New paper on sculpin fins!

Our paper examining the surface of sculpin pectoral fin rays using Scanning Electron Microscopy (SEM) is now available in Royal Society Open Science!

https://royalsocietypublishing.org/doi/10.1098/rsos.241965

Scanning Electron Microscopy images of the ventral fin ray pad of an intertidal sculpin.

We found new unicellular, microscopic epidermal protrusions on sculpin fin rays (image above) that have not been reported previously in these fish! Further, distinct channels separate these protrusions, and channels are more prominent on more extreme intertidal species that endure breaking waves. These features suggest that sculpins may be an overlooked group for examining adaptations of skin to harsh environments.

For now, we're calling the new features 'fibrillar microridges' because we hypothesize they are modifications of the normal reticulated, raised pattern on fish skin (below, left). In fact, along the edge of the fin pad we saw a transitional zone where the fibrils were less elongate along the sides of the fin (below, right). However, we still need to test this hypothesis to verify that our name is appropriate.

Typical fish skin, as found on the webbing between the dorsal fin rays of the same fish as the first

The transitional zone along the edge of the ventral fin ray pad showing a transition in fibril lengt

We also hypothesize that the fibrillar microridges function to enhance friction with the substrate, kind of like having sandpaper on their fins. Other animals have similar features and functions. For example, algae eaters and related fishes have 'unculi' - unicellular keratinous projections - on the ventral surfaces of their fins (images below) that enhance contact with the substrate for station-holding as well as feeding. Despite similarities to sculpins, there are some important differences in feature composition, size, and density that preclude us from using the term 'unculi' more broadly to describe what we found in sculpins.

Unculi on the ventral side of the pelvic fin on a yellow flying fox algae eater.

Unculiferous multicellular tubercles on the mouth of a yellow flying fox algae eater.

Plauteau-like unculi on the mouth of a yellow flying fox.

We are excited about this finding and believe it will lead to new research avenues in both fish form and function as well as bio-inspired design. Prior designs have been modeled after fish with suction cups (such as clingfish). Sculpins don't have suction cups and represent a more intermediate morphology that has previously been under-appreciated.

Look for more work on these features soon!