Histologic Observations of Dermal Wound Healing in a Free‐Ranging Blacktip Shark from the Southeastern U.S. Atlantic Coast: A Case Report

Abstract

Despite indications that sharks have an exceptional capacity to heal from traumatic injuries, no detailed microscopic observations of integumental wounds have been reported for sharks. This study details the histopathological features of such wounds in a freeranging shark. An adult male Blacktip Shark Carcharhinus limbatus was collected in 2017 during fisheries-independent sampling efforts in the coastal southeastern U.S. Atlantic. The shark had numerous lesions on his head, torso, and left pectoral fin that were compatible with shark bites. Representative samples from two wounds on the head were examined by light microscopy. The epidermal changes included hyperplasia and hypertrophy; intracellular edema; and the absence of goblet cells, denticles, and chromatophores. In the dermis, fibrinocellular exudation, granulation tissue, and marked skeletal muscle necrosis and regeneration were observed. The above features were comparable to wound healing in bony fish, albeit minor differences were found. Although this case documents exceptionally good regeneration of skeletal muscle in the shark, we found no evidence of unique morphological healing patterns. Further studies on wound healing are needed because recent molecular and genetic findings do suggest evolutionary adaptations enhancing healing in sharks.

Depredation rates and spatial overlap between Great Hammerheads and Tarpon in a recreational fishing hot spot

“…Three sharks that were tagged during the study and a fourth shark that was observed during the visual survey had clear propeller injuries on their dorsal fins or the dorsal surface of their bodies. These injuries could be detrimental to individual Great Hammerhead health (Borucinska et al 2020).…”

The salamander blastema within the broader context of metazoan regeneration

“…Whether vertebrate limb regeneration is a vestige of ancestral whole-body regeneration, or an evolutionary novelty depends on whether "the entire ancestral line of animals has had a similar regenerative ability" (Slack, 2017). Recent evidence supports this ancestral continuity: tunicates have extensive regenerative abilities, cephalochordates regenerate the tail through a mechanism at least superficially similar to axolotl regeneration (Ferrario et al, 2020), larval jawless fish such as lampreys can regenerate their tails (Bayramov et al, 2018), sharks have recently been shown to regenerate fins (Lu et al, 2013;Alibardi, 2019;2022a;Borucinska et al, 2020;Marconi et al, 2020;Womersley et al, 2021), and of course there are many examples of appendage regeneration throughout the bony fish (Yoshinari and Kawakami, 2011;Nogueira et al, 2016;Darnet et al, 2019).…”

“…Sharks and cartilaginous fish have only recently been demonstrated to exhibit enhanced muscle, cartilage, CNS and organ regeneration in comparison to amniotes ( Lu et al, 2013 ; Alibardi, 2019 ; Borucinska et al, 2020 ; Marconi et al, 2020 ; Womersley et al, 2021 ; Alibardi, 2022a ). As most of these studies are observational, the molecular basis of these processes remains unexamined, and it is unclear how closely they resemble salamander limb regeneration on the molecular level.…”

Observations of fin injury closure in Great Hammerheads and implications for the use of fin‐mounted geolocators

“…The risk of attaining an injury due to predation (e.g., van den Hoff and Morrice 2008), mating (e.g., Schulte et al 2021), or human actions (e.g., Jakes et al 2018) is prevalent throughout all life stages. In marine habitats, members of Chondrichthyes in the subclass Elasmobranchii (i.e., sharks and rays) seem to withstand trauma (e.g., Borucinska et al 2020; Gardiner and Wiley 2020) and recover from severe, life‐threatening injuries (Towner et al 2012; Womersley et al 2021). Bird (1978) documented extensive tissue healing of three carcharhinid sharks that suffered from deep wounds caused by plastic straps.…”