Mucus matters the complex and slippery surfaces of fish

Meeting Abstract

P1-36  Thursday, Jan. 4 15:30 – 17:30  Mucus matters: the complex and slippery surfaces of fish WAINWRIGHT, DK*; LAUDER, GV; Harvard University; Harvard University

Teleost scales differ greatly in morphology and yet we have a poor understanding of the form to function relationship in this system. Researchers have often hypothesized hydrodynamic functions for fish scales, but have largely ignored the mucus and epidermal coatings that cover the surfaces of fish scales in most teleost species. Mucus potentially obscures surface features such as spines and ridges that have been hypothesized to alter flow dynamics over the fish surface. We use gel-based profilometry to examine the surface topography of seven species of fish both with and without mucus and epidermis. Comparisons among surfaces with and without mucus indicate that mucus generally obscures surface features of scales. However, we demonstrate considerable variation in the effect of a mucus coating, and mucus can cause roughness decreases anywhere from 0% to 93%, depending on species and location on the body. Thus, scale morphology alone is not a good predictor of live fish surface topography because diversity also exists in the epidermis and mucus layers. We go further and calculate a k+ parameter that indicates if surface features are likely to change boundary layer flow. We use data from our topography measurements to calculate k+ values for mucus-covered surfaces for all seven species at slow (1 length/second) and fast (3 lengths/second) swimming speeds. These results show that only the surfaces of certain species are likely to change boundary layer flow, providing a theoretical framework for future experimental studies of scales, mucus, and boundary layer flows over fish surfaces.

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