Symbiotic relationship between udonella sp (monogenea) and caligus rogercresseyi (copepoda), a parasite of the chilean rock cod eleginops maclovinus

This paper studies the host-parasite relationship between the worm Udonella sp. (Monogenea) found on the genital segment of the sea lice Caligus roger cresseyi (Copepoda), a common parasite of the ruck cod Eleginops maclovinus found off the coast of southern Chile. The biological association beta een these invertebrates is interesting because C. rogercresseyi also infects f armed salmon (Boxshall and Brave, 2000) and eventually Udonella sp. could b e used for the biological control of sea lice. Rock cod were captured with hook and lint: and examined in the laboratory for lice, selecting only thos e C. rogercresseyi ovigerous females with Udonella sp. A video camera place d on a stereomicroscope was used for the in vitro observation of worms on t he copepods on which they survive. Egg strings of copepod females with Udon ella were later fixed in buffered formalin at 5% and stained with hematoxyl in-eosin and prepared for histological sections of the structures involved in host-parasite attachment. For histochemical analysis toluidine blue at d ifferent pH levels was used. Observations with hematoxilin - eosin showed t hat the external cuticle of the egg sac is acidofilic and remains undamaged while Udonella adhesive disc is attached. When toluidine blue was used, th e attachment area showed slight basophylic stains and metachromasia visible at pH of 1.2. Udonella at the caudal gland level as well as C. rogercresse yi at the sub-cuticular region of the egg sacs showed basophylic reaction a t pH of 4.5. The present paper clarify the absence of possible mechanical d amage in the parasite-host attachment site and provides an histological des cription of the wall dependent contact points between Udonella - Caligus pl us the extracellular space that separates them. Udonella survived on mucus secreted by the rock cod's skin and not on the content of the copepod's egg sacs, which serve more as an attachment area given that in this zone what is seen is a metachromatic stained strip corresponding to acid glycosaminog lycans (Aranishi & Nakane, 1998; Buchmann, 1998). The association between t he worm and the copepod is commensalistic.