Drop Knifefish (Gymnorhamphichthys britskii) is a ray-finned fish of the family Rhamphichthyidae. It inhabits freshwater waters. This species can reach a maximum total length of 18 cm. With a trophic level of 3.2, it is a low-level carnivore, feeding on invertebrates and small organisms. It is assessed as Least Concern on the IUCN Red List.
This species is distinguished from its congeners except G. hypostomus in having 5-16 (usually 9-13) large dark saddle-shaped pigment bars over the dorsal midline, extending between the nape and a vertical with the end of the anal fin, and sometimes reaching to or slightly below the lateral line; differs from G. hypostomus in having 141-172 (vs. 178-211) anal-fin rays; a shorter snout, preorbital distance 48.1-60.3% of head length (mean 54.6%) (vs. 58.3-68.6%, mean 63.9%); a larger eye, with diameter 5.7-9.0% of head length (mean 7.0%) (vs. 3.3-5.9%, mean 4.3%); a longer distance from tip of snout to posterior nares, 17.1-22.0% of head length (mean19.2%) (vs. 11.2-17.1%, mean 13.8%); 7 (vs. 9-13) displaced hemal spines; and 64-69 (vs. 71-75) vertebrae to end of anal fin .
Behavioural data for Drop Knifefish is currently being reviewed.
Freshwater; benthopelagic. Tropical South America: Paraguay.
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