Description
One of the gymnotiforms most specialized to living in deep river channels, O. tamandua resembles fishes adapted to caves in several respects. Their elongated, laterally compressed bodies are nearly unpigmented, appearing bright pink due to the blood underneath. The eyes are tiny and virtually non-functional, and are placed asymmetrically on the head. The asymmetry of the eyes is not correlated with size, sex or environment, but may be related to their degenerate state. The snout is distinctive, being a long, evenly tapering, nearly straight tube measuring four times as long as high. The mouth is relatively small. The dorsal throng (a whip-like appendage used for electroreception) is unusually long and thick, which led it to originally be described as a "very strongly developed adipose fin" by Boulenger. The throng originates close to the rear margin of the skull, which is much more anterior than in other apteronotids.
O. tamandua has a long anal fin, a small caudal fin, and tapering pectoral fins; the dorsal and pelvic fins are absent. The caudal fin shows a great deal of variation due to regeneration after tail loss; in some cases the regenerated fin becomes merged with the anal fin. The fin rays number 9 in the caudal fin, 14-15 in the pectoral fins, and 207-256 in the anal fin. Almost the entire body, except for the dorsal midline, is densely covered with flimsily attached scales, being small and circular towards the front and larger and more rectangular towards the back. There are around 12 rows of scales above the lateral line and 40-42 rows below. The first 5-10 scales along the lateral line are modified into overlapping elongate tubes. The maximum known size is 44 cm long and 125 g.
Read more about this topic: Orthosternarchus Tamandua
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