The "Betta Fish Nebula" or "the Mermaid nebula" (ESO 217-25 or SNR G296.5+10.0) is a supernova remnant in the Centaurus constellation.
Famous for its shape resembling a betta fish or mermaid.
Characterized by blue-tinged oxygen emissions, this 14,000-year-old cosmic structure is a popular, faint target for astrophotography, often capturing a "fighting fish" appearance.
It Spans over 1 degree, making it a very large, faint object in the sky.

Please see the next starless image for a better "fishy" view....

This is a narrowband composite image with RGB stars:
O3 - 240 minutes (as luminance)
S2,Ha - 60 min each
RGB 30 min each
Total of about 7.5 hrs.

Telescope: ASA600 24" RC with Reducer at f4.5
Mount: ASA DDM200 Direct Drive with Absolute Encoders
Camera: Moravian G3 61000 pro

Imaged from Tivoli farm, Namibia