During the culture of Isostichopus badionotus in tanks at Telchac, Yucatán, we found high abundance of harpacticoid copepods producing skin lesions. The wounds were colonized by opportunistic pathogens such as bacteria, which in turn led to Skin Ulceration Disease (SUD). Organophosphate pesticides such as trichlorfon have been used in concentrations between 1-5 ppm for up to 12 h, to control copepods in sea cucumber aquaculture, followed by a comprehensive water exchange to eliminate the compound from the farming system. However, trichlorfon has been banned in Mexico since 2019.
An alternative compound could be Temephos, an organophosphate endorsed by the World Health Organization (WHO) to control the freshwater copepod Cyclops vernalis, an intermediate host of the nematode Dracunculus medinensis. Therefore, our aims were to determine the Lethal Dose 50 (LD50) and 99 (LD99) of the organophosphate temephos to control the opportunistic harpacticoid copepods as well as to calculate the therapeutic margin of this compound for I. badionotus.
We have identified five different copepod morphotypes and the taxonomic specific identification is on its way. The toxic effect of temephos was evaluated through 96h static bioassays using stage 5 copepodites and adult copepods. After performing a range detection test, 0.062, 0.125, 0.250, 0.500, 0.100, and 2.000 mg/L were determined as the final bioassay doses and were evaluated for 24 and 48 h of exposition. Preliminary results suggest that temephos LD50 and LD99 at 48 h exposure are 0.312 and 0.715 mg/L respectively. Tests are still in progress to obtain the LD50 and LD99 of temephos at 24 h, and to calculate the therapeutic margin of this compound for I. badionotus.