Friday, March 25, 2016

[Ichthyology • 2016] Tetrapod-like Pelvic Girdle in A Walking Cavefish, Cryptotora thamicola ปลาผีเสื้อถ้ำ

An excerpt from a video of the blind cave fish Cryptotora thamicola walking up an incline of approximately 90 degrees on an aquarium wall in the direction of a trickle of water.
by A. Suvarnaraksha  ||  DOI:  10.1038/srep23711

Fishes have adapted a number of different behaviors to move out of the water, but none have been described as being able to walk on land with a tetrapod-like gait. Here we show that the blind cavefish Cryptotora thamicola walks and climbs waterfalls with a salamander-like diagonal-couplets lateral sequence gait and has evolved a robust pelvic girdle that shares morphological features associated with terrestrial vertebrates. In all other fishes, the pelvic bones are suspended in a muscular sling or loosely attached to the pectoral girdle anteriorly. In contrast, the pelvic girdle of Cryptotora is a large, broad puboischiadic plate that is joined to the iliac process of a hypertrophied sacral rib; fusion of these bones in tetrapods creates an acetabulum. The vertebral column in the sacral area has large anterior and posterior zygapophyses, transverse processes, and broad neural spines, all of which are associated with terrestrial organisms. The diagonal-couplet lateral sequence gait was accomplished by rotation of the pectoral and pelvic girdles creating a standing wave of the axial body. These findings are significant because they represent the first example of behavioural and morphological adaptation in an extant fish that converges on the tetrapodal walking behaviour and morphology.

Cryptotora thamicola, a waterfall-climbing cave fish that appears to walk the way land vertebrates do, researchers say.
photo: Danté Fenolio 

Figure 2: Computed microtomography scan (voxel size = 8 μm) of Cryptotora thamicola (47 mm total length).
(A) transverse view of pelvic girdle, (B) dorsal (left) and ventral (right) view pelvic girdle (cranial to top), (C) anterolateral view of pelvic girdle. il, iliac region (dark purple); im, intermuscular bone (light purple); is, ischial region of puboischiadic plate (tan); pf, pelvic fin (blue); pu, pubic region of puboischiadic plate (tan); sr, sacral ribs (dark purple). Vertebrae numbers 6,7,8 designate position from skull, (D) close-up image of acetabular symphysis, (E) close up image of obturator foramen, of.

Brooke E. Flammang, Apinun Suvarnaraksha, Julie Markiewicz and Daphne Soares. 2016. Tetrapod-like Pelvic Girdle in A Walking Cavefish.
Scientific Reports. 6, Article number: 23711. DOI:  10.1038/srep23711