescence was seen at the rim of the classic lesions within the junctional zone. Membrane demarcation was improved (90%) in classic membranes 2 to 3 months after PDT. After PDT for occult membranes, a transformation into classic membranes with residual leakage and need for further PDT was observed (6 of 7 eyes), showing the described autofluorescence patterns. For the mixed type of CNV, both described patterns of autofluorescence distribution were found. Especially classic CNVs reveal distinct characteristics of significantly decreased autofluorescence, presumably due to their localization above the retinal pigment epithelium level, leading to blockage of autofluorescence. Autofluorescence patterns after PDT included enhanced demarcation of the membrane, suggesting reactive retinal pigment epithelial changes. Autofluorescence might be an interesting tool to distinguish noninvasively between classic and occult CNV in age-related macular degeneration and to monitor changes after PDT.

Ituglanis macunaima, a new catfish from the rio Araguaia basin, Brazil (Siluriformes: Trichomycteridae)

Ituglanis macunaima, new species, is described from the rio Araguaia basin, Mato Grosso, Brazil. It is distinguished from its congeners by the following combination of characters: posterior fontanel absent; pectoral-fin rays usually i,4; pelvic-fin rays usually i,4; branched caudal-fin rays usually 5,5; mottled color pattern formed by irregular to roundish dark brown spots on whitish background; reduced supraorbital canal with pores s1 and s2 lacking; reduced infraorbital canal with pores i1 and i3 lacking; 2-3 pleural ribs; and 35-38 vertebrae. A detailed description and illustrations of the skeleton of I. macunaima are also provided. Comparisons with other trichomycterids are presented, and several reductive traits of I. macunaima are discussed. Some comments are made about the systematics and phylogeny of the genus.

(367) Symptom Expression of Mixed Virus Infections in `Chickasaw' Blackberry

Latent infection of Blackberry yellow-vein associated virus (BYVaV) in `Chickasaw' blackberry has been reported. However, plants with characteristic leaf symptoms, such as vein yellowing, chlorotic mottling, and oak-leaf patterns, have tested positive for BYVaV using reverse-transcription polymerase chain reaction. Experiments were initiated to determine if the symptoms expressed in BYVaV infected `Chickasaw' were caused by mixed virus infections. BYVaV, a recently identified crinivirus, was evaluated for synergistic interactions with Tobacco ringspot virus (TRSV), Tomato ringspot virus (ToRSV), and Raspberry bushy dwarf virus (RBDV). `Chickasaw' blackberry plants infected with BYVaV (single infection) were used as receptor plants to establish mixed virus infections with TRSV and ToRSV transmitted by nematodes and RBDV transmitted by bottle grafts. Characteristic symptoms of multi-virus infection will be presented and discussed.

Perceptual assessment of simulated print noise with random and periodic structure

Lightness variation in a supposedly uniform printed surface is referred to as “print mottle.” This phenomenon is one of the most detrimental to overall print quality. A fundamental problem in the evaluation of human sensitivity to a print quality variable such as mottle is the difficulty in controlling external variables, such as variations in color or in average print density, that arise in the printing process. These variables can influence the rating of quality. To analyze the impact of a systematic mottle pattern compared to that of the common case of a random pattern, a digital simulation technique was used to create gray test samples with various amounts of stochastic and systematic noise of different characters. The samples were printed using a high quality inkjet printer and evaluated by a panel of judges. Two different evaluation methods were used. Observers rated dissimilarity and preference in a pairwise comparison task, and also by positioning samples in the horizontal and vertical directions of a digitizing tablet. The results show that individuals rate the samples in a very consistent way and that systematic noise is perceived to be more annoying than random noise of a similar physical magnitude. Furthermore, the consistency between the two different evaluation methods is very good, which suggests that two-dimensional scaling on a digitizing tablet is a viable method for grouping samples in a plane. The results also show that digital simulation of print artifacts is a powerful tool for creating samples with controlled disturbances.

Demography and decline of the Mentasta caribou herd in Alaska

We evaluated population trends in the Mentasta caribou (Rangifer tarandus (L., 1758)) herd in Wrangell – St. Elias National Park and Preserve, Alaska, from 1990 to 1997 and determined factors contributing to its decline. We postulated that predation-related mortality of adult females and juveniles was the proximate cause of the decline, and that survival of juvenile caribou reflected interactions with winter severity, calving distribution, timing of births, density of caribou, and physical condition of neonates at birth. The population declined at its greatest rate from 1990 to 1993 (r = –0.32) and at a lower rate from 1994 to 1997 (r = –0.09). Recruitment (number of calves/100 females during September) averaged 4/100 during the rapid population decline from 1990 to 1993 and 13/100 from 1994 to 1997. Parturition rate of adult females ranged from 65% to 97%. Survival of adult females and juveniles ranged from 0.77 to 0.86 and from 0.00 to 0.22, respectively. Approximately 43%, 59%, and 79% of all juvenile mortality occurred by 1, 2, and 4 weeks of age, respectively. We confirmed predation-related mortality as the primary proximate cause of population decline, with gray wolves (Canis lupus L., 1758), bears (species of the genus Ursus L., 1758), and other predators accounting for 57%, 38%, and 5%, respectively, of all juvenile mortality, and bears causing disproportionate mortality among 0- to 1-week-old neonates. We supported the hypotheses that timing of birth and habitat conditions at the birth site, particularly mottled snow patterns, affected vulnerability and survival of neonates, and birth mass affected survival of juveniles through summer. We speculate that the population will continue to decline before reaching a low-density equilibrium that is sustained by density-dependent changes in the functional responses of predators.

Trichomycterus maracaya, a new catfish from the upper rio Paraná, southeastern Brazil (Siluriformes: Trichomycteridae), with notes on the T. brasiliensis species-complex

Trichomycterus maracaya, a new species of Trichomycteridae, is described from a streamlet in the upper rio Paraná, Poços de Caldas, State of Minas Gerais, southeastern Brazil. The following putative autapomorphies distinguishes T. maracaya from congeneric species: 1) row of lateral blotches not forming a stripe at any phase during ontogeny; 2) superficial layer of pigmentation of juveniles and large (presumably adults) specimens consisting solely of scattered chromatophores. Furthermore, the new species is characterized by a combination of yellow ground color in life and mottled pattern formed by small to medium-sized, brown, irregularly-coalescent, well-defined deeper-lying blotches, and more superficial dots on the body. Trichomycterus maracaya is assigned to the T. brasiliensis species-complex (which includes T. brasiliensis, T. iheringi, T. mimonha, T. potschi, T. vermiculatus, and several undescribed species apparently endemic to the main river basins draining the Brazilian Shield) based on the presence of: 1) blotches in four longitudinal rows of deeper-lying pigmentation on the trunk large, horizontally-elongated, and well-defined; 2) pectoral fin with I+5-6 rays; 3) separation between the anterior and posterior cranial fontanels by the primordial epiphyseal cartilaginous bar being present only in larger specimens; and 4) pelvic-fin bases very close to each other, sometimes in contact.

High-resolution MR imaging for nodal staging in rectal cancer: are there any criteria in addition to the size?

Purpose: MR staging of nodal metastases in patients with rectal cancer using criteria based on size, shape and signal intensity can be difficult, because ≥50% of the nodes are less than 5 mm in size. Therefore new MR criteria were evaluated to see whether it can improve the MR assessment of nodal metastases in rectal cancer patients. Materials and methods: Ninety-nine patients with primary rectal carcinoma underwent 1.5 T high-resolution MRI with a quadrature phased array coil. Among them, 75 patients who had undergone total mesorectal excision were enrolled in this study. An MR radiologist, blinded for the histological results, randomly recorded the characteristics of each detectable node (LN); common criteria such as short-axis diameter, the ratio of long- to short-axis diameter, and signal intensity on each sequence; new criteria such as the margin (smooth, lobulated, spiculated, indistinct), a homogenous or mottled heterogeneous appearance, gross enhancement and its pattern, the venous encasement, and the dirty perirectal fat signal. Results: Among 75 patients, 22 (29%) were node-positive. All patients who did not have detectable LN on MR were node-free ( n=15). Presence of LNs>4 mm was significantly higher in the node-positive group. Presence of LNs>8 mm was seen only in the node-positive group. Presence of a spiculated border and an indistinct border shows sensitivities of 45 and 36%, and specificities of 100 and 100%, respectively. Presence of a mottled heterogeneic pattern shows a sensitivity of 50%, a specificity of 95%. The presence of these three features were strongly correlated with LN positivity ( P<0.001, respectively). Presence of a venous encasement ( n=4) and dirty perirectal fat signal ( n=3) were also significantly ( P<0.05, respectively) correlated with LN positivity. Conclusion: In addition to size, new criteria such as a spiculated or indistinct border and a mottled heterogeneous appearance could be useful to predict regional lymph node involvement in patients with rectal cancer.

Steatogenys ocellatus: A New Species of Neotropical Electric Fish (Gymnotiformes: Hypopomidae) from the Lowland Amazon Basin

Abstract Steatogenys ocellatus sp. nov. is described from the lowland Amazon basin at localities near Tefe (Brazil) and Iquitos (Peru). This species is described using features of external morphology, meristics, pigmentation, osteology, and the electric organ discharge. The new species is diagnosed by (1) a relatively large maximum body size (maximum length to end of anal fin 320 mm vs 172 mm in other species); (2) a distinctive round or oval spot on the pectoral-fin base; and (3) irregular dark blotches on the pectoral fin forming a mottled pattern. Several morphometric and meristic features also unambiguously distinguish S. ocellatus sp. nov. from the two known congeners, Steatogenys elegans and Steatogenys duidae. Steatogenys elegans is common in riverine and lacustrine habitats throughout the lowland Amazon and Orinoco basins and the Guyanas. Steatogenys duidae is found in terra firme forest creeks throughout the Amazon and Orinoco basins. Steatogenys ocellatus sp. nov. inhabits static or slow-flowing...