To me it looks like A mikoljii....from the Rio Negro
The origiinal disription is below...copied from the CRC
But to actually diagnose.. as you can see....is no simple task
Diagnosis: Astronotus mikoljii is distinguished from congeners by the following combination of characters: two or three supraneural bones (versus two); absence of the spinous process (hypurapophysis) on the anterosuperior border of the parahypural bone (hypural complex) in A. mikoljii (versus present in A. ocellatus and A. crassipinnis). The sagitta otolith in A. mikoljiiis oval, with strongly crenulated ventral and dorsal margins (versus elliptical and smooth-lobed margins in A. crassipinnis, and elliptical and smooth-dentate margins A. ocellatus); the rostrum is projected with an elongated process, in A. mikoljii (versus rostrum process short in A. crassipinnis and A. ocellatus); the posterior region of the sagitta otolith is rounded in A. mikoljii (versus straight or flat in A. crassipinnis and A. ocellatus). The aspect ratio of sagitta otoliths in A. mikoljii (AR = 0.665) is higher than that of A. ocellatus (AR = 0.606), and A. crassipinnis (AR = 0.585), and the differences are statistically significant at P < 0.05. The roundness index was highest in A. mikoljii (Rd = 0.597) versus A. ocellatus (Rd = 0.545) and A. crassipinnis (Rd = 0.543) (P < 0.05). Also, the morphometric index showed higher values in A. mikoljii compared to A. ocellatus (0.837 versus 0.767) and A. crassipinnis (0.735). The new species also is distinguished from congeners by the following combination of morphometric characteristics: the mean head length of A. mikoljii (36.72% SL) is longer than that of A. crassipinnis (35.01% SL), and also A. ocellatus (33.26% SL); the mean diameter of the orbit of A. mikoljii (9.06% SL) is greater than that of A. ocellatus (7.36%SL) and that of A. crassipinnis (7.73% SL); the mean pre-orbital depth of A. mikoljii (14.22% SL) is greater than that of A. crassipinnis (10.14% SL) but less than that of A. ocellatus (15.91% SL); the mean snout length of A. mikoljii (11.53% SL) is longer than that of A. crassipinnis (5.36% SL), and A. ocellatus (10.67% SL) (Perez Lozano et al., 2022:123).
The origiinal disription is below...copied from the CRC
But to actually diagnose.. as you can see....is no simple task
Diagnosis: Astronotus mikoljii is distinguished from congeners by the following combination of characters: two or three supraneural bones (versus two); absence of the spinous process (hypurapophysis) on the anterosuperior border of the parahypural bone (hypural complex) in A. mikoljii (versus present in A. ocellatus and A. crassipinnis). The sagitta otolith in A. mikoljiiis oval, with strongly crenulated ventral and dorsal margins (versus elliptical and smooth-lobed margins in A. crassipinnis, and elliptical and smooth-dentate margins A. ocellatus); the rostrum is projected with an elongated process, in A. mikoljii (versus rostrum process short in A. crassipinnis and A. ocellatus); the posterior region of the sagitta otolith is rounded in A. mikoljii (versus straight or flat in A. crassipinnis and A. ocellatus). The aspect ratio of sagitta otoliths in A. mikoljii (AR = 0.665) is higher than that of A. ocellatus (AR = 0.606), and A. crassipinnis (AR = 0.585), and the differences are statistically significant at P < 0.05. The roundness index was highest in A. mikoljii (Rd = 0.597) versus A. ocellatus (Rd = 0.545) and A. crassipinnis (Rd = 0.543) (P < 0.05). Also, the morphometric index showed higher values in A. mikoljii compared to A. ocellatus (0.837 versus 0.767) and A. crassipinnis (0.735). The new species also is distinguished from congeners by the following combination of morphometric characteristics: the mean head length of A. mikoljii (36.72% SL) is longer than that of A. crassipinnis (35.01% SL), and also A. ocellatus (33.26% SL); the mean diameter of the orbit of A. mikoljii (9.06% SL) is greater than that of A. ocellatus (7.36%SL) and that of A. crassipinnis (7.73% SL); the mean pre-orbital depth of A. mikoljii (14.22% SL) is greater than that of A. crassipinnis (10.14% SL) but less than that of A. ocellatus (15.91% SL); the mean snout length of A. mikoljii (11.53% SL) is longer than that of A. crassipinnis (5.36% SL), and A. ocellatus (10.67% SL) (Perez Lozano et al., 2022:123).
