Fusarium solani species complex associated with carapace lesions and branchitis in captive American horseshoe crabs Limulus polyphemus

Abstract

Captive American horseshoe crabs Limulus polyphemus housed at the National Aquarium presented with a variety of shell and gill lesions over a 3 yr period. Carapace lesions were located on both the dorsal and ventral prosoma and opisthosoma and included multifocal circular areas of tan discoloration, ulcerations, and/or pitting lesions, extending from superficial to full thickness. Gill lesions involved both the book gill cover (operculum) and individual book gill leaflets and included multifocal circular areas of tan discoloration, tan to off-white opaque proliferative lesions, and/or areas of black discoloration. Histopathology revealed fungal hyphae, with variable morphology throughout the thickened and irregular cuticle of the carapace and occasionally penetrating into subcuticular tissues, with associated amebocytic inflammation. Book gill leaflets were infiltrated by fungal hyphae and contained necrotic debris and amebocytes. Thirty-eight of 39 animals (97%) evaluated via histopathological examination had intralesional fungal hyphae. Fungal cultures of carapace and gill lesions were attempted in 26 tissue samples from 15 individuals and were positive in 13 samples (50%), with 10 cultures (77%) yielding identification to genus. Fusarium sp. was identified in 8 of the 10 cultures (80%) via culture morphology. The Fusarium solani species complex was confirmed in 6 of these 8 (75%) via polymerase chain reaction amplification of 2 different ribosomal-specific sequences of isolated fungal DNA. Ante-mortem systemic and topical treatments were performed on some affected individuals, but no appreciable change in lesions was observed. Mycotic dermatitis and branchitis are serious health issues for captive American horseshoe crabs.

Microbiome shifts associated with the introduction of wild Atlantic horseshoe crabs (Limulus polyphemus) into a touch-tank exhibit

“…Additionally, several species of Pseudoalteromonas are widely discussed in the literature as symbionts, given their diverse metabolic potential and their ability to produce a variety of antibacterial, antifungal, algicidal, and antifouling compounds (Atencio et al 2018; Offret et al 2016). Fungi have been identified as possible chitinase containing pathogens that could be involved in this process (Tuxbury et al, 2014; LaDouceur et al, 2019). In our study, we excluded eukaryotic sequences from analysis and therefore were unable to document the fungal communities of our samples.…”

“…A common affliction of captive horseshoe crabs are lesions that occur on the carapace (Nolan and Smith 2009). These lesions have been associated with a variety of microorganisms including heterotrophic bacteria (e.g., Thompson et al, 2011), Cyanobacteria (Leibovitz 1986), fungi (Tuxbury et al, 2014), and green algae (Braverman et al, 2012). However, no systematic studies have explored the microbiomes of wild or captive horseshoe crabs using cultivation-independent techniques.…”

Zoothamnium duplicatum infestation of cultured horseshoe crabs (Limulus polyphemus)

“…Discolouration (white to reddish-brown) of the soft tissues, such as the arthroidal membrane and gill lamellae, is related to tissue necrosis, lesion formation and subcuticular damages (Allender et al, 2008;Nolan and Smith, 2009). Invasive fungal hyphae were observed in lethargic crabs within an aquarium touch tank (Tuxbury et al, 2014). The fungus was identified as Fusarium solani, a plant pathogen that has been associated with mycosis in invertebrates and many polyphemus (Leibovitz and Lewbart, 2004;Braverman et al, 2012).…”

Population Structure and Development of Resistance to Hymexazol Among Fusarium solani Populations from Date Palm, Citrus and Cucumber

“…In addition, it can be an opportunistic pathogen and cause superficial mycoses in humans and animals (Tuxbury et al. ). Fusarium solani causes different types of diseases such as wilt, slow decline and fruit rot (Al‐Sadi et al.…”

“…Fusarium solani has a wide host range and is pathogenic to different plant species including vegetables, flowers and field crops. In addition, it can be an opportunistic pathogen and cause superficial mycoses in humans and animals (Tuxbury et al 2014). Fusarium solani causes different types of diseases such as wilt, slow decline and fruit rot (Al-Sadi et al 2011b;Bueno et al 2014).…”