Scanning electron microscopy of gill copepod, Caligus sp. at chalimus stages in sea bass fry (Lates calcarifer)

Objective: Crustacean infections by Caligus sp. are serious problems in cage-cultured fish. This paper the attachment of Caligus sp. at chalimus stages on sea bass fry (Lates calcarifer) is described under Scanning Electron Microscopy(SEM). The present study was conducted to determine the damage done on the host tissues. Method & Materials: Adult Caligus sp. with two egg sacs were placed in cavity block individually and were observed 6-hourly, in order to obtain the copepodid stage. Experimental infection of the fish was carried out in 100 ml of filtered sea water (29ppt). Thirty copepodes were exposed to individual sea bass fry and sampled four hourly before fixing in McDowell-Trump fixative for 24 hours, postfixed in 1% osmium tetroxide. The samples were washed, dehydrated in series of ethanol and hexamethydisilazane. The dried samples were then mounted, coated with gold and viewed under LeoSupra 50VP Field Emission SEM at magnifications of 25x–10Kx. Results & Conclusion: When an uninfected sea bass fry was exposed to Caligus sp., the copepods immediately attached themselves to the body and fins of the fish. After 4 hours, the copepodids managed to erode the epidermis for their frontal filament to attach to the basement membrane on the fins and scales. Observation 8 and 12 hours later showed more tissue response associated with redundant frontal filament attachment. Chalimus stages II, III and IV were observed between 16 to 24 hours. The attachment were associated with healed epidermis and some showed epidermal and fibroblast proliferation. Future study by histology on the pathological effect of the attachment will be carried out.

کلیدواژه ها:

Caligus sp. ، copepod ، chalimus ، sea bass ، Lates calcarifer