Splenic mycobacteriosis in an Atlantic guitarfish, Rhinobatos lentiginosus Garman

Short-Term Alternate Feeding between Terrestrially Sourced Oil- and Fish Oil-Based Diets Modulates the Intestinal Microecology of Juvenile Turbot

A nine-week feeding trial was conducted to investigate changes in the intestinal microbiota of turbot in response to alternate feeding between terrestrially sourced oil (TSO)- and fish oil (FO)-based diets. The following three feeding strategies were designed: (1) continuous feeding with the FO-based diet (FO group); (2) weekly alternate feeding between soybean oil (SO)- and FO-based diets (SO/FO group); and (3) weekly alternate feeding between beef tallow (BT)- and FO-based diets (BT/FO group). An intestinal bacterial community analysis showed that alternate feeding reshaped the intestinal microbial composition. Higher species richness and diversity of the intestinal microbiota were observed in the alternate-feeding groups. A PCoA analysis showed that the samples clustered separately according to the feeding strategy, and among the three groups, the SO/FO group clustered relatively closer to the BT/FO group. The alternate feeding significantly decreased the abundance of Mycoplasma and selectively enriched specific microorganisms, including short-chain fatty acid (SCFA)-producing bacteria, digestive bacteria (Corynebacterium and Sphingomonas), and several potential pathogens (Desulfovibrio and Mycobacterium). Alternate feeding may maintain the intestinal microbiota balance by improving the connectivity of the ecological network and increasing the competitive interactions within the ecological network. The alternate feeding significantly upregulated the KEGG pathways of fatty acid and lipid metabolism, glycan biosynthesis, and amino acid metabolism in the intestinal microbiota. Meanwhile, the upregulation of the KEGG pathway of lipopolysaccharide biosynthesis indicates a potential risk for intestinal health. In conclusion, short-term alternate feeding between dietary lipid sources reshapes the intestinal microecology of the juvenile turbot, possibly resulting in both positive and negative effects.

Genital mycobacteriosis caused by Mycobacterium marinum detected in two captive sharks by peptide nucleic acid-fluorescence in situ hybridization

Mycobacterium marinum is a prevalent nontuberculous mycobacterium (NTM)-infecting teleosts. Conversely, little is known about mycobacteriosis in elasmobranchs, and M. marinum infection has never been reported from the subclass. This study investigated the histopathological characteristics and localization of this mycobacterium through molecular analysis of two captive sharks, a scalloped hammerhead Sphyrna lewini and a Japanese bullhead shark Heterodontus japonicus, exhibited in the same aquarium tank. We detected genital mycobacteriosis caused by M. marinum infection using molecular analyses, including polymerase chain reaction (PCR) and DNA sequencing targeting the 60 kDa heat-shock protein gene (hsp65), and peptide nucleic acid-fluorescence in situ hybridization (PNA-FISH) targeting the 16S rRNA gene. Both sharks showed granulomas in connective tissues of the gonads without central necrosis or surrounding fibrous capsules, which is unlike the typical mycobacterial granulomas seen in teleosts. This study reveals that elasmobranchs can be aquatic hosts of M. marinum. Because M. marinum is a representative waterborne NTM and a potential zoonotic agent, cautious and intensive research is needed to overcome a lack of data on the relationship between NTM and the aquatic environment in association with this subclass of Chondrichthyes.

Elasmobranch-associated microbiota: a scientometric literature review

Elasmobranchs provide greatly relevant ecosystem services for the balance of the environments in which they are inserted. In recent decades, sharp population declines have been reported for many species in different regions worldwide, making this taxonomic group currently one of the most threatened with extinction. This scenario is almost entirely due to excessive fishing pressure, but any contributing factor that may cause additional mortality to populations must be mapped and monitored. In a fast-changing world, emerging marine pollution associated with climate change display the potential to increase the spread of infectious agents. These can, in turn, lead to mortality events, both directly and indirectly, by reducing immune responses and the physical and nutritional condition of affected individuals. In this context, the present study aimed to analyze data concerning elasmobranch-associated microbiota, identifying study trends and knowledge gaps in order to direct future studies on this topic of growing relevance for the health of wild populations, as well as individuals maintained in captivity, considering the zoonotic potential of these microorganisms.

Acute disseminated mycobacteriosis in captive Atlantic guitarfish (Rhinobatos lentiginosus)

An adult female captive-born Atlantic guitarfish ( Rhinobatos lentiginosus) was found acutely moribund on exhibit and died soon after presentation. Abnormalities on autopsy were focal cutaneous erythema on the tail, a small liver, many variably sized friable ovarian follicles, and coelomic effusion. Histologic examination revealed systemic bacterial embolization, and yolk coelomitis with minimal associated inflammation and some mineralization. Bacterial culture of blood and coelomic effusion grew a rapidly growing Mycobacterium species that was further identified as Mycobacterium chelonae by PCR amplification and sequencing of the RNA polymerase subunit beta ( rpoB) gene of isolated genomic DNA. Concurrent reproductive disease may have caused immunosuppression, thus predisposing to the mycobacterial infection. At another institution, an adult male wild-caught Atlantic guitarfish was found dead on exhibit with no premonitory signs. Abnormalities on autopsy were a thin body condition, small liver, and coelomic effusion. Histologic examination revealed acute mycobacterial septicemia. M. chelonae was also identified in this fish by PCR amplification and sequencing. Mycobacteriosis has rarely been reported in captive elasmobranchs. Guitarfish may have greater susceptibility to mycobacteriosis than other elasmobranchs, and acute and chronic manifestations of the disease may exist in this species.

FIRST ISOLATION OF TENACIBACULUM MARITIMUM IN A CAPTIVE SAND TIGER SHARK (CARCHARIAS TAURUS)

This report describes a case of the first isolation of Tenacibaculum maritimum from a captive-bred adult female sand tiger shark (Carcharias taurus) housed at the Cattolica Aquarium (Italy). The animal showed, between the second dorsal fin and the precaudal pit, skin lesions characterized by the presence of abundant whitish necrotic tissue. Through routine bacteriological examination, a bacterium was isolated from a skin lesion and subsequently identified as T. maritimum by phenotypic characters and species-specific polymerase chain reaction. The antimicrobial sensitivity of the isolated strain was evaluated for 11 antimicrobial agents by disk diffusion method. Antibiotic therapy was conducted with enrofloxacin at 10 mg kg(-1) i.m. on alternate days for 10 days. One month after the end of treatment skin lesions showed complete resolution and the shark recovered completely. The case presented here represents the first report of infection by T. maritimum in a sand tiger shark and highlights the potential pathogenic role of this microorganism in elasmobranchs kept in an aquarium.