Study on the Characteristics and Ecological Control Techniques of Leech (Zeylanicobdella arugamensis) Parasitic on Grouper

Purpose To study the basic characteristics and ecological control of the grouper parasitic fish leeches.

Method The phylogenetic tree of COI, NDI, 18s rDNA gene was constructed by extracting genetic material from parasitic leeches. The grouper parasitic fish leeches were cultured under laboratory conditions. Its growth and development characteristics were studied, so also to determine the species, biological characteristics and life history of the leeches. In addition, through the grouper and Penaeus vannamei or Penaeus monodon polyculture, ecological control techniques of leech were studied.

Result The leech was Zeylanicobdella arugamensis. Under laboratory conditions: temperature 25-27 ℃, salinity 28.0‰, pH 7.5-8.0, dissolved oxygen 5.30-5.80 mg/L, it took 10 to 11 days from laying eggs to hatching larvae, and 9 to 11 days to lay eggs from larva to adult under the condition of hybrid grouper (Epinephelus fuscoguttatus♀×Epinephelus lanceolatus♂) as host. It took 19 to 22 days to accomplish a complete life cycle. The longest survival time of leech larvae in fresh water was 60 min, and that of adult in fresh water was 200 min. Leech larvae and adult could not survive in fresh water for a long time. Adult leeches could survive up to 12 d at 40.0‰ salinity, up to 14 d at 30.0‰ salinity, up to 18 d at 20.0‰ salinity and up to 19 d at 10.0‰ salinity without host while the water temperature was 25-27 ℃. Both species of shrimp have the ability to scavenge the Z. arugamensis, and the P. vannamei has the highest clearance rate to Z. arugamensis, and the clearance rate can reach 100% within 24 h.

Conclusion In this study, leeches of parasitic fish breeding grouper in Daya Bay, Guangdong Province were identified as Z. arugamensis which took 19 to 22 days to accomplish a complete life cycle. The Z. arugamensis larvae and adult could not survive in fresh water for a long time, therefore freshwater immersion could be used to remove it. In the absence of a host, the Z. arugamensis survived for no more than 20 days, therefore, the natural extinction of the Z. arugamensis can be achieved by isolating the host. The polyculture of P. vannamei or P. monodon and grouper can also effectively clear the Z. arugamensis.