Structure of venomous spines of Pelteobagrus fulvidraco

Pelteobagrus fulvidraco, Richardson, 1846 is a typical freshwater venomous fish. Poisoning events of P. fulvidraco stings often occur, which brings great harm to human health. In order to study the venomous spines structure of P. fulvidraco, in this study, the methods of macroscopic skelet and microscopic histological section were used. The results indicated that both pectoral fin and dorsal fin of P. fulvidraco had sharp spines. Spines were surrounded by integument, which were associated with venom gland cells. The venom gland cells could secrete venom. P. fulvidraco venomous spines apparatus is composed of spine shaft, venom gland, and surrounding tissues. Macroscopic observation showed that venomous spines in dorsal and pectoral fins of P. fulvidraco had integument surrounding the spine shaft and central canal. Central canal ran through the whole spine shaft. Dorsal venomous spines were elongated, tapered, and slightly arched. Venomous spines of the dorsal fin had a sharp crest and weakly serrated posterior edge. Both anterior and posterior edges of pectoral venomous spines were serrated, but the posterior edge was serrated more obviousely. The shape, size and location of the condyle were completely different in the base structure of dorsal and pectoral venomous spines. Microscopic examination showed that the venom gland cells in the integument gathered in layers and were located between the squamous epithelium and the pigment layer. The catheter was not attached to the venom gland cells. Venom gland cells were not found in the branched bony tubes of venomous spines of the dorsal and pectoralis fin. In addition, the branched bony tubes also connect the central canal and integument. Spines of pectoralis fin are triangular as they extend distally outward, with the central canal narrowing and disappearing completely at the apex. The pectoral and dorsal fin locking apparatus could keep the venomous spines in a lodging or upright locking state, thus reducing the probability of prey breaking free, and this behavioral mechanism may be important for its adaptation to complex environments. In the future, the research on venomous fishes should be strengthened. Overall, this study can help deeply understand the structure and characteristics of venomous spines of P. fulvidraco, enrich the basic knowledge of freshwater venomous fishes, enhance people's understanding of venomous fish and lay a foundation for further research on freshwater venomous fish.