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Gobiesox maeandricus (Girard, 1858). Northern Clingfish. To 16.5 cm (6.5 in) TL (Eschmeyer and Herald 1983). Noyes Island, south-eastern Alaska (Mecklenburg et al. 2002) to central Baja California (between Isla Guadalupe and mainland on drifting kelp) (Miller and Lea 1972). Benthic; depth: intertidal to 18 m (59 ft) (min.: Miller and Lea 1972; max.: Cross 1981). DFO reports one bottom trawl record from northern Hecate Strait in 2005 at 140 m (459 ft). However, there is no voucher specimen., Published as part of Love, Milton S., Bizzarro, Joseph J., Cornthwaite, Maria, Frable, Benjamin W. & Maslenikov, Katherine P., 2021, Checklist of marine and estuarine fishes from the Alaska-Yukon Border, Beaufort Sea, to Cabo San Lucas, Mexico, pp. 1-285 in Zootaxa 5053 (1) on page 201, DOI: 10.11646/zootaxa.5053.1.1, http://zenodo.org/record/5578008, {"references":["Eschmeyer, W. N. & Herald, E. S. (1983) A Field Guide to Pacific Coast Fishes of North America from the Gulf of Alaska to Baja California. Houghton Mifflin, Boston.","Miller, D. J. & Lea, R. N. (1972) Guide to the coastal marine fishes of California. California Department of Fish and Game Fish Bulletin, 157."]}

The clingfish attaches to rough surfaces with considerable strength using an intricate suction disc, which displays complex surface geometries from structures called papillae. However, the exact role of these structures in adhesion is poorly understood. To investigate the relationship between papillae geometry and adhesive performance, we developed an image processing tool that analyzed the surface and structural complexity of papillae, which we then used to model hydrodynamic adhesion. Our tool allowed for the automated analysis of thousands of papillae in specimens across a range of body sizes. The results led us to identify spatial trends in papillae across the complex geometry of the suction disc and to establish fundamental structure-function relationships used in hydrodynamic adhesion. We found that the surface area of papillae changed within a suction disc and with fish size, but that the aspect ratios and channel width between papillae did not. Using a mathematical model, we found that the surface structures can adhere considerably when subjected to disturbances of moderate to high velocities. We concluded that a predominant role of the papillae is to leverage hydrodynamic adhesion and wet friction to reinforce the seal of the suction disc. Overall, the trends in papillae characteristics provided insights into bioinspired designs of surface microstructures for future applications in which adhesion is necessary to attach to diverse surfaces (in terrestrial or aquatic environments), even when subjected to disturbance forces of randomized directionality.

Adhesion is difficult to achieve on rough surfaces both in air and underwater. In nature, the northern clingfish (Gobiesox maeandricus) has evolved the impressive ability to adhere onto substrates of various shapes and roughnesses, while subject to strong intertidal surges. The suction disc of the clingfish relies on suction and friction to achieve and maintain adhesion. Inspired by this mechanism of attachment, we designed an artificial suction disc and evaluated its adhesive stress on rough surfaces and non-planar geometries. The artificial suction disc achieved adhesion strengths of 10.1 ± 0.3 kPa in air on surfaces of moderate roughness (grain size, 68 µm), and 14.3 ± 1.5 kPa underwater on coarse surfaces (grain size, 269 µm). By comparison, a commercially available suction cup failed to exhibit any significant adhesion in both scenarios. The roughly 2 g heavy clingfish-inspired suction discs gripped concave surfaces with small radii of curvature (12.5 mm) and supported payloads up to 0.7 kg. We correlated the effect of key bioinspired features (i.e. slits, a soft outer layer, and body geometry) to adhesion performance using contact visualization techniques and finite element analysis (FEA). The suction discs were then tested on a remotely operated vehicle (ROV) to demonstrate their utility in the soft manipulation of fragile objects.

The Northern clingfish is a small, Eastern North Pacific fish that can attach to rough, fouled rocks in the intertidal. Their ability to attach to surfaces has been measured previously in the laboratory, and in this study, we show the roughness and fouling of the natural habitat of these fish. We introduce a new method for measuring surface roughness of natural substrates with time-limited accessibility. We expect this method to be broadly applicable in studies of animal/substrate surface interactions in habitats difficult to characterize. Our roughness measurements demonstrate that the fish's ability to attach to very coarse roughness is required in its natural environment. Some of the rocks showed even coarser roughness than the fish could attach to in the lab setting. We also characterized the clingfish's preference for other habitat descriptors such as the size of the rocks, biofilm, and Aufwuchs (macroalgae, encrusting invertebrates) cover, as well as grain size of underlying substrate. Northern clingfish seek shelter under rocks of 15-45 cm in size. These rocks have variable Aufwuchs cover, and gravel is the main underlying substrate type. In the intertidal, environmental conditions change with the tides, and for clingfish, the daily time under water (DTUW%) was a key parameter explaining distribution. Rather than location being determined by intertidal zonation, an 80% DTUW, a finer scale concept of tidal inundation, was required by the fish. We expect that this is likely because the mobility of the fish allows them to more closely track the ideal inundation in the marine intertidal.

While artificial suction cups only attach well to smooth surfaces, the Northern clingfish can attach to surfaces ranging from nanoscale smooth to rough stone. This ability is highly desirable for technical applications. The morphology of the fish's suction disc and its ability to attach to rough and slimy surfaces have been described before, and here we aim to close gaps in the biomechanical understanding, and transfer the biomechanical principles to technical suction cups. We demonstrate that the margin of the suction disc is the critical feature enabling attachment to rough surfaces. Second, friction measurements show that friction of the disc rim is increased on rough substrates and contributes to high tenacity. Increased friction causes a delay in failure of the suction cup and increases the attachment force. We were able to implement these concepts to develop the first suction cups bioinspired by Northern clingfish. These cups attach with tenacities up to 70 kPa on surfaces as rough as 270 µm grain size. The application of this technology is promising in fields such as surgery, industrial production processes and whale tagging.This article is part of the theme issue ‘Transdisciplinary approaches to the study of adhesion and adhesives in biological systems'.

Northern clingfish use a ventral suction disc to stick to rough substrates in the intertidal zone. Bacteria, algae and invertebrates grow on these surfaces (fouling) and change the surface properties of the primary substrate, and therefore the attachment conditions for benthic organisms. In this study, we investigate the influence of fouling and surface roughness on the adhesive strength of northern clingfish, Gobiesox maeandricus. We measured clingfish tenacity on unfouled and fouled substrates over four surface roughnesses. We exposed surfaces for 6 weeks in the Pacific Ocean, until they were covered with periphyton. Clingfish tenacity is equivalent on both fouled and unfouled smooth substrates; however, tenacity on fouled rough surfaces is less compared with tenacity on unfouled ones. We hypothesize that parts of biofilm may act as a lubricant and decrease friction of the disc margin, thereby making disc margins slip inwards and fail at lower tenacities. Nevertheless, even on fouled surfaces the adhesive forces are approximately 150 times the body weight of the fish. To identify the upper threshold of surface roughness the fish can cling to, we tested seven unfouled substrates of increasing surface roughness. The threshold roughness at which northern clingfish failed increased with specimen size. We hypothesize that because of the elastic properties of the disc margin, a larger disc can adapt to larger surface irregularities. The largest specimens (length 10–12 cm) were able to cling to surfaces with 2–4 mm grain size. The fish can attach to surfaces with roughness between 2 and 9% of the suction disc width.

[Figure][1] Northern clingfish ( Gobiesox maeandricus ). Photo credit: Petra Ditsche. Life in the intertidal zone is rough, with waves continually pounding anything that chooses to live there. Some intertidal residents huddle in crevices for protection, while others simply anchor

The northern clingfish,Gobiesox maeandricus, is able to adhere to slippery, fouled and irregular surfaces in the marine intertidal environment. We have found that the fish can adhere equally well to surfaces with a broad range of surface roughness, from the finest sandpaper (Ra= 15 µm) to textures suitable for removing finish from flooring (Ra= 269 µm). The fishes outperform man-made suction cups, which only adhere to the smoothest surfaces. The adhesive forces of clingfish correspond to pressures 0.2–0.5 atm below ambient and are 80–230 times the body weight of the fish. The tenacity appears related to hierarchically structured microvilli around the edges of the adhesive disc that are similar in size and aspect ratio to the setae found on the feet of geckoes, spiders and insects. This points to a possible biomimetic solution to the problem of reversibly adhering to irregular, submerged surfaces.

An undergraduate tested the sticking ability of 22 freshly killed Gobiesox maeandricus on eight surfaces mimicking the range of sandpaper grades and reported at the meeting that the fish adhered to them all with an average force 180 times their body weight. (In contrast, rubber suction cups fell off rougher surfaces, sticking only to the three smoothest ones.) Scanning electron microscopy of the clingfish9s belly fins revealed that the secret to its staying power may be a rim of microscopic hairs akin to what geckos utilize on their toes to enable them to walk upside down on ceilings.

Light microscopy and scanning and transmission electron microscopy of the ventral adhesive disc of the northern clingfish, Gobiesox maeandricus, demonstrate that two distinct types of epidermis are present on the disc surface. Most of the disc is covered with cuboidal epithelium in which four cell types can be distinguished: acidophil cells, mucous cells, epithelial cells, and "alarm substance" cells. The surfaces of the epithelial cells feature whorled microridges typical of teleost epidermis. Near the margin of the disc, on the lateral fin rays, and in discrete raised patches inside the disc are papillae of stratified columnar epithelium. The surface cells of these papillae are microvillous and secrete a noncellular cuticle which is firmly anchored to the microvillous surface of the papillae. The cuticle is not adhesive. It contains keratin-like proteins but no mucins or mucoproteins are demonstrable histochemically. Connective tissue layers and muscle underlying the epidermis of the disc are arranged to provide structural integrity and shock absorption while allowing some flexibility to the disc and papillae. The adhesive force generated by the disc was demonstrated using a pressure transducer. Negative pressure decays over time and is periodically renewed by the fish. Thus suction is largely maintained passively and the disc's seal is subject to some leakage. The fish can also actively apply suction pressure when agitated but fatigues and cannot sustain high negative pressures for long. The epidermal papillae, coupled with the fish's ability to flex the disc, represent an additional gripping mechanism for irregular surfaces. The papillary surface cuticle apparently acts as an abrasion-resistant, frictional surface.