Sexual Dimorphisms in the Dermal Denticles of the Lesser-Spotted Catshark, Scyliorhinus canicula (Linnaeus, 1758)

Biofluorescence has recently been found to be widespread in marine fishes, including sharks. Catsharks, such as the Swell Shark (Cephaloscyllium ventriosum) from the eastern Pacific and the Chain Catshark (Scyliorhinus retifer) from the western Atlantic, are known to exhibit bright green fluorescence. We examined the spectral sensitivity and visual characteristics of these reclusive sharks, while also considering the fluorescent properties of their skin. Spectral absorbance of the photoreceptor cells in these sharks revealed the presence of a single visual pigment in each species. Cephaloscyllium ventriosum exhibited a maximum absorbance of 484 ± 3 nm and an absorbance range at half maximum (λ1/2max) of 440–540 nm, whereas for S. retifer maximum absorbance was 488 ± 3 nm with the same absorbance range. Using the photoreceptor properties derived here, a “shark eye” camera was designed and developed that yielded contrast information on areas where fluorescence is anatomically distributed on the shark, as seen from other sharks’ eyes of these two species. Phylogenetic investigations indicate that biofluorescence has evolved at least three times in cartilaginous fishes. The repeated evolution of biofluorescence in elasmobranchs, coupled with a visual adaptation to detect it; and evidence that biofluorescence creates greater luminosity contrast with the surrounding background, highlights the potential importance of biofluorescence in elasmobranch behavior and biology.

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“…5 ). Sexual dimorphism in the dermal denticles has also previously been reported for the Lesser-Spotted Catshark ( Scyliorhinus canicula ) 54 .…”

Section: Discussionsupporting

confidence: 57%

Biofluorescence in Catsharks (Scyliorhinidae): Fundamental Description and Relevance for Elasmobranch Visual Ecology

Gruber

Loew

Deheyn

et al. 2016

Sci Rep

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“…Inherently, the rate of elasmobranch healing likely depends on individual physiology and adaptive immunology ( Luer et al, 2004 ; Marra et al, 2017 ). Morphological adaptations such as the thicker epidermal layers exhibited in female blue sharks ( Prionace glauca ) ( Nakano and Stevens, 2008 ) and small-spotted catsharks ( Scyliorhinus canicula ) ( Crooks et al, 2013 ) may assist in intrinsic healing capacity in the females of these species. Additionally, neonatal individuals may have a higher rate of healing than adults associated with the importance of allocating resources and energy effectively during early life stages to optimize growth and maximize survival ( Chin et al, 2015 ).…”

Section: Discussionmentioning

confidence: 99%

Wound-healing capabilities of whale sharks (Rhincodon typus) and implications for conservation management

Womersley

Hancock

Perry

et al. 2021

Conservation Physiology

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Wound healing is important for marine taxa such as elasmobranchs, which can incur a range of natural and anthropogenic wounds throughout their life history. There is evidence that this group shows a high capacity for external wound healing. However, anthropogenic wounds may become more frequent due to increasing commercial and recreational marine activities. Whale sharks are particularly at risk of attaining injuries given their use of surface waters and wildlife tourism interest. There is limited understanding as to how whale sharks recover from injuries, and often insights are confined to singular opportunistic observations. The present study makes use of a unique and valuable photographic data source from two whale shark aggregation sites in the Indian Ocean. Successional injury-healing progression cases were reviewed to investigate the characteristics of injuries and quantify a coarse healing timeframe. Wounds were measured over time using an image standardization method. This work shows that by Day 25 major injury surface area decreased by an average of 56% and the most rapid healing case showed a surface area reduction of 50% in 4 days. All wounds reached a point of 90% surface area closure by Day 35. There were differences in healing rate based on wound type, with lacerations and abrasions taking 50 and 22 days to reach 90% healing, respectively. This study provides baseline information for wound healing in whale sharks and the methods proposed could act as a foundation for future research. Use of a detailed classification system, as presented here, may also assist in ocean scale injury comparisons between research groups and aid reliable descriptive data. Such findings can contribute to discussions regarding appropriate management in aggregation areas with an aim to reduce the likelihood of injuries, such as those resulting from vessel collisions, in these regions or during movements between coastal waters.

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“…Denticles consist of hydroxylapatite, which has a low solubility and is not likely affected by weak acids [22]. The larger denticle size of females is likely for protection from male aggression during courtship [23].…”

Section: Discussionmentioning

confidence: 99%

Elevated carbon dioxide alters the plasma composition and behaviour of a shark

Green

Jutfelt

2014

Biol. Lett.

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Increased carbon emissions from fossil fuels are increasing the pCO 2 of the ocean surface waters in a process called ocean acidification. Elevated water pCO 2 can induce physiological and behavioural effects in teleost fishes, although there appear to be large differences in sensitivity between species. There is currently no information available on the possible responses to future ocean acidification in elasmobranch fishes. We exposed smallspotted catsharks (Scyliorhinus canicula) to either control conditions or a year 2100 scenario of 990 matm pCO 2 for four weeks. We did not detect treatment effects on growth, resting metabolic rate, aerobic scope, skin denticle ultrastructure or skin denticle morphology. However, we found that the elevated pCO 2 group buffered internal acidosis via HCO À 3 accumulation with an associated increase in Na þ , indicating that the blood chemistry remained altered despite the long acclimation period. The elevated pCO 2 group also exhibited a shift in their nocturnal swimming pattern from a pattern of many starts and stops to more continuous swimming. Although CO 2 -exposed teleost fishes can display reduced behavioural asymmetry (lateralization), the CO 2 -exposed sharks showed increased lateralization. These behavioural effects may suggest that elasmobranch neurophysiology is affected by CO 2 , as in some teleosts, or that the sharks detect CO 2 as a constant stressor, which leads to altered behaviour. The potential direct effects of ocean acidification should henceforth be considered when assessing future anthropogenic effects on sharks.

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Sexual Dimorphisms in the Dermal Denticles of the Lesser-Spotted Catshark, Scyliorhinus canicula (Linnaeus, 1758)

Cited by 29 publications

References 48 publications

Biofluorescence in Catsharks (Scyliorhinidae): Fundamental Description and Relevance for Elasmobranch Visual Ecology

Biofluorescence in Catsharks (Scyliorhinidae): Fundamental Description and Relevance for Elasmobranch Visual Ecology

Wound-healing capabilities of whale sharks (Rhincodon typus) and implications for conservation management

Elevated carbon dioxide alters the plasma composition and behaviour of a shark

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